Ancillary Ligand Effects on Fundamental Transformations in Metallocene Catalyzed Olefin Polymerization Citation Chirik, Paul James (2000) Ancillary Ligand Effects on Fundamental Transformations in Metallocene Catalyzed Olefin Polymerization. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/2qx2-9753. https://resolver.caltech.edu/CaltechTHESIS:11112025-205555750 Abstract The preparation of a series of unlinked and ansa-zirconocene dihydride complexes from hydrogenation of the corresponding dimethyl complexes is described. In general, sterically demanding ligands promote formation of monomeric dihydride complexes. The ansa-zirconocene dihydride, meso-[Equation. See abstract in scanned thesis for details], has been characterized by X-ray diffraction. The monomeric, ansa-zirconocene, rac-[Equation. See abstract in scanned thesis for details] undergoes thermal reductive elimination of dihydrogen forming, BpZr(μ2-N2)ZrBp which displays a side-on coordination of the dinitrogen fragment. Rates of olefin insertion and β-hydrogen elimination have been measured for a series of zirconocene and hafnocene dihydride and alkyl hydride complexes. In both cases, increased cyclopentadienyl substitution slows the rate of insertion or elimination, although the former is more sensitive to steric perturbations. From these studies, the transition state for olefin insertion/β-hydrogen elimination has been established. Equilibration of zirconocene isobutyl hydride complexes with the corresponding normal butyl hydrides has allowed for determination of the relative ground state energies of the two alkyl hydride metallocenes. These data in combination with the activation barriers for β-hydrogen elimination have allowed for delineation of ground and transition state effects in these processes. Likewise, ancillary ligand effects on the rate of alkyl isomerization have also been examined with a series of isotopically labeled zirconocene alkyl complexes. In general, increasing the substitution on the cyclopentadienyl rings has little effect on the rates of isomerization. The preparation of ansa-tantalocene olefin-hydride complexes is described. These complexes serve as models for the transition state for olefin insertion in the corresponding group IV metallocene olefin polymerization catalysts. Preparation of the Ci-symmetric ethylene hydride complex, [Equation. See abstract in scanned thesis for details] affords predominantly (-95 %) of one isomer, where the ethylene ligand is coordinated on the side of the wedge away from the isopropyl substituent. Similar results have been obtained with related tantalocene propylene-hydride and styrene-hydride complexes, the latter being characterized by X-ray diffraction. Additionally, several singly and doubly bridged tantalocene trimethyl complexes have been prepared and characterized by X-ray diffraction. Item Type: Thesis (Dissertation (Ph.D.)) Subject Keywords: (Chemistry) Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemistry Thesis Availability: Public (worldwide access) Research Advisor(s): Bercaw, John E. Thesis Committee: Grubbs, Robert H. (chair) Gray, Harry B. Rees, Douglas C. Bercaw, John E. Defense Date: 3 April 2000 Record Number: CaltechTHESIS:11112025-205555750 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:11112025-205555750 DOI: 10.7907/2qx2-9753 ORCID: Author ORCID Chirik, Paul James 0000-0001-8473-2898 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 17756 Collection: CaltechTHESIS Deposited By: Ben Maggio Deposited On: 13 Nov 2025 22:22 Last Modified: 13 Nov 2025 22:25 Thesis Files PDF - Final Version See Usage Policy. 155MB Repository Staff Only: item control page

Ancillary Ligand Effects on Fundamental Transformations in Metallocene Catalyzed Olefin Polymerization Thesis by Paul James Chirik In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Division of Chemistry and Chemical Engineering California Institute of Technology Pasadena, California 2000 (Submitted April 3, 2000) 11 ©2000 Paul James Chirik All Rights Reserved iii For Mom and Dad iv Acknowledgments It is difficult for me to fully express my gratitude and appreciation for all those who have offered their support during my education at Caltech but I will do my best in the next couple of pages. First, I would like to thank my research advisor, John Bercaw, for his guidance, thoughtfulness and friendship during my tenure in his group. Working with John has been an exceptional experience and I am indebted to him for the education he has provided. Additionally, Jay Labinger has served as an excellent "second advisor" and I am grateful for his suggestions and input. I would also like to thank my committee: Bob Grubbs, Harry Gray, Doug Rees and Andy Myers for their time and helpful suggestions throughout my graduate career. Special thanks go to Harry for warming up the crowd before every talk I have given at Caltech. I would also like to acknowledge my undergraduate advisor, Joe Merola, for inspiring me to go to graduate school and sharing his passion for organometallic chemistry and science in general. The Bercaw group is a unique cast of characters and I would like to mention some of them here. I would like to thank Tim Herzog and Jim Gilchrist for showing me all there is to know about vacuum lines and air-sensitive chemistry, Shannon Stahl for teaching me how to think about mechanisms and how to get away with a cheap elbow on the basketball court, and Mike Abrams for keeping me away from chemical physics seminars. I have been fortunate to share a lab with s?me truly wonderful people. Steve Miller has been an excellent line mate and friend and was very understanding when I made him split his pants in a softball game. In addition to being a fine tennis partner and authority on fashion, Susan Schofer has been offered a tremendous amount of support and friendship for which I never express in words and am truly grateful. Chris Jones has been a great addition to the lab and will be the first person I call when the Flyers win the Stanley Cup and Virginia Tech wins a national championship. Deanna Zubris has been an amazing friend, confidant and colleague since I started at Caltech and I certainly would not have made it this far without her. Best of luck to my new line mate Sara Klamo. I would like to thank Chris Brandow for all of his help and suggestions with both theory and experiments and for all of those body checks he threw at V me walking down the hall. Lily Ackerman has been a great addition to the group V project and I appreciate her help with proofreading and EPR experiments. Thanks to John Scollard for all of his computer wizardry and Chris Levy for keeping me honest in the Hogs homerun race. Ola Wendt and Matt Holtcamp were excellent postdocs who were always there to answer a tough question. Dario Veghini provided me with lots of inspirational pep talks about science and kept me from getting lost when running in San Marino. I would also like to thank some other "Hogs": Jeff Yoder, Antek Wong-Foy, Andy Kiely, Endy Min, Cory Nelson and Shigenobu Miyake. Several people outside of the Bercaw group have been very helpful throughout my time at Caltech. I would like to acknowledge the efforts of Nathan Dalleska and Peter Green with the GC/MS experiments described in Chapter 5. I would also like to thank "Slick" Rick Gerhart, Dian Buchness, Steve Gould, Chris Smith and Pat Anderson for attempting to keep the place sane and running smoothly. I am also indebted to the Caltech X-ray crystallographic facility for all of my structural data. In addition to being a fine outfielder and having a nose for a free lunch, Larry.Henling mounted all of my crystals, no matter how poor in quality, and managed to get data from them. Mike Day, Dick Marsh and Bill Schaefer were also helpful in solving structures and providing a quiet place for me to work on my thesis. I also would like to thank a very special group of people who made an enormous contribution to my Caltech experience. "Michigan" Jim Brauher has been a great training partner and an even better friend; "Big" Don Thomas and Frank "The Chief" Camacho for keeping me in my place but at the same time being great role models. Kathy Miller has been my San Marino Mom for the past four years and I will never forget cruisin' on the freeway in Porsche. "Chicago" Paul Kulesa, Richard Maya, Carlo Cossu and Gerard O'Rielly were always quick to make me laugh, even though it was usually at my expense. Carl Foote has been a great basketball teammate and source of 70's music trivia. I would also like to thank Jim Anderson and Miguel Francis for always keepin' it real. I will never forget the "Friday Night Feasts" and the great times we all had together. Finally, I would like to thank my parents, Joseph and Carol Chirik, and my brother, Joseph Chirik, for being so supportive throughout the years. You guys are the best! Vl Abstract The preparation of a series of unlinked and ansa.-zirconocene dihydride complexes from hydrogenation of the corresponding dimethyl complexes is described. In general, sterically demanding ligands promote formation of monomeric dihydride complexes. The ansa-zirconocene dihydride, meso[Me2Si(ri 5-C5H3-3-CMe3)zZrH2h, has been characterized by X-ray diffraction. The monomeric, ansa-zirconocene, rac-Me2Si(ri 5-CsH2-2-SiMe3-4-CMe3)zZrH2 (BpZrH2) undergoes thermal reductive elimination of dihydrogen forming, BpZr(µ2-N2)ZrBp which displays a side-on coordination of the dinitrogen fragment. Rates of olefin insertion and ~-hydrogen elimination have been measured for a series of zirconocene and hafnocene dihydride and alkyl hydride complexes. In both cases, increased cyclopentadienyl substitution slows the rate of insertion or elimination, although the former is more sensitive to steric perturbations. From these studies, the transition state for olefin insertion/~hydrogen elimination has been established. Equilibration of zirconocene isobutyl hydride complexes with the corresponding normal butyl hydrides !las allowed for determination of the relative ground state energies of the two alkyl hydride metallocenes. These data in combination with the activation barriers for ~-hydrogen elimination have allowed for delineation of ground and transition state effects in these processes. Likewise, ancillary ligand effects on the rate of alkyl isomerization have also been examined with a series of isotopically labeled zirconocene alkyl complexes. In general, increasing the substitution on the cyclopentadienyl rings has little effect on the rates of isomerization. The preparation of ansa-tantalocene olefin-hydride complexes is described. These complexes serve as models for the transition state for olefin insertion in the corresponding group IV metallocene olefin polymerization catalysts. Preparation of the Ci-symmetric ethylene hydride complex, Me2Si(ri 5-Csfii)(ri 5C5H3-3-CHMe2)Ta(ri 2-C2H2)(H) affords predominantly (-95 %) of one isomer, where the ethylene ligand is coordinated on the side of the wedge away from the isopropyl substituent. Similar results have been obtained with related tantalocene propylene-hydride and styrene-hydride complexes, the latter being characterized by X-ray diffraction. Additionally, several singly and doubly vii bridged tantalocene trimethyl complexes have been prepared and characterized by X-ray diffraction. viii Ancillary Ligand Effects on Fundamental Transformations in Metallocene Catalyzed Olefin Polymerization TABLE OF CONTENTS Acknowledgments .......................................................................................................... .iv Abstract ............................................................................................................................. vi Table of Contents ........................................................................................................... viii List of Figures .................................................................................................................... x List of Tables ................................................................................................................... xiv Chapter 1: Preparation and Characterization of Monomeric and Dimeric Group 4 Metallocene Dihydrides Having Alkyl-Substituted Cyclopentadienyl Ligands ............................................................................................................................... l Abstract. ................................................................................................................. 2 Introduction ........................................................................................................... 3 Results and Discussion .........................................................................................4 Conclusions .......................................................................................................... 17 Experimental. ....................................................................................................... 18 Chapter 2: Synthesis of Singly and Doubly Bridged Ansa-Zirconocene Dihydrides and Activation of Dinitrogen by a Monomeric Zirconocene DihydrideComplex........................................................................................................ 30 Abstract ................................................................................................................. 31 Introduction .........................................................................................................32 Results and Discussion ............................................................... ......................... 33 Conclusions ..........................................................................................................50 Experimental. .............. :........................................................................................ 51 Chapter 3: Ancillary Ligand Effects on Fundamental Transformations in Group 4 Metallocene Chemistry. Kinetics and Mechanism of Olefin Insertion and ~-Hydrogen Elimination...................... ...... ............ .... ............... ................. ........... 62 Abstract ................................................................................................................. 63 Introduction ......................................................................................................... 64 Results ................................................................................................................... 66 lX Discussion............................................................................................................. 85 Experimental. ....................................................................................................... 96 Chapter 4: Alkyl Rearrangement Processes in Organozirconium Complexes. Observation of Internal Alkyl Complexes during Hydrozirconation ..............114 Abstract ............................................................................................................... 115 Introduction ....................................................................................................... 116 Results ................................................................................................................. 117 Discussion ........................................................................................................... 127 Experimental. ..................................................................................................... 139 Chapter 5: Kinetic Isotope Effects for ~-Methyl Elimination. Experimental Observation of y-Agostic Interactions during the Ziegler-Natta Polymerization of Olefins ....................................................................................................................... 151 Abstract ............................................................................................................... 152 Introduction ....................................................................................................... 153 Results and Discussion ................................................................................ .-.....154 Conclusions ........................................................................................................ 159 Experimental. ............ .-........................................................................................ 160 Chapter 6: Preparation and Characterization of Ansa-Tantalocene Derivatives as Transition State Models for Metallocene Olefin Polymerization Catalysts ......................................................................................................................... 169 Abstract ............................................................................................................... 170 Introduction....................................................................................................... 171 Results and Discussion ...................................................................................... 174 Conclusions ........................................................................................................ 208 Experimental. ..................................................................................................... 209 Appendix A: Select Kinetic Plots ............................................................................. .231 Appendix B: X-ray Crystallographic Data ................... ........................ .......... ........ 236 X List of Figures Chapter 1: Figure 1. A series of zirconocene dichloride complexes ............................................ 5 Figure 2. Molecular structure of ('r1 5-CsMes)(ri 5-C5f4-CMe3)ZrCl2 ........................ 6 Figure 3. Molecular structure of (ri 5-C5Me5)(ri 5-C5H3-l,3-(CHMe2)2)ZrCh ......... 7 Figure 4. Molecular structure of (ri 5-CsH3-l,3-(CMe3)2)2ZrCh ............................... 7 Figure 5. Molecular structure of (ri 5-C5Me5)2HfH2 ...................................................9 Figure 7. Monomer-dimer equilibrium for [(ri 5-CsMes)(ri 5-C5H3-l,3(CHMe2)2)ZrH2]2 ............................................................................................................ 13 Chapter 2: Figure 1. Molecular structure of meso-Me2Si(ri 5-C5H3-3-CMe3)2ZrMe2 ............... 34 Figure 4. Molecular structure of rac-BpZr(µ2-N2)ZrBp ............................................ 38 Figure 5. Molecular structure of one of the zirconium centers of BpZr(µ2-N2)ZrBp ............................................................................................................. 39 Figure 6. Partially labeled view of BpZr(µ2-N2)ZrBp .............................................. .40 Figure 7. Possible mechanism for the conversion of rac-BpZrH2 to BpZr(µ2-N2)ZrBp ............................................................................................................. 43 Figure 8. Preparation of Me2Si(ri 5-C5Me4)(ri 5-CsH2-2,4-(CHMe2)2)ZrH2 ........... 44 Figure 9. Molecular structure of [RpZrl3(µ3-H)2(µ2-H)3 ......................................... 46 Figure 10. View of the zirconium hydride core of [RpZr]3(µ3-H)2(µ2-H)3 ......... .47 Xl Figure 11. Preparation of {[TIP]ZrH2}2 ..................................................................... .49 Figure 12. Steric blocking of the la1 orbital by the dimethylsilylene linker ........ .50 Chapter 3: Figure 1. Proposed transition state for olefin insertion and ~-hydrogen elimination ........................................................................................................................ 66 Figure 2. Relative rates of olefin insertion with Cp*2HfH2 at 230 K ...................... 71 Figure 3. Hammett plot for reaction of Cp*2ZrH2 with para-substituted amethylstyrenes at 296 K................................................................................................. 73 Figure 4. Zirconocene isobutyl hydride complexes ................................................. 77 Figure 5. Mechanism of trapping the zirconocene dihydride with 37 ................... 78 Figure 6. Relative rates of ~-hydrogen elimination for a series of zirconocene isobutyl hydride complexes at 296 K........................................................................... 81 Figure 7. Proposed mechanism for olefin insertion with neutral zirconocene isoutyl hydrides at 296 K. ............................................................................................... 86 Figure 8. Rationale for the preference for ~-methyl elimination over ~-hydrogen elimination in sterically demanding metallocene catalysts ....................................... 91 Chapter 4: Figure 1. Molecular structure of Cp2Zr(cyclo-C5H9)(Cl) ........................................ 121 Figure 2. 500 MHz 1H NMR spectra of the butyl resonances following hydrozirconation of cis-2-butene (a) after 6 hours and (b) 3 days ........................ 122 Figure 3. 125.77 MHz {lH}l3C NMR spectra of the heptyl resonances following hydrozirconation of cis-2- 13CH2CH=CHCH2CH2CH2CH3 .................................. 124 Figure 4. Upfield region of the 125.77 MHz {1H} 13C NMR spectrum obtained at 240 K following hydrozirconation of cis-2-heptene with Cp2Zr(H)(Cl) ............... 125 Figure 5. 76.77 MHz {1H} 2H NMR spectra of deuterated alkenes by treatment of 3 with cis-2-butene, cis-2-pentene and cis-2-heptene, followed by a CH3OD quench ............................................................................................................................. 127 xii Chapter 5: Figure 1. Types of agos tic interactions ..................................................................... 153 Figure 2. Molecular structure of Cp2Zr(CH2CMe3)(CH3) .................................... lS6 Figure 3. Allylic activation of isobutene by zirconocene methyl cations forming zirconocene crotyl complexes ..................................................................................... 157 Figure 4. Reversible ~-methyl elimination and olefin insertion to form d6isobutene ........................................................................................................................ 158 Chapter 6: Figure 1. Doubly coordinatively unsaturated, 14 electron metallocene catalysts for olefin polymeriztion.............................................................................................. 171 Figure 2. Model for the olefin insertion transition state in chiral yttrocene catalysts ........................................................................................................................... 172 Figure 3. Proposed transition state for syndiospecific metallocene catalysts ..... 173 Figure 4. Isotactic polypropylene produced by Ci-symmetric metallocene catalysts ........................................................................................................................... 173 Figure 5. Resonance structures of niobocene and tantalocene olefin hydride complexes ....................................................................................................................... 174 Figure 6. EPR spectrum of 23 in dichloromethane at 296 K. ................................. 182 Figure 7. The major isomer for 26 ............................................................................. 184 Figure 8. Molecular structure of 27b with 50% probability ellipsoids .................. 185 Figure 9. Top view of 27b with 50% probability ellipsoids ................................... 186 Figure 10. Two predominant isomers of 27 ............................................................. 186 Figure 11. Possible mechansims for styrene hydride isomer interconversion ... 187 Figure 12. Partially labeled view of the molecular structure of 29a with 50% probability ellipsoids ..................................................................................................... 190 Figure 13. Top view of 27a with 50% probability ellipsoids .................................. 191 xiii Figure 14. Molecular structure of 30 with 50% probability ellipsoids and atom labeling scheme ............................................................................................................. 192 Figure 15. Top view of 30 with 50% probability ellipsoids ................................... 193 Figure 16. Synthetic route for the preparation of Cp2Ta(ri 2-CH2=CH2)(CH3) .. 195 Figure 17. Molecular structure of 31 with 50% probability ellipsoids and partial atom labeling scheme ................................................................................................... 196 Figure 18. Top view of the solid state structure of 31 with 50% probability ellipsoids ......................................................................................................................... 196 Figure 19. Preparation of 34 ....................................................................................... 197 Figure 20. Molecular structure of 35 with 50% probability ellipsoids and atom labeling scheme ............................................................................................................. 199 Figure 21. Side view of 35 with 50% probability ellipsoids ................................... .200 Figure 22. Molecular structure of 35a with atom labeling scheme and 50% probability ellipsoids .................................................................................................... .201 Figure 23. Molecular structure of 38 with 50% probability ellipsoids and atom labeling scheme ............................................................................................................. 202 Figure 24. Molecular structure of 40 with 50% probability ellipsoids and atom labeling scheme ............................................................................................................. 204 Figure 25. Side view of 40 with 50% probability ellipsoids .................................... 205 XIV List of Tables Chapter 1: Table 1. Centroid-M-Centroid (0) and Cyclopentadienyl-NormalCyclopentadienyl (a) Angles for Cp*2HfH2, 1, 3, 6 and related hafnocene dichlorides .......................................................................................................................... 8 Table 2. Molecular weights for zirconocene dihydrides and molecularity indicated by 1.H NMR spectroscopy ............................................................................. 11 Chapter 3: Table 1. Rate constants for insertion of disubstituted olefins with 1 at 296 K. ..... 68 Table 2. Rate constants as a function of solvent for the reaction of 1 with isobutene at 296 K........................................................................................................... 68 Table 3. Rate constants for the reaction of 1 with isobutene and trans-2-butene as a function of temperature ......................................................................................... 69 Table 4. Rate constants for the reaction of 2 with isobutene, trans-2-butene and cis-2-butene as a function of temperature ................................................................... 70 Table 5. Activation parameters for reaction of 1 and 2 with a variety of olefins ................................................................................................................................ 70 Table 6. Data for the linear free energy relationship for insertion of parasubstituted a-methylstyrenes with l ........................................................................... 72 Table 7. Regiospecificity of styrene insertion with a series of zirconocene dihydrides ......................................................................................................................... 75 Table 8. Observed rate constants for reaction of zirconocene isobutyl hydride complexes with 37 ....................... ................................................. ................................... 79 Table 9. Activation parameters for ~-hydrogen elimination at 296 K.................. 80 Table 10. Kinetic isotope effects for ~-hydrogen elimination at 296 K. ................ 81 Table 11. Linear free energy relationship data for Cp*(C5Me4H)Zr(CH2CH2-pC6fi4-X)(H) ....................................................................................................................... 82 Table 12. Rates of ~-hydrogen elimination as a function of alkyl ligand ............. 83 Table 13. Comparison of the rates of ~-hydrogen elimination for a series of zirconocene alkyl hydride complexes .......................................................................... 83 xv Table 14. Equilibrium constants and free energy data for equation 9 .................. 84 Table 15. Rate constants for isobutene insertion as a function of solvent dielectric ............................................................................................................................ 87 Table 16. Relative ground state energies for zirconocene isobutyl and normal butyl hydride complexes ................................................................................................ 94 Table 17. Relative ground state and transition state energies for zirconocene alkyl hydride complexes ................................................................................................ 95 Chapter 5: Table 1. Distribution of isotopomers for ~-methyl elimination for 1 at 296 K.. 156 Table 2. Kinetic isotope effect for ~-methyl elimination with a series of zirconocene catalysts .................................................................................................... 159 Chapter 6: Table 1. Measured rate constants for the reaction of 6 with ethylene forming 15 ...................................................................................................................................... 178 Table 2. Reaction of 8 with PR3 at 87 °C. ................................................................. 181 1 Chapter 1 Preparation and Characterization of Monomeric and Dimeric Group IV Metallocene Dihydrides Having Alkyl-Substituted Cyclopentadienyl Ligands.* 2 Abstract A series of zirconocene dihydride complexes of the general form, [(RnCp )2ZrH2]n having substituted cyclopentadienyl ligands has been prepared by hydrogenation of the corresponding dimethyl complexes. The most sterically crowded members (Cp*(T1 5-CsHMe4)ZrH2, (Cp* = T1 5-CsHs)), Cp*{T1 5-C5H3-l,3-(CMe3)2}ZrH2 and {T1 5-C5H3-l,3-(CMe3)2}2ZrH2) are monomeric; those less crowded members ([Cp*{T1 5-C5H4(CMe3)lZrH2h, [Cp*(THI)ZrH2]2 (THI =T1 5-tetrahydroindenyl) and [{T1 5-C5H3-l,3-(CHMe2)2hZrH2h) are predominantly dimeric in benzene solution. Cp*{T1 5-C5H3-l,3-(CHMe2)2}ZrH2 and (T1 5-CsHMe4)2ZrH2 exist as equilibrium mixtures of monomer and dimer in benzene solution. The hydride ligands rapidly exchange with D2, affording the dideuteride complexes. Deuterium incorporation into some of the substituents on the cyclopentadienyl rings of the monomeric dihydride complexes is also observed. The X-ray structures of Cp*2HfH2, Cp*{T1 5-Csfi4(CMe3)}ZrCb, Cp*{T1 5-C5H3-l,3-(CHMe2)2}ZrCb and {T1 5-CsH3-l,3-(CMe3)2}2ZrCb are reported. 3 Introduction Transition metal hydrides constitute an important class of compounds due to their prevalence in both catalytic and stoichiometric processes. 1 Hydride complexes of group 4 metallocenes have been implicated as catalysts and as important intermediates in olefin hydrogenation2 and polymerization reactions. 3 Despite their widespread utility, the molecularity and structures of zirconocene and hafnocene dihydrides have not been systematically investigated. Early reports of zirconocene dihydride complexes concern the preparation of simple alkyl substituted bis(cyclopentadienyl) complexes of the general form, {(rt5-CsHiR)2ZrH2}n (R = H, Me, CHMe2, CMe3; n ~ 2t obtained via hydrogenation of the corresponding dimethyl complexes at elevated temperature (80 °C) and pressure (60 atrn). 4 Bis(tetrahydroindenyl)zirconium dihydride dimer has also been prepared via hydrogenation of the corresponding bis(indenyl)zirconium dimethyl complex as a result of hydrogenation of both the zirconium methyl bonds as well as the benzo groups of the indenyl ligands. 5 Zirconocene dihydrides, [(ri5-CsHiCMe3)2ZrH2h and [(ri 5-CsHiSiMe3)2ZrH2h have been prepared via an alternate route, reduction of metallocene dichloride complexes with borohydride or aluminohydride reagents. 6, 7 More recently, ansa-zirconocene dihydride complexes have been synthesized. Buchwald8 has reported the synthesis of [rac-(EBTHI)MH2h (EBTHI = ethylene-l,2-bis-(ri 5-tetrahydroindenyl); M = Zr, Hf) via reduction of the corresponding dichloride complexes with NaBEt3H. Royo 9 has used similar methodology to prepare dimeric, doubly [SiMe2]-bridged [(Me2Si)2(ri 5-CsH3)2MH2h (M = Zr, Hf) . Parkin has prepared [OpZrH2h (Op= Me2Si(ri 5-C5Me4)2) via hydrogenation of the dimethyl complex at elevated temperatures in cyclohexane solution. 10 In all cases, stable dimeric zirconocene dihydrides resulted, with no reports of detectable amounts of the monomer in solution, although facile interconversion of [OpZrH2h with monomer was implicated by its variable temperature 1H NMR behavior. 10 Very few monomeric zirconocene and hafnocene dihydride complexes have been prepared and isolated. Like their group 3 counterparts,11 most group 4 4 metallocene hydride complexes are subject to dimerization through formation of relatively robust 3 center, 2 electron hydride bridges. In fact, to our knowledge, the only monomeric zirconocene and hafnocene dihydride complexes prepared to date are those employing two bulky pentamethylcyclopentadienyl (Cp*) ligands, Cp*2MH2.12 Elucidation of the effects of ligand array on the position of the monomer-dimer equilibrium has not been established. In this report we describe the preparation and solution behavior of a variety of new zirconocene dihydride complexes, and through this study explore some of the factors that govern the monomer-dimer equilibrium. The HID exchange reactions of these hydride complexes with deuterium are described. We also present the results of X-ray crystal structure determinations for monomeric Cp*2HfH2, together with some representative precursors, Cp*{'r1 5-CsH4(CMe3)}ZrCh, Cp*{ri 5-CsH3-l,3-(CHMe2)2}ZrCh and {ri 5-CsH3-l,3-(CMe3)2}2ZrCh. Results and Discussion Synthesis and Solution Behavior of Zirconocene Dihydrides. Preparations of "mixed ring" zirconocene dichloride complexes have been carried out in a straightforward manner by addition of the corresponding lithiocyclopentadienide to readily available Cp*ZrCb. 13 Thus, Cp*{ri 5-Cs~(CMe3)}ZrCh 14 (1), Cp*{ri 5-CsH3-l,3-(CMe3)2}ZrCh (2), Cp*{ri 5-CsH3-l,3-(CHMe2)2}ZrCh (3), Cp*(lnd)ZrCh (4) (Ind= (ri 5-C9H7)), and Cp*(ri 5-C5HMe4)ZrCl2 (5) have been prepared in yields ranging from 60 - 83%. Additionally, {ri 5-CsH3-l,3-(CMe3)2}2ZrCh (6) and {ri 5-C5H3-l,3-(CHMe2)2}2ZrCh (7) have been obtained in moderate yield from the reaction of two equivalents of the lithiocyclopentadienide with ZrC4 in refluxing toluene. All of the dichloride complexes are air stable and can be purified either by recrystallization or sublimation at 140 °C (10-4 Torr). 5 1 4 5 6 7 Figure 1. A series of zirconocene dichloride complexes. Single crystals of 1, 3 and 6 were obtained from toluene solution and their structures were established by X-ray diffraction. As shown in Figures 2 - 4 the cyclopentadienyl substituents arrange themselves to avoid both the narrow ("back") portion of the zirconocene wedge and the large chloride ligands. Thus, the tert-butyl substituent of 1 is situated slightly off the center of the wedge with [CMe3] methyl groups arranged to minimize interactions with the cyclopentadienyl [CH]'s and the chloride ligands; the isopropyl groups for 3 are lateral, related by a mirror plane that bisects the Cl-Zr-Cl plane, with one [C-CH3] bond oriented perpendicular to the cyclopentadienyl plane and the other directed into the wedge away from the chlorine atom; the four tert-butyl groups for 6 are pairwise related by a crystallographic two-fold symmetry axis that bisects the Cl-Zr-Cl angle. During the course of our investigations, we have obtained X-ray quality crystals of Cp*2HfH2, which has been prepared via reduction of the dichloride 12 complex with two equivalents of n-BuLi under an atmosphere of dihydrogen. b To our knowledge, this is the first monomeric group IV rnetallocene dihydride to be characterized crystallographically. The crystals obtained for the diffraction experiment were twinned, and as a result location of the hydride ligands was not possible. Despite the complications of crystal twinning, we are confident that the structure is indeed the monomeric dihydride as shown in Figure 5. It is 6 noteworthy that, presumably due to the small size of the hydride ligands, the two (11 5-CsMes) ligands assume a very "closed" metallocene structure. As can be seen from the data in Table 1, the centroid-Hf-centroid ( e= 144.1(2) and 145.0(2) 0 ) and cyclopentadienyl normal-cyclopentadienyl normal (a= 145.2(2) and 145.9(2) 0) angles for the two independent molecules in the unit cell are much larger than those for 1, 3, 6 or other hafnocene dichloride complexes that have been structurally characterized ( e = 129 to 131 °; a= ca. 121 to 128°). Chloride ligands thus exert an unfavorable steric repulsion on those ring carbons most out of the metallocene wedge, resulting in smaller values fore and a, and larger differences between these two angles. Cl 1 Figure 2. Molecular structure of 1 with selected atoms labeled (50% probability ellipsoids). 7 Figure 3. Molecular structure of 3 with selected atoms labeled (50% probability ellipsoids; hydrogen atoms omitted for clarity). C 13 Figure 4. Molecular structure of 6 with selected atoms labeled (50% probability ellipsoids; hydrogen atoms omitted for clarity). 8 Compounda e <o> a (o) Cp*2HfH2 144.1(2) 145.0(2) 130.68(1) 131.49(2) 129.7(1) 129.23 129.14 130.59 129.96 145.2(2) 145.9(2) 124.73(1) 126.87(8) 121.1(1) 126.54 127.60 126.70 125.71 Cp* {'ri 5-C5H4( CMe3)} ZrCl2 (1) Cp*{ri5-CsH3-l,3-(CHMe2)2}ZrCb (3) {ri 5-C5H3-l,3-(CMe3)2}2ZrCb (6) Cp2HfCli0 Cp*CpHfCli 1 (Cs~-CH2CH3)2HfCb32 a A search of the Cambridge Structural Database produced 3 hafnocene dichloride complexes. Allen, F.H.; Davies, J.E.; Galloy, J.J.; Johnson, O.; Kennard, O.; Macrae, C.F.; Mitchell, E.M.; Smith, J.M.; Watson, D.G. J. Chem. Info . Comp. Sci. 1991, 31, 187. Table 1. Centroid-M-Centroid (0) and Cyclopentadienyl Normal-Cyclopentadienyl Normal (ex) Angles for Cp*2HfH2, 1, 3, 6 and related hafnocene dichlorides. Treatment of the metallocene dichloride complexes with two equivalents of methyllithium in diethyl ether affords the zirconocene dimethyl complexes in good yields (eq. 1). 9 (1) The dimethyl complexes are air sensitive and are readily soluble in aromatic, hydrocarbon and ethereal solvents. For each compound, a diagnostic Zr-CH3 resonance in the 1H NMR spectrum is observed slightly upfield of SiMe4 (see Experimental Section). Purification of these compounds can be achieved either by recrystallization from cold petroleum ether or by sublimation at 80 °C (lo-4 Torr). Cl •_ /__ . / ,~ C 14a -='-'~"1JC4a -- c 15a Hfa Figure 5. Molecular structure of ('r1 5-C5Me5)2HfH2 (50% probability ellipsoids). Hydrogenation of the entire series of dimethylzirconcenes proceeds readily and quantitatively (1H NMR), even at room temperature and 1 atm H2, unlike the more forcing conditions previously reported for the preparation of zirconocene dihydrides from the dimethyl derivatives (eq. 2). 10 H 2 (1 atm) 2s c 0 ·---------------------- dimer (2) benzene or cyclohexane The resulting highly air sensitive dihydride complexes are soluble in aromatic solvents. In general, the dimeric dihydrides are less soluble than the monomeric dihydrides. This procedure provides an attractive alternate route to previously reported [Cp*CpZrH2lz (Cp = (ri 5-CsHs)). 13 Hydrogenation of Cp*(Ind)ZrMe2 results in quantitative formation of [Cp*(THI)ZrH2h (11), as a result of cr bond metathesis reactions of the Zr-CH3 with H2 and subsequent hydrogenation of the indenyl ring. This finding is similar to that reported for the hydrogenation of bis(indenyl)zirconium dimethyl. 5 Monitoring the reaction of Cp*(Ind)ZrMe2 with H2 by 1H NMR reveals the intermediacy of Cp*(THI)ZrMe2, suggesting that the zirconocene dihydride that is generated in the early stages of the reaction serves as a catalyst for hydrogenation of the benzo groups of both starting Cp*(lnd)ZrMe2 and initially formed Cp*(lnd)ZrH2. This suggestion is further supported by the qualitative rate enhancement for final conversion to 11 that is observed when Cp*(lnd)ZrMe2 is hydrogenated in the presence of 11. Moreover, 11 also catalyzes the hydrogenation of dibenzoferrocene 15 to bis( tetrahydroindenyl)iron.16 Proton NMR spectroscopy has proven particularly useful for the characterization of the new zirconocene dihydride complexes.5 The number of zirconium hydride resonances observed and their chemical shifts are useful in determining the molecularity of the dihydride species in solution. Monomeric zirconium dihydrides exhibit a single downfield resonance (o ~ 7 to 8), whereas dimeric dihydrides display separate resonances for terminal (o ~ 4 to 5) and bridging hydrides (o ~ 1 to -1). Solution molecular weights for the new dihydrides and 1H NMR determined molecularities, along with those for 11 previously reported Cp*2ZrH2, 12a [Cp*('r1 5-CsHs)ZrH2]2, 13 and [Cp*('r1 5-CsH2-l,2,4-Me3)ZrH2]213 are given in Table 2. Compound MWa [Zr] (M) molecularity in solutionb [Cp*CpZrH2h 606 (294) ref. 13 dimeric 8 675 (348) 0.013 dimeric 11 670 (344) 0.040 dimeric 14 773 (392) 0.014 dimeric 10 740 (369) 0.049 monomer and dimer observed 15 564 (335) 0.041 monomer and dimer observed 9 5 Cp*(T1 -CsH2-l,2,4-Me3)ZrH2 446 (406) 0.044 monomeric 342 (336) ref. 13 monomeric 13 480 (448) 0.033 monomeric 12 346 (349) 0.029 monomeric Cp*2ZrH2 402 (394) ref. 12a monomeric a Solution molecular weights determined by ebulliometry at indicated concentration in benzene-d6 (calculated MW for monomer) at 296K. Errors in molecular weights are estimated as +/ -20 %. b Molecularity at 296K as established by 1H NMR in benzene-d6 or toluene-ds (see text). Table 2. Molecular weights for zirconocene dihydrides and molecularity indicated by 1H NMR spectroscopy. In all cases the measured molecular weights and 1H NMR data are in agreement. Thus, for example, the molecular weight indicates that Cp*2ZrH2 is monomeric and accordingly a single resonance at <5 7.46 is observed at room temperature in benzene-d6 for the equivalent [ZrH2]. Similarly, monomeric Cp*(T1 5-CsHMe4)ZrH2 (12), Cp*{T1 5-CsH3-l,3-(CMe3)2)ZrH2 (9) and (T1 5-C5H3-l,3-(CMe3)2)2ZrH2 (13) exhibit singlets at 8 7.45, 8 7.09 and 8 7.36, respectively, for their [ZrH2] resonances. 12 The other dihydride complexes exhibit 1H NMR spectra that are quite temperature dependent, suggesting equilibria between at least two forms. Thus, the 500 MHz spectrum for [Cp*CpZrH2h at room temperature displays no resonances attributable to [ZrH2]. Cooling a sample to 250K in toluene-ds solution allows for observation of signals for terminal (8 4.26 (br, multiplet)) and bridging (8 -2.65 (br, multiplet) hydrides and one set of cyclopentadienyl resonances (8 5.72 (ri 5-CsHs) and 8 1.93 {ri 5-Cs(CH3)5}). Somewhat unexpectedly, further cooling to 225K reveals two sets of hydride signals (8 4.31 multiplet) and 8 4.14 (multiplet); 8 -0.10 (multiplet) and 8 -2.68 (br, multiplet)) and two sets of cyclopentadienyl resonances (8 5.77 (major) and 8 5.65 (minor); 8 2.00 (minor) and 8 1.95 (major); [major]:[minor]::::: 3:1). These data suggest that above 225K two dimeric hydride isomers are in rapid equilibrium, presumably the cis and . trans isomers via monomeric [Cp*CpZrH2] as shown in Figure 6. cis Figure 6. Isomers of [Cp*CpZrH2]z. trans Considering the unfavorable steric interactions between cyclopentadienyl ligands across the [HZr(µ2-H)2ZrH] units, we tentatively assign the major isomer as trans (Figure 6). The related complex [Cp*(ri 5-C5ff4-CMe3)ZrH2h (8) exhibits very similar behavior, although the two isomeric dihydride dimers are observable at room temperature in approximately equal amounts. Signals for the terminal hydrides are observed at 8 4.08 (br, multiplet) and 8 3.90 (br, multiplet) whereas the bridging hydrides appear at 8 -0.76 and 8 -2.56. Heating the sample in cyclohexane-d12 to 340 K results in coalescense of the peaks attributable to protons of the Cp* (8 1.97) and CMe3 (8 1.38) groups. Curiously, the more sterically congested (8) undergoes slower isomer interconversion in comparison to [Cp*CpZrH2h- 13 Variable temperature NMR studies on [Cp*(ri 5-C5H3-l,3-CHMe2)ZrH2h (10) reveal yet another dynamic equilibrium for this complex. At room temperature the 500 MHz NMR spectrum displays a single set of ligand resonances in addition to a broad signal centered at S 4.06 for the zirconium hydride resonance, intermediate between those found for the monomeric and dimeric chemical shift values. We interpret a shift in this range as a weighted average between monomeric and dimeric dihydrides that are in rapid equilibrium. Cooling a sample of 10 ([Zr]= 0.049 M) to 200 Kin toluene-ds allows for observation of roughly equal amounts of two isomeric dihydride dimers. Terminal hydride resonances are observed at S 4.20 and S 3.92 whereas bridging hydrides appear at S-1.14 and S -1.25. Warming the sample to 240 K results in coalescence of the CHMe2 peaks (S = 1.39) as well as the terminal hydrides (S = 4.02). At 250 K, the signals attributable to the protons of the Cp* ligands for the two isomers coalesce at S 2.05. Continued heating of a sample of 10 above room temperature results in a gradual shift of the zirconium hydride resonance downfield, implicating increased concentration of the monomeric dihydride at higher temperatures. At 310 K, the zirconium hydride appears as a broad singlet centered at S = 5.45 and at 340 K the resonance shifts to S = 6.70. At 360 K, the hydride resonance approaches its maximum value of S = 6.90, and the value of the chemical shift of this peak does not change with further heating of the sample (T = 380 K). At these temperatures, we propose that monomeric 10 is the predominant species in solution (Figure 7) . ~H~ ~ ~ ~r-- ~--~8$: cis-10 2 ~z ···".H predominant species at T > ==350K 4?:z~H~- trans-IO Figure 7. Monomer-dimer equilibria for 10. Variable temperature NMR data for (ri 5-C5Me4H)2ZrH2 (15) also reveal significant amounts of both monomer and dimer in rapid equilibrium. Thus, the 500 MHz NMR spectrum at 296 K ([Zr]= 0.041 M) displays a very broad singlet for the zirconium hydride resonance centered at S = 2.80. Warming of the 14 sample results in both a sharpening of the zirconium hydride resonance as well as a shift downfield. As with 10, the spectrum of 15 at 380 Kin benzene-d6 solution displays a zirconium hydride resonance at◊= 7.11, implicating the presence of a monomeric zirconocene hydride. At temperatures between 296 K and 380 K, the chemical shift gradually shifts downfield from 8 = 2.80 to 8 = 7.11. Perhaps the most intriguing feature of 15 is its ability to form hydride bridges and hence a dimer, albeit only at low temperatures. Considering that Cp*2ZrH2 and 12 are monomeric, it is quite remarkable that removal of one methyl group from the other (T1 5-C5Me5) ligand of 12 is sufficient to permit formation of a dimeric 15. Clearly, there is just enough steric protection to dimer formation for both Cp*2ZrH2 and 12. HID exchange reactions for zirconocene dihydrides with D2. When each member of the series of zirconocene dihydrides is exposed to one atmosphere of dideuterium in benzene solution, rapid exchange of hydride ligands is observed (e.g., equation 3). ~H ~" H ~ 9 excess D2 benzene solution 25°C; seconds ~D ~" D (3) ~ 9-d 2 The rate of exchange is sufficiently rapid to be observed by 1H NMR. Exposure of a benzene-d6 solution of 9 to one atmosphere of H2 results in broadening and upfield shifting of the [ZrH2] resonance (toward that for dissolved H2); no resonance for H2 is observed, indicative of exchange on the 1H NMR time scale. Treatment of dimeric 8 and 11 with dideuterium results in rapid exchange of deuterium into both bridging and terminal hydride positions at room temperature (e. g., equation 4). 15 (4) Although we are unable to rule out direct reaction of D2 with the terminal and/ or bridging hydride ligands of the dimers, rapid exchange of both bridging and terminal hydride positions of the dimeric complexes suggests a facile monomer-dimer equilibrium (consistent with the variable temperature 1H NMR studies above), allowing for rapid incorporation of deuterium into both hydride positions. Deuterium incorporation into the C-H positions of the cyclopentadienyl ligands is much slower than for the hydride positions, and H/D exchange occurs preferentially only with certain of the C-H bonds of the monomeric dihydride complexes. Thus, reaction of monomeric Cp*2ZrH2 with D2 at 23 °C results in gradual incorporation of deuterium into the C-H positions of the two (ri 5-CsMes) ligands over a period of 12 hours. Benzene-d6 solutions of Cp*(ri 5-CsHMe4)ZrH2 (12) under D2 result in rapid exchange of the two hydride positions at room temperature, and over the course of several hours at 25 °C, selective deuteration of the Cp* ligands and two of the methyl groups of the tetramethylcyclopentadienyl ligand occurs, the ones that appear at o1.81 in the 1H NMR spectrum; the latter is approximately five times faster than the former. NOE difference spectroscopy reveals that these are the 1,4 methyl groups of the (ri 5-CsMe~) ligand. Thus, irradiation of the methyl groups at o= 1.81 results in an NOE enhancement of the (ri 5-CsMe4ffl resonance, while irradiation of the downfield methyl groups (o = 2.45) does not produce a detectable NOE enhancement. Deuteration of the two other methyl groups of the (ri 5-C5Me4H) ligand is eventually observed (2H NMR), although this exchange occurs at a much slower rate, requiring several days at room temperature or several hours at 80 °C. Similar observations have been made by Parkin, et al.: exposure of [{Me2Si(ri 5-CsMe4)2}ZrH2]2 to D2 results in rapid exchange of the hydride positions and slower deuterium incorporation preferentially into the methyl 16 groups a to the [SiMe2] linker. 17 As might be expected, the X-ray structure of (ri 5-CsHMe4)2ZrCl2 reveals that the less sterically demanding [C-H] groups are in the narrow portion of the zirconocene wedge. 18 Taken together these observations suggest that the methyl groups that are most accessible for formation of "tuck-in" intermediates are those directed toward the side of the metallocene wedge in the ligand array (eq. 5). -49(D *~ -HD ~D l2-d 2 + D2 ~D ~--..,.D (5) DH2C ~ l2-d 3 The remarkably exacting orientations for metallation of a methyl-substituted cyclopentadienyl ligand is perhaps most evident in the H/D exchange reactions for Cp*{ri 5-CsH3-l,3-(CMe3)2}ZrH2 (9). Treatment of 9 with D2 at 23 °C results in slow exchange with the C-H positions of the [CMe3] groups over a period of several hours. Interestingly, no deuterium incorporation into the Cp* ligand (or remaining three C-H bonds of the (ri 5-C5H3-l,3-(CMe3)2} ligand) is observed under these conditions (eq. 6). ~H Z ... ~ "-H ex~:ss -------benzene solution (H3ChC~C(CH3h 9 250c; hours ~D Zr'' 'D s:b (6) (D3ChC~C(CD3)} 9-d 20 Since no "tuck-in" derivative resulting from metallation of a [CMe3] builds up to 1H NMR detectable concentrations under these conditions, we conclude that the two tert-butyl substituents of the other cyclopentadienyl ligand must constrain the Cp* ligand in orientations unsuited to metallation of a methyl group. Treatment of dimeric [Cp*{11 5-CsH3-l,3-(CHMe2)2}ZrH2h (10) or 17 [('r1 5-CsHMe4)2ZrH2h (15) with dideuterium in benzene-d6 rapidly leads to exchange of the hydride positions, but not the methyl groups of the Cp*, isopropyl substituents or (11 5-CsHMe4) ligands, even after several days at room temperature. 19 This large reduction in rate likely reflects the requirement that formation of the "tuck-in" intermediates occurs from the monomer, which is present in only very low concentrations for the (predominantly) dimeric complexes. Con cl us ions A series of zirconocene dihydride complexes of the general form, [(RnCp )2ZrH2]x, having substituted cyclopentadienyl ligands has been prepared by hydrogenation of the corresponding dimethyl complexes. The molecularity of these compounds in solution varies with the size and/ or number of alkyl substituents on the cyclopentadienyl rings. The most sterically crowded members of the series: Cp*{11 5-C5H3-l,3-(CMe3)2}ZrH2 (9), Cp*(11 5-CsHMe4)ZrH2 (12) and {11 5-CsH3-l,3-(CMe3)2}2ZrH2 (13) are monomeric; the less crowded members: [Cp*(11 5-CsH4-CMe3)ZrH2h (8), [Cp*(THI)ZrH2h (11) and [{11 5-C5H3-l,3-(CHMe2)2hZrH2h (14) are predominantly dimeric in solution, whereas [Cp*{11 5-CsH3-l,3-(CHMe2)2}ZrH2h (10) and [(11 5-CsHMe4)2ZrH2h (15) form equilibrium mixtures of both monomers and dimers, the predominant form depending on temperature and concentration. Variable temperature NMR studies on the dimeric dihydride complexes having mixed cyclopentadienyl ligands, e.g., 9 and even [Cp*CpZrH2h, reveal comparable amounts of two different dimeric hydrides, presumably cis and trans isomers. It is likely that unfavorable steric interactions in the cis isomers are relieved by twisting of the two zirconocene units such that their "equatorial planes" are not coincident. Such twisting has been established for an ansa titanocene monohydride20 and for ansa yttrocene hydrides. 21 Whether monomeric or dimeric the hydride ligands of these dihydride complexes undergo rapid exchange with D2. For the monomeric members of the series, further H/D exchange leads to incorporation of deuterium into some of the alkyl substituents of the cyclopentadienyl ligands. The likely mechanism involves the monomeric dihydride undergoing intramolecular cr bond 18 metathesis between an alkyl C-H bond and a Zr-H bond, leading to "tuck-in" intermediates. The relative rates for HID exchange of methyl substituents indicate this process has a strong orientational preference for the back of the zirconcene wedge. Tert-butyl groups undergo HID exchange at a similar rate. Metallation of these C-H bonds also likely involves a reversible, intramolecular a bond metathesis process analogous to that reported earlier for (ri 5-CsMe4R)2ZrH2 (R = CH3, CH2CH3, CH2CMe3). 17 Experimental General Considerations. All air and moisture sensitive compounds were manipulated using standard vacuum line, Schlenk or cannula techniques, or in a drybox under a nitrogen atmosphere as described previously. 22 Molecular weights were determined by ebulliometry as described previously. 23 Argon, dinitrogen, dihydrogen and dideuterium were purified by passage over columns of MnO on vermiculite and activated molecular sieves. Solvents for air and moisture sensitive reactions were stored under vacuum over titanocene 23 or sodium benzophenone ketyl. Toluene-ds and cyclohexane-d12 were distilled from sodium beniophenone ketyl and stored over titanocene. Preparations of CsHs-CMei4, Cslit-t3-CMei5 , C5H4-l,3-CHMel6 , Cp*ZrCl3B, (ri 5-C5HMe4)2ZrCl219 and lithium indenide27 were carried out as described previously. Tetramethylcyclopentadiene was purchased from Quantum Chemical Company and used as received. Preparation of the lithiocyclopentadienides was accomplished via addition of 1.6 M n-BuLi to a petroleum ether solution of the cyclopentadiene followed by filtration. NMR spectra were recorded on a Bruker AM500 (500.13 MHz for 1H, 125.77 MHz for Be) spectrometer. All 1H and Be NMR chemical shifts are relative to TMS using 1H (residual) or 13C chemical shifts of the solvent as a secondary standard. Elemental Analyses were carried out at the Caltech Elemental Analysis Facility by Fenton Harvey. Complete combustion of the zirconocene dihydrides has proven difficult and many times V2Os or Thermo lite oxidant was added in order to gain satisfactory analyses. Cp*(ri 5-C5H4-CMe3)ZrClz (1). A 250 mL round bottom flask equipped with stir bar was charged with Cp*ZrCl3 (5.16 g, 15.60 mmol) and Me3CCpLi (2.00 g, 15.60 mmol) and a 180° needle valve was attached. On the vacuum line, 100 mL 19 of toluene was added by vacuum transfer, and the reaction mixture was warmed to room temperature and stirred for 5 days. Toluene was removed in vacuo, leaving a yellow solid. In air, about 50 mL of CH2Clz was added along with 20 mL of 4 M HCL The CH2Clz layer was separated and combined with the 15 mL extracts of the aqueous layer. The CH2Clz solution was dried over MgSO4 and filtered. Crystallization from CH2Cl2/hexanes afforded (1) in 60.5% yield (3.94 g). Anal. for C19H2sZriClz: C: 54.52% H: 6.74%. Found C: 54.63% H: 6.82%. 1H NMR (benzene-d6): 8 = 1.80 (s, 15H, Cp*), 1.45 (s, 9H, CMe3), 6.15 (m, 2H, C5H4); 5.55 (m, 2H, C5H4). 13C NMR (benzene-d6): 8 = 12.60 (CsMes), 112.6 (CsMes); 32.45 (CMe3), 146.6 (CMe3); 118.4, 122.5 (Cs~CMe3). Cp*('r1 5-C5H4-CMe3)ZrMe2. A medium frit assembly was charged with Cp*(T1 5-Cs~-CMe3)ZrCl2 (2.20 g; 5.28 mmol) and evacuated. Et2O was added by vacuum transfer at -78 °C forming a slurry. At -78 °C, against an Ar counterflow, 1.4 M MeLi (8.30 mL, 11.60 mmol) solution was added via syringe. The reaction mixture was stirred and warmed to room temperature. With stirring a clear solution and white precipitate forms. The reaction mixture was stirred for 16 hours after which time the Et2O was removed in vacuo and replaced with toluene. The yellow toluene solution was filtered, and the remaining white precipitate was washed with toluene. The toluene was removed leaving a yellow powder. Recrystallization from cold petroleum ether affords Cp*(T1 5-C5H4-CMe3)ZrMe2 in 60.4% yield (1.20 g). Anal. for C21H34Zq C: 66.78% H: 9.07% Found: C: 65.96 % H: 9.11 %. 1H NMR (benzene-d6): 8 = 1.74 (s, 15H, Cp*), 1.26 (s, 9H, CMe3), -0.30 (s, 6H, Zr-CH3 ), 5.80 (m, 2H, C5H4); 5.44 (m, 2H, C5H4). 13C NMR (benzene-d6): 8 = 12.11 (CsMes), 110.15 (CsMes); 32.25 (CMe3), 142.97 (CMe3), 33.17 (Zr-CH3) 117.82, 108.67 (Cs~CMe3). [Cp*(T1 5-C5H4-CMe3)ZrH2h (8). In the dry box, a thick-walled glass reaction vessel equipped with stir bar was charged with Cp*(T1 5-C5~-CMe3)ZrMe2 (0.754 g, 2.01 mmol). On the vacuum line, the thick-walled reaction vessel was evacuated, and about 25 mL of petroleum ether was added by vacuum transfer. The reaction vessel was warmed to room temperature and 1 atmosphere of H2 was admitted. The reaction vessel was sealed, and the mixture was stirred for one week, depositing a white solid over time. The reaction vessel was taken into the dry box, the contents transferred into a frit assembly, and the solid was collected on the frit and was washed with cold petroleum ether. Drying the solid 20 in vacuo for five hours affords [Cp*(T1 5-CsHi-CMe3)ZrH2h in 65% yield (0.452 g). Anal. for C19H30Zr: C: 65.26% H: 8.65%. Found (V2Os oxidant) C: 63.37 % H: 8.61 %; Found (Added Thermolite oxidant) C: 60.50%; H: 8.34%. 1H NMR (benzene-d6): 8 = 1.95, 1.97 (s, 15H, Cp*), 1.36, 1.39 (s, 9H, CMe3), 4.08, 3.09 (m, 2H, Zr-Ht), -0.76, -2.56 (m, 2H, Zr-Hb), 4.55, 4.83, 4.96, 5.85, 6.07, 6.62 (m, C5H4). 13c NMR (benzene-d6): 8 = 13.77, 13.89 (CsMes), 115.85, 116.01 (CsMes); 33.26, 33.36 (CMe3), 141.40, 141.62 (CMe3); 105.50, 104.85, 104.50, 103.49, 103.07, 100.70, 98.65 (C5li4CMe3). Cp*(Indenyl)ZrClz (4). This compound was prepared in the same manner as 1 with 4.10 g (12.34 mmol) of Cp*ZrCb and 1.52 g of lithium indenide (12.34 mmol). Crystallization from CH2Cb/hexanes afforded Cp*(Indenyl)ZrCb in 82.4 % yield (4.20 g). Anal. Calcd for C19H22ZriCb: C: 55.32% H: 5.38%. Found C: 55.22% H: 5.10%. 1H NMR (benzene-d6): 8 = 1.81 (s, 15H, Cp*), 5.89 (m, 2H, Cp); 5.80 (m, 2H, Cp), 7.08 (m, 2H, benzo), 7.51 (m, 2H, benzo). 13c NMR (benzene-d6): 8 = 12.69 (CsMes), 104.27 (CsMes), 118.30, 121.87, 123.50, 125.72, 127.04 (Ind). Cp*(Indenyl)ZrMe2. This compound was prepared in the same manner as Cp*(T15-C5H4-CMe3)ZrMe2 with 2.35 g of Cp*(Indenyl)ZrCb (5.69 mmol) and 8.90 mL of 1.4 M MeLi. Recrystallization from cold petroleum ether affords Cp*(Indenyl)ZrMe2 in 70.8% yield (1.50 g). Anal. for C21H2sZri C: 67.86% H: 7.56% Found: C: 67.88% H: 8.06%. 1H NMR (benzene-d6): 8 = 1.71 (s, 15H, Cp*), -0.84 (s, 3H, Zr-CH3), 5.81 (m, 2H, Cp ); 5.37 (m, 2H, Cp ), 7.39 (m, 2H, benzo ), 7.09 (m, 2H, benzo ). 13C NMR (benzene-d6): 8 = 11.79 (C5Me5), 100.70 (CsMes), 36.06 (Zr-CH3), 117.45, 118.34, 122.78, 124.61, one peak not located (Ind). [Cp*(THI)ZrH2h (11). This compound was prepared in the same manner as 8 with 1.35 g of Cp*(Indenyl)ZrMe2 (3.63 mmol) yielding [Cp*(THI)ZrH2]2 in 68.0% yield (0.850 g). Anal. for C19H2sZri Calculated C: 65.64% H: 8.12%. Found (with V2Os oxidant) C: 65.46% H: 8.36%. 1H NMR (benzene-d6): 8 = 2.01 (s, 15H, Cp*), 5.18 (s, 2H, Zr-Ht), -1.86 (s, 2H, Zr-Hb), 5.78 (m, lH, Cp); 5.01 (m, lH, Cp), 4.65 (m, lH, Cp), 0.85, 1.92, 2.12, 2.65 (m, THI). 13C NMR (benzene-d6): 8 = 13.61 (CsMes), 116.47 (CsMes), 98.78, 103.45, 108.93 (Cp ), 22.38, 24.36, 25.17, 28.03 (THI). Cp*{r1 5-C5H3-l,3-(CHMe2h}ZrCl2 (3). This compound was prepared in the 21 same manner as 1 with 2.73 g Cp*ZrCl3 (8.22 mmol) and 1.22 g {C5H3-l,3-(CHMe2)2}Li (8.22 mmol). Crystallization from CH2Cb/hexanes afforded Cp*(ri 5-C5H3-l,3-(CHMe2)2)ZrCl2 in 83.3% yield (3.00 g). Anal. for e21H32ZriCb: C: 56.48% H: 7.22%. Found C: 56.53% H: 7.32%. 1H NMR (benzene-d6): 8 = 1.83 (s, 15H, Cp*), 3.19 (sept., 2H, CHMe2), 0.96 (d, 6H, eHMe2), 1.16 (d, 6H, CHMe2), 5.30 (d, 2H,C5H3) 6.05 (t, lH, C5H3). Be NMR (benzene-d6): 11.34 (esMes), 106.47 (CsMes); 36.06 (CHMe2), 22.00, 23.85 (eHMe2), 112.5, 114.73, 122.84 (C5H3). Cp*{ri 5-C5H3-l,3-(CHMe2h}ZrMe2. This compound was prepared in the same manner as Cp*(T1 5-CsHt-eMe3)ZrMe2 with 2.00 g of ep*{ri 5-esH3-l,3-(CHMe2)2}ZrCb (4.56 mmol) and 6.80 mL of 1.4 M MeLi (9.56 mmol). Recrystallization from cold petroleum ether affords ep*{ri 5-C5H3-l,3-(CHMe2)2}ZrMe2 in 91.2% yield (1.65 g). Anal. for C23H3sZri C: 68.08 H: 9.44 Found: C: 68.06 H: 9.22. 1H NMR (benzene-d6): 8 = 1.78 (s, 15H, Cp*), -0.39 (s, 3H, Zr-CH3), 2.83 (sept., 2H, CHMe2), 0.94 (d, 6H, CHMe2), 1.22 (d, 6H, eHMe2), 4.93 (d, 2H,C5H3) 6.05 (t, lH, C5H3). Be NMR (benzene-d6): 12.08 (CsMes), 103.30 (C5Me5); 28.84 (Zr-CH3), 35.79 (CHMe2), 22.70, 25.90 (CHMe2), 111.42, 117.68, 137.78 (C5H3). [Cp*(ri 5-C5H3-l,3-(CHMe2h)ZrH2h (10). This compound was prepared in the same manner as 8 with 0.680 g of Cp*{ri 5-C5H3-l,3-(CHMe2)2}ZrMe2 (1.71 mmol). Recrystallization from cold petroleum ether affords [Cp*({ri 5-CsH3-l,3-(CHMe2)2}ZrH2h in 72.2% yield (0.456 g). Anal. for C21H34Zq C: 66.78% H: 9.07% Found: C: 67.13% H: 9.04%. 1H NMR (benzene-d6): 8 = 2.05 (s, 15H, Cp*), 4.06 ( br s, 2H, Zr-H2), 3.21 (sept., 2H, CHMe2), 1.27 (d, 6H, CHMe2), 1.30 (d, 6H, eHMe2), 5.03 (d, 2H,C5H3) 6.15 (t, lH, C5H3). Be NMR (benzene-d6): 13.44 (CsMes), 107.55 (CsMes), 30.01 (CHMe2), 25.58, 23.77 (CHMe2), 95.51, 103.16, 118.48(C5H3). Cp*{ri 5-C5H3-l,3-(CMe3h}ZrCh (2). This compound was prepared in the same manner as 1 with 3.00 g of ep*Zrel3 (10.09 mmol) and 3.62 g of {C5H3-l,3-(CMe3)2}Li(DMEh.s (10.09 mmol). Recrystallization from CH2Clz/hexanes afforded Cp*{ri 5-CsH3-l,3-(CMe3)2}Zre1z in 71.0% yield (3.56 g). Anal. for C23H36ZriCl2: C: 58.20% H: 7.62%. Found C: 57.75% H: 7.89%. 1H NMR (benzene-d6): 8 = 1.82 (s, 15 H, Cp*), 1.28 (s, 18 H, CMe3), 5.46 (d, 2H, 22 C5H3), 6.38 (d, lH, C5H3). 13C NMR (benzene-d6): 12.05 (CsMes), 113.45 (CsMes), 31.60 (CMe3), 142.50 (CMe3), 109.75, 114.63, 123.50 (C5H3). Cp*{11 5-CsH3-l,3-(CMe3)z}ZrMe2. This compound was prepared in the same manner as Cp* {ri 5-C5H4-CMe3]ZrMe2 with 1.25 g of Cp*{ri 5-CsH3-l,3-(CMe3)2}ZrC!i (2.64 mmol) and 4.10 mL of 1.4 M MeLi (5.79 mmol). Recrystallization from cold petroleum ether affords Cp* {ri 5-CsH3-l,3-(CMe3)2}ZrMe2 in 84.1 % yield (0.96 g). Anal. for C23H36Zri C: 68.42% H: 8.99% Found: C: 68.26% H: 9.30%. 1H NMR (benzene-d6): 8 = 1.78 (s, 15 H, Cp*), -0.20 (s, 6H, Zr-CH3), 1.25 (s, 18 H, CMe3), 5.00 (d, 2H, CsH3), 6.41 (d, lH, C5H3). 13C NMR (benzene-d6): 12.28 (CsMes), 117.86 (CsMes), 33.95 (Zr-Me), 31.93 (CMe3), 143.18 (CMe3), 103.82, 106.87, 130.54 (CsH3). Cp*{ri 5-CsH3-1,3-(CMe3)z}ZrH2 (13). This compound was prepared in the same manner as 8 with 0.950g of Cp*(ri 5-CsH3-l,3-(CMe3)2)ZrMe2 (2.19 mmol). Drying the solid in vacuo for several hours affords Cp*{ri 5-CsH3-l,3-(CMe3)2}ZrH2 in 78.8% yield (0.700 g). Anal for C21H32Zr C: 60.08% H: 9.44% Found C: 66.60% H: 8.60%; (Added Thermolite oxidant) C: 66.85% H: 9.14%. 1H NMR (benzene-d6): 8 = 2.05 (s, 15 H, Cp*), 7.09 (s, 2H, Zr-H2), 1.30 (s, 18 H, CMe3), 4.92 (d, 2H, C5H3), 6.70 (d, lH, C5H3). 13C NMR (benzene-d6): 13.06 (CsMes), 101.08 (CsMes), 32.22 (CMe3), 135.45 (CMe3), 105.60, 109.08, 120.04 (C5H3). Cp*(ri 5-CsHMe4)ZrCl2 (5). A 100 mL round bottom flask equipped with stir bar was charged with Cp*ZrCb (3.00 g, 9.03 mmol), (CsHMe4)Li (1.15 g, 9.03 mmol), and a 180° needle valve and reflux condenser were attached. On the vacuum line 50 mL of toluene was added by vacuum transfer, and reaction mixture was heated to reflux for 2 days. The toluene removed in vacuo leaving a yellow solid. In air, about 50 mL of CH2Cl2 was added along with 20 mL of 4 M HCL The CH2Cl2 layer was separated and combined with the 15 mL extracts of the aqueous layer. The CH2Cb solution was dried over MgSO4 and filtered. Crystallization from CH2Cb / hexanes afforded Cp*(ri 5-CsHMe4)ZrCl2 in 82.1 % yield (3.10 g). Anal. for C19H2sZriCl2: C: 54.52% H: 6.74%. Found C: 54.68% H: 6.76%. 1H NMR (benzene-d6): 8 = 1.85 (s, 15 H, Cp*), 1.65 (s, 6H, C5Me4H), 23 2.03 (s, 6H, esMe4H), 5.14 (s, lH, esMe,iH). Be NMR (benzene-d6): 8 = 12.83 (CsMes), 110.45 (esMes), 12.98, 12.39 (C5Me4H), 119.32, 123.42, 132.40 (C5Me4H). Cp*(C5HMe4)ZrMe2. This compound was prepared in the same manner as Cp*('n 5-esH4- eMe3)ZrMe2 with 2.00 g of ep*(11 5-esHMe4)Zreb (4.78 mmol) and 7.50 mL of 1.4 M MeLi (10.5 mmol). Drying the solid in vacuo affords Cp*(11 5-esHMe4)ZrMe2 in 79.3% yield (1.43 g). Anal. for e21H34Zq C: 66.78% H: 9.07% Found: C: 66.68% H: 9.36%. 1H NMR (benzene-d6): 8 = 1.78 (s, 15 H, Cp*), -0.56 (s, 6H, Zr-eH3) 1.57 (s, lH, esMe,iH), 1.96 (s, 6H, esMe4H), 4.45 (s, 6H, esMe4H). Be NMR (benzene-d6): 8 = 12.10 (CsMes), 104.96 (esMes), 12.71, 12.08 (CsAfe4H), 35.74 (Zr-eH3), 117.13, 116.42, 123.39(CsMe4H). Cp*(11 5-CsHMe4)ZrH2 (15). This compound was prepared in the same manner as 8 with 1.40 g of ep*(11 5-esHMe4)ZrMe2 (3.71 mmol). Recrystallization from cold petroleum ether affords ep*(11 5-esHMe4)ZrH2 in 76.9% yield (1.00 g). Anal. for e19H30Zr Calculated C: 65.26% H: 8.65%. Found C: 65.44% H: 9.09%. 1H NMR (benzene-d6): 8 = 1.99 (s, 15 H, ep*), 1.81 (s, 6H, CsAfe4H), 2.45 (s, 6H, C5Me4H), 7.45 (s, 2H, Zr-H), 4.49 (s, lH, esMe,iH). Be NMR (benzene-d6): 8 = 13.02 (CsMes), 106.15 (esMes), 13.38, 14.37 (esMe4H), 118.75, 119.18, 125.47 (CsMe4H). {17 5-C5H3-l,3-(CMe3)i}zZrC}z (6). In a dry box, a 100 mL round bottom flask was charged with [Li(DME)][C5H3-l,3-(eMe3)2] (5.00 g, 18.13 mmol) and Zre4 (2.11 g, 9.07 mmol). A reflux condenser and a 180° needle valve were attached. Via cannula, 50 mL of toluene was added to the reaction flask. The reaction mixture was heated to reflux forming a yellow solution. After three days, the toluene was removed_in vacuo leaving a yellow/ orange solid. In air, CH2el2 (~50 mL) was added along with 25 mL of 4 M HCL The organic layer was collected, and the aqueous layer was washed with 10 mL portions of CH2e1i. The combined organic layers were dried over MgSO4 and filtered. The solvent was removed, leaving a yellow solid. The material was further purified by sublimation at 160 °e and 10-4 Torr yielding 3.10 g (66.70%) of a white solid. Anal for e26~2Zrieh. ealcd C: 60.43% H: 8.19%. Found C: 60.74% H: 8.41 %. 1H NMR (benzene-d6): 8 = 1.30 (s, 18H, esH3-(CMe3)2), 5.83 (m, 2H, esH3-(CMe3)2), 6.62 (m, lH, esH3-(eMe3)2). 13C NMR (benzene-d6): 8 =31.61 (esH3-(eMe3)2), 145.09 (C5H3-(CMe3)2), 105.88, 118.79, 123.31 (C5H3-(eMe3)2). 24 {11 5-C5H3-l,3-(CMe3hhZrMe2. A medium frit assembly was charged with {11 5-C5H3-l,3-(CMe3)2}2ZrCl2 and evacuated. Diethyl ether (15 mL) was added by vacuum transfer. Against an Ar counterflow at-80 °C, 1.4 M MeLi in Et2O was added via syringe. The reaction mixture was slowly warmed to room temperature with stirring. After stirring for 36 hours, Et2O removed in vacuo and replaced with toluene. The toluene solution was filtered away from white precipitate. The precipitate was washed three times with toluene on the frit. The toluene was removed in vacuo, and the product was recrystallized from cold petroleum ether affording 1.20 g (65.1 %) of {11 5-C5H3-l,3-(CMe3)2}2ZrMe2. Anal for C2sH4sZri. C: 70.67% H: 10.17%. Found C: 70.75% H: 10.57%. 1H NMR (benzene-d6): 8 = 1.28 (s, 18H, C5H3-(CMe3)2), 5.41 (m, 2H, C5H3-(CMe3)2), 6.55 (m, lH, C5H3-(CMe3)2), 0.17 (s, 3H, Zr-CH3). 13C NMR(benzene-d6): 8 = 32.02 (C5H3-(CMe3)2), 139.14 (C5H3-(CMe3)2), 34.08 (Zr-CH3) 101.32, 106.50, 116.12 (C5H3-(CMe3)2). {11 5-C5H3-l,3-(CMe3hhZrH2 (13). This compound was prepared in the same manner as 8 with 1.06 g of {'r1 5-C5H3-l,3-(CMe3)2}2ZrMe2 (2.44 mmol). After 5 days the material was transferred into a frit assembly, and the resulting white solid was filtered and dried in vacuo yielding 0.650 g (65.0%) of {11 5-C5H3-l,3-(CMe3)2}2ZrH2. Anal for C26H42Zr C: 69.73% H: 9.90% Found C: 69.58% H: 10.06%. 1H NMR (benzene-d6): 8 = 1.26 (s, 18H, C5H3-(CMe3)2), 5.34 (m, 2H, C5H3-(CMe3)2), 6.94 (m, lH, C5H3-(CMe3)z), 7.36 (s, 2H, Zr-H). 13C NMR(benzene-d6): 8 = 32.11 (C5H3-(CMe3)z), 142.19 (CsH3-(CMe3)z), 100.40, 105.75, not located (C5H3-(CMe3)z). {11 5-C5H3-l,3(CHMe2hhZrCl2 (7). In the dry box, a 250 mL round bottom flask was charged with Li2[C5H3-l,3(CHMe2)z] (5.10 g, 34.29 mmol) and ZrCl4 (3.99 g, 17.14 mmol). A reflux condenser and a 180° needle valve were attached. Via cannula, 100 mL of toluene was added to the reaction flask. The reaction mixture was heated to reflux, forming a yellow solution. After three days, the toluene was removed in vacuo leaving a tan powder. In air the solid was transferred into a sublimator, and the material sublimed at 160 °C and 10-4 Torr, yielding 5.30 g (69.4%). Anal for C22H34ZqCl2 C: 57.36% H: 7.44%. Found C: 57.20% H: 7.31 %. 1H NMR(benzene-d6): 8 = 1.04 (d, 12H, CHMe2), 1.17 (d, 12H, CHMe2), 3.11 (sept, 4H, CHMe2), 5.62 (d, 2H, C5H3-(CHMe2)2), 6.26 (t, lH, 25 C5H3-(l,3-CHMe2)2. 13C NMR(benzene-d6): 23.61 (CHMe2), 23.81 (CHMe2), 29.74 (CHMe2), 107.53, 116.49, 142.29 (CsH3-(l,3-CHMe2)2). {'n 5-C5H3-l,3(CHMe2)z}zZrMe2. A medium frit assembly was charged with {ri 5-C5H3-l,3(CHMe2)2}2ZrCh (2.00 g, 4.49 mmol) and evacuated. Diethyl ether (25 mL) was added by vacuum transfer. Against an Ar counterflow at -80 °C, 1.4 M MeLi (7.1 mL, 9.9 mmol) in Et2O added via syringe. The reaction mixture was slowly warmed to room temperature with stirring. After stirring for 16 hours Et2O was removed in vacuo and replaced with toluene. The toluene solution was filtered away from white precipitate. The precipitate was washed three times with toluene on the frit. The toluene was removed in vacuo, and the product was recrystallized from cold petroleum ether, affording 1.60 g (88.1 %) of {ri 5-CsH3-l,3(CHMe2)2hZrMe2. Anal for C24fi4oZri. Calcd C: 68.67% H: 9.60%. Found C: 68.49% H: 9.46%. 1H NMR (benzene-d6): b = 1.10 (d, 12H, CHMe2), 1.20 (d, 12H, CHMe2), -0.11 (s, 6H, Zr-CH3), 2.74 (sept, 4H, CHMe2), 5.38 (d, 2H, C5H3-(CHMe2)2), 6.08 (t, lH, CsH3-(l,3-CHMe2)2. 13C NMR (benzene-d6): 24.12 (CHMe2), 24.44 (CHMe2), 33.09 (Zr-CH3), 29.04 (CHMe2), 104.8, 110.40, 134.92( C5H3-(l ,3-CHMe2)2). [{(ri 5-CsH3-l,3(CHMe2)z}zZrH2h (14). In the dry box, a thick-walled glass reaction vessel was charged with {ri 5-CsH3-l,3(CHMe2)2hZrMe2 (0.700 g, 1.73 mmol). On the vacuum line the reaction vessel was degassed, and approximately 10 mL of petroleum ether was added by vacuum transfer. One atmosphere of H2 was admitted to the reaction vessel, and the reaction mixture was stirred at room temperature depositing a white solid. After 3 days, the material was transferred into a frit assembly, and the resulting white solid was filtered and dried in vacuo yielding 0.550 g (85.0%) of [{(ri 5-CsH3-l,3(CHMe2)2}2ZrH2]2. Anal for C22H36Zri. Calcd C: 67.45% H: 9.26%. Found C: 67.17% H: 9.58%. 1H NMR (benzene-d6): b = 1.35 (br s, 24H, CHMe2), 3.15 (sept, 4H, CHMe2), 3.85 (br s, 2H, Zr-Ht), -2.10 (br s, 2H, Zr-Hb), 5.05 (d, 2H, CsH3-(CHMe2)2), 5.85 (t, lH, C5H3-(l,3-CHMe2)2. 13C NMR (benzene-d6): 22.71 (CHMe2), 26.98 (CHMe2), 30.14 (CHMe2), 98.23, 99.57, 104.56 (CsH3-(l,3-CHMe2)2). (ri 5-CsHMe4)zZrMe2. A medium frit assembly was charged with (ri 5-CsHMe4)2ZrCh (2.15 g, 5.32 mmol) and evacuated. Diethyl ether (25 mL) 26 was added by vacuum transfer. Against an Ar counterflow at -80 °C, 1.4 M MeLi (8.4 mL, 11.7 mmol) in Et2O added via syringe. The reaction mixture was slowly warmed to room temperature with stirring. After stirring for 12 hours, the solution filtered away from white precipitate. The precipitate was washed three times with Et2O on the frit. The Et2O was removed in vacuo, affording 1.93 g (94.3 %) of (T1 5-CsHMe4)2ZrMe2. Anal for C20H32Zri. Calcd C: 66.05% H: 8.87%. Found C: 65.88% H: 9.09%. 1H NMR (benzene-d6) 8 = 1.68 (s, 12H, CsMqH), 1.95 (s, 12H, CsAfe4H), -0.55 (s, 6H, Zr-CH3), 4.72 (CsMe,i.H). 13C NMR (benzene-d6) 8 = 12.01, 13.50 (CsMqH), 35.30 (Zr-CH3), 105.56, 111.45, 122.29 (C5Me4H). [(T1 5-CsHMe4)zZrH2h (15). In the dry box, a thick-walled glass reaction vessel was charged with (T1 5-CsHMe4)2ZrMe2 (1.00 g, 2.75 mmol). On the vacuum line the reaction vessel was degassed, and approximately 25 mL of petroleum ether was added by vacuum transfer. One atmosphere of H2 was admitted to the reaction vessel, and the reaction was stirred at room temperature. After 5 days the material was transferred into a frit assembly, and the resulting yellow solid was washed with petroleum ether and dried in vacuo, yielding 0.800 g (86.8%) of [(T1 5-CsHMe4)2ZrH2]2. Anal for C1sH23Zq. Calcd C: 64.41 % H: 8.40%. Found C: 64.35% H: 8.77%. 1H NMR (benzene-d6) 8 = 2.02 (s, 12H, CsAfe4H), 2.14 (s, 12H, C5Me4H), 2.08 (br s, 2H, Zr-H2), 45.56 (CsMe~). 13C NMR (benzene-d6) 8 = 13.36, 15.13 (CsMqH), 108.39, 111.86, 115.41 (CsMe4H). Deuteration Experiments. In a typical experiment, a J. Young NMR tube is charged with 5 mg of the a dihydride complex and dissolved in 0.5 mL of benzene-d6 in the dry box. On the vacuum line the tube was frozen in liquid nitrogen and degassed using three freeze-pump-thaw cycles. While immersed in liquid nitrogen, one atmosphere of deuterium gas was admitted to the tube. The solution was then thawed rapidly in a water bath, and the tube rotated at room temperature to insure thorough mixing. Structure Determination for 1, 3, 6. For all samples: 1) Suitable fragments were cut from single crystals, attached to a glass fiber and centered on an EnrafNonius CAD-4 diffractometer under an 85K stream of N 2 gas. 2) Unit cell parameters were obtained from the setting angles of 25 high angle reflections. 3) Two equivalent data sets were collected and merged in the appropriate point 27 group. 4) Three reference reflections were measured every hour during data collection to monitor crystal decay. 5) Lorentz and polarization corrections were applied. The data for 1 and 6 were corrected for decay of 0.32% and 0.19% respectively. An absorption correction was made for 6. The structures of 1 and 6 were solved by Direct Methods, 3 was solved by the Patterson method. For 1, 3 and 6 difference Fourier maps were used to locate all missing atoms, including hydrogens. All hydrogen atoms were refined without restraints. For 1, 2439 data were refined to R=0.015 (GOF=l.66); for 3, 2546 data were refined to R=0.029 (GOF=l.83) and for 6, 2330 data were refined to R=0.044 (GOF=2.04). Acknowledgments: This work has been supported by the USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431) and Exxon Chemicals America. Supplemental Information Available: ORTEP drawings showing the complete atom labeling schemes, cell and crystal packing diagrams, tables of atomic coordinates, complete bond distances and angles and anistropic displacement parameters for complexes 1, 3, 6 and Cp*2HfH2 (36 pages). 28 Ordering and Internet access information is given on any current masthead page. References. The work in this chapter has been published previously. See Chirik, P.J.; Day, M.W.; Bercaw, J.E. Organometallics 1999, 18, 1873. 1. Collman, J.P.; Hegedus, L.S.; Norton, J.R.; Finke, R.G. in Principles and Applications of Organotransition Metal Chemistry: University Science Books, Mill Valley, California (1987) p. 80, 669. 2. Hoveyda, A.H.; Morken, J.P.; Agnew. Chem. Int. Engl. 1996, 35, 1262. 3. (a) Brintzinger, H.H.; Fischer, D.; Miilhaupt, R.; Rieger, B.; Waymouth, R.M. Agnew. Chem. Int. Ed. Engl. 1995, 34, 1143. (b) Piers, W.E. Chem. Eur. J. 1998, 4, 13. (c) Jordan, R.F. Adv. Organomet. Chem. 1991, 32,325. 4. Couturier, S.; Gautheron, B. J. Organomet. Chem. 1978, 157, C61. 28 5. Weigold, H.; Bell, A.P.; Willing, R.I.; J. Organomet. Chem. 1974, 73, C23. 6. (a) Jones, S.B.; Peterson, J.L. Inorg. Chem. 1981, 20, 2289. (b) Larsonneur, A.; Choukroun, R.; Jaud, J. Organometallics 1993, 12, 3216. 7. Jones, S.B.; Peterson, J.L. Organometallics 1985, 4, 966. 8. Grossman, R.B.; Doyle, R.A.; Buchwald, S.L. Organometallics 1991, 10, 1501. 9. Cuenca, T.; Galakhov, M.; Royo, E.; Royo, P. J. Organomet. Chem. 1996, 515, 33. 10. Lee, H.; Desrosiers, P.J.; Guzei, I.; Rheingold, A.L.; Parkin, G. J. Am. Chem. Soc. 1998,120,3255. 11. Piers, W.E.; Shapiro, P.J.; Bunel, E.E.; Bercaw, J.E. Synlett 1990, 74. 12. (a) Manriquez, J.; McAlister, D.R.; Sanner, R.D.; Bercaw, J.E. J. Am. Chem. Soc. 1978, 100, 2716. (b) Roddick, D.M.; Fryzuk, M.D.; Seidler, P.F.; Hillhouse, G.L.; Bercaw, J.E. Organometallics 1985, 4, 97. 13. Wolczanski, P.T.; Bercaw, J.E. Organometallics 1982, 1, 793. 14. This compound has been reported previously: Vanderheijen, H.; Hessen, B.; Orpen, A.G. J. Am. Chem. Soc. 1998, 120, 1112. 15. Wilkinson, G.; Pauson, P.L. J. Am. Chem. Soc. 1954, 70, 2024. 16. Hydrogenation of rac-(EBI)ZrMe2 in benzene solution affords the previously reported {rac-(EBTHI)ZrH2h in 57% yield. See reference 8. 17. Parkin, G., personal communication. 18. Janiak, C.; Versteeg, U.; Lange, K.C.H.; Weiman, R.; Hahn, E. J. Organomet. Chem. 1995, 501, 219. 19. Under more forcing conditions (ca. 2 atm D2, 80 °C, 12 hr, benzene-d6) HID exchange for the methyl groups of the (115-CsHMe4) ligands is accompanied by formation of (11 5-CsHMe5)2Zr(H)(C6DxHs-x) and cyclohexane-dn. Chirik, P. J.; Bercaw J.E., unpublished results. 29 20. Xin, S.; Harrod, J. F.; Samuel, E. J. Am. Chem. Soc. 1994, 116, 11562. 21. Mitchell, J.P.; Hajela, S.; Brookhart, S. K.; Hardcastle, K. I.; Henling, L. M.; Bercaw, J.E. J. Am. Chem. Soc. 1996, 118, 1045. 22. Burger, B.J.; Bercaw, J.E. In Experimental Organometallic Chemistry; ACS Symposium Series No. 357; Wayda, A.L.; Darensbourg, M.Y. Eds.; American Chemical Society: Washington, DC 1987; Chapter 4. 23. Marvich, R.H.; Brintzinger, H.H.; J. Am. Chem. Soc. 1971, 93, 2046. 24. Sullivan, M.F.; Little, W.F. J. Organomet. Chem. 1967, 8, 277. 25. Venier, C.G.; Casserly, E.W. J. Am. Chem. Soc. 1990, 112, 2808. 26. Herzog, T.A. Ph.D. Thesis California Institute of Technology, Pasadena, CA 1997. 27. Christopher, J.N.; Diamond, G.M.; Jordan, R.F.; Peterson, J.L. Organometallics 1996, 15, 4038. 28. Crystallographic data have been deposited at CCDC, 12 Union Road, Cambridge CB2 lEZ, UK, and copies can be obtained on request, free of charge, by quoting the publication citation and the deposition number 102518. 30. Soloveichik, G.L.; Arkihireeva, T.M.; Bel'skii, V.K.; Bulychev, B.M. Metalloorg. Khim. 1988, 1, 226. 31. Rogers, R.D.; Benning, M.M.; Kurihara, L.K.; Moriarity, K.J.; Rausch, M.D. J. Organomet. Chem. 1985, 293, 51. 32. Yicheng, D.; Shen, W.; Rongguang, Z.; Shousan, C. Kexue Tongbao (Chin.) 1982, 1436 27. I 30 Chapter 2 Synthesis of Singly and Doubly Bridged Ansa-Zirconocene Dihydrides and Activation of Dinitrogen by a Monomeric Zirconocene Dihydride Complex. 31 Abstract A series of singly and doubly bridged ansa-zirconocene dihydride complexes has been prepared from hydrogenation of the corresponding dimethyl complexes. For the singly [SiMe2]-bridged species, the hydrogenation reaction is facile at 25 °C whereas for the doubly [SiMe2]-bridged complexes hydrogenation occurs over the course of days at 87 °C. Hydrogenation of mesoMe2Si(11 5-C5H3-3-CMe3)2ZrMe2 affords the dimeric dihydride, [Me2Si(n 5-C5H3-3CMe3)2ZrH2h, which has been characterized by X-ray diffraction. The racemo isomer of Me2Si(11 5-CsH2-2-SiMe3-4-CMe3)2ZrMe2 (BpZrMe2) reacts with dihydrogen affording the first example of a monomeric, ansa-zirconocene dihydride, rac-Me2Si(n 5-CsH2-2-SiMe3-4-CMe3)2ZrH2 (BpZrH2). In the presence of dinitrogen, rac-BpZrH2 undergoes thermal reductive elimination of H2 yielding the dinitrogen complex, BpZr(µ2-N2)ZrBp, in which the dinitrogen ligand is coordinated in a side-on fashion with an N-N bond distance of 1.2450(38) A. The doubly [SiMe2]-bridged zirconium dimethyl complex, [(Me2Si)2(11 5-C5H3)2]ZrMe2 (RpZrMe2), undergoes hydrogenation affording the hydride trimer, [RpZrb (µ3-H)2(µ2-H)3, which has been characterized by X-ray diffraction. More substituted doubly [SiMe2]-bridged zirconocene dihydrides such as [(Me2Si)2(11 5-CsH-3,5-(CHMe2)2)(11 5-CsH2-4-CH(CH3)(CH2CH3))ZrH2h ([sec-BuThpZrH2h) and [(Me2Si)2(11 5-CsH-2,4-(CHMe2)2)(11 5-CsH2-4CHMe2)ZrH2h ([iPrThpZrH2h) have been prepared and shown to be robust dimers in solution. 32 Introduction Group 4 ansa-metallocene complexes have received considerable attention due to their utility in olefin polymerization1 and applicability as catalysts for a host of other enantioselective bond-forming processes. 2 For many of these transformations, a metallocene hydride or dihydride is believed to be the active species during the catalytic cycle. In the asymmetric hydrogenation of 1,1disubstituted and trisubstituted alkenes with chiral ansa-zirconocene3 and titanocene catalysts,4 olefin insertion into metallocene hydride bonds is believed to be essential for stereoselectivity and catalyst turnover. Although group 4 ansa-metallocene hydrides are often implicated in a variety of catalytic cycles, the synthesis and characterization of these complexes has not been fully explored. The synthesis of rac-[(EBTHI)ZrH2h (EBTHI = ethylene-1,2-bis(17 5tetrahydroindenyl) from reduction of the dichloride complex has been reported by Buchwald and coworkers. 5 The dimeric structure of the dihydride has been proposed based on the observation of distinct terminal and bridging zirconium hydride resonances in 1H NMR spectrum. Royo 6 has used similar synthetic methodology to prepare the doubly [SiMe2]-bridged, [(Me2Si)2(17 5C5H3)2ZrH2h, which has also been reported to be dimeric in solution on the basis of its 1H NMR spectrum. Parkin has prepared [Me2Si(17 5-C5Me4)2ZrH2h ([OpZrH2h) from hydrogenation of the dimethyl complex at elevated temperatures in cyclohexane solution.7 Characterization of the hydride dimer has been accomplished by NMR spectroscopy and X-ray crystallography. As part of our systematic investigation of ancillary ligand effects in group 4 metallocene chemistry, we sought to extend the scope of our studies to include ansa-zirconocene dihydride complexes. In this report, we describe the preparation and characterization of both singly and doubly [SiMe2]-bridged zirconocene dihydrides from the hydrogenation of the corresponding dimethyl complexes. During the course of our investigations, we have been able to prepare the first example of a monomeric, ansa-zirconocene dihydride which undergoes reductive elimination of dihydrogen, resulting in the coordination and activation of dinitrogen. The zirconocene dinitrogen complex has been 33 characterized by X-ray diffraction and displays side-on coordination of the dinitrogen fragment. Results and Discussion Preparation of Singly Silylene-Bridged Zirconocene Dihydride Complexes. The first synthetic target in our study was [Me2Si(CsHi-3-CMe3)2ZrH2]n (DpZrH2) since the preparation of the zirconocene dichloride as the pure meso isomer has been reported. 8 Methylation of meso-DpZrCh in diethyl ether affords a 2:1 mixture of meso:rac DpZrMe2, arising from epimerization of the ligand at the zirconium center. Similar racemo-meso interconversions promoted by various salts and Grignard reagents have been observed previously with both group 3 and 4 metallocenes. 9 Preparation of pure meso-DpZrMe2 (1) may be accomplished by addition of AlMe3 to DpZr(NMe2)2 (eq. 1).1° Slow cooling of a petroleum ether solution of 1 affords large yellow crystals suitable for X-ray diffraction. The solid state structure of 1 is shown in Figure 1 and confirms the identity of the meso isomer. (1) 1 Compound 1 crystallizes in space group P2i/ c and contains two molecules in the asymmetric unit. There are no differences in the geometry of these two molecules. The molecule displays a normal coordination environment for an ansa-metallocene with the two zirconium methyl groups contained in the metallocene wedge, displaying typical zirconium methyl bond lengths of 2.275( 4) A and 2.273(4) A, respectively. 34 Figure 1. Molecular Structure of 1 with 50% probability ellipsoids. Hydrogenation of 1 in benzene-d6 proceeds over the course of hours at 25 °C, affording the dihydride dimer, meso-[DpZrH2]2 (2) (eq. 2). The 1H NMR spectrum in benzene-d6 indicates a C1 symmetric structure, displaying inequivalent tert-butyl, dimethylsilyl and cyclopentadienyl resonances. Terminal zirconium hydride resonances are observed at 3.94 and 4.03 ppm whereas the bridging hydride resonances are located at-2.35 and -5.29 ppm. Upon standing in benzene-d6, clear, colorless crystals of 2 are deposited over the course of several days at 25 °C. Complex 2 crystallizes in space group P_1 and the two halves of the dimer are related by a crystallographic center of inversion which is not consistent with the solution NMR spectrum. As result, the dihedral angle between the planes formed by the two metallocene wedges is zero and places the terminal hydrides in a trans relationship (eq. 2). Unfortunately, neither the bridging nor terminal hydride ligands have been found in the difference map. However, the zirconium-zirconium distance of 3.492 A in 2 is consistent with other crystallographically characterized zirconocene hydride dimers which display metal-metal distances between 3.4 to 3.5 A. 11 35 A dihedral angle of zero degrees between the two zirconocene equatorial planes contrasts previous results for ansa-metallocene hydride complexes. The ansa-zirconocene dihydride, [OpZrH2]27 and the ansa-titanocene rac[(EBTHI)TiH]212 display significant, 53 ° in the latter case, twisting of the metallocene equatorial planes in order to alleviate unfavorable steric interactions between cyclopentadienyl substituents. A similar dihedral angle of 40 ° has been measured for the ansa-yttrocene hydride, rac-[(ri 5-CsH2-2-SiMe3-4CMe3)2Si(OC10H6C10H6O)YH2] [(BnBpYH2)2].1 3 For 2, the unfavorable steric interactions between the tert-butyl groups is reduced by rotating the ligand about the metal-cyclopentadienyl centroid, thus placing these substituents in a trans-like arrangement in the dihydride dimer. ~~ ~--if-Ii~ Me2S 1 ~ - - Y S i M e2 (2) 1 2 Figure 2. Molecular structure of one zirconium center of 2 with 30% probability ellipsoids and atom labeling scheme, as viewed in the equatorial plane. Hydrogen atoms omitted for clarity. 36 Figure 3. Molecular structure of 2 with 30% probability ellipsoids. Since the solid state structure of 2 demonstrates the propensity of the tert-butyl substituents to adopt a trans-like arrangement allowing for the formation of hydride bridges, we sought to prepare the racemo isomer of 2 which would force the tert-butyl groups over the center of the metallocene wedge. Unfortunately, a synthetic method for the preparation of pure rac-DpZrMe2 has not been devised. As a result, we turned our attention to [Me2Si(CsH2-2-SiMe34-CMe3)2]ZrCb (BpZrC!i) which yields solely the racemo isomer upon metallation.1 4 One possible limitation of this approach is the synthetic difficulty associated with the preparation of rac-BpZrCl2. The synthesis requires heating ZrCl4 with the dipotassio salt of the ligand for one month and produces only a 15% yield of the desired zirconocene dichloride. 14 Once prepared, rac-BpZrC!i may be converted to rac-BpZrMe2 by addition of methyllithium in diethyl ether (eq. 3). Unlike 1, rac-BpZrMe2 does not undergo epimerization in the presence of alkyllithium reagents or salts such as LiCl. 37 2MeLi 3 BpZrC12 Hydrogenation of 3 in toluene affords rac-BpZrH2 (4) (eq. 4). Following the hydrogenation reaction by NMR spectroscopy reveals that conversion of 3 to 4 takes place over the course of hours at 25 °C. This is considerably more rapid than the rates observed for the unlinked systems which hydrogenate over the course of days under the same conditions. 15 The 1H NMR spectrum of 4 displays a singlet at 7.20 ppm for the Zr-H resonance indicative of a monomeric structure in solution.1 5 This is in agreement with the experimentally determined solution molecular weight of 625 g/mol (568.6 g/mol calculated for monomer). In the presence of dihydrogen, no Zr-H resonance is observed in the lH NMR spectrum of 4, suggesting rapid exchange between free dihydrogen and the zirconium hydrides on the 1H NMR timescale. Confirmation of this rapid exchange process has been obtained from addition of dideuterium gas to 4. Exchange of the zirconium hydrides with deuterium is observed instantaneously at -78 °C. Interestingly, deuteration of the CMe3 and SiMe3 groups on the ligand array is observed over the course of 12 hours at 25 °C. Deuteration of the cyclopentadienyl substituents arises from formation of "tuck-in" intermediates, in which a C-H bond of an alkyl group adds to the zirconium center and is then deuterated via a-bond metathesis with D2.1 5 Si(CD ) C(CD3h Me2S1 -D z,D (4) (CD3)~C(CD3l3 38 Allowing a yellow toluene solution of 4 to stand in the dry box under an atmosphere of dinitrogen results in rapid formation of a forest green solution. Cooling the solution to -30 °C precipitates rose colored crystals over the course of several days. X-ray diffraction reveals that the crystals are not the starting dihydride, 3, but rather the dinitrogen complex, BpZr(µ2-N2)ZrBp (5). The solid state structure of 5, shown in Figure 4, reveals a dimeric structure with a bridging, side-on dinitrogen fragment. )b Me2S~cbr...H, TMs~ 5 Figure 4. Molecular structure of 5 with 50% probability ellipsoids. Hydrogen atoms omitted for clarity. 39 Conversion of an early transition metal hydride to a dinitrogen complex is quite rare. Typically, coordinated dinitrogen undergoes rapid and irreversible displacement by dihydrogen forming a dihydride complex; competitive recoordination of N2 is generally not observed. For example, treatment of [(riSC5Me5)2ZrN2hN2 with dihydrogen at O°C affords (ri 5-CsMe5)2ZrH2 in good yield.1 6 Late transition metal (e.g., Co, Ni) hydrides have been shown to eliminate dihydrogen and coordinate dinitrogen, although minimal perturbation of the N-N bond in the resulting dinitrogen complexes is observed.1 7 To date, the only example of such a transformation with an early metal system is the conversion of [PhP(CH2SiMe2NPh)2]TaH2 ([NPN]TaH2) to ([NPN]TaH)2N2 which displays both an end-on and side-on bound dinitrogen fragment.1 8 Displacement of coordinated hydride ligands by dinitrogen may be essential in developing a transition metal based catalyst for N2 fixation. Figure 5. Molecular structure of one of the zirconium centers of 5 with 50% probability ellipsoids, as viewed in the equatorial plane. Hydrogen atoms omitted for clarity. Side-on coordination of dinitrogen in a metallocene complex is also atypical. Classically, sodium reduction of metallocene dichloride complexes such 40 as (11S-C5Me5)2MC!i (M = Ti, 19 Zr,20 Hf'21) provides end-on bound dinitrogen ligands with relatively short (< 1.2 A) N-N bond distances. More recently, Fryzuk has prepared a series of macrocyclic amido-phosphine zirconium complexes with side-on dinitrogen ligands. 22 In these molecules, long N-N bond distances (~ 1.4 -1.5 A) are observed. To our knowledge, the only other example of a metallocene with a side-on dinitrogen fragment is (11 5-CsMe5)2SmN2Sm(11SCsMe5)2 which has an unusually short N-N distance of 1.088 A. 23 The N-N bond distance of 1.2450(38) A of the dinitrogen ligand in 5 is intermediate between these structures. Comparison of this value to the established distance of 1.255 A for (C6Hs)N=N(C6Hs) 24 suggests that the dinitrogen fragment in 5 posesses some double -bond character. The two nitrogen atoms are approximately equidistant from the metal center with Zr-N(l) equal to 2.2680(8) A and Zr-N(l) equal to 2.2712(8) A. Bisection of the 147.8 ° Zr-N1-Zr(A) bond angle yields a value of 73.9 ° which is contracted considerably from those typically observed with organic diazenes. 25 Figure 6. Partially labeled view of 5 with 50% probability ellipsoids. Hydrogen atoms and ligand substituents are omitted for clarity. Unlike the solid state structure for 2, 5 displays a dihedral angle of 46.4 ° between each metallocene wedge (Figure 6). The origin of this twist is believed 41 to be due to unfavorable steric interactions between the bulky tert-butyl substituents on each of the cyclopentadienyl rings (Figure 4). The twist angle observed in 5 is larger than the value of 32 ° observed with [BnBp YH]2.12 The distance between the two zirconium atoms in 5 is 4.366 A which is significantly longer than the metal-metal distance observed in 2. The increased distance between the metal centers is a consequence of the large bridging nitrogen atoms in 5 compared to the bridging hydrides in 2. Based on the solid state structure of 5, the 1H and 13C NMR spectra would be expected to display equivalent tert-butyl, trimethylsilyl and [Me2Si] resonances based on the local C2 symmetry of each zirconium center. However, twice the number of the expected peaks are observed in equal amounts. One possibility is that 5 coordinates additional dinitrogen in solution thus eliminating the C2 symmetry of the molecule and results in additional NMR resonances. However, samples of 5 prepared under vacuum or under an atmosphere of argon both display the same NMR spectra as samples prepared under N2, thus ruling out coordination of additional dinitrogen ligands. Another possibility is the presence of two sets of diastereomeric dimers, whereby one set of dimers is comprised of the (R, R) and (S, S) enantiomers (homochiral dimer) while the other set contains (R, S) and (S, R) chiralities at zirconium (heterochiral dimer). Similar behavior has been observed in the preparation of rac-[Bp YH2] and rac[Abp YH2] where both homochiral and heterochiral dimers are observed. 26 Although we have not confirmed this hypothesis by preparing enantiomerically pure 4 and consquently enantiopure 5, we favor this explanation for the observed solution NMR behavior for 5. Toluene solutions of 5 are forest green and display two absorption bands at 392.0 nm and 612.0 nm. The solution FT-Raman spectrum has been collected in benzene solution and displays three resonances at 1182.6, 1001.5 and 984 cm- 1 attributable to the Zr2N2 core. Assuming the Zr2N2 core is of D2h symmetry, three bands, two of A1g and one of B3g symmetry, are predicted. Attempts to obtain resonance Raman spectra have been unsuccessful due to sample decomposition upon irradiation. Exposure of 5 to one atmosphere of dihydrogen bleaches the green solution and regenerates the starting dihydride, 4 (eq. 5). Addition of a slight 42 excess of PMe3 to 5 results in an immediate reaction, liberating dinitrogen and forming the bis-phosphine complex, rac-BpZr(PMe3)2 (eq. 6). Reactions of 4 with either carbon monoxide or ethylene result in decomposition. ~Me3 Me2Si~4 r...._P~e3 (6) TMS~ 6 The mechanism of formation of 5 from 4, whereby dihydrogen is displaced by dinitrogen, is of considerable interest due to its relevence in a potential catalytic cycle for the fixation of dinitrogen to ammonia. One mechanism is a photoinduced reductive elimination of H2 from 5 followed by coordination of dinitrogen to the intermediate Zr(II) species (Figure 7, pathway i). However, parallel experiments have been conducted in the presence and absence of light and the rates (qualitatively) of conversion are identical thus ruling out a photochemical reaction. Another pathway is coordination of dinitrogen to 4 which induces reductive elimination of dihydrogen (Figure 7, pathway ii). 27 Stirring a toluene solution of 4 under argon open to a mercury bubbler results in decomposition of the dihydride at a comparable rate to conversion to 5 in presence of dinitrogen. In combination, these experiments suggest that formation of the dinitrogen complex, 5, proceeds via thermal reductive elimination of dihydrogen followed by rapid trapping by dinitrogen (Figure 7, pathway iii). The thermal reductive elimination of dihydrogen from 4 is quite unusual, considering unlinked, monomeric zirconocene dihydrides such as Cp*2ZrH2 and Cp*('r1 5-C5H3-l,3-(CMe3)2)ZrH2 display no propensity to eliminate H2 even after months in solution.1 5 From these observations, it would appear that the ansabridge in combination with the monomeric nature of 4 promotes reductive elimination and hence coordination of dinitrogen. This pathway contrasts those obtained in molybdocene dihydride complexes where an ansa-bridge inhibits reductive elimination. The origin of this effect is the apparent requirement for a 43 parallel ring structure in the intermediate Mo(II) complex which can not be readily achieved in the ansa-metallocene. 28 Reductive elimination promoted by an ansa bridge has been observed in a d0, Ta(V) trihydride complex. The ansatantalocene, Me2Si(11 5-C5Me4)2TaH3, undergoes reductive elimination over 100 times faster than (11 5-C5Me5)2TaH3. 29 The observed rate enhancement has been attributed to the reduced electron donating ability and hence destabilization of the Ta(V) complex in the ansa system. Similar electronic effects may be the reason for the increased rate of reductive elimination of 4 compared to unlinked zirconocene dihydrides. ' ' / z Me2S i ~ J:...H, Me Si zr,H + Zr(II) \~ ll TMS~ ' ~hermal )I, 5 Me2Si Zr(II) +N lll T~ Figure 7. Possible mechanisms for the conversion of 4 to 5. Since the ansa bridge and the monomeric nature of 4 are believed to be responsible for the observed reactivity with dinitrogen, we sought to prepare other monomeric ansa-group 4 zirconocene dihydrides. These complexes would not only be useful in determining the generality of this unusual transformation but also may allow preparation of multigram quantities of a dinitrogen complex 44 which has not been possible with 5 due to the inability to prepare rac-BpZrCb in reasonable yield. Preparation of Li2[Me2Si(C5Me4)(CsH2-2,4-(CHMe2)2] (Li2[iPr2Tp]) has been accomplished via standard procedures. 30 The design of this ligand was inspired by the observation that [Me2Si(11 5-C5Me4)2ZrH2h can be prepared in multigram quantities and is both monomeric and dimeric in solution? We surmised that increasing the steric disposition of this ligand framework may afford zirconocenes that are monomeric in solution and hence would undergo facile thermal reductive elimination and coordinate dinitrogen. Reaction of Li2[iPr2Tp] with ZrC4 in refluxing toluene for 24 hours affords iPr2TpZrCl2 in 50% yield. Methylation of the dichloride affords iPr2 TpZrMe2 (8) which undergoes hydrogenation affording [iPr2TpZrH2h (9) (Figure 8). The dihydride is completely insoluble in aromatic hydrocarbon solvents and as a result has been characterized in THF-ds as the solvento complex, iPr2TpZrH2(THF-ds ). Addition of five equivalents of PMe3 to a benzene-d6 solution of 9 provides no reaction, thus demonstrating the robust nature of the dihydride dimer. Accordingly, no reaction is observed with dinitrogen. ~J 2MeLi Me2S1~~r...._Cl ~ ~e Me2S1~~r___M, Et20 ~ THF-d 8 2 Figure 8. Preparation of [iPr2TpZrH2h (9). 45 Attempts to increase the steric bulk of the ligand by replacement of the isopropyl substituents with tert-butyl groups have not been successful. The attempted synthesis of Me2Si(C5Me4H)(C5H3-2,4-(CMe3)2) via addition of LiC5Me4 to a THF solution of C5H3-(CMe3)2SiMe2Cl or via addition of Li[CsH31,3-(CMe3)2] to C5Me4SiMe2Cl does not produce the desired product. Preparation of Doubly Silylene-Bridged Zirconocene Dihydride Complexes. In addition to singly [SiMe2]-bridged metallocenes, we also targeted the preparation of doubly silylene bridged ansa-zirconocene dihydrides. Initially we focused on the preparation of complexes derived from the [(Me2Si)2(Y1S-C5H3)2] ligand which has been previously reported by Royo. 31 Attempts to hydrogenate [(Me2Si)2(rt 5-C5H3)2]ZrMe2 (10) at 25 °C produce no reaction, contrary to previous results with unlinked and singly [SiMe2]-bridged zirconocenes. Heating the reaction mixture to 100 °C in benzene-d6 results in formation of methane (by 1H NMR) and precipitation of black crystals. The solid state structure of the black crystals has been determined by X-ray diffraction and reveals that the product of the reaction is not the expected dihydride, but rather the trimeric zirconocene cluster, [(rt 5-Me2Si)2(C5H3)2)Zr]3(µ3-H)2(µ-H)3 (11) (Figure 9). Preparation of [(rt 5-Me2Si)2(C5H3)2]ZrH2h has been achieved by reduction of the zirconocene dichloride with NaBEt3. 32 Attempts to dissolve 11 in common organic solvents such as benzene, THF, toluene and methylene chloride have been unsuccessful and hence no spectroscopic data has been obtained. The trimeric hydride, 11, crystallizes in the tetragonal space group P43212 as dichroic dark green / colorless crystals. The molecule lies on a two-fold axis through Zr(2) and H(2) and also contains a plane of symmetry that is defined by. the three zirconium centers and the three µ2-hydride ligands. All five hydride ligands have been found in the difference map and freely refined. The three zirconium centers and the three µ2-hydride ligands are all coplanar and are capped above and below the plane with two µ3-hydride ligands. As shown in Figure 10, the metallocene wedge defined by Zr(2) is tilted with respect to the plane formed by the three zirconium centers. The zirconium-µ2-hydride 46 distances are shorter (1.93 A and 1.96 A) than the zirconium-µ3-hydride ligand distances (2.04 A, 2.17 A). ) HI Cl6 C21 l 7 C18 •-w="{( Figure 9. Molecular structure for 11 with 50% probability ellipsoids. Hydrogen atoms other than the five hydrides have been omitted for clarity. The zirconium-zirconium distance in 11 is slightly shorter than the 3.492 A observed for 2 and related dihydride dimers. 13 This distance is significantly longer than 3.124 A observed in the triple hydride-bridged dimer, [Zr2H3(BH4)5(PMe3)2],33 and the tetrahydride-bridged dimer, [Zr2H4(Bf¼)4(PMe3)4]. 34 In these structures, only µ2-hydride bridges are observed. 47 CplC Figure 10. View of the zirconium hydride core of 11. Distances are reported in Angstroms. Increasing the substitution on the cyclopentadienyl ligand array has a dramatic impact on the hydrogenation reaction. Hydrogenation of secBuThpZrMe2 (12) in benzene-d6 solution at 87 °C results in clean and quantitative formation of [sec-BuThpZrH2h (13). The 1H NMR spectrum displays two triplets, one at 4.25 ppm and the other at 0.13 ppm for the terminal and bridging hydrides, respectively. Although each zirconium is C1 symmetric, the zirconium hydride resonances are accidently equivalent. The solution molecular weight for 13 has been determined and found to be 914 g/mol (monomer= 477 g/mol). Both the 1H NMR and the solution molecular weight data are consistent with a dimeric structure in solution (eq. 7). 48 (7) or isomer R' = CH(CH 3 )(CH2CH3): 13 R' = CHMe2 : 15 Similar experiments have been conducted with iPrThpZrMe2 (14). Hydrogenation of the dimethyl complex proceeds smoothly at 87 °C producing methane and one isomer of [iPrThpZrH2h (15). As with 13, 15 displays a triplet at 4.25 ppm for the terminal zirconium hydrides and a triplet at 0.20 ppm for the bridging hydrides. Both 13 and 15 undergo exchange with 02 gas over the course of several days at room temperature whereas the unlinked metallocene hydride dimers, [Cp*(CpRn)ZrH2h, undergo rapid exchange with deuterium at 25 °C. 15 These results suggest that 13 and 15 form more robust dimers than the corresponding unlinked zirconocene dihydride dimers. In an attempt to prepare a monomeric, doubly silylene-bridged zirconocene dihydride, a tertiary center was incorporated into the 4-position of the monosubstituted cyclopentadienyl ring. Preparation of TMSThpZrMe2 (16) has been accomplished via methylation of the dichloride complex. Unfortunately, hydrogenation of 16 at 87 °C results in liberation of methane and decomposition of the organozirconium complex. Perturbation of the overall symmetry of the zirconocene was also attempted with the goal of preparing a monomeric, doubly silylene-bridged zirconocene dihydride. Methylation of the C2 symmetric, (Me2Si)2(11 5-CsH(CHMe2)2)2ZrC!i35 (TipZrCh) (17) affords the dimethyl complex, TipZrMe2 (18) in high yield. Hydrogenation at 87 °C over the course of 24 hours results in formation of [TipZrH2h (19) (Figure 11). At 22 °C, the 1H NMR spectrum of 19 in benzene-d6 displays resonances at -5.65 and 2.10 for the terminal and bridging hydride ligands. Warming the sample to 67 °C results in a gradual shift 49 of the hydride resonance downfield to 3.10 ppm. We interpret a chemical shift in this range to be a weighted average of both the monomer and dimer in solution (Figure 11). Continued heating of the sample produces no further change in the NMR spectrum. 18 j H2 87°c fast.. • Me2Si Me2Si H H 19 predominant species at T < 340 K Figure 11. Hydrogenation of 18 to 19. Although the increased substitution of 19 compared to 13 and 15 resulted in some destabilization of dihydride dimer, a monomeric dihydride was still not obtained. Another approach is to prepare doubly silylene-bridged C2v symmetric metallocenes with bulky substituents in front of the metallocene wedge. Reaction of (Me2Si)2(11 5-CsH2-4-(CMe3)2)2ZrCl2 (BsZrClz, 20) 40 with two equivalents of methyl lithium results in formation of BsZrMe2 (21). Addition of dihydrogen to a benzene-d6 solution of 21 at 87 °C results in formation of methane, although no tractible zirconocene dihydride product has been identified. Monitoring the reaction by 1H NMR spectroscopy reveals that the 50 benzene-d6 is hydrogenated to isotopomers of cyclohexane, thus implicating the presence of a zirconocene dihydride. 15 Performing the reaction in cyclohexaned12 produces methane and results in H/D exchange in the alkane solvent but no zirconocene dihydride could be observed. It appears that the zirconocene dihydride is formed in the above reactions, but may be too unstable for observation and as a result, readily decomposes upon formation. In all of the doubly silylene-linked zirconocene dimethyl complexes studied, elevated temperatures are required for hydrogenation of the zirconium methyl groups. This contrasts previous results with unlinked and singly-bridged systems wher_e hydrogenation occurs readily at room temperature. The higher barrier for a-bond metathesis is believed to be due to steric blocking of the empty la1 orbital of the zirconocene dimethyl complex by the dimethylsilylene linker (Figure 12) thus increasing the energy for H2 binding. A similar effect has been noted in the chlorination of these compounds with PbCl2. 36 Figure 12. Sterically blocking of the la1 orbital by the dirnethylsilylene linkers. Conclusions A series of ansa-zirconocene dihydride complexes has been prepared from hydrogenation of the corresponding dimethyl complexes. The tert-butyl substituted metallocene 2 is dimeric in the solid state and in solution, due to the ability of the tert-butyl groups to orient themselves in a trans disposition. The first example of a monomeric ansa-zirconocene dihydride has been prepared via hydrogenation of 3, yielding 4. Exposure of 4 to dinitrogen results in thermal reductive elimination of dihydrogen and coordination of dinitrogen, forming the side-on bound dinitrogen complex, 5, which has an atypical N-N bond length of 51 1.2450(38) A. Doubly silylene bridged zirconocene dihydrides have also been prepared via hydrogenation of the dimethyl complexes. In these complexes, elevated temperatures are required for hydrogenation due to steric blocking of the la1 orbital by the dimethylsilylene linking groups. Experimental General Considerations. All air and moisture sensitive compounds were manipulated using standard vacuum line, Schlenk or cannula techniques, or in a drybox under. a nitrogen atmosphere as described previously. 37 Molecular weights were determined by ebulliometry as described previously.3 7 Argon, dinitrogen, dihydrogen and dideuterium gases were purified by passage over columns of MnO on vermiculite and activated molecular sieves. Solvents for airand moisture-sensitive reactions were dried over titanocene38 or sodium benzophenone ketyl. Toluene-ds and cyclohexane-d12 were distilled from sodium benzophenone ketyl and stored over titanocene. Tetahydrofuran-ds was distilled from benzophenone ketyl and stored over 4A molecular sieves. Preparations of meso-Me2Si(11 5-C5H3-3-CMe3)2Zr(NMe2)2,8 12, 14, 39 1735 , 20, 21,40 and 1031 were carried out as described previously. meso-[Me2Si(C5H3-3-CMe3)i]ZrMe2 (1). In the dry box, a 50 mL round bottom flask was charged with 0.500 g (1.04 mmol) of meso-DpZr(NMe2)2. Approximately 25 mL of toluene was added forming an orange solution. Via pipette, 0.500 g (6.94 mmol) of trimethylaluminum was added. With time, a darker orange solution forms. The reaction was stirred for 16 hours after which time a 180 ° needle valve was attached to the flask and the toluene was removed in vacuo leaving a dark, oily solid. Petroleum ether was added forming an orange solid and recrystallization at -30 °Cover the course of 3 days afforded 0.257 g (58.3%) of 1. 1H (benzene-d6): 8 = 0.026 (s, 6H, ZrMe2); 0.158 (s, 3H, SiMe2); 0.258 (s, 3H, SiMe2); 1.39 (s, 18H, CMe3); 5.39 (s, lH, Cp ); 5.73 (s, lH, Cp ); 6.71 (s, lH, Cp ). 13C (benzene-d6): -5.682 (SiMe2); -3.237 (SiMe2); 31.39 (ZrMe2); 33.81 (ZrMe2); 31.99 (CMe3) 144.76 (CMe3); 98.08, 111.75, 112.15, 120.45, 1 not located (Cp ). Anal. Calcd. for C22H36ZtiSi1: C, 62.94; H, 8.64. Found C, 62.76; H, 8.42. 52 meso-[[Me2Si(C5H3-3-CMe3h]ZrH2h (2). In the dry box, a thick-walled glass bomb was charged with 0.150 g (0.354 mmol) of 1. On the vacuum line, approximately 15 mL of toluene was added by vacuum transfer. At room temperature, 1 atmosphere of dihydrogen was added. The reaction mixture was stirred for 16 hours and the toluene was removed in vacuo and replaced with petroleum ether affording a white solid. The solid was collected by filtration and dried in vacuo yielding 0.087 g (62.1 %) of 2. 1H (benzene-d6): 8 = 0.202 (s, 3H, SiMe2); 0.239 (s, 3H, SiMe2); 0.370 (s, 3H, SiMe2); 0.386 (s, 3H, SiMe2); 3.94 (m, lH, ZrHterm); 4.03 (m, lH, ZrHterrn); -2.35 (t, 7.5 Hz, lH, ZrHbr); -5.30 (m, lH, ZrHbr); 1.34 (s, 18 H, CMe3); 1.40 (s, 18 H, CMe3); 4.99, 5.06, 5.90, 6.06, 6.16, 6.23 (m, lH, Cp ). l3C (benzene-d6): -6.60 (SiMe2); -6.40 (SiMe2); -1.93 (SiMe2); -1.79 (SiMe2); 33.30 (CMe3); 33.40 (CMe3); 152.49 (CMe3); 152.88 (CMe3); 91.25, 101.92, 102.66, 104.72, 106.90, 110.25, 110.51, 118.74, 2 not located (Cp). Anal. Calcd. for C20H32ZriSi1: C, 61.32; H, 8.23. Found C, 61.76; H, 8.56. rac-[Me2Si(C5Hr2-SiMe3-4-CMe3h]ZrMe2 (3). In the dry box, a medium swivel frit assembly was charged with 1.10 g (1.82 mmol) of BpZrCl2. On the vacuum line, approximately 30 mL of diethyl ether was added by vacuum transfer. At -80 °C against an argon counterflow, 2.90 mL (4.1 mmol) of 1.4 M MeLi solution in ether was added. The reaction was warmed to room temperature and stirred. Upon reaching room temperature, a yellow solution and white precipitate formed. After 24 hours, the ether was removed in vacuo and was replaced with toluene. The white precipitate was removed by filtration and was washed with recycled toluene. The toluene was removed in vacuo and the yellow solid was recrystallized from cold petroleum ether affording 0.980 g (91 %) of 3. 1H (benzene-d6): 8 = 0.23 (s, 6H, ZrMe2); 0.31 (s, 18 H, SiMe3); 1.38 (s, 18 H, CMe3); 6.05 (s, 2H, Cp ); 7.21 (s, 2H, Cp ). 13C (benzene-d6): 8 = -0.810 (SiMe2); 2.16 (SiMe3); 30.94 (CMe3 ); 34.09 (ZrMe2); 106.65, 116.14, 125.60, 129.47, 1 not located (Cp), 148.92 (CMe3). Anal. Calcd. for C20H32ZriSii: C, 61.32; H, 8.23. Found C, 61.76; H, 8.56. Anal. Calcd. for C2sHs2ZriSi3: C, 59.61; H, 9.29. Found C, 59.27; H, 9.01. rac-[Me2Si(C5H2-2-SiMe3-4-CMe3h]ZrH2 (4). Prepared in an analogous manner to 2 with 0.940 g (1.58 mmol) of 3 yielding 0.750 g (84%) of a green solid identified as 4. 1H (benzene-d6): 8 = 0.35 (s, 18H, SiMe3); 0.49 (s, 6H, SiMe2); 1.49 (s, 18H, CMe3); 5.96 (s, 2H, Cp ); 7.83 (s, 2H, Cp ); 7.25 (bs, 2H, ZrH); 13C (benzene- 53 d6): 8 = 2.23 (SiMe3); 2.82 (SiMe2); 32.17 (CMe3); 152.9 (CMe3); 98.63, 11.34, 118.27, 119.49, 123.22 (Cp). Anal. Calcd. for C26I-4sZriSi3: C, 58.25; H, 9.02. Found C, 57.98; H, 8.67. rac-[[Me2Si(C5H2-2-SiMe3-4-CMe3)z]Zrh(µ2-N2) (5). In the dry box, a Teflon capped scintillation vial was charged with 57.0 mg (0.100 mmol) of 4 and approximately 2.0 mL of toluene. The solid was dissolved forming a green solution and allowed to stand at room temperature for 1 week after which time a red solid had deposited on the bottom of the vial. The solid was collected by filtration, washed with petroleum ether, transferred into a flask and dried in vacuo affording 21.0 mg (35.7%) of 5. 1H NMR (toluene-ds): 8 = 0.441 (s, 18H, SiMe3); 0.454 (s, 18H, SiMe3 ); 0.651 (s, 6H, SiMe2); 0.923 (s, 6H, SiMe2); 1.47 (s, 18 H, CMe3); 1.67 (s, 18H, CMe3); 4.77 (s, 2H, Cp ); 5.11 (s, 2H, Cp ); 6.14 (s, 2H, Cp ); 6.66 (s, 2H, Cp ). 13C NMR (toluene-ds): 8 = -0.940 (SiMe2); -0.108 (SiMe2); 32.51 (CMe3); 33.50 (CMe3); 2 CMe3 not located; 104.0, 104.20, 105.4, 107.91, 110.18, 112.24, 115.67, 117.21, 117.34 (Cp). UV-VIS (toluene): 392.0 nm; 612.0 nm. FTRAMAN (benzene-d6): 1182.6 cm-1; 1001.5 cm- 1; 984 cm-1. Anal. Calcd. for Cs2H92Si6Zr2N2: C, 56.97; H, 8.46; N, 2.56. Found C, 56.69; H, 8.76; N, 2.68 rac-[Me2Si(C5H2-2-SiMe3-4-CMe3)z]Zr(PMe3)z (6). In the dry box, a J. Young NMR tube was charged with 5.0 mg (4.30 x 10-3 mmol) of 5. On the vacuum line, the tube was degassed with three freeze-pump-thaw cycles. Via calibrated gas volume, 3 equivalents of PMe3 were added at -196 °C. The tube was thawed and shaken and the progress of the reaction monitored by NMR spectroscopy. 1H (benzene-d6): 8 = -0.15 (s, 18H, SiMe3); 0.19 (s, 6H, SiMe2); 0.85 (d, 36 Hz, 18H, PMe3); 1.22 (s, 18H, CMe3); 6.44, 6.70 (m, 2H, Cp ). 31 P (benzene-d6): 8 = 34.04. Me2 Si(11 5-CsMe4)(11 5-CsH2-2,4-(CHMe2)z)ZrC}z (7). In the dry box, a round bottom flask was charged with 3.66 g (11.23 mmol) of Li2[iPr2Tp] and 2.61 g (11.23 mmol) of ZrC4. A reflux condensor and 180° needle valve were attached. On the vacuum line, approximately 50 mL of toluene were added along with 5 mL of THF. The reaction mixture was heated to reflux for 3 days after which time the toluene was removed in vacuo leaving a yellow paste. Approximately 100 mL of CH2Cl2 and 25 mL of 4 M HCl were added. The organic layer was collected and the aqueous layer washed with 3 small portions of CH2Cl2. The organic layers were combined and dried over MgSO4 for 1 hour. After filtration, the solvent was removed by rotovap, leaving a yellow tar. Pentane was added 54 and a white solid precipitated. The solid was washed with small portions of diethyl ether and pentane and dried in vacuo. Analytically pure material may be obtained via vacuum sublimation (10-4 torr) at 160 °C. 1H (benzene-d6): 8 = 0.816 (s, 3H, SiMe2); 0.945 (s, 3H, SiMe2); 1.10 (d, 6.6 Hz, 3H); 1.21 (d, 6.5 Hz, 3H); 1.24 (d, 6.5 Hz, 3H); 1.26 (d, 6.5 Hz, 3H); 1.87 (s, 3H, CsAfe4); 1.90 (s, 3H, CsMq); 1.98 (s, 3H, CsAfe4); 2.01 (s, 3H, CsAfe4); 2.71 (sept, 7.0 Hz, lH, CHMe2); 3.06 (sept, 7.0 Hz, lH, CHMe2); 5.25 (s, lH, Cp ); 6.50 (s, lH, Cp ). 13C (benzene-d6): 8 = 1.22 (SiMe3); 1.25 (SiMe3); 11.90, 12.61, 14.63, 14.93 (CsAfe4); 20.30, 22.25, 22.75, 29.39 (CHMe2); 29.24, 29.89 (CHMe2); 96.28, 99.50, 110.79, 117.79, 112.90, 113.99, 137.07, 143.49, 149.63 (Cp). Anal. Calcd. for C22H34ZqCl2: C, 57.36; H, 7.44. Found C, 57.57; H, 7.14. Me2 Si(T1 5-CsMe4)(T1 5-CsH2-2,4-(CHMe2h)ZrMe2 (8). This compound was prepared in an analogous manner to 3 employing 0.760 g (1.56 mmol) of 7 and 2.5 mL of 1.4 M MeLi solution in diethyl ether yielding 0.560 g (80.4%) of a white solid identified as 8. 1H (benzene-d6): 8 = 0.440 (s, 3H, SiMe2); 0.575 (s, 3H, SiMe2); -0.352 (s, 3H, ZrMe2); -0.258 (s, 3H, ZrMe2); 1.14 (d, 7.0 Hz, 3H); 1.23 (d, 6.8 Hz, 3H); 1.29 (d, 6.9 Hz, 3H); 1.33 (d, 7.0 Hz, 3H); 1.63 (s, 3H, CsAfe4); 1.79 (s, 3H, CsAfe4); 1.95 (s, 3H, CsAfe4); 1.98 (s, 3H, CsAfe4); 2.54 (sept, 7.0 Hz, lH, CHMe2); 3.03 (sept, 7.0 Hz, lH, CHMe2); 5.04 (s, lH, Cp ), 6.65 (s, lH, Cp ). 13C (benzene-d6): 8 = 1.54 (SiMe3); 1.65 (SiMe3); 11.36, 11.64, 14.37, 14.53 (CsAfe4); 20.56, 23.39, 23.89, 29.54 (CHMe2); 28.37, 29.72 (CHMe2); 32.88 (ZrCH3); 35.93 (ZrCH3) 91.02, 93.77, 109.76, 113.04, 120.94, 123.22, 140.18, 140.49 (Cp ). [Me2 Si(T1 5-CsMe4)(T1 5-CsH2-2,4-(CHMe2h)ZrH2h (9). This compound was prepared in an analogous manner to 2 employing 0.320 g (0.716 mmol) of 8 and 1 atmosphere of H2. After stirring for 2 days, the product was collected by _filtration and dried in vacuo yielding 0.170 g (56.7%) of 9. 1H (THF-ds): 8 = 0.421 (s, 3H, SiMe2); 0.620 (s, 3H, SiMe2); 3.87 (d, 20 Hz, lH, Zr-H2); 4.13 (d, 20 Hz, lH, Zr-H2); 1.10 (d, 7.0 Hz, 3H); 1.15 (d, 7.0 Hz, 3H); 1.20 (d, 7.0 Hz, 3H); 1.60 (d, 7.0 Hz, 3H); 1.92 (s, 3H, CsAfe4); 2.02 (s, 3H, CsAfe4); 2.23 (s, 3H, C5Me4); 2.32 (s, 3H, CsAfe4); 2.83 (sept, 7.0 Hz, lH, CHMe2); 3.08 (sept, 7.0 Hz, lH, CHMe2); 4.86 (s, lH, Cp ), 5.69 (s, lH, Cp ). Anal. Calcd. for C22H34Zq Cl2: C, 62.94; H, 8.64. Found C, 62.07; H, 8.63. [((Me2Sih(C5H3)i)Zrfa(µ3-H)i(µ-Hh (11). In the dry box, a J. Young NMR tube was charged with 10.5 mg of 10 and the sample dissolved in benzene-d6. On the 55 vacuum line, the tube was degassed with three-freeze-pump thaw cycles and 1 atmosphere of dihydrogen was admitted at -196 °C. The tube was thawed, shaken and placed into a 100 °Coil bath. After heating for 24 hours, dark green crystals were desposited in the tube and were collected in the dry box for X-ray diffraction. [(Me2SD2h1 5-CsH-3,5-( CHMe2hHT1 5-CsH2-4-CH(CH3)(CH2CH3)) ]ZrH2h (13). In the dry box, a thick walled glass bomb was charged with 0.560 g (1.10 mmol) of 12. On the vacuum line, cyclohexane was added by vacuum transfer. Upon warming to room temperature, the bomb was then charged with 1 atmosphere of dihydroge_n. The bomb was then placed in an 80 °C oil bath and stirred. The reaction was continued for 2 days after which time the contents of the bomb were transferred into a swivel frit assembly. The cyclohexane was removed in vacuo and replaced with petroleum ether. Cooling the solution to -80 °C afforded a white solid that was collected by filtration and dried in vacuo yielding 0.325 g (61.6%) of 3. 1H (benzene-d5): b = 0.13 ppm (t, 5 Hz, 2H, ZrH, bridging); 0.583 (s, 3H, Silvle2); 0.604(s, 3H, SiMe2); 0.614 (s, 3H, SiMe2); 0.638 (s, 3H, SiMe2); 1.02 (t, 7 Hz, 3H, CH(CH3)(CH2CH3)); l.78(d, 6.5 Hz, 3H, CH(CH3)(CH2CH3)); 1.19 (d, 6.5 Hz, 3H, CHMe2); 1.40 (d, 6.5 Hz, 3H, CHMe2); 1.61 (d, 6.5 Hz, 3H, CHMe2); 1.72 (d, 6.5 Hz, 3H, CHMe2); 1.80 (m, 2H, CH(CH3)(CH2CH3)); 3.53 (m, lH, CH(CH3)(CH2CH3); 3.14 (sept, 6.5 Hz, lH, CHMe2); 3.66 (sept, 6.5 Hz, lH, CHMe2); 4.25 (t, 5Hz, 2H, ZrH, terminal); 5.86 (s, lH, Cp ); 6.56 (s, lH, Cp ); 7.14 (s, lH, Cp ). 13C (benzene-d5): b = -0.475 (SiMe2); -0.071 (SiMe2); 4.16 (SiMe2); 4.21 (SiMe2); 11.30, 19.34, 22.68, 23.22, 29.79, 30.13, 20.40, 33.79, 34.65 (CHMe2 and CH(CH3)(CH2CH3); 97.88, 99.08, 102.60, 104.20, 109.28, 117.32, 119.09, 139.09, 155.91, 159.62 (Cp ). Anal. Calcd. for C24J-40ZriSi2: C, 60.56; H, 8.47. Found C, 59 .54; H, 8.32. [(Me2Sih(T1 5-CsH-3,5-(CHMe2hHT1 5-CsH2-4-CH(CH3h]ZrH2h (15). In the dry box, a J. Young NMR tube was charged with 10.0 mg (0.0189 mmol) of 14 and the sample was dissolved in benzene-d6 forming a clear solution. On the vacuum line, the tube was degassed with three freeze-pump thaw cycles. The tube was then cooled to -196 °C and 1 atmosphere of dihydrogen added. The tube was then heated in an 87 °Coil bath and the reaction monitored by NMR spectroscopy. 1H NMR (benzene-d6): b = 0.20 ppm (t, 5 Hz, 2H, ZrH, bridging); 0.561 (s, 3H, SiMe2); 0.601(s, 3H, SiMe2); 0.635 (s, 3H, SiMe2); 0.681 (s, 3H, SiMe2); 56 0.891 (d, 6.5 Hz, 3H, CHMe2); 0.954 (d, 6.5 Hz, 3H, CHMe2); 1.12 (d, 6.5 Hz, 3H, CHMe2); 1.18 (d, 6.5 Hz, 3H, CHMe2); 1.21 (d, 6.5 Hz, 3H, CHMe2);1.51 (d, 6.5 Hz, 3H, CHMe2); 2.45 (sept, 6.5 Hz, lH, CHMe2); 2.94 (sept, 6.5 Hz, lH, CHMe2); 3.43 (sept, 6.5 Hz, lH, CHMe2); 4.25 (t, 5Hz, 2H, ZrH, terminal); 5.73 (s, lH, Cp ); 6.27 (s, lH, Cp ); 7.09 (s, lH, Cp ). [(Me2Si)i(l1 5-CsH-3,5-(CHMe2)i)(11 5-CsH2-4-SiMe3) ]ZrMe2 (16). This compound was prepared in an analogous manner as those published for 12 and 14. lH NMR (benzene-d6): 8 = -0.142 (s, 6H, ZrMe2); 0.392 (s, 9H, SiMe3); 0.387 (s, 6H, SiMe2); 0.555 (s, 6H, SiMe2); 1.05 (d, 7 Hz, 6H, CHMe2); 1.27 (d, 7 Hz, 6H, CHMe2); 2.69 (sept, 7Hz, 2H, CHMe2); 6.86 (m, 2H, Cp ); 6.44 (m, lH, Cp ). l3C NMR (benzened6): 8 = 0.94 (SiMe3); -1.12 (SiMe2); 3.85 (SiMe2); 21.39, 29.18 (CHMe2); 29.32 (CHMe2); 105.34, 111.40, 115.45, 124.68, 134.78, 154.22 (Cp ). Anal. Calcd. for ZriSi3C2sH44 C, 57.73%, H, 8.53%; Found C, 57.90%; H, 8.82%. [(Me2Si)i(11 5-CsH-3,5-(CHMe2hh ]ZrMe2 (18). In the drybox, a 25 mL round bottom flask was charged with 2.00 g (2.72 mmol) of 17. On the vacuum line, approximately 15 mL of ether was added by vacuum transfer. At -80 °C against an Ar counterflow, 4.3 mL (6.00 mmol) of 1.4 M Meli was added via syringe. The reaction was warmed to room temperature and stirred. With time a white slurry forms. The reaction was stirred for 5 hours and the solvent was removed in vacuo .. Toluene was added and the white precipitate was removed by filtration. The toluene was removed in vacuo leaving 1.20 g (65%) of a yellow solid identified as 18. 1H NMR (benzene-d6): 8 = -0.207 (s, 6H, ZrCH3); 0.498 (s, 6H, SiMe2); 0.616 (s, 6H, SiMe2); 1.14 (d, 6 Hz, 12H, CHMe2); 1.38 (d, 6 Hz, 12H, CHMe2); 2.97 (sept, 6.5 Hz, 4H, CHMe2), 6.61 (s, 2H, Cp ). 13C NMR (benzened6): 8 = 1.61 (SiMe2 ); 6.14 (SiMe2); 21.53 (CHMe2); 29.30 (CHMe2); 29.92 (CHMe2); 30.25 (ZrCH3); 106.14, 111.53, 153.08 (Cp). [(Me2SD2(11 5-CsH-3,5-(CHMe2hh ]ZrH2 (19). This compound was prepared in an analogous manner to 2 employing 0.950 g (1.69 mmol) of 18 and 4 atmospheres of dihydrogen. The reaction was heated to 87 °C for one week and affords 0.650 g (72.3%) of 19. 1H NMR (benzene-d6): 8 = -5.649 (m, 2H, ZrH (bridging)); -5.205 (m, lH, ZrH (bridging); 0.161 (s, 6H, SiMe2); 0.783 (s, 6H, SiMe2); 1.18 (d, 7 Hz, 12H, CHMe2); 1.22 (d, 7 Hz, 12H, CHMe2); 3.16 (sept, 6,5 Hz, 4H, CHMe2); 6.23 (s, 2H, Cp ). 13C NMR (benzene-d6): 8 = 3.99 (SiMe2); 6.73 57 (SiMe3); 23.15 (CHMe2); 28.83 (CHMe2); 29.64 (CHMe2); 116.44, 118.00, 152.78 (Cp ). Anal. Calcd. for C26H«ZriSi2: C, 61.96; H, 8.80. Found C, 61.43; H, 8.43. Solid State Structure for 1. A suitable fragment of 1 was cut from one massive crystal, attached to a glass fiber and centered on an Enraf-Nonius CAD-4 diffractometer under an 85 K stream of N2 gas. Unit cell parameters were obtained from the setting angles of 25 high-angle reflections. Two equivalent data sets were collected and merged in P21 / c. Three reference reflections were measured every 75 minutes to monitor crystal decay. The structure was solved using direct methods and the difference Fourier maps were used to locate the missing atoms, including hydrogens. A total of 6632 data were refined to R = 0.0342 (GOF = 1.304).41 Solid State Structure for 2. A small, clear and colorless crystal of 2 was mounted on a glass fiber with Paratone-N oil. The data was collected on a Bruker Smart 1000 CCD diffractometer under a stream of N2 gas at 98 K. Four runs of data were collected with 20 second long, -0.20 ° wide co-scans at four values of <j) (0, 120,240 and 300°) with the detector 5 cm (nominal) distant at 0 of -28 °. The initial cell for data reduction was calculated for just under 1000 reflections chosen throughout the data frames. For data processing with SAINT v.602, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to a minimum value of 0.001, Laue class integration restraints were not used, the model profiles from all nine areas were blended and for the post-integration global least squares refinement, no constraints were applied. The data were corrected with SADABS v. 2.0 (beta) using a g value of 0.05. No decay correction was needed. The structure was solved using direct methods and the difference Fourier maps were used to locate all missing atoms, including hydrogens. Refinement of F2 was against all reflections. A total of 7795 reflections were refined to R = 0.0458 (GOF = 2.286). Solid State Structure for 5. The crystal was mounted and the data were collected in a manner similar to 2. Three runs of data were collected with 20 second long, -0.20 ° wide ffi-scans at four values of <j) (0, 120 and 240) with the 58 detector 5 cm (nominal) distant at 0 of -28 °. The initial cell for data reduction was calculated for just under 1000 reflections chosen throughout the data frames. For data processing with SAINT v. 6.02, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to a minimum value of 0.001, Laue class integration restraints were not used, the model profiles from all nine areas were blended and for the post-integration global least squares refinement, no constraints were applied. The data were corrected with SADABS v. 2.0 (beta) using a g value of 0.058. No decay correction was needed. The structure was solved using direct methods and the difference Fourier maps were used to locate all missing atoms, including hydrogens. Refinement of F2 was against all reflections. A total of 4312 reflections were refined to R = 0.0610 (GOF = 1.73). Solid State Structure for 11. The data were collected in the same manner for 1. Unit cell parameters were obtained from 25 high angle reflections. Two equivalent data sets were collected and merged in P43212 (#96). Three reflections were measured every 75 minutes to monitor crystal decay. The structure was solved using direct methods and the difference Fourier maps were used to locate the missing atoms, including hydrogens. A total of 3746 data were refined to R = 0.0163 (GOF = 1.627). References. 1. a) Brintzinger, H.H.; Fischer, D.; Miilhaupt, R.; Reiger, B.; Waymouth, R.M. Angew. Chem. Int. Ed. Engl. 1995, 34, 1143. b) Bachmann, M. J. Chem. Soc., Dalton Trans. 1996, 255. 2. Hoveyda, A.H.; Morken, J.P. in The Metallocenes vol. 2; Togni, A. and Haltermann, L. Eds., Wiley-VCH Publishers, Weinheim, 1988, Chapter 10. 3. a) Waymouth, R.M.; Pino, P. J. Am. Chem. Soc. 1990, 112, 4911. b) Troutman, M.V.; Appella, D.H.; Buchwald, S.L. J. Am. Chem. Soc. 1999, 121, 4916. 4. Broene, R.D.; Buchwald, S.L. J. Am. Chem. Soc. 1996, 118, 11688. 5. Grossman, R.B.; Doyle, R.A.; Buchwald, S.L. Organometallics 1991, 10, 1501. 6. Cuenca, T.; Galakhov, M.; Royo, B.; Royo, P. J. Organomet. Chem. 1996, 515, 33. 59 7. Lee, H.; Desrosiers, P.J.; Guzei, I.; Rheingold, A.L.; Parkin, G. J. Am. Chem. Soc. 1998, 120, 3255. 8. Diamond, G.M.; Jordan, R.F.; Peterson, J.L. Organometallics 1996, 15, 4045. 9. Yoder, J.C.; Day, M.W.; Bercaw, J.E. Organometallics 1998, 17, 4946. 10. Kim, I.; Jordan, R.F. Macromolecules 1996, 29,489. 11. a) [(T1 5-Csf4-CH3)2ZrH2h (3.460 A): Jones, S.B.; Peterson, J.L. Inorg. Chem. 1981, 20, 2889. b) [(T1 5-Csf4-CMe3)zZrH2h (3.471 A): Choukroun, R.; Dahan, F.; Larsonneur, A.M.; Samuel, E.; Peterson, J.; Meunier, P.; Sornay, C. Organometallics 1991, 10,374. <=) [(T1 5-Csf4-SiMe3)zZrH2h (3.437 A): Larsonneur, A.M.; Choukroun, R.; Jaud, J. Organometallics 1993, 12, 3216. d) [Me2Si(T15_ C5Me4)zZrH2h (3.549 A): Lee, H; Desrosiers, P.J.; Guzei, I.; Rheingold, A.L.; Parkin, G. J. Am. Chem. Soc. 1998, 120, 3255. 12. Xin, S.; Harrod, J.F.; Samuel, E. J. Am. Chem. Soc. 1994, 116, 11562. 13. Mitchell, J.P.; Hajela, S.; Brookhart, S.K.; Hardcastle, K.I.; Henling, L.M.; Bercaw, J.E. J. Am. Chem. Soc. 1996, 118, 1045. 14. Chacon, S.T.; Coughlin, E.B.; Henling, L.M.; Bercaw, J.E. J. Organomet. Chem. 1995, 497, 171. 15. Chirik, P.J.; Day, M.D.; Bercaw, J.E. Organometallics 1999, 18, 1873 16. Manriquez, J.M.; McAlister, D.R.; Sanner, R.D.; Bercaw, J.E. J. Am. Chem. Soc. 1978, 100, 2716. 17. a) Bianchini, C.; Meli, A.; Perruzzini, M.; Vizza, F.; Zanobini, F. Organometallics 1989, 8, 2080. b) Chaudret, B.; Devillers, J.; Poilblanc, R. Organometallics 1985, 4, 1727. 18. Fryzuk, M.D.; Johnson, S.A.; Rettig, S.J. J. Am. Chem. Soc. 1998, 120, 11024. 19. Sanner, R.D.; Duggan, D.M.; McKenzie, T.C.; Marsh, R.E.; Bercaw, J.E. J. Am. Chem. Soc. 1976, 98, 8358. 20. Sanner, R.D.; Manriquez, J.M.; Marsh, R.E.; Bercaw, J.E. J. Am. Chem. Soc. 1976, 98, 8351. 21. Roddick, D.M.; Fryzuk, M.D.; Siedler, P.F.; Hillhouse, G.L.; Bercaw, J.E. Organometallics 1985, 4, 97. 22. a) Fryzuk, M.D.; Love, J.B.; Rettig, S.J.; Young, V.G. Science 1997, 275, 1445. b) Cohen, J.D.; Fryzuk, M.D.; Loehr, T.M.; Mylvaganam, M.; Rettig, S.J. Inorg. Chem. 1998, 37, 112. 60 23. Evans, W.J.; Ulibarri, T.A.; Ziller, J.W. J. Am. Chem. Soc. 1988, 110, 6877. 24. Allen, F.H.; Kennard, O.; Watson, D.G.; Brammer, L.; Orpen, A.G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2, 1987, Sl. 25. a) trans-PhN=NPh (114.706 degrees): Bouwstra, J.A.; Schouten, A.; Kroon, J. Acta Cryst. C. 1983, 39, 1121. b) trans-Me3CN=NCMe3 (112.210 degrees): Argay, G.; Sasvari, K. Acta Cryst. B. 1971, 27, 1851. 26. Abp = Me2Si{3-[2-SiMe3-4-[2-(2-CH3-C10H14)]-CsH2h ♦ Abrams, M.A. Ph.D. Thesis, California Institute of Technology, 1998. 27. Ligand promoted reductive elimination has been observed in zirconocene alkyl hydride complexes. See McAlister, D.R.; Erwin, D.R.; Bercaw, J.E. J. Am. Chem. Soc. 1978, 100, 5966. 28. Chemaga, A.; Cook, J.; Green, M.L.H.; Labella, L.; Simpson, S.J.; Souter, J.; Stephens, A.H.H. J. Chem. Soc., Dalton Trans. 1997, 3225. 29. Shin, J.; Parkin, G. Chem. Comm. 1999, 187. 30. Herzog, T.A. ~h.D. Thesis California Institute of Technology, 1997. 31. Cano, A.; Cuenca, T.; Gomez-Sal, P.; Royo, B.; Royo, P. Organometallics 1994, 13, 1688. 32. Cuenca, T.; Galakhov, M.; Royo, B.; Royo, P. J. Organomet. Chem. 1996, 515, 33. 33. Gozum, J.E.; Girolami, G.S. J. Am. Chem. Soc. 1991, 113, 3829. 34. Bown, M. Acta Cryst. C 1994, 50, 367. 35. Miyake, S.; Bercaw, J.E. J. Mal. Cat. A 1998, 128, 29. 36. Brandow, C.G.; Wendt, O.F., Bercaw, J.E. unpublished results. 37. Burger, B.J.; Bercaw, J.E. in Experimental Organometallic Chemistry, ACS Symposium Series, No 357; Wayda, A.L., Darensbourg, M.Y., Eds.; American Chemical Society: Washington, DC 1987; Chapter 4. 38. Marvich, R.H.; Brintzinger, H.H. J. Am. Chem. Soc. 1971, 93, 2046. 39. Veghini, D.; Day, M.D.; Bercaw, J.E. Inorg. Chem. Acta 1998, 280,226. 40. Bulls, A.R. Ph.D. Thesis, California Institute of Technology, 1988. 61 41. Crystallographic data for 1 have been deposited at the CCDC, 12 Union Road, Cambridge CB2 lEZ, UK, and copies can be obtained on request, free of charge, by quoting the publication citation and the deposition number 114738. 62 Chapter 3 Ancillary Ligand Effects on Fundamental Transformations in Group 4 Metallocene Chemistry. Kinetics and Mechanism of Olefin Insertion and ~-Hydrogen Elimination. 63 Abstract Reactions of the metallocene dihydrides, (RnCp )2MH2 (RnCp = alkylsubstituted cyclopentadienyl; M = Zr, Hf), with olefins afford stable zirconocene alkyl hydride adducts of the general formula, (RnCp )2M(CH2CHR'2)(H) (R' = H, alkyl). For sterically crowded, monomeric dihydrides: Cp*2ZrH2 (Cp* = 11sC5Me5); Cp*( 11 5-CsMe4H)ZrH2, Cp*(11 5-CsMe4-CH2CH3)ZrH2, Cp*2HfH2 and Cp*(11 5-C5H3-l,3-(CMe3)2)HfH2, rate constants for olefin insertion have been measured. For Cp*2HfH2, the relative rates of olefin insertion have been found to be 1-pentene > styrene > cis-2-butene > trans-2-butene > isobutene. The rate of isobutene insertion into Cp*(11 5-CsMe4H)ZrH2 is 3.8 x 103 times greater than that for Cp*2ZrH2 at 210 K, demonstrating the large steric effect imposed by ancillary ligand substitution for the insertion reaction. A primary kinetic isotope effect of 2.4(3) at 296 K and a linear free energy relationship with correlation to cr (p = -0.46(1)) indicate that olefin insertion into a zirconium-hydride bond proceeds via rate determining hydride (H8-) transfer from the metal to the incipient alkyl. The rates of ~-hydrogen elimination for a series of zirconocene alkyl hydride complexes, (RnCp )2Zr(CH2CHR')(H), have been measured via trapping of the intermediate zirconocene dihydride with 4,4-dimethyl-2-pentyne. Primary isotope effects between 3.9-4.5 have been measured at 296 K for a variety of zirconocene isobutyl hydride complexes. A linear free relationship for the phenethyl hydride series, Cp*(11 5-CsMe4H)Zr(CH2CH2-p-C6H4-X)(H) (X = H, CH3, CF3, OCH3), has been established with a better correlation to cr than cr+, p = -1.80(5). For the series of ziroconocene isobutyl hydride complexes, the rate of ~-hydrogen elimination depends on the cyclopentadienyl ligand array, where more substituted metallocenes yield slower rates. Equilibration of a series of Cp*(CpRn)Zr(CH2CHMe2)(H) and Cp*(CpRn)Zr(CH2CH2CH2CH3)(H) complexes with free olefin has established the relative ground state energies of zirconocene isobutyl and normal butyl complexes. These data in combination with the free energies of activation for ~-hydrogen elimination have established the relative transition state energies of each alkyl group for these complexes. 64 Introduction Olefin insertion into a metal-hydrogen bond and its microscopic reverse, B-hydrogen elimination from a transition metal alkyl, represent fundamental transformations in organometallic chemistry and constitute key steps in a variety of catalytic processes. 1 Olefin insertion and B-hydrogen elimination have special relevence to metallocene catalyzed olefin polymerization since insertion of an olefin into a metal-hydrogen bond is often the initiation step; subsequent insertions into metal carbon bonds comprise the chain propagation sequence and B-hydrogen elimination has been identified as a major chain termination pathway. 2 The relative rates of these processes determine the chain length of the resulting polymer and hence influence many important polyolefin properties. Although the effect of metallocene symmetry on polymer stereochemistry is fairly well-understood,3 a definitive correlation between ancillary ligand substitution and polymer molecular weight has not been established. In fact, the commercialization of current metallocene catalysts is hampered by the low molecular weights of the polymers produced by these catalysts, especially when the polymerization reaction is carried out at plant operating temperatures (60 - 80 °C for polypropylene). 4 End group analysis of these polymers reveals that chain termination occurs primarily by B-hydrogen and B-methyl elimination pathways. Hence, a thorough mechanistic understanding of each of the fundamental transformations related to olefin polymerization may lead to the development of metallocene catalysts that can be tailored to produce polymers with desired stereochemistry and molecular weight. The details of olefin insertion and B-hydrogen elimination reactions have been the subject of several experimental and theoretical investigations. Early work of Jordan,5 Watson6 and Marks 7 has established olefin insertion into a metal alkyl bond as the mode of propagation for d0 and d0f1 metal catalyzed polymerizations. However, attempts to gain further insight into the mechanism and rates of olefin binding, insertion and subsequent B-hydrogen elimination reactions have met with limited success. The active species for olefin polymerization is well established as doubly coordinatively unsaturated, 14 65 electron cationic group 4 metallocene alkyl, but the high activity of these catalysts, and the presence of cocatalysts such as methylalumoxane (MAO) in high concentration prevent a detailed analysis of each of the individual transformations involved during the polymerization reaction. Previous investigations from our research group have focused on understanding the kinetics and mechanism of both olefin insertion and Bhydrogen elimination in metallocene catalysts. Using both coalesence and magnetization transfer NMR techniques, the kinetics of olefin insertion into a metal hydrogen bond has been examined with a series of group V metallocene complexes of the general formula, ('r1 5-CsR5)2M(11 2-CH2=CHR')(H) (M = Nb, Ta; R = H, Me; R' = H, CH3, C6Hs). 8 For the series of ethylene hydride compounds, increased rates of insertion were observed for niobium (kNb > kTa) and for less crowded cyclopentadienyl rings (kcp > kcp* ). Similar effects are also observed in the propylene hydride complexes, although the steric effects dominate the electronic contributions. The rates of olefin insertion for a series of meta- and para-substituted niobocene styrene hydride complexes have been examined and the electronic effects were found to be primarily inductive in origin. Furthermore, these rates were used to construct a linear free energy relationship that indicated a concerted four center transition state with moderate positive charge development at the B-carbon. Permethylscandocene complexes, (11 5-CsMe5)2ScR (R = H, alkyl), insert ethylene rapidly at low temperature (-80 °C) without complication from chain transfer from B-hydrogen elimination. Hence, the kinetics of ethylene insertion have been measured for a series of scandium alkyls. The rates of ethylene insertion are reflected by the strength of the scandium-carbon bond, where stronger bonds result in slower rates. 9 The rates of B-hydrogen elimination for a variety of scandium alkyls and phenylethyl complexes have been determined via trapping of the intermediate scandium hydride with 2-butyne. 9 Utilizing these measurements, the transition states for B-hydrogen elimination, and hence that for olefin insertion have been probed by systematically varying the substituent at the B-carbon. In accord with the niobocene styrene hydride complexes, a linear free energy correlation is also found with scandium-phenylethyl series, indicating that the transition state for these processes is quite polar with the electropositive scandium center abstracting hydride (and by extension (R8-) for 66 insertion/B-alkyl elimination) of the postively charged B-carbon atom (Figure 1). Figure 1. Proposed transition state for olefin insertion and ~-hydrogen elimination. More recent studies have focused on elucidating the rates of chain propagation and transfer in cationic zirconocene catalysts. Erker has reported an experimental estimate for olefin insertion into cationic zirconium allyl fragments 10 whereas Siedle has determined the relative rates of chain propagation and transfer for zirconocene dimethyl/methylalumoxane mixtures.1 1 Additionally, numerous theoretical studies have been aimed toward understanding the rates and mechanism of these fundamental transformations. 12 Although the effect of cyclopentadienyl substitution on the stereo- and regiochemical outcome of a metallocene catalyzed polymerization has been well documented, 13,2,3 the influence of cyclopentadienyl sterics on the rates of olefin insertion and B-hydrogen elimination are not well understood. Using 16 electron zirconocene and hafnocene dihydride and alkyl hydride complexes as models for the active polymerization catalyst, we describe our efforts towards understanding the effects of ancillary ligand substitution on olefin insertion and B-hydrogen elimination and, through these studies, reveal the relative contributions of ground and transition state effects on the rates of these processes. Results Reactions of the metallocene dihydride complexes, (CpRnhMH214 (CpRn = alkyl substituted cyclopentadienyl; M = Zr, Hf), with olefins such as propylene, 1butene and isobutene afford stable metallocene alkyl hydride complexes, (CpRnhM(CH2CHR'2)(H) (R' = alkyl), in quantitative yield (by NMR) (eq. 1). In general, the remaining metal-hydride bond is unreactive toward excess olefin.1 5 67 The metallocene alkyl hydride complexes are stable in benzene-d6 for days at 25 oc. + (1) Kinetic Studies with Cp*2MH2 Complexes. Permethylzirconocene dihydride, (11 5-CsMe5)2ZrH2 (1), and permethylhafnocene dihydride, (11 5-CsMe5)2HfH2 (2), are monomeric in benzene-d6 solution and as a result are amenable for kinetic study. Reactions of 1 and 2 with 1,1-disubstituted olefins (e.g., isobutene) and a-olefins are first order in both olefin and·the metallocene dihydride (eq. 2). In an attempt to probe olefin steric effects on the rate of insertion, reaction of 1 with a variety of 1,1disubstituted olefins has been examined. Thus reaction of 1 with isobutene, 2methyl-1-butene, 2,4-dimethyl-1-pentene, 2,3-dimethyl-1-pentene and amethylstyrene yields (11 5-CsMe5)2Zr(CH2CH(CH3)2)(H) (3), (T1 5C5Me5)2Zr(CH2CH(CH3)(CH2CH3))(H) (4), (11 5C5Me5)2Zr(CH2CH(CH3)CH2CH(CH3)2)(H) (5), (11 5CsMe5)2Zr(CH2(CH(CH3))2CH2CH3)(H) (6) and (11 5C5Me5)2Zr(CH2CH(CH3)(C6Hs))(H) (7), respectively. Reaction of 1 with 2,4,4trimethyl-1-pentene produces no reaction. Likewise no alkane is observed upon attempted hydrogenation of this olefin with 1 as the catalyst. The rate constants for these reactions have been measured at 296 Kand the results are presented in Table 1. 68 ~H R1 + ~H ==< kins, 296 K C6D6 4f~l ~ Olefin Metallocene Product kins x 104 (M-1sec-1 ) isobutene 2-methyl-1-butene 2,4-dimethyl-1-pentene 2,3-dimethyl-1-pentene a-methylstyrene 3 7 65(3) 24(3) 6.3(4) 7.3(2) 14(2) -- no reaction 2,4,4-trimethyl-1-pentene 4 5 6 (2) Table 1. Rate constants for insertion of disubstituted olefins with 1 at 296 K. The effect of solvent on the rate of isobutene insertion with 1 has also been examined. The experimentally determined rate constants for the insertion reaction have been measured in a variety of deuterated solvents at 296 Kand these values are contained in Table 2. Solvent kins x 104 (M- 1 sec-1 ) toluene-ds diethyl ether-d10 tetrahydrofuran-ds pyridine-ds 65(3) 35(2) 17(5) no reaction Table 2. Rate constants as a function of solvent for reaction of 1 with isobutene at 296 K. Addition of either cis or trans-2-butene to a toluene-ds solution of 1 affords the zirconocene n-butyl hydride complex, (11 5-C5Me5)2Zr(CH2CH2CH2CH3)(H) (8) (eq. 3). The zirconocene sec-butyl hydride intermediate has not been detected even when the reaction is monitored at -90 °C. 16 These results are contrary to those obtained in related organoactinide complexes, where detection of the 69 internal alkyl hydride complex has been achieved.1 7 Monitoring the reaction between 1 and trans-2-butene at low temperatures (T < 250 K) allows for measurement of the rate constant for insertion (Table 3). Likewise, the effect of temperature on the rate of isobutene insertion has also been determined and the rate constants are reported in Table 3. Attempts to measure similar rate constants for the insertion of cis-2-butene, propene, styrene and 1-pentene have been unsuccessful due to the rapid rates of these reactions. Trisubstituted olefins such as 3-methyl-2-butene do not react with 1 at elevated temperatures over the course of several days at room temperature. (3) Temperature (K) 220 240 250 263 275 296 kmisobutene x 104 kin/-2-butene x 104 (M-1sec-1) (M- 1sec-1) --- 4.2(1) 29(2) 69(3) ------- --- 3.3(1) 8.5(1) 19(3) 65(3) Table 3. Rate constants for reaction of 1 with isobutene and trans-2-butene as a function of temperature. Isobutene, cyclopentene, styrene and 1-pentene react with 2 affording (11 5C5Me5)2Hf(CH2CH(CH3)2)(H) (9), (C5Me5)2Hf(cyclo-C5H9)(H) (10), (C5Me5)2Hf(CH2CH2C6Hs)(H) (11) and (C5Me5)2Hf(CH2(CH2)3CH3)(H) (12) . As with 1, addition of cis- or trans-2-butene to 2 affords (C5Me5)2Hf(CH2CH2CH2CH3)(H) (13). In general, the rates of olefin insertion with 2 are slower than those for 1. For example, the rate constant (296 K) for isobutene insertion with 2 is 2.6 x 1Q3 times slower than for 1. The slower rates of 70 insertion for 2 permits quantitative determination of olefin insertion rate constants for this series of olefins. The rate constants for insertion of isobutene, cis-2-butene, trans-2-butene and cyclopentene have been determined over a range of temperatures (Table 4). These data allow for construction of Eyring plots and extraction of the activation parameters for olefin insertion. These values are contained in Table 5. Likewise, the rate constants for insertion of 1pentene and styrene have been measured at 230 K. Temperature (K) 265 275 296 320 340 345 362 kmisobutene x 106 kin/-2-butene x 106 kinsc-2-butene x 106 (M-1sec- 1) (M- 1sec-1) (M-1sec-1) --- --- --- --- 2.5(1) 62(5) 220(50) 590(30) 1200(100) 1900(400) 6200(200) 65(3) 120(1) ----- Table 4. Rate constants for reaction 2 with isobutene, trans-2-butene andcis-2-butene as a function of temperature. From monitoring the reactions of 1 and 2 with isobutene, cis-2-butene and trans-2-butene over a range of temperatures, the activation parameters for these reactions have been determined. These values are contained in Table 5. Compound Olefin L'.1S+a Mf+b i1G+296 Kb 1 isobutene trans-2-butene isobutene trans-butene -38(3) -29(3) -43(10) -45(6) -48(8) -43(8) 9.0(1) 9.9(1) 12.2(2) 9.7(1) 9.6(3) 7.7(5) 20.2(1) 18.5(1) 24.9(2) 23.1(2) 23.7(3) 20.4(5) 1 2 2 2 2 cyclopentene cis-2-butene a. Units= J/mol-K; b. Units= kJ/mol. Table 5. Activation parameters for reaction of 1 and 2 with a variety of olefins. 71 Using the experimentally determined rate constants, a quantititative comparison of the rates of insertion for each olefin studied has been obtained from extrapolation of the measured rates to a common temperature of 230 K. The relative rates of insertion are shown in Figure 2. 0 8.2 X 10 7 4.6 X 106 7.7 X 103 104 38 1 Figure 2. Relative rates olefins insertion with 2 at 230 K. Isotope Effects on the Rate of Insertion. Preparation of (11 5-CsMe5)2ZrD2 (l-d2) may be accomplished via addition of deuterium gas to 1 at -5 °C. At higher temperatures, incorporation of deuterium into the pentamethylcyclopentadienyl ligands is observed.1 4 Mixing equimolar quantities of 1 and l-d2 in toluene-ds followed by addition of isobutene allows for measurement of the kinetic isotope effect for olefin insertion. Measurement of the relative rates of insertion into the Zr-H and Zr-D bond has been achieved by using the integration of the 1H NMR isobutyl methine resonance versus the isobutyl methyl groups (both relative to an internal standard). From this analysis, a kinetic isotope effect of 2.4(3) has been measured at 296 K. Linear Free Energy Relationship for Insertion of a-Methylstyrene with 1. Addition of a-methylstyrene to a benzene-d6 solution of 1 affords (11 5C5Me5)2Zr(CH2CH(CH3)Ph)(H) (7) (eq. 4). The 1H NMR spectrum of 7 displays two inequivalent Cp* rings and two diastereotopic Ca protons on the alkyl. Heating a sample of 7 does not result in coalescence of the Cp* or alkyl resonances and eventually reductive elimination of alkane and decomposition of the organometallic complex is observed. However, the clean reaction of 1 with a-methylstyrene lent itself to variations in the para position of the incoming 72 olefin, thus allowing for construction of a free energy relationship for olefin insertion. Addition of 4-fluoro-a-methylstyrene, 4-methyl-a-methylstyrene, 4methoxy-a-methylstyrene and 4-trifluoromethyl-a-methylstyrene to 1 affords (17 5-CsMe5)2Zr(CH2CH(CH3)-p-C6H4-F)(H) (14), (17 5-CsMe5)2Zr(CH2CH(CH3)p-C6~-CH3)(H) (15), (17 5-CsMe5)2Zr(CH2CH(CH3)-p-C6~-0CH3)(H) (16) and (17 5-CsMe5)2Zr(CH2CH(CH3)-p-C6H4-CF3)(H) (17), respectively (eq. 4). The rates of insertion for each reaction have been measured at 296 Kand the observed rate constants are contained in Table 6. Construction of a Hammett plot reveals a better correlation to a (r 2 = 0.996) than cr+ (r2 = 0.667), with p = -0.46(1) (Figure 3).18 X X X = H, F, Me, OCH3, CF 3 Substituent kins x 105 a a+ 6.92(1) 0 0 6.35(2) 0.15 -0.07 7.72(1) -0.25 -0.78 7.47(2) -0.14 -0.30 5.45(2) 0.52 0.08 (M- 1sec-1) H F OCH3 CH3 CF3 Table 6. Data for the linear free energy relationship for insertion of p-substituted amethylstyrenes with 1. 73 -9.45 -9.5 -9.55 ···················i·············· ....., ..................... ,......................,................... -9.6 7ii' C g C -9.65 -9.7 ::::::::::::::::::r:::::::::::::::::::r...::::::::::···:::r::::::::::::::::::::c::::::::::::::: i i a= i -9.75 -9.8 ···················l······················!·····················i····················!······· ••••••••• -9. 8 5 ...._._~..........~_..._.....___.__.__............ -0.4 -0.2 0 0.2 0.4 0.6 __,__.a.......i.,....,.__.i......,..............,. sigma Figure 3. Hammett plot for reaction of 1 with p-substituted a-methylstyrenes at 296 K. Effect of Cyclopentadienyl Substitution on the Rate of Isobutene Insertion. In addition to 1 and 2, other monomeric zirconocene and hafnocene dihydrides have been reported.1 4 Addition of isobutene to Cp*(ri 5C5Me4H)ZrH2 (18) results in quantitative formation of Cp*(ri 5C5Me4H)Zr(CH2CH(CH3)2)(H) (19). At 210 K, a rate constant of 3.3(4) x 10-2 M1secl has been measured for the rate of isobutene insertion. Attempts to measure the rate of the reaction at higher temperatures have been unsuccessful due to the rapid rate of conversion. Extrapolating the isobutene insertion rate constant for 1 to 210 K using the experimentally determined activation parameters yields a value of 8.7 x 10-6 M-lsecl, thus demonstrating that 18 inserts isobutene 3800 times faster than 1. Attempts to measure the rate of isobutene insertion for Cp*(ri 5-C5H3-l,3(CMe3)z)ZrH2 (20) and (ri 5-C5H3-l,3-(CMe3)2)2ZrH2 (21) have been unsuccessful sinces the rates of insertion are too fast to be measured by low temperature NMR techniques. A rate constant of 5.1(2) x 10-3 M- 1sec 1 has been measured for 74 the reaction of Cp*(ri 5-C5Me4-CH2CH3)ZrH2 (22) with isobutene affording Cp*(ri 5-C5Me4-CH2CH3)Zr(CH2CH(CH3)2(H) (23) and is approximately the same value as that for the insertion of isobutene with 1. Preparation of Cp*(ri 5-C5H3-l,3-(CMe3)2)HfH2 (24) has been accomplished via addition of n-BuLi to Cp*(ri 5-C5H3-l,3-(CMe3)2)HfCl2 under an atmosphere of H2 as reported for 2.1 9 Reaction of 24 with isobutene results in clean formation of Cp*(ri 5-C5H3-l,3-(CMe3)2)Hf(CH2CH(CH3)2)(H) (25). Rate constants for isobutene insertion have been measured between 225 and 270 K and yield activation parameters of Aff+ = 11.8(1) kcal/mol and ~S+ = -27(5) eu. Effect of Cyclopentadienyl Substitution on the Regiospecficity of Styrene Insertion. The influence of cyclopentadienyl substitution on the regiospecificity of olefin insertion has been examined by reaction of styrene with a series of zirconocene dihydride complexes. Reaction of 1 with styrene in benzene-d6 results in clean formation of (ri 5-C5Me5)2Zr(CH2CH2Ph)(H) (26) (eq. 5). The only product observed is that arising from the 1,2 or primary insertion of the carbon-carbon double bond of the olefin. Likewise, reaction of styrene with 20 and 21 affords solely primary insertion products, Cp*(ri 5-CsH3(CMe3)2)Zr(CH2CH2Ph) (27) and (ri 5-C5H3-(CMe3)2)2Zr(CH2CH2Ph) (28), respectively (Table 7). Reaction of the less substituted zirconocene dihydride, [Cp*(ri5-C5H4-CMe3)ZrH2h (30), with styrene yields only the secondary insertion product, Cp*(ri 5-C5H4-CMe3)Zr(CH(CH3)(Ph)(H) (30) as a 1:1 mixture of diastereomers. Confirmation of the regioselectivity of these reactions has been assayed via addition of CH3OD to a benzene solution of the zirconocene phenethyl hydride. The resulting ethylbenzenes have been analyzed by 2H{1H} NMR spectroscopy and the signals of 1-deutero-ethylbezene and 2-deuteroethylbenzene determined by integration versus an internal standard. 75 ~H Zr............_ d::s ~ styrene H Rn ~H z ~ I Rn 4(5--0H --~ ~ \ (5) /J I Rn Addition of styrene to [Cp*(THI)ZrH2h (31) (THI = tetrahydroindenyl), [(11 5-CsMe4H)2ZrH2h (32) and Cp*(11 5-CsH3-l,3-(CHMe2)2)ZrH2 (33) results in a mixture of regioisomers depending on the substitution of the metallocene (Table 7). For the "mixed-ring" metallocenes, the 2,1 insertion products are formed as a 1:1 mixture of diastereomers. Metallocene 1,2-Product (%) 2,1-Product (%) 1 20 21 31 32 33 30 100 100 100 60 80 0 0 0 40 20 56 100 44 0 Table 7. Regiospecificity of styrene insertion with a series of zirconocene dihydrides. ~-Hydrogen Elimination Studies. Reaction of the zirconocene dihydride complexes with alkynes leads to a variety of products depending on the reaction conditions. Terminal alkynes such as 3,3-dimethyl-1-butyne produce mixtures of products arising from insertion of the alkyne forming the alkenyl hydride complex, as well as those arising from abond metathesis with the hydride, forming the alkynyl complex (eq. 6). Small internal alkynes such as 2-butyne undergo rearrangement to afford crotyl hydride complexes.20 However, sterically demanding, internal alkynes such as 4,4-dimethyl-2-pentyne (37) react with the series of zirconocene dihydrides to yield solely the insertion product, (CpRn)2Zr(CH3C=CH(CMe3))(H). In all cases 76 examined, only one alkenyl hydride product is observed. Addition of CD30D to the series of zirconocene alkenyl-hydride complexes and analysis of the resulting deuterated olefin by 2H {1H} NMR spectroscopy reveals that zirconium center coordinates to C2 of the acetylene in each case (eq. 7). ~H Zr.......__ ~· H ~-,~H ~H 'fl+ %~ Zr. ~ (6) I Rn Rn Reaction of 37 with the zirconocene alkyl hydride complexes also forms the alkenyl hydride complex and free olefin. These products are consistent with ~-hydrogen elimination from the alkyl hydride liberating free olefin and the zirconocene dihydride which is then trapped by the acetylene in solution. Under the appropriate conditions (vide infra), this reaction may allow for measurement of the rates of ~-hydrogen elimination from a series of zirconocene alkyl hydride complexes. + (7) A series of zirconocene isobutyl hydride complexes has been prepared from addition of isobutene to a benzene-d6 solution of the zirconocene dihydride. In this manner, Cp*('17 5-CsHs)Zr(CH2CHMe2)(H) (38), Cp*('17 5-CsH4CMe3)Zr(CH2CHMe2)(H) (39); Cp*(THI)Zr(CH2CHMe2)(H) (40), Cp*('17 5-CsH2l,3-(CHMe2)z)Zr(CH2CHMe2)(H) (41), Cp*('17 5-C5H3-l,3(CMe3)2)Zr(CH2CHMe2)(H) (42), Cp*('17 5-CsMe4H)Zr(CH2CHMe2)(H) (19), (ri 5- 77 C5Me4H)2Zr(CH2CHMe2)(H) (43) and Cp*2Zr(CH2CHMe2)(H) (3) have been prepared (Figure 4). The observed rate constants for reaction of 3, 19, 38-43 with 37 have been determined and found to be independent of the concentration of 37 over the range of 0.244 to 4.88 M (Table 8). For 3, 2-butyne was used as the dihydride trap since the reaction of 1 and 37 was not straightforward. This kinetic situation allows for direct measurement of the rate of ~-hydrogen elimination (k1 = kobs) since the reverse process (k_1) does not effectively compete with acetylene trapping (Figure 5). 38 39 40 41 42 19 43 Figure 4. Zirconocene isobutyl hydride complexes. 3 78 Further evidence for the dissociative nature of the reaction on the acetylene concentration has been obtained through the use of two different • acetylene traps. Reaction of 42 with five equivalents of 37 or 2,2-dimethyl-1butyne at 268 K forms the alkenyl hydride complexes with observed rate constants of 3.3(4) x 10-4 secl and 2.7(3) x 10-4 sec 1, respectively. ~~H ~ I Rn k1 k_1 47f_H ;;~H ~ Rn k2 j 37 47f_H z ~¥ I Rn Figure 5. Mechanism for trapping of zirconocene dihydrides with 37. . + ~ 79 Metallocene [37] (M)a kobs x 104 (sec-1) 38 T = 275 K 0.244 0.672 0.244 10.6(2) 11.2(5) 10.3(4) 39 T = 275K 0.244 1.37 4.88 3.35(4) 3.40(5) 3.82(9) 40 T = 296K 0.152 0.908 1.32 10.8(2) 10.8(4) 10.7(3) 41 T = 296K 1.22 0.244 1.22 28.4(6) 29.8(8) 27.0(5) 42 T = 296K 0.122 1.37 4.88 3.35(5) 3.40(2) 3.82(8) 19 T = 296K 0.244 1.05 2.44 0.134(5) 0.123(3) 0.146(7) 43 0.061 0.244 0.976 5.44(2) 5.43(5) 5.26(3) 0.244 0.650 1.10 0.028(4) 0.025(6) 0.031(5) T = 296K 3 T = 296K a. The estimated errors in the concentrations are± 5%. b. Rates measured with 2-butyne Table 8. Observed rate constants for the reaction of zirconocene isobutyl hydride complexes with 37. The rates of ~-hydrogen elimination have also been measured as a function of temperature. The activation parameters derived from the experimentally determined rate constants are shown in Table 9. In all cases, the entropy of activation (LiSt) is small, further supporting dissociative substitution of the alkyl by the alkenyl (Figure 5). 80 Complex L\S+ (eu) L\H+ (kcal/mol) L\G+ (kcal/mol) 296K 38 39 40 41 42 7.7(8) -4.4(4) 3.1(8) -4.1(9) -5.19(3) 21.9(4) 18.8(6) 23.3(3) 19.6(7) 20.5(3) 19.6(4) 20.1(6) 21.3(4) 20.8(8) 22.0(3) Table 9. Activation parameters for ~-hydrogen elimination. From these data, the relative rates of P-hydrogen elimination as a function of ligand array can be established. All of the reported values are compared to the normalized rate of P-hydrogen elimination for 3 at 296 K. If the experimentally observed rate constant for a given metallocene has not been measured at 296 K, an extrapolated rate constant obtained from the experimentally determined activation parameters is reported. The relative rates of P-hydrogen elimination for the series of zirconocene isobutyl hydride complexes is shown in Figure 6. Kinetic Isotope Effects for P-Hydrogen Elimination. Preparation of isotopically labeled zirconocene isobutyl hydride complexes of the general formula, (CpRnhZr(CH2CDMe2)(D), has been accomplished via addition of isobutene to (CpRn)2ZrD2.1 4 The isotopic purity of all of the compounds has been determined to be > 95% based on 1H and 2H NMR spectroscopy. The rates of P-hydrogen elimination for Cp*(THI)Zr(CH2CDMe2)(D) (40-d2), Cp*(11 5-CsH3-l,3(CHMe2)z)Zr(CH2CHMe2)(H) (41-d2), Cp*(ri 5-CsH3-l,3(CMe3)z)Zr(CH2CHMe2)(H) (42-d2), Cp*(ri 5-CsMe4H)Zr(CH2CHMe2)(H) (19-d2) and (115-C5Me4H)zZr(CH2CHMe2)(H) (43-d2) have been determined at 296 K by employing 37 as the trap for the intermediate zirconocene dideuteride. Comparison of these rate constants to those determined for protio complexes yields the kinetic isotope effects for P-hydrogen elimination (Table 10). 81 8000a 400 100 1000 5 ~H ~H ~ C H2CH(CH3)z ~CH2CH(CH3)z z~ z~ 1 190 a. Extrapolated value from experimentally determined activation parameters. Figure 6. Relative rates of ~-hydrogen elimination for a series of zirconocene isobutyl hydrides at 296 K. Metallocene ktt (sec-1) ko (sec-1) kttlko 40-d2 1.06(6) X 10-3 4.1(2) 41-d2 2.8(8) X 10-3 2.64(1) X 10-4 7.10(7) X 10-4 42-d2 3.52(9) X 10-4 7.81(10) X 10-5 4.5(1) 19-d2 1.34(9) X 10-5 5.38(6) X 10-4 3.29(12) X 10-6 4.1(3) 1.34(8) X 10-4 4.0(2) 43-d2 Table 10. Kinetic isotope effects for ~-hydrogen elimination at 296 K. 3.9(3) 82 Linear Free Energy Relationship for P-Hydrogen Elimination. Reaction of 18 with p-substituted styrenes affords the phenethyl hydride complexes, Cp*(11 5-C5Me4H)Zr(CH2CH-p-C6Hi-X)(H) (X = H, 44; OCH3, 45; CH3, 46; CF3, 47) (eq. 8). Reaction of each of the phenethyl hydride complexes with 37 as the dihydride trap affords rates of P-hydrogen elimination for each complex. The observed rate constants for these reactions are contained in Table 11. From these data, a linear free energy relationship has been constructed and displays a better correlation to cr (r2 = 0.992) than cr+ (r2 = 0.922) with a p value of -1.80(5). k~_H, 296 K X Compound k[3-H x 104 (sec-1) (J a+ 44 4.87(9) 8.53(6) 6.94(14) 2.04(15) 0 -0.25 -0.14 0.53 0 -0.78 -0.30 0.08 45 46 47 Table 11. Linear free energy relationship data for Cp*(C5Me4H)Zr(CH2CHrp-C6Hs-X)(H). Rates of P-Hydrogen Elimination with Different Alkyls. The effect of alkyl group on the rate of P-hydrogen elimination has been examined with a series of Cp*(ri 5-Csfi4-CMe3)Zr(R)(H) complexes. Addition of the appropriate olefin to the hydride dimer, 29, affords the zirconocene alkyl hydride complexes, Cp*(ri 5-Csfi4-CMe3)Zr(R)(H) (R = CH2CH2CMe3, 48; 83 CH2(CH2)2CH(CH3)z, 49; CH2CH2CH2CH3; 50; cyclopentyl, 51). As with the zirconocene isobutyl hydride complexes, the rate of substitution of the alkyl ligand by the acetylene is independent of the concentration of 37. The rates of Phydrogen elimination have been measured at 296 K and the rate constants are contained in Table 12. The general trend in rate constants for P-hydrogen elimination differ substantially from those observed for olefin insertion with 2. For example, the cyclopentyl hydride undergoes P-hydrogen elimination approximately 50 times faster than corresponding n-butyl hydride complex, whereas for msertion with 2, 1-butene inserts 105 times faster than cyclopentene. Metallocene kf3-H x 104 (sec-l)a Relative Rate 48 49 50 39 1.47(8) 17.8(6) 18.3(5) 90.6(6) 1000(25) 1 12.1 12.4 61.6 680 51 a. T= 296K Table 12. Rates of ~-hydrogen elimination as a function of alkyl ligand. Ligand Array [Cp*(11 5-CsMe4H)Zr] [Cp*(11 5-CsH3-l ,3-CMe3)zZr] [Cp*(11 5-THI)Zr] [Cp*(11 5-CsH3-l,3-(CHMe2)2Zr] [Cp*(11 5-CsH4-CMe3)Zr] kn-Bu (sec-1) ki-Bu (sec- 1) kn-Bulki-Bu 7.85(2) X lQ-5 3.35(9) X 10-4 1.34(9) X lQ-S 3.5(2) X 10-4 9.28(1) X 10-4 1.06(6) X lQ- 3 9.88(2) X 10-4 2.8(8) X 10-3 1.83(5) X lQ-3 9.06(6) X 10-3 5.86 0.96 0.875 0.357 0.201 Table 13. Comparision of the rates of ~-hydrogen elimination for a series of zirconocene alkyl hydride complexes. Since the trend for ~-hydrogen elimination for Cp*(11 5-CsH4CMe3)Zr(R)(H) differs from the trend for olefin insertion with 2, we wished to examine the effect of ancillary ligand substitution on the relative rates of Phydrogen elimination for a series of n-butyl and i-butyl hydrides. The observed rate constants for these reactions are contained in Table 13. From these data, a general trend is observed; namely more substituted metallocenes have a ratio of 84 ~-hydrogen elimination rate constants (kn-Bu i ki-Bu) greater than 1, whereas less substituted metallocenes have kn-Bu l ki-Bu less than unity. Relative Ground State Energies of Zirconocene Alkyl Hydride Complexes. Addition of five equivalents of 1-butene to the series of zirconocene isobutyl-hydride complexes results in formation of an equilibrium mixture of the zirconocene i-butyl hydride and the zirconocene n-butyl hydride complexes along with the appropriate amounts of free olefins (eq. 9). Likewise, the equilibrium may be approached from addition of isobutene to the zirconocene nbutyl hydride. complexes. The experimentally determined equilibrium constants and the corresponding free energy changes for these reactions are reported in Table 14. ~H I _-_-_-__ z ~ + -\ ~ I ~ Ligand Array Keq296K ~G 0 rxn (296 K) [('r1 5-CsMe5)2Zr] [Cp*(17 5-CsMe4H)Zr] [Cp*(11 5 -CsH3-l,3-(CMe3)2)Zr] [Cp*(11 5-CsH3-l,3-(CHMe2)2)Zr] [Cp*(11 5- THI)Zr] 51(3) -2.3(2) 43(3) -2.1(2) 25(4) -1.9(2) 16(2) -1.7(1) 9.6(3) -1.3(1) [Cp*(11 5-CsH4-CMe3)Zr] 9.1(4) -1.3(1) Table 14. Equilbrium constants and free energy data for equation 9. (9) 85 Discussion Olefin Insertion into (CpRn)zMH2 The zirconocene dihydride complexes, (CpRnhMH2, undergo facile reaction with a variety of olefins affording the zirconocene alkyl hydride complexes, (CpRnhM(R')(H) (R, R' = alkyl). For monomeric zirconocene dihydrides, the rates of olefin insertion can be conveniently measured using 1H NMR spectroscopy. Using these kinetic measurements as a basis for our studies, we have been.able to elucidate the mechanism of olefin insertion into neutral, ao metallocene dihydride complexes. Furthermore, these experiments allow for careful study of the influence of olefin and cyclopentadienyl sterics on the rates of olefin insertion. A proposed mechanism for olefin insertion into (CpRnhZrH2 is shown in Figure 7. The reaction proceeds via initial coordination of the alkene to the metallocene dihydride followed by transfer of hydrogen from the metal center to the incipient metal alkyl. Although the geometry of the olefin dihydride adduct is unknown, we propose that olefin insertion takes place when the olefin occupies the lateral position (i.e., cis to only one zirconium hydride) based on preliminary density functional theory calculations with ethylene and Cp2ZrH2. 21 Reaction of isobutene with an equimolar mixture of 1 and l-d2 reveals a kinetic isotope effect of 2.4(3) at 296 K. A normal, primary isotope effect is consistent with a preequilibrium involving rapid coordination and dissociation of olefin followed by rate determining hydride transfer. A similar kinetic profile has been proposed for reactions of olefins with ('11 5-CsMeshM(OR)(H) (M = Th, U) where primary kinetic isotope effects of 1.4(1) and 1.3(2) have been measured for the insertion of cyclohexene and 1-hexene at 60 °C. 17 86 Rn R kH M'-.... ~ ~ Rn + H R = alkyl M = Zr, Hf =< k1 k_1 tb • ~HR ~ ~ Rn k2 l k_2 ~ d ~<-z ~ R' I Rn Figure 7. Proposed mechanism for olefin insertion with neutral zirconocene and hafnocene dihydrides. The effect of solvent on the rate of isobutene insertion has also been measured. As shown in Table 15, the chemical shift of the zirconium hydride and the rate of isobutene insertion correlate with the dielectric constant of the NMR solvent; the reaction proceeds more rapidly in solvents with lower dielectric constants. It has been shown previously that the 1H NMR chemical shift of a group IV metallocene hydride resonance may be used as a measure of ligand binding, where more upfield resonances indicate a greater degree of coordinative saturation about the metal center. 22 For the 16 electron dihydride complex, 1, the zirconium hydride resonance appears at 7.48 ppm (toluene-ds) substantially downfield from 0.55 ppm and 1.07 ppm observed for the 18 electron complexes, (11 5-CsMe5)2ZrH2(PF3) and (11 5-C5Me5)2ZrH2(CO) (both in toluene-ds). 23 In donor solvents such as THF-ds, the zirconocene hydride resonance for 1 shifts to 5.75 ppm, implicating a significant contribution from the formally 18 electron solvento complex. Coordination of solvent to the zirconium center decreases the rate of insertion since the incoming olefin can not compete as effectively with the high concentration of competing ligand. A similar solvent 87 effect has been noted in the related organoactinide complex, where kTHFlktoluene = 0.59.1 7 Solvent kins x 104 (M-1sec-1) 5Zr-H (ppm) Dielectric a toluene-ds diethyl ether-d10 65(3) 7.48 2.4 35(2) 7.30 4.3 THF-ds 17(5) 5.75 7.6 pyridine-ds no reaction 5.10 12.3 a. Data taken from CRC Handbook of Chemistry and Physics 67th Ed.; CRC Press, Boca Raton, Florida. Table 15. Rate constants for isobutene insertion as a function of solvent dielectric. Addition of para-substituted a-methylstyrenes, p-CH2=C(CH3)(C6Hi-X) (X = H, CH3, CF3, OCH3) to 1 affords the zirconocene alkyl hydrides, 7, 14-17. Construction of a linear free energy relationship reveals a better correlation of the observed rate constants with the Hammett constant cr than cr+ with p = -0.46(1). The better correlation to cr is indicative of poor orbital overlap between the empty p orbital on the B-carbon and the 1t system of the phenyl ring and in the transition state for olefin insertion. Similar observations have been made with permethylniobocene and permethyltantalocene styrene-hydride complexes where ground state crystal structures and the linear free energy relationship indicate that the B-carbon and the 1t system of the phenyl ring are twisted out of resonance by approximately 30 degrees. 8b The modest, negative p value of -0.46(1) is indicative of a cyclic transition state with little charge separation, with a slight positive charge development at the Bcarbon of the coordinated olefin, thus implicating transfer of hydrogen as "H0-". Also consistent with these findings are the highly negative entropies of activation (-30 to -48 e.u.) indicating a highly ordered transition structure for olefin insertion. Therefore, the transition state model developed for the permethylniobocene and tantalocene olefin hydride complexes may be extended to ('r1 5-CsMe5)2MH2 (Figure 1). The effect of olefin substitution on the rate of insertion has also been examined with 1 and 2. Insertion of a variety of 1,1-disubstituted olefins has been examined with 1 at 296 K. In general, increasing the substitution of the olefin descreases the rate of insertion. For example, the rate of isobutene insertion is approximately 10 times faster than that for 2,4-dimethyl-1-pentene. 88 However, placing a methyl substituent in either the 3 or 4 position of the olefin has little effect on the rate of insertion. This result contrasts with the polymerization activity of [(EBTHI)Zr-R]+ (EBTHI = ethylene-1,2-bis(T1 5-tetrahydroindenyl)) which readily polymerizes 4-substituted a-olefins but displays minimal activity with 3-substituted alkenes. 24 Increasing the substitution of the 4-position of olefin, as in the case of 2,3,4-trimethyl-1-pentene, produces no reaction with the zirconium hydride. Attempts to hydrogenate the olefin in the presence of 1 also results in no reaction, demonstrating the inability of the olefin to insert into the zirconium hydride bond. Changing the steric disposition of the olefin (e.g., cis-2-butene versus isobutene) has dramatic impact on the rate of insertion with 1 and 2. Internal olefins such as cis- and trans-2-butene insert much faster than 1,1-disubstituted olefins. For both metallocenes, the rate of cis-2-butene insertion is faster than the rate observed for the trans isomer with the cis isomer reacting with 2 approximately 200 times faster at 230 K than the trans. Although the ground state of the trans isomer is approximately 0.70 kcal/mol more stable that the cis, this energy difference is not enough to account for the observed difference in rates. This difference could either be a result of transition state stabilization imparted by the cis olefin isomer or be a result of increased binding of the cis isomer to the dihydride forming a higher concentration of the dihydride olefin intermediate which in tum increases the rate of insertion. The rate of insertion for a-olefins (e.g., 1-pentene, styrene) with 2 is approximately ms times faster than that for 1,1-disubstituted olefins at 230 K. Unfavorable steric interactions between the more substituted isobutene and the bulky pentamethylcyclopentadienyl ligands are responsible for the dramatic difference in rates. These results are in accord with previous studies that demonstrate a-olefins undergo hydrozirconation more rapidly than 1,1disubstituted olefins. 25 Similar observations have been made in metallocene catalyzed olefin polymerization where it is commonly found that a-olefins undergo insertion at a much greater rate than 1,1-disubstituted olefins. 26 These results have special relevance to the chain epimerization mechanism proposed by Busico to account for the tacticity dependence on monomer concentration in metallocene-catalyzed isospecific olefin polymerization. 27 The 89 change in olefin enantioface is accomplished via a series of ~-hydrogen elimination and reinsertion steps. A key feature of the mechanism involves inplane olefin rotation about then face of the coordinated alkene. It is assumed that once the 1,1-disubstituted olefin is lost from the metal center, it can not compete with the high concentration of monomer present. The results obtained for the insertion of isobutene and 1-pentene with 2 support this assertion. The observed rate difference in the two olefins would not allow reinsertion of the formed polymer chain especially in the presence of such a large excess of aolefin. In addition to olefin steric effects, the influence of cyclopentadienyl substitution on the rate of olefin insertion has also been examined. Comparing the rate of isobutene insertion for 1 and 18 at 210 K reveals a 3.8 x 103 fold rate enhancement for the latter. As with the olefin substituent studies, the large rate difference is a result of unfavorable steric interactions between the incoming olefin and the bulky pentamethylcyclopentadienyl rings. Slightly alleviating the steric interactions by replacement of a methyl group with a hydrogen atom greatly enhances the observed rates. Similar effects are observed with 20 and 21 where the reduced steric disposition of ligand results in insertion rates that are too fast to measure with NMR techniques. The rate of isobutene insertion is not changed by replacement of one of the pentamethylcyclopentadienyl methyl groups with an ethyl group as evidenced by the similar rates of isobutene insertion with 1 and 22. Cyclopentadienyl substitution also has a large impact on the regiospecificity of styrene insertion. More crowded metallocenes such as 1, 18, 20 and 21 proceed with high regioselectivity, yielding solely the 1,2-insertion product. However, more open metallocenes, 31, 32 and 33, form mixtures of both 1,2 and 2,1-insertion products and in one case, 29, only 2,1 insertion products are formed. From these results, it appears that in absence of overriding steric effects, styrene preferrs to insert in a 2,1 fashion, presumably due to electronic stabilization of the metal center by the phenyl ring. 28 However, this electronic stabilization can be offset by unfavorable interactions between the cyclopentadienyl substitution and the alkyl group thus resulting in solely 1,2 insertion products. 90 The experimentally determined rate constants and resulting activation parameters allow for direct comparison of the insertion barrier for zirconium and hafnium. In general, the barrier for insertion into a zirconium hydrogen bond is approximately 4 kcal/ mol lower than that for the corresponding hafnium hydrogen bond. The differences in activation barriers correspond to an approximate rate difference of 102 . Similar differences in activity have been observed in a variety of zirconium and hafnium catalytic systemsl and may be attributed to the ground state stabilization of the hafnium complex due to the increased metal hydrogen bond strength. B-Hydrogen Elimination from (CpRnhM(R')(H) (R, R' = alkyl). Zirconocene alkyl hydride complexes of the general formula (CpRnhZr(R')(H) (R, R' = alkyl) undergo facile B-hydrogen elimination as determined by trapping with 37. Using this kinetic technique, the rates of Bhydrogen elimination for a series of zirconocene isobutyl hydride complexes has been established (Figure 6). In general, more substituted metallocenes display slower rates of B-hydrogen elimination. In comparison to olefin insertion, rates of B-hydrogen elimination are less affected by ancillary ligand substitution. For example, insertion of isobutene with 1 versus 18 results in a 3800-fold rate enhancement. However, in the reverse reaction, B-hydrogen elimination from 3 and 19, only a 5-fold enhancement in rate is observed. Since the rates of both olefin insertion and B-hydrogen elimination have been measured for the [('11 5-C5Me5)2Zr] metallocene, the equilibrium constant for the addition of isobutene to 1 can be computed (eq. 10). At 296 K, the equilibrium constant for this reaction is 2.3 x 103, corresponding to a spontaneous reaction with a Gibb's free energy change of -4.6 kcal/mol. Assuming a negative value for the reaction entropy, the insertion of isobutene with 1 is highly exothermic. According to the Hammond postulate,18 the reaction possesses an "early" transition state, meaning it resembles reactants more than the products. An early transition state magnifies the unfavorable steric interactions between the olefin methyl groups and the pentamethylcyclopentadienyl ligand array, resulting in a larger steric effect on the rate of insertion as compared to the rate of B-hydrogen elimination. 91 kinsertion (10) kJ3-H elimination T = 296K Keq = 2.3 X 10-3 M-1 LiGrxn =4.6 kcal/mol Similar_cyclopentadienyl steric effects on P-hydrogen elimination have been observed for the polymerization of propylene with metallocene catalysts. Polypropylene produced from Cp2ZrCl2/MAO mixtures terminates primarily by P-hydrogen elimination, whereas the polyolefin generated from Cp*2ZrCl2/MAO mixtures contains end groups arising from chain termination by P-methyl elimination. The increased rate of P-methyl elimination for the latter system is believed to be a result of inhibition of P-hydrogen elimination by the sterically demanding pentamethylcyclopentadienyl rings (Figure 8).29 l favored ~-CH3 elimination disfavored l ~-H elimination Figure 8. Rationale for preference for ~-methyl elimination over ~-hydrogen elimination in sterically demanding metallocene catalysts. The kinetic isotope effects for P-hydrogen elimination have been determined with a series of zirconocene isobutyl hydride complexes, (CpRnhZr(CH2CL(CH3)2)(L) (L = H or D). In all cases examined, a normal, 92 primary isotope effect has been obtained (Table 10). These data suggest that Bhydrogen elimination proceeds via rate determining C-H(D) bond cleavage followed by rapid dissociation of the coordinated olefin. The values obtained in this study (~ 4) are larger than those measured for other transition metal systems. A primary kinetic isotope effect of 2.0 has been measured for Bhydrogen elimination in the scandium phenethyl complex, (TlS_ C5Me5)2ScCH2CH2C6Hs. 9 Likewise, a kinetic isotope effect of 1.6 has been measured for the ~-hydrogen elimination in the polymerization of propene with 2-d1-propene with [(Me2Sih(T1 5-CsH-3,5-(CHMe2)z)(11 5-CsH2-4-CHMe2)]ZrCl2/ methyalumoxane mixtures.30 The electronic effects on the rate of B-hydrogen elimination have been examined with a series of para-substituted styrene hydride complexes of the general formula, (T1 5-C5Me5)('r1 5-C5Me4H)Zr(CH2CH2-p-C6Hs-X) (X = H, Me, OCH3, CF3). From the rates of B-hydrogen elimination, a linear free energy relationship has been established. The Hammett plot displays a better correlation to a than cr+ with a p value of -1.80(5). This value is similar in sign and magnitude to the p value of -1.87 obtained for the P-hydrogen elimination of (T1 5-CsMe5)zScCH2CH2-p-C6~-X. 8 The kinetic isotope effect and linear free energy data are consistent with Bhydrogen elimination proceeding through the same transition state as olefin insertion; namely a four centered transiton state with slight positive charge development at the P-carbon. Likewise, the rate determining step for BI hydrogen elimination is consistent with being the microscopic reverse of olefin insertion where the rate determining step is scission of the alkyl C-H bond (Figure 7). Delineation of Ground and Transition State Effects in B-Hydrogen Elimination. Measurement of the rates of P-hydrogen elimination as well as the relative free energy changes for a variety of zirconocene isobutyl and n-butyl hydride complexes allows for the unique opportunity to differentiate between 93 the relative contributions of ground state and transition state effects for the reaction. From measuring the equilibrium constant and hence free energy change for the addition of both isobutene and 1-butene to a given zirconocene dihydride (Table 14), the relative ground state energies of the two zirconocene alkyl hydride complexes may be established (eq. 11). The change in free energy for the experimentally determined reaction is not the free energy change for the zirconocenes of interest but rather a composite of the relative zirconocene alkyl hydride ground states and the change in free energy for the isomerization of 1butene to isobutene. Subtraction of the established value of -3.2 kcal/mol31 for the isomerization of 1-butene to isobutene, the experimentally determined free energy of reaction yields the relative ground state energies of two zirconocene alkyl hydride complexes (Table 16). It is important to note that these calculations allow ordering of the relative ground states of the n-butyl hydride as compared to the isobutyl hydride for a given ligand array. Comparison of the ground states of two isobutyl hydride complexes of different ancillary ligation can not be compared with this analysis. ---¥._H z~ r- ~Gorxn __/___ 296K + ~ I ~ 296K (11) ~G 0 2 = -3.2 kcal/mol 296K 94 Ligand Array LlG 0 rxn (kcal/mol) LlG 0 zr (kcal/mol) [(rt 5-CsMes)z] [Cp*(rt 5-CsMe~)] [Cp*(rt 5-CsH3-1,3-CMe3)2] [Cp*(rt 5-CsH3-l,3-CHMe2)2] -2.3(2) -2.1(2) -1.9(2) -1.7(1) -1.3(1) -1.3(1) 0.90 1.0 1.3 1.5 1.9 1.9 [Cp*(THI)] [Cp*(rt 5-CsH4-CMe3)] . Table 16. Relative ground state energies for zirconocene isobutyl and n-butyl hydride complexes. • In all cases examined, the zirconocene isobutyl hydride is thermodynamically favored over the corresponding n-butyl hydride complex. In an attempt to understand the electronic contribution of this effect, the free energies of formation of isobutane and n-butane have been examined. At 296 K, the branched alkane is favored by 1.10 kcal/mol over the linear alkane,3 2 in accord with the observed preference for the zirconocene. Previous reports have established a correlation between metal-carbon and carbon-hydrogen bond strengths where the relative energy of the C-H bond may be used to predict the relative strength of the M-C bond. 32 Therefore, the zirconium center, behaving analogously to a hydrogen atom, wishes to form the more stable alkane and therefore prefers the isobutyl hydride over the n-butyl hydride. Although electronic effects are dominant, the ancillary ligand substitution does influence the position of the equilibrium. For less substituted zirconocenes such as [Cp*(rt5-C5B4-CMe3)Zr] and [Cp*(THI)], the electronic contributions dominate since the free energy difference exceeds that for the alkanes. 33 For more crowded members of the series, [(rt 5-CsMes)zZr] and [Cp*(rt 5-CsMe4H)], steric destabilization of the isobutyl hydride complex is observed. From these data, the energetics of this steric contribution can be estimated to be approximately 1 kcal/mol. Grubbs34 has found similar behavior with alkyl-substituted titanocyclobutanes, where the more stable titanocycle is derived from the more stable olefin and is believed to be a result of the structural features of the 95 metallocycle. Likewise, Wolczanski has found a similar correlation between metal-carbon bond strengths and carbon-hydrogen bond strengths in the equilibration of tris-imido zirconium alkyl complexes.35 From the experimentally determined rates of ~-hydrogen elimination and the relative ground state energies of the zirconocene isobutyl and n-butyl hydrides, the relative transition state energies for the ~-hydrogen elimination reaction can be determined. Using the Arrhenius relationship, the activation free energy may be calculated for each reaction. Subtraction of the relative ground state contributions for each of the zirconocene alkyl hydrides affords the relative transition state energies for both zirconocene alkyl hydrides for a given ligand array. The relative ground state, activation, and transition state energies are contained in Table 17. Ligand Array ~GOzr [Cp*(11 5-CsMe4H)] [Cp*('17 5-CsH3-l,3-CMe3)2] [Cp*('17 5-C5H3-l,3~CHMe2)2] 1.0 1.3 1.5 1.9 1.9 [Cp*(THI)] [Cp*(11 5-Cs~-CMe3)] ~GJ3tt+ (iBu) ~GJ3tt+ (nBu) 23.9 22.0 21.3 20.8 20.1 22.9 22.0 21.4 21.4 21.0 MG+ 0 1.3 1.6 2.5 2.8 All energies are given in kcal/ mol. Table 17. Relative ground and transition state energies for zirconocene alkyl hyride complexes. Based on electronic considerations and the model established for the transition state for ~-hydrogen elimination (vide supra), the relative energy of a zirconocene isobutyl hydride would be expected to be lower in energy than the corresponding zirconocene n-butyl hydride since the more substituted alkyl would better stabilize the developing positive charge on the ~-carbon (Figure 8). However, based on steric considerations, the zirconocene n-butyl hydride would be favored due to decreased steric interactions with the ligand array. The experimentally determined transition state energy differences indicate that for the sterically crowded metallocene, [Cp*(11 5-CsMe4H)Zr], these effects exactly cancel and as a result the isobutyl and n-butyl hydride transition states are of equal energy. Thus, the increased rate of ~-hydrogen elimination for the n-butyl hydride observed for this metallocene is a result of electronic stabilization of the isobutyl hydride in the ground state. 96 For less substituted metallocenes, the electronically favored isobutyl hydride transition state dominates over the sterically preferred n-butyl hydride transition state. This effect increases with decreasing substitution on the metallocene and, as a result, the least crowded metallocene, [Cp*(yt5-C5If4CMe3)Zr ], displays the largest transition state energy difference. From these data, the relative rates of B-hydrogen elimination can be rationalized. For less crowded metallocenes such as [Cp*(rt 5-Cslf4-CMe3)Zr] and [Cp*(THl)Zr], the electronic stabilization of the isobutyl hydride transition state overcomes the ground state destabilization of n-butyl hydride ground state and, as a result, faster rates of isobutyl hydride P-hydrogen elimination are observed. For intermediate metallocenes, these effects are similar, although the transition state effects dominate and faster isobutyl hydride P-hydrogen elimination rates are observed. Only in the most crowded member of the series, [Cp*(ytSC5Me4H)Zr], are the transition state effects overcome by ground state effects. From these studies, a complete description of the P-hydrogen elimination reaction has been established. The reaction proceeds via rate determining C-H bond scission, forming a four-centered transition state structure which has a build up of positive charge on the B-carbon, resulting in transfer of H&- to the metal center. The rate of P-hydrogen elimination is greatly influenced by the structure of the ancillary ligation. For a given alkyl, the rate of P-hydrogen elimination decreases with increasing cyclopentadienyl ligand substitution. When considering P-hydrogen elimination for two different alkyls, both ground state and transition state effects must be considered. The relative ground state energetics may be predicted on electronic grounds from the free energies of the alkanes, although increased cyclopentadienyl substitution perturbs this value. For less substituted metallocenes, the electronic portion of the transition state effect dominates and as a result the most substituted alkyl undergoes more facile P-hydrogen elimination. Experimental General Considerations. All air- and moisture-sensitive compounds were manipulated using standard vacuum line, Schlenk or cannula techniques or in a 97 drybox as described previously. 36 Argon, dinitrogen, dihydrogen and dideuterium gases were purified by passage over columns of MnO on vermiculite and activated molecular sieves. Solvents for air and moisture sensitive reactions were stored under vacuum over titanocene37 or sodium benzophenone ketyl. NMR solvents: benzene-d6, toluene-ds, tetrahydrofuran-ds, diethyl ether-d10 and pyridine-ds were purchased from Cambridge Isotope Laboratories. Benzene-d6 and toluene-ds were dried over LiAlHi and sodium and then stored over titanocene. Tetrahydrofuran-ds and diethyl ether.:.d10 were dried over CaH2 and stored over sodium/benzophenone ketyl. Pyridine-d5was dried over CaHz. Preparation of 1,38 2,18 3,15 20, 21,14 22,23 24,16 29, 31, 32 and 3314 were accomplished as described previously. Isobutene, 2-methyl-1-butene, 2,4-dimethyl-1-pentene, 2,3-dimethyl-1pentene and propylene were purchased from Aldrich. Isobutene and propene were dried over Al(i-Bu)3 and distilled by vacuum transfer before use. The other olefins were distilled from CaH2 and stored over LiAlfi4. Both cis- and trans-2butene were purchased from Matheson and dried over activated 4A molecular sieves. Styrene and a-methylstyrene were purchased from Aldrich; p-fluoro-amethylstyrene was purchased from Lancaster. All were distilled under reduced pressure from CaH2 and stored frozen in the drybox. Preparations of p-methyla-methylstyrene, p-trifluoromethyl-a-methylstyrene and p-methoxy-amethylstyrene were accomplished by reaction of Ph3P=CH2 with the appropriate acetophenone as described previously39 and the resulting product distilled at reduced pressure from CaH2. Ferrocene used as an internal standard was purchased from Aldrich and sublimed before use. NMR spectra were recorded on a Bruker AM500 (500.13 MHz for lH, 76.77 for 2H, 125.77 MHz for 13C) spectrometer. All chemical shifts are relative to TMS using lH (residual), 2H or 13c chemical shifts of the solvent as a secondary standard. The temperature of the NMR probe was measured before and after each kinetic run with a standard CH3OH reference tube. Kinetics of the Reaction of 1 or 2 with Volatile Olefins. In the dry box, a J. Young NMR tube was charged with 0.50 mL of 0.0488 M (0.0244 mmol) of a stock toluene-ds solution of metallocene dihydride containing a known amount of ferrocene. The NMR tube was then attached to the vacuum line via a 98 calibrated gas volume. The tube was evacuated at-78 °C and 10 equivalents of olefin were charged into the gas bulb by vacuum transfer and the gas condensed in the tube at-78 °C. The NMR probe was calibrated to the desired temperature and the sample was shaken several times just before insertion into the probe. Approximately 10-15 spectra were recorded at regular intervals over the duration of 2-3 half lives. Peak intensities of the ferrocene and metallocene dihydride were measured for each spectrum. The observed rate constants were obtained from slopes of plots of ln[Cp*2MH2] versus time. Second order rate constants were obtained by dividing the observed psuedo first order rate constants by the concentration of olefin. Activation parameters were obtained by measuring second order rate constants over a temperature range. A plot of ln(k/ T) versus 1/ T resulted in a slope of MI+ / R and an intercept of [(~S+ / R) + 23.76]. Reported errors in the rate constants represent one standard deviation from the least squares fit of the experimental data. These errors were then used to determine the errors in the activation parameters. Kinetics of the Reaction of 1 with Substituted a-Methylstyrenes. In the dry box, 0.25 mL of 0.096 M stock benzene-d6 solution of 1 containing a known amount of ferrocene was charged into a J. Young NMR tube. Via microsyringe, 0.25 mL of a benzene-d6 stock solution of a-methylstyrene was added to the tube and the sample was then immediately frozen in liquid nitrogen. The tube was then quickly thawed and inserted into NMR probe. Approximately 10-15 spectra were recorded at regular intervals over the duration of 2-3 half lives. Work up of the data was carried out as described for the previous experiments. Determination of ~-Hydrogen Elimination Rate Constants. In a typical experiment, a J. Young NMR tube was charged with 0.50 mL of 0.0488 M stock benzene-d6 or toluene-ds solution of zirconocene dihydride containing a known amount of ferrocene. On the vacuum line, the tube was frozen in liquid nitrogen and degassed with three freeze-pump-thaw cycles. Via a 6.9 mL calibrated gas volume, 100 Torr of the desired olefin was added at-196 °C. The tube was thawed and shaken. The 1H NMR spectrum was then recorded to ensure complete conversion to the alkyl hydride complex had occurred. The tube was reattached to the vacuum line and via a 56.8 mL calibrated gas bulb, the desired amount of 37 was collected in the tube at-196 °C. The tube remained frozen in liquid nitrogen until insertion into the thermostated NMR probe. Approximately 99 10-15 spectra were recorded over regular intervals over the course of 2-3 half lives. Work up of the data was carried out as described for the previous experiments. Determination of Equilibrium Constants for Zirconocene Alkyl Hydride Complexes. In a typical experiment, a J. Young NMR tube was charged with 0.50 mL of 0.0488 M stock benzene-d6 solution containing a known amount of ferrocene. On the vacuum line, the tube was degassed and the appropriate amount of isobutene and 1-butene was then added via calibrated gas volume. The tube was thawed and shaken thoroughly and allowed to stand at room temperature for several hours. The 1H NMR spectrum was then recorded and the equilibrium constant computed from the integration of the various species in solution. NMR Spectroscopic Data (r1 5-CsMe5)zZr(CH2CH(CH3)CH2CH3)(H) (4). 1H NMR (benzene-d6): 8 = 1.92 (s, 30H, CsMes); 6.31 (s, lH, ZrH); -0.531 (dd, lH, CH2CH(CH3)CH2CH3); 0.290 (dd, lH, CH2CH(CH3)CH2CH3); not located (CH2CH(CH3)CH2CH3); 1.36 (m, 2H, CH2CH(CH3)CH2CH3); 0.877 (t, 7 Hz, 3H, CH2CH(CH3)CH2CH3); 1.76 (d, 5 Hz, 3H, CH2CH(CH3)CH2CH3). 13C NMR (benzene-d6): 8 = 12.83 (Cs.Mes); 118.26 (CsMes); 70.28 (CH2CH(CH3)(CH2CH3); 31.17 (CH2CH(CH3)(CH2CH3); 22.87 (CH2CH(CH3)(CH2CH3); 13.52 (CH2CH(CH3)(CH2CH3); 29.09 (CH2CH(CH3)(CH2CH3). ('r1S-C5Me5)zZr(CH2CH(CH3)CH2CH(CH3)z)(H) (5). 1H NMR (benzene-d6): 8 = 1.94 (s, 30H, CsMes); 6.39 (s, lH, ZrH); -0.669 (dd, lH, CH2CH(CH3)CH2CH(CH3)z ); 0.492 (dd, lH, CH2CH(CH3)CH2CH(CH3)2); 2.24 (m, 2H,CH2CH(CH3)CH2CH(CH3)2); 1.12 (m, 2H, CH2CH(CH3)CH2CH(CH3)2); 2.16 (m, lH, CH2CH(CH3)CH2CH(CH3)2); 1.02 (d, 6.5 Hz, 3H, CH2CH(CH3)CH2CH(CH3)z); 0.98 (d, 6.5 Hz, 6H, CH2CH(CH3)CH2CH(CH3)2). 13C NMR (benzene-d6): 8 = 12.30 (CsMes); 12.50 (CsMes); 117.34 (CsMes); 117.71 CsMes); 66.60 (CH2CH(CH3)CH2CH(CH3)2); 39.09 (CH2CH(CH3)CH2CH(CH3)z); 20.58 (CH2CH(CH3)CH2CH(CH3)2); 22.64 (CH2CH(CH3)CH2CH(CH3)z); 35.93 (CH2CH(CH3)CH2CH(CH3)2); 13.53, 13.62 (CH2CH(CH3)CH2CH(CH3)2). 100 (11 5-CsMeshZr(CH2CH(CH3)CH(CH3)CH2CH3)(H) (6). 1H NMR (benzene-d6): 8 = 1.93 (s, 30H, CsMes); 6.35 (s, lH, ZrH); -0.386 (dd, lH, CH2CH(CH3)CH(CH3)CH2CH3); 0.220 (dd, lH, CH2CH(CH3)CH(CH3)CH2CH3); 2.21 (m, lH, CH2CH(CH3)CH(CH3)CH2CH3); 1.31 (m, lH, CH2CH(CH3)CH(CH3)CH2CH3); 1.18 (m, 2H, CH2CH(CH3)CH(CH3)CH2CH3); 1.01 (t, 7 Hz, 3H, CH2CH(CH3)CH(CH3)CH2CH3). (11 5-CsMeshZr(CH2CH(CH3)(C6Hs))(H) (7). 1H NMR (benzene-d6): 8 = 1.87 (s, 15H, CsMes); 1.94 (s, 15H, CsMes); 6.55 (s, lH, ZrH); -0.944 (dd, lH, CH2CH(CH3)(C6Hs)); -0.969 (dd, lH, CH2CH(CH3)(C6Hs)); 1.56 (t, 6.5 Hz, lH, CH2CH(CH3)(C6Hs)); 1.65 (d, 7 Hz, 3H, CH2CH(CH3)(C6Hs)); 7.42 (d, 7.1 Hz, 2H, CH2CH(CH3)(ortho-C6Hs)); 7.11 (t, 7.5 Hz, 2H, CH2CH(CH3)(meta-C6Hs)); 7.29 (t, 7.3 Hz, lH, CH2CH(CH3)(para-C6Hs)). 13C NMR (benzene-d6): 8 = 12.24 (CsMes); 12.48 (CsMes); 118.44 (CsMes); 118.77 (C5Me5); 67.06 (CH2CH(CH3)(C6Hs); 39.45 (CH2CH(CH3)(C6Hs); 30.10 (CH2CH(CH3)(C6Hs); 117.39, 117.65, 119.54, 123.75, 134.51, 1 not located (C6Hs). (11 5-C5MeshZr(CH2CH2CH2CH3)(H) (8). 1H NMR (benzene-d6): 8 = 1.89 (s, 30H, CsMes); 6.27 (s, lH, Zr-H); 0.159 (t, 9 Hz, 2H, CH2 CH2CH2CH3); 1.24 (m, 2H, CH2 CH2CH2CH3); 1.39 (m, 2H, CH2 CH2CH2CH3); 1.05 (t, 7.3 Hz, 3H, CH2 CH2CH2CH3). 13C NMR (benzene-d6): 8 = 12.09 (CsMes); 113.00 (C5Me5); 52.48 (CH2CH2CH2CH3); 31.62 (CH2CH2CH2CH3); 25.57 (CH2CH2CH2CH3); 11.40 (CH2CH2CH2CH3). (11 5-C5Me5)zHf(CH2CH(CH3)z)(H) (9). 1H NMR (benzene-d6): 8 = 1.95 (s, 30H, C5Me5); 9.76 (s, lH, Hf-H); -0.25 (d, 6.5 Hz, 2H, CH2 CH(CH3)2); 2.09 (m, lH, CH2 CH(CH3)2); 1.00 (d, 6Hz, 6H, CH2CH(CH3)2). 13C NMR (benzene-d6): 8 = 12.24 (CsMes); 117.52 (CsMes); 76.33 (CH2CH(CH3)2); 31.94 (CH2CH(CH3)2); 13.63 (CH2CH(CH3)2). (115-C5Me5)zHf(cyclo-C5H9)(H) (10). 1H NMR (benzene-d6): 8 = 1.95 (s, 30H, C5Me5); 13.31 (s, lH, HfH); -0.17, .456, 1.08, 1.93, 2.27 (m, C5H9). 13C NMR (benzene-d6): 8 = 12.27 (CsMes); 117.57 (CsMes); 73.17 (C1-cyclopentene); 29.86 (C2-cyclopentene); 23.51 (C3-cyclopentene). 101 o= 1.88 (s, 30H, CsMes); 12.96 (s, lH, HfH); -0.09 (t, 6.5 Hz, 2H, CH2 CH2Ph); 2.22 (t, 6.5 Hz, 2H, CH2 CH2Ph); 6.85 (m, lH, para-CH2CH2C6-Hs); 6.98 (m, 2H, meta-CH2CH2C6Hs); 7.34 (m, 2H, ortho-CH2CH2C6-Hs). 13C NMR (benzene-d6): o= 12.12 (CsMes ); 118.26 (C5Me5); 62.45 (CH2CH2Ph); 30.36 (CH2CH2Ph); 125.52 (para-C6Hs); 137.50 (ortho-C6Hs); 150.07 (meta-C6Hs), 1 not located (ipso-C6Hs). ('r1 5-CsMe5)zHf(CH2CH2C6Hs)(H) (11). 1H NMR (benzene-d6): ('11 5-C5Me5)zHf(CH2CH2CH2CH3)(H) (12). 1H NMR (benzene-d6): o= 1.95 (s, 30H, CsMes); 9.80 (s, lH, HfH); -0.005 (t, 9 Hz, 2H, CH2 CH2CH2CH3); not located (CH2 CH2CH2CH3); 0.981 (m, 2H, CH2 CH2CH2CH3); 1.06 (t, 7.4 Hz, 3H, CH2 CH2CH2CH3) .. 13C NMR (benzene-d6): o= 12.06 (CsMes ); 116.97 (C5Me5); 62.55 (CH2CH2CH2CH3); 31.50 (CH2CH2CH2CH3); 26.93 (CH2CH2CH2CH3); 14.76 (CH2CH2CH2CH3). (ri 5-CsMe5)zHf(CH2CH2CH2CH2CH3)(H) (13). 1H NMR (benzene-d6): o= 1.94 (s, 30H, CsMes); 9.81 (s, lH, HfH); -0.005 (t, 9 Hz, 2H, CH2 CH2CH2CH2CH3); not located (CH2 CH2CH2CH2CH3); 0.991 (m, 4H, CH2 CH2CH2CH2CH3); 1.12 (t, 7.4 Hz, 3H, CH2 CH2CH2CH2CH3). (rt 5-CsMe5)iZr(CH2CH(CH3)(C6H4-p-F))(H) (14). 1H NMR (benzene-d6): o= 1.84 (s, 15H, CsMes); 1.86 (s, 15H, CsMes); 6.31 (s, lH, ZrH); -0.984 (dd, lH, CH2CH(CH3)(C6!4-p-F)); -0.368 (dd, lH, CH2CH(Me)(C6H4-p-F)); 2.56 (m, lH, CH2CH(CH3)(C6H4-p-F)); 1.78 (d, 3H, CH2CH(CH3)(C6H4-p-F)); 7.19 (m, 2H, CH2CH(CH3)(ortho-C6H4-p-F)); 6.94 (m, 2H, CH2CH(CH3)(meta-C(5.H4-p-F)). (rt 5-C5Me5)zZr(CH2CH(CH3)(C6H4-p-CH3))(H) (15). 1H NMR (benzene-d6): o= 1.89 (s, 15H, CsMes); 1.94 (s, 15H, CsMes); 6.54 (s, lH, ZrH); 0.959 (dd, lH, CH2CH(CH3)(C6H4-p-CH3)); 0.912 (dd, lH, CH2CH(CH3)(C6H4-p-CH3)); 2.22 (m, lH, CH2CH(CH3)(C6H4-p-CH3)); 1.19 (d, 7 Hz, 3H, CH2CH(CH3)(C6!4-pCH3)); 2.16 (s, 3H, CH2CH(CH3)(C6H4-p-CH3)); 6.99 (d, 6 Hz, 2H, CH2CH(Me)(meta-C6H4-p-CH3)); 7.34 (d, 6 Hz, 2H, CH2CH(CH3)(ortho-C~4-pCH3)). (rt 5-CsMe5)zZr(CH2CH(CH3)(C6H4-p-OCH3))(H) (16). 1H NMR (benzene-d6): = 1.89 (s, 15H, CsMes); 1.95 (s, 15H, CsMes); 6.53 (s, lH, ZrH); 0.904 (dd, lH, CH2CH(CH3)(C6H4-p-OCH3)); 0.912 (dd, lH, CH2CH(CH3)(C6H4-p-OCH3)); o 102 1.62 (m, lH, CH2CH(CH3)(C6fi4-p-OCH3)); 1.78 (d, 6.5 Hz, 3H, CH2CH(CH3)(C6If4-p-OCH3)); 3.34 (s, 3H, CH2CH(Me)(C6fi4-p-OCH3)); 6.92 (d, 6 Hz, 2H, CH2CH(Me)(meta-C6ii4-p-OCH3)); 7.34 (d, 6 Hz, 2H, CH2CH(Me )( ortho-C6ii4-p-OCH3) ). ('r1 5-CsMe5)zZr(CH2CH(CH3)(C6H4-p-CF3))(H) (17). 1H NMR (benzene-d6): 8 = 1.84 (s, 15H, CsMes); 1.92 (s, 15H, CsMes); 6.54 (s, lH, ZrH); -1.11 (dd, lH, CH2CH(CH3)(C6H4-p-CF3)); 0.053 (dd, lH, CH2CH(CH3)(C6H4-p-CF3)); 3.31 (m, lH, CH2CH(CH3)(C6~-p-CF3)); 1.05 (d, 6.8 Hz, 3H, CH2CH(CH3)(C6H4-pCF3)); 7.24 (d, 6 Hz, 2H, CH2CH(Me)(meta-C6ii4-p-CF3)); 7.48 (d, 6 Hz, 2H, CH2CH(CH3)(ortho-C6ii4-p-CF3) ). (l1 5-C5Me5)(Y1 5-C5Me4H)Zr(CH2CH(CH3)z)(H) (19). 1H NMR (benzene-d6): 8 = 1.91 (s, 15H, CsMes); 1.60, 1.87, 2.10, 2.33 (s, 3H, CsAfe4H); 4.52 (s, lH, CsMet!ffl; 6.26 (s, lH, ZrH); -0.445 (dd, lH, CH2 CH(CH3)2); 0.443 (dd, lH, CH2 CH(CH3)2); 2.15 (m, lH, CH2 CH(CH3)2); 0.953 (d, 7 Hz, 3H, CH2CH(CH3)2); 1.06 (d, 7 Hz, 3H, CH2CH(CH3)2). 13C NMR (benzene-d6): 8 = 12.73 (CsMes); 117.98 (C5Me5); 12.17, 12.32, 13.46, 14.56 (CsAfe4H); 68.38 (CH2C(CH3)2); 31.76 (CH2CH(CH3)2); 24.47, 29.64 (CH2CH(CH3)2); 111.51, 115.70, 119.70, 120.79, 121.63 (Cp). (fl 5-CsMesHY1 5-C5Me4CH2CH3)Zr(CH2CH(CH3)z)(H) (23). 1H NMR (benzene- d6): 8 = 1.92 (s, 15H, CsMes); 1.76, 1.79, 1.94, 1.98 (s, 3H, C5Me4CH2CH3); 1.85 (q, 6.5 Hz, 2H, C5Me4CH2CH3); 1.90 (t, 7 Hz, 2H, C5Me4CH2CH3); 6.34 (s, lH, ZrH); -0.381 (dd, lH, CH2 CH(CH3)2); 0.053 (dd, lH, CH2 CH(CH3)2); 2.43 (m, lH, CH2 CH(CH3)2); 0.82 (d, 7 Hz, 3H, CH2CH(CH3)2); 1.10 (d, 7 Hz, 3H, CH2CH(CH3)2). (115-C5Me5)(Y1 5-CsH3-(CMe3)i)Hf(CH2CH(CH3)i)(H) (25). 1H NMR (benzene- d6): 8 = 1.98 (s, 15H, CsMes); 1.22 (s, 9H, CMe3); l.48(s, 9H, CMe3); 12.98 (s, lH, HfH); -1.06 (m, lH, CH2CH(CH3)2); 0.75 (m, lH, CH2CH(CH3)2); 2.50 (m, lH, CH2CH(CH3)2); 1.04 (d, 7 Hz, 3H, CH2CH(CH3)2); 1.17 (d, 7 Hz, 3H, CH2CH(CH3)2); 4.92, 4.62, 6.50 (m, lH, Cp ). 13C NMR (benzene-d6): 8 = 12.71 (C5Me5); 116.96 (CsMes); 32.34 (CMe3); 32.99 (CMe3); 145.06 (CMe3); 145.96 (CMe3); 76.44 (CH2CH(CH3)2); 32.34 (CH2CH(CH3)2); 24.33 (CH2CH(CH3)2); 30.30 (CH2CH(CH3)2); 99.86, 104.61, 105.64, 2 not located (Cp ). 103 (11 5-CsMe5)zZr(CH2CH2C6Hs)(H) (26). 1H NMR (benzene-d6): ci = 1.88 (s, 30H, CsMes); not located (ZrH); 0.54 (t, 6.9 Hz, 2H, CH2 CH2Ph); 1.78 (t, 6.3 Hz, 2H, CH2 CH2Ph); 7.08 (m, lH, para-CH2CH2C6Hs); 7.25 (m, 2H, meta-CH2CH2C6Hs); 7.40 (m, 2H, ortho-CH2CH2C6H5). 13C NMR (benzene-d6): ci = 12.18 (CsMes); 117.51 (C5Me5); 51.79 (CH2CH2C6Hs); 26.49 (CH2CH2C6Hs); 125.67, 126.15, 138.00, 1 not located (C6Hs). fr1 5-CsMesHri 5-CsH3-1,3-(CMe3h)Zr(CH2CH2C6Hs)(H) (27). 1H NMR (benzene-d6): ci = 1.89 (s, 15H, CsMes); 1.16 (s, 9H, CMe3); 0.956 (s, 9H, CMe3); 6.49 (s, lH, ZrH); -0.122 (td, 13.9 Hz, 3.8 Hz, lH, CH2 CH2Ph); 0.693 (td, 13.9 Hz, 3.8 Hz, lH, CH2 CH2Ph); 2.48 (td, 13.6 Hz, 4.8 Hz, lH, CH2 CH2Ph); 2.86 (td, 13.6 Hz, 4.8 Hz, lH, CH2 CH2Ph); 7.05 (m, lH, para-CH2CH2C6Hs); 7.25 (m, 2H, metaCH2CH2C6Hs); 7.31 (m, 2H, ortho-CH2CH2C6Hs); not located (ipso-C6Hs). (ri 5-CsH3-1,3-(CMe3)z)zZr(CH2CH2C6Hs)(H) (28). 1H NMR (benzene-d6): ci = 1.28, (s, 9H, CMe3); 1.45 (s, 9H, CMe3); 5.33 (s, lH, ZrH); 0.55 (t, 10 Hz, 2H, CH2CH2C6Hs); 2.76 (t, 10 Hz, 2H, CH2CH2C6Hs); 4.85, 5.22, 6.26 (s, lH, Cp ). 13C NMR (benzene-d6): ci = 32.77 (CMe3); 32.48 (CMe3); 141.28 (CMe3); 144.70 (CMe3); 60.96 (CH2CH2C6Hs); 34.29 (CH2CH2C6Hs); 125.56, 126.95, 137.68, 1 not • located (C6Hs); 97.41, 100.53, 106.63, 114.13, 122.65 (Cp ). (ri 5-CsMesHri 5-C5H4-CMe3)Zr(CH(C6Hs)(CH3))(H) (30). 1H NMR (benzene-d6): ci = 1.75 (s, 15H, CsMes); 1.83 (s, 15H, CsMes); 1.11 (s, 9H, CMe3); 1.36 (s, 9H, CMe3);1.37 (s, lH, ZrH); 5.40 (s, lH, ZrH); -0.18 (d, 6.5 Hz, 3H, CH(C6Hs)(CH3)); 1.86 (d, 6.5 Hz, 3H, CH(C6Hs)(CH3)); not located (CH(C6Hs)(CH3)); 6.85, 6.89 (m, lH, para-C6Hs); 7.19, 7.25 (m, 2H, meta-C6Hs); 7.39, 7.44 (m, 2H, para-C6Hs); 3.18, 3.45, 3.66, 4.48, 4.62, 4.72, 4.77, 4.78 (Cp ). 13C NMR (benzene-d6): ci = 12.51, 12.85 (CsMes); 114.30, 114.68, (C5Me5); 32.84, 32.88 (CMe3); 136.62, 145.88 (CMe3); 39.09, 47.91 (CH(C6Hs)(CH3)); -7.240, 17.68 ((CH(C6Hs)(CH3)); 112.09, 123.75 (paraC6Hs); 125.71, 126.73 (ortho-C6Hs); 129.16, 132.36 (meta-C6Hs); 2 not located (ipsoC6Hs); 99.98, 100.03, 100.10, 102.43, 104.08, 105.02, 110.04, 113.79, 120.77, 121.66 (Cp). (ri 5-C5Me5)(THI)Zr(CH2CH2C6Hs)(H) (34a). 1H NMR (benzene-d6): ci = 1.86 (s, 15H, CsMes); 5.89 (s, lH, ZrH); 2.0-2.4 (m, THI); 0.706 (m, 2H, CH2CH2Ph); 0.870 104 (m, 2H, CH2CH2Ph); 6.94 (m, lH, para-CH2CH2C6i{5); 7.24(m, 2H, metaCH2CH2C6i{5); 7.37 (m, 2H, ortho-CH2CH2C6Hs); 4.13, 4.57, 4.99 (Cp ). ('r1 5-C5Me5)(THl)Zr((CH(C6Hs)(CH3))(H) (34b). 1H NMR (benzene-d6): 8 = 1.79 (s, 15H, CsMes); not located (ZrH); 2.2-2.6 (m, THI); -0.90 (d, 8 Hz, 3H, CH(C6Hs)(CH3)); 1.20 (d, 8 Hz, 3H, CH(C6Hs)(CH3)); 7.10 (m, lH, paraCH2CH2C6Hs); 7.22 (m, 2H, meta-CH2CH2C6Hs); 7.29 (m, 2H, orthoCH2CH2C6Hs); 3.54, 4.58, 4.71, 4.90, 2 not located (Cp ). (ri 5-C5Me4H)zZr(CH2CH2C6Hs)(H) (35a). 1H NMR (benzene-d6): 8 = 1.79, 1.82, 1.91, 1.99 (s, 6H, CsAfe4); 6.47 (ZrH); 0.38 (t, 6.5 Hz, 2H, CH2 CH2Ph); not located (CH2 CH2Ph); 6.96 (m, lH, para-CH2CH2C6i{5); 7.35 (m, 2H, meta-CH2CH2C6i{5); 7.40 (m, 2H, ortho-CH2CH2C6i{5). (ri 5-C5Me4H)zZr((CH(C6Hs)(CH3))(H) (35b). 1H NMR (benzene-d6): 8 = 1.60, 1.66, 1.73, 1.79, 2.14, 2.15, 2.18, 2.32 (s, 6H, CsAfe4H); 4.36, 1 not located (s, lH, ZrH); 0.485, 1 not located (q, 6 Hz, lH, CH(C6Hs)(CH3)); 1.26, 1 not located (CH(C6Hs)(CH3); 4.84, 4.89 (Cp ). (ri 5-CsMesHri 5-C5H3-1,3-(CHMe2)z)Zr(CH2CH2C6Hs)(H) (36a). 1 H NMR (benzene-d6): 8 = 1.82 (s, 15H, CsMes); 0.51 (d, 7 Hz. 6H, CHMe2); 0.84 (d, 7 Hz. 3H, CHMe2); 0.88 (d, 7 Hz. 3H, CHMe2); 1.07 (d, 7 Hz. 3H, CHMe2); 2.45 (sept, 6.5 Hz, lH, CHMe2); 2.59 (sept, 6.5 Hz, lH, CHMe2); 6.42 (s, lH, ZrH); -0.179 (m, lH, CH2 CH2Ph); 0.82 (m, lH, CH2 CH2Ph); 2.43 (m, lH, CH2 CH2Ph); 2.84 (m, lH, CH2 CH2Ph); 7.06 (m, lH, para-CH2CH2C6Hs); 7.29 (m, 2H, meta-CH2CH2C6Hs); 7.42 (m, 2H, ortho-CH2CH2C6Hs); 4.89, 5.26, 5.45 (Cp). (11 5-CsMes)(ri 5-C5H3-1,3-(CHMe2)z)Zr(CH(C6Hs)(CH3))(H) (36b). 1H NMR (benzene-d6): 8 = 1.76 (s, 15H, CsMes); 1.83 (s, 15H, CsMes); 0.68 (d, 7 Hz. 3H, CHMe2); 0.73 (d, 7 Hz. 3H, CHMe2); 1.04 (d, 7 Hz. 3H, CHMe2); 1.06 (d, 7 Hz. 3H, CHMei); 1.14 (d, 7 Hz. 3H, CHMe2); 1.17 (d, 7 Hz. 3H, CHMe2); 1.21 (d, 7 Hz. 3H, CHMe2); 1.24 (d, 7 Hz. 3H, CHMe2); not located (CHMe2); 6.19, 1 not located (s, lH, ZrH); 4.25, 4.60, 4.63, 4.83, 4.89, 5.76 (Cp). (ri5-C5MesHri 5-CsHs)Zr(CH2CH(CH3)z)(H) (38). 1H NMR (benzene-d6): 8 = 1.89 (s, 15H, CsMes); 6.22 (s, lH, ZrH); -1.93 (dd, lH, CH2 CH(CH3)2); 0.25 (dd, lH, 105 CH2 CH(CH3)2); 2.21 (m, lH, CH2 CH(CH3)2); 1.03 (d, 7Hz, 3H, CH2CH(CH3)2); 1.10 (d, 7Hz, 3H, CH2CH(CH3)2); 5.74 (s, SH, CsHs). 13C NMR (benzene-d6): o= 12.18 (CsMes); 117.62 (CsMes); 71.65 (CH2CH(CH3)2); 33.17 (CH2CH(CH3)2); 29.91 (CH2CH(CH3)2); 28.81 (CH2CH(CH3)2); 111.07 (Cp). (T1 5-CsMesHTt 5-CsH4-CMe3)Zr(CH2CH(CH3)i)(H) (39). 1H NMR (benzene-d6): o= 1.86 (s, 15H, CsMes); 1.34 (s, 9H, CMe3); 6.22 (s, lH, ZrH); -1.95 (dd, lH, CH2 CH(CH3)z); 0.14 (dd, lH, CH2 CH(CH3)2); 2.41 (m, lH, CH2 CH(CH3)z); 0.97 (d, 7Hz, 3H, CH2CH(CH3)2); 0.99 (d, 7Hz, 3H, CH2CH(CH3)2); 4.87, 4.92, 5.41, 5.90 (Cp). 13C NMR (benzene-d6): o= 12.18 (CsMes); 110.85 (C5Me5); 2.31 (CMe3); 145.60 (CMe3); 74.39 (CH2CH(CH3)2); 33.53 (CH2CH(CH3)z); 28.20 (CH2CH(CH3)2); 89.75, 98.92, 104.04, 107.98, 109.58 (Cp). ('f\5-C5Me5)(THI)Zr(CH2CH(CH3)i)(H) (40). 1H NMR (benzene-d6): o= 1.89 (s, 15H, CsMes); 6.24 (s, lH, ZrH); -1.67 (dd, lH, CH2 CH(CH3)2); 0.870 (dd, lH, CH2 CH(CH3)2); 2.17 (m, lH, CH2 CH(CH3)2); 0.975 (d, 7 Hz, 3H, CH2CH(CH3)2); 1.04 (d, 7 Hz, 3H, CH2CH(CH3)2); 2.49, 2.55, 2.69, 2.78 (m, THI),4.70, 4.98, 5.61 (m, lH, Cp). 13C NMR (benzene-d6): o= 12.70 (CsMes); 117.39 (CsMes); 24.32, 25.63, 26.18 28.47 (THI), 87.95 (CH2C(CH3)2); 34.33 (CH2C(CH3)2); 30.21 (CH2C(CH3)2); 103.46, 105.21, 111.86, 126.45, 127.93 (Cp). (Tt 5-CsMesHT\ 5-C5H3-l,3-(CHMe2h)Zr(CH2CH(CH3)i)(H) (41). 1H NMR (benzene-d6): o= 1.92 (s, 15H, CsMes); 6.34 (s, lH, ZrH); 1.10 (d, 7 Hz. 3H, CHMe2); 1.23 (d, 7 Hz. 3H, CHMe2); 1.30 (d, 7 Hz. 3H, CHMe2); 1.34 (d, 7 Hz. 3H, CHMe2); 2.79 (sept, 6.5 Hz, lH, CHMe2); 3.25 (sept, 6.5 Hz, lH, CHMe2); -0.359 (dd, lH, CH2 CH(CH3)2); 0.220 (dd, lH, CH2 CH(CH3)2); 2.22 (m, lH, CH2 CH(CH3)2); 0.965 (d, 7Hz, 6H, CH2CH(CH3)2); 4.74, 4.85, 5.94 (m, lH, C5H3-l,3CHMe2). 13C NMR (benzene-d6): o= 12.89 (CsMes); 117.18 (C5Me5); 71.82 (CH2CMe2); 21.89, 22.64, 26.60, 27.34, 28.29, 29.07, 29.68, 30.48, 31.28 (CHMe2, CH2CMe2); 88.31, 95.92, 100.52, 109.56, 123.00 (Cp). ('f\5-C5MesHT\ 5-C5H3-1,3-(CMe3)i)Zr(CH2CH(CH3)i)(H) (42). 1H NMR (benzene-d6): o= 1.88 (s, 15H, CsMes); 6.48 (s, lH, ZrH); 0.956 (s, 9H, CMe3); 1.23 (s, 9H, CMe3); -0.825 (dd, lH, CH2 CH(CH3)2); -0.836 (dd, lH, CH2 CH(CH3)2); 2.31 (m, lH, CH2 CH(CH3)2); 0.956 (d, 7 Hz, 6H, CH2CH(CH3)z); 4.59, 4.75, 4.79 (m, lH, C5H3-l,3-(CMe3)2). 13C NMR (benzene-d6): o= 12.89 (CsMes); 117.86 106 (C5Me5); 32.06 (CMe3); 33.03 (CMe3); 2 not located (CMe3); 70.44 (CH2CH2(CH3)z); 31.90 (CH2CH2(CH3)2); 31.32 (CH2CH2(CH3)z); 29.98 (CH2CH2(CH3)z); 99.87,103.77, 105.82, 106.71, 116.87 (Cp). (11 5-CsMe4HhZr(CH2CH(CH3h)(H) (43). 1H NMR (benzene-d6): 8 = 2.01, 2.07 (s, 12H, CsMe4fi); 5.10 (s, 2H, CsMe-4-ffl; 5.96 (s, lH, ZrH); -0.06 (d, 6.8 Hz, 2H, CH2 CH(CH3)z); 2.28 (m, lH, CH2 CH(CH3)z); 1.03 (d, 6 Hz, 6H, CH2CH(CH3)z). 13C NMR (benzene-d6): 8 = 12.49, 13.14, 13.72, 14.22 (CsAfe4H); 75.33 (CH2CH(CH3)z); 31.17 (CH2CH(CH3)z); 30.21 (CH2CH(CH3)z); 108.37, 116.98, 117.45, 121.25, 121.76 (Cp ). (11 5-C5MesHT1 5-CsMe4H)Zr(CH2CH2C6Hs)(H) (44). 1H NMR (benzene-d6): 8 = 1.85 (s, 15H, CsMes); 1.81, 1.84 (s, 6H, CsAfe4H); 5.28 (bs, lH, ZrH); -0.131 (m, lH, CH2 CH2Ph); 0.470 (m, lH, CH2 CH2Ph); not located (CH2 CH2Ph); 7.10 (m, lH, para-CH2CH2C6Hs); 7.24 (m, 2H, meta-CH2CH2C6Hs); 7.42 (m, 2H, orthoCH2CH2C~5); 4.48 (Cp ). 13C NMR (benzene-d6): 8 ~ 12.56 (CsMes); 116.59 (C5Me5); 11.67, 12.19, 13.33, 14.71 (CsAfe4H); 47.14 (CH2CH2Ph); 22.68 (CH2CH2Ph); 96.10, 105.77, 119.62, 2 not located (Cp ); 122.42 (para-C6Hs); 125.86 (ortho-C6Hs); 129.40 (meta-C6Hs); 1 not located (ipso-C6Hs). (T1 5-C5MesHT1 5-CsMe4H)Zr(CH2CH2(C6H4-p-OCH3))(H) (45). 1H NMR (benzene-d6): 8 = 1.86 (s, 15H, CsMes); 1.71, 1.77, 2.06, 2.10 (s, 6H, CsAfe4H); 5.06 (s, lH, ZrH); 0.51 (m, 2H, CH2CH2C6Hs-p-OCH3); 1.52 (m, 2H, CH2CH2C6Hs-pOCH3); 3.24 (s, 3H, CH2CH2C6Hs-p-OCH3); 6.88 (d, 8.6 Hz, 2H, CH2CH2-metaC6Hs-p-OCH3); 7.36 (d, 8.6 Hz, 2H, CH2CH2-ortho-C6Hs-p-OCH3), 4.49 (Cp). 13C NMR (benzene-d6): 8 = 12.56 (CsMes); 114.32 (C5Me5); 11.62, 12.23, 13.26, 14.78 (CsAfe4H); 55.14 (CH2CH2(C6fi4-p-OCH3)); 20.35 (CH2CH2(C6fi4-p-OCH3)); 45.25 (C6fi4-OCH3); 105.56, 113.05, 116.18, 116.72, 117.09 (Cp ); 122.01 (orthoC6fi4-p-OCH3); 127.45 (para-C6fi4-p-OCH3); 130.32 (meta-C6fi4-p-OCH3); 159.16 (ipso-C6fi4-p-OCH3). (11 5-CsMesHT1 5-CsMe4H)Zr(CH2CH2(C6H4-p-CH3))(H) (46). 1H NMR (benzene- d6): 8 = 1.86 (s, 15H, CsMes); 1.69, 1.79, 2.04, 2.11 (s, 6H, CsAfe4H); 5.62 (bs, lH, ZrH); 0.510 (m, 2H, CH2CH2C6Hs-p-CH3); 1.57 (m, 2H, CH2CH2C6Hs-p-CH3); 6.94 (d, 8.6 Hz, 2H, CH2CH2-meta-C6Hs-p-CH3); 7.37 (d, 8.6 Hz, 2H, CH2CH2ortho-C~s-p-CH3), 4.48 (Cp ). 13C NMR (benzene-d6): 8 = 12.57 (CsMes); 116.27 107 (C5Me5); 11.66, 12.19, 13.30, 14.76 (CsAfe4H); 58.03 (CH2CH2(C6H4-p-OCH3)); 29.21 (CH2CH2(C6!4-p-OCH3)); 38.06 (C6f4-CH3); 113.04, 116.57, 116.84, 117.29, 117.82 (Cp ); 122.28 (ortho-C6H4-p-CH3); 137.97 (para-C6f4-p-CH3); 143.97 (metaC6f4-p-OCH3); 159.03x (ipso-C6~-p-CH3). (17 5-CsMe5)('r1 5-CsMe4H)Zr(CH2CH2(C6H4-p-CF3) )(H) (47). 1H NMR (benzene- d6): b = 1.84 (s, 15H, CsMes); 1.63, 1.77, 1.95, 2.16 (s, 6H, CsAfe4H); 4.82 (s, lH, ZrH); -0.237 (m, lH, CH2CH2C6Hs-p-CF3); 0.334 (m, lH, CH2CH2C6Hs-p-CF3); 1.51 (m, 2H, CH2CH2C6Hs-p-CF3); 7.19 (d, 8.6 Hz, 2H, CH2CH2-meta-C6Hs-pCF3); 7.48 (d, 8.6 Hz, 2H, CH2CH2-ortho-C6Hs-p-CF3), 4.48 (Cp). 13C NMR (benzene-d6): -b = 12.50 (CsMes); 116.16 (C5Me5); 11.71, 12.06, 13.45, 14.54 (CsAfe4H); 49.30 (CH2CH2C6H4-p-CF3); 25.23 (CH2CH2C6H4-p-CF3); 32.84 (q, 28 Hz, (CH2CH2C6!4-p-CF3); 106.29, 114.88, 115.87, 117.32, 119.43 (Cp); 125.67, 125.96, 141.44, 3 not located (CH2CH2C6Hi-p-CF3). 19F NMR (benzene-d6): b = -62.19 ppm (CF3). (17 5-CsMe5)(17 5-C5H4-CMe3)Zr(CH2CH2C(CH3>3)(H) (48). 1H NMR (benzene- d6): b = 1.89 (s, 15H, CsMes); 1.47 (s, 9H, C5!4-CMe3); not located (s, lH, ZrH); -0.99 (m, lH, CH2CH2CMe3); 0.30 (m, lH, CH2CH2CMe3); 2.32 (m, 2H, CH2CH2CMe3); 1.04 (s, 9H, CH2CH2CMe3); 4.91 (m, 2H, Cp ); 5.00 (m, lH, Cp ); 5.90 (m, 2H, Cp ). 13C NMR (benzene-d6): b = 12.58 (CsMes); 116.34 (C5Me5); 32.84 (CMe3); 29.90 (CMe3); 146.06 (CMe3); 1 not located (CMe3); 49.98 (CH2CH2CMe3); 35.94 (CH2CH2CMe3); 102.68, 104.01, 107.25, 109.89, 120.76 (Cp). (17 5-CsMe5)(17 5-CsH4-CMe3)Zr(CH2CH2CH2CH(CH3h)(H) (49). 1H NMR (benzene-d6): b = 1.83 (s, 15H, CsMes); 1.41 (s, 9H, C5H4-CMe3); 5.39 (s, lH, ZrH); -0.450 (m, lH, CH2CH2CH2CH(CH3)2); -0.450 (m, lH, CH2CH2CH2CH(CH3)2); 0.651 (m, 2H, CH2CH2CH2CH(CH3)2); 0.589 (m, 2H, CH2CH2CH2CH(CH3)2); 2.56 (m, lH, CH2CH2CH2CH(CH3)2); 0.999 (d, 6Hz, 6H, CH2CH2CH2CH(CH3)2); 4.22, 4.91, 5.34, 5.98 (m, lH, Cp ). 13C NMR (benzened6): b = 12.46 (CsMes); 112.77 (C5Me5); 32.09 (CMe3); 139.36 (CMe3); 56.14 (CH2(CH2)2CH(CH3)2); 18.39, 22.29 (CH2(CH2)2CH(CH3)2) 32.78 (CH2(CH2)2CH(CH3)2); 23.45 (CH2(CH2)2CH(CH3)2; 103.56, 105.92, 109.53, 115.77, 118.64 (Cp ). 108 h1 5-CsMesH11 5-C5H4-CMe3)Zr(CH2CH2CH2CH3)(H) (50). 1H NMR (benzened6): 8 = 1.82 (s, 15H, CsMes); 1.40 (s, 9H, CMe3); 5.94 (s, lH, ZrH); -0.504 (dd, lH, CH2CH2CH2CH3); -0.02 (dd, lH, CH2CH2CH2CH3); 1.26 (m, 2H, CH2CH2CH2CH3); 0.650 (m, 2H, CH2CH2CH2CH3); 1.06 (t, 7Hz, 3H, CH2CH2CH2CH3); 4.23, 4.88, 4.91, 5.33 (Cp ). 1H NMR (benzene-d6): 8 = 12.35 (CsMes); 115.38 (C5Me5); 32.49 (CMe3); 156.10 (CMe3); 46.58 (CH2CH2CH2CH3); 29.56 (CH2CH2CH2CH3); 18.66 (CH2CH2CH2CH3); 12.71 (CH2CH2CH2CH3); 101.09, 103.48, 104.00, 105.83, 109.43 (Cp). (11 5-CsMe5)(11 5-CsH4-CMe3)Zr(cyclo-C5H9)(H) (51). 1H NMR (benzene-d6): 8 = 1.76 (s, 15H, CsMes); 1.40 (s, 9H, C5f4-CMe3); 5.71 (s, lH, ZrH); -0.512, 0.105, 1.13, 1.93, 2.31 (m, C5H9); 4.73, 4.89, 4.96, 5.83 (m, lH, Cp). 13C NMR {benzened6): 8 = 12.42 (CsMes); 114.16 (C5Me5); 32.89 (CMe3); 146.33 (CMe3); 47.65 (ipso-C5H9); 23.51, 29.23, 34.10, 37.53 (C5H9); 99.90, 103.00, 104.41, 109.96, 125.51 (Cp ). (11 5-C5Me5)(11 5-C5H5)Zr(C(CH3)=C(H)(CMe3))(H) (52). 1H NMR (benzene-d6): 8 = 1.81 (s, 15H, CsMes); 3.51 (s, lH, ZrH); 1.10 (s, 9H, C(CH3)=C(H)(CMe3)); 2.45 (s, 3H, C(CH3)=C(H)(CMe3); 3.45 (s, lH, C(CH3)=C(H)(CMe3); 5.48 (Cp). 13C NMR (benzene-d6): 8 = 12.57 (CsMes); 114.39 (C5Me5); 30.77 (C(CH3)=C(CMe3)(H)); not located (C(CH3)=C(CMe3)(H)); 3.68 (C(CH3)=C(CMe3)(H)); 186.82 (C(CH3)=C(CMe3)(H)); 95.71 (Cp ). ('r1 5-CsMesH11 5-C5H4-CMe3)Zr(C(CH3)=C(H)(CMe3))(H) (53). 1H NMR (benzene-d6): 8 = 1.81 (s, 15H, CsMes); 1.41 (s, 9H, C5H4-CMe3); 3.54 (s, lH, ZrH); 1.14 (s, 9H, C(CH3)=C(H)(CMe3)); 2.49 (s, 3H, C(CH3)=C(H)(CMe3); 3.48 (s, lH, C(CH3)=C(H)(CMe3); 4.52, 5.00, 5.08, 5.81 (Cp ). 13C NMR (benzene-d6): 8 = 12.42 (CsMes); 114.17 (C5Me5); 33.32 (CMe3); 32.81 (CMe3); 150.46 (CMe3); 150.59 (CMe3); 12.68 (C(CH3)=C(CMe3)(H)); 190.23 (C(CH3)=C(CMe3)(H)); 20.52 (C(CH3)=C(CMe3)(H)); 95.65, 95.94, 98.55, 99.07, 104.03 (Cp ). (11S-C5Me5)(THI)Zr(C(CH3)=C(H)(CMe3))(H) (54). 1H NMR (benzene-d6): 8 = 1.84 (s, 15H, CsMes); 0.80-1.10 (m, THI); 3.84 (s, lH, ZrH); 1.24 (s, 9H, C(CH3)=C(H)(CMe3)); 2.49 (s, 3H, C(CH3)=C(H)(CMe3); 3.70 (s, lH, C(CH3)=C(H)(CMe3); 4.98, 5.08, 5.55 (Cp ). 13C NMR (benzene-d6): 8 = 12.60 (C5Me5); 114.31 (CsMes); 31.90 (CMe3); 159.11 (CMe3); 3.77 (C(CH3)=C(CMe3)(H)); 187.12 (C(CH3)=C(CMe3)(H)); 20.17 109 (C(CH3)=C(CMe3)(H)); 23.94, 24.58, 24.70, 26.86 (THI); 92.75, 100.32, 100.84, 101.83, 106.21 (Cp ). (11 5-CsMesHri 5-C5H3-1,3-(CHMe2h)Zr(C(CH3)=C(H)(CMe3))(H) (55). 1H NMR (benzene-d6): 8 = 1.85 (s, 15H, CsMes); 3.68 (s, lH, ZrH); 1.06 (d, 7 Hz. 3H, CHMe2); 1.28 (d, 7 Hz. 3H, CHMe2); 1.34 (d, 7 Hz. 3H, CHMe2); 1.41 (d, 7 Hz. 3H, CHMe2); 2.75 (sept, 6.5 Hz, lH, CHMe2); 3.20 (sept, 6.5 Hz, lH, CHMe2); 1.18 (s, 9H, C(CH3)=C(H)(CMe3)); 2.48 (s, 3H, C(CH3)=C(H)(CMe3); 86.25 (C(CH3)=C(CMe3)(H)); 3.34 (s, lH, C(CH3)=C(H)(CMe3); 4.65, 4.74, 4.98 (m, lH, C5H3-l,3-(CMe3)2). 13C NMR (benzene-d6): 8 = 12.95 (CsMes); 117.29 (C5Me5); 25.21, 25.48, 27.05, 27.26 (CHMe2); 30.22, 21.14 (CHMe2); 30.97 (CMe3); 139.72 (CMe3); 3.73 (C(CH3)=C(CMe3)(H)); not located (C(CH3)=C(CMe3)(H)); 21.90 (C(CH3)=C(CMe3)(H)) 88.37, 99.72, 99.42, 104.73, 114.49 (Cp). (r1 5-CsMesHri 5-C5H3-l,3-(CMe3h)Zr(C(CH3)=C(H)(CMe3))(H) (56). 1H NMR (benzene-d6): 8 = 1.85 (s, 15H, CsMes); 3.56 (s, lH, ZrH); 1.17 (s, 9H, C5H5-l,3(CMe3)2)); 1.55 (s, 9H, CsHs-l,3-(CMe3)2); 1.22 (s, 9H, C(CH3)=C(H)(CMe3)); 2.55 (s, 3H, C(CH3)=C(H)(CMe3); 3.34 (s, lH, C(CH3)=C(H)(CMe3); 4.49, 4.68, 4.95 (m, lH, C5H3-l,3-(CMe3)2). 13C NMR (benzene-d6): 8 = 13.06 (C5Me5); 119.88 (C5Me5); 32.88 (CMe3); 32.20 (CMe3); 114.16 (CMe3); 117.44 (CMe3); 31.88 (CMe3); 136.18 (CMe3); 3.83 (C(CH3)=C(CMe3)(H)); 167.31 (C(CH3)=C(CMe3)(H)); 28.04 (C(CH3)=C(CMe3)(H)); 100.99, 105.46, 109 .02, 2 not located (Cp ). (T15-CsMesHri 5-C5Me4H)Zr(C(CH3)=C(H)(CMe3))(H) (57). 1H NMR (benzene- d6): 8 = 1.85 (s, 15H, CsMes); 1.86, 1.88, 1.91, 2.01 (s, 3H, C5Me4 H); 4.47 (s, lH, ZrH); 4.47 (s, lH, C5Me4 H); 1.21 (s, 9H, C(CH3)=C(H)(CMe3)); 2.46 (s, 3H, C(CH3)=C(H)(CMe3); 3.53 (s, lH, C(CH3)=C(H)(CMe3). 13C NMR (benzene-d6): 8 = 12.71 (CsMes); 114.47 (CsMes); 11.83, 12.41, 12.89, 13.32 (CsAfe4H); 31.66 (CMe3); 150.89 (CMe3); 15.45 (C(CH3)=C(CMe3)(H)); 162.71 (C(CH3)=C(CMe3)(H)); 18.41 (C(CH3)=C(CMe3)(H)); 98.57, 102.25, 105.49, 122.54, 1 not located (Cp ). (17S-C5Me4H}iZr(C(CH3)=C(H)(CMe3))(H) (58). 1H NMR (benzene-d6): 8 = 2.12, 2.21 (s, 6H, C5Me4H); 5.15 (s, 2H, CsMe~); 3.73 (s, lH, ZrH); 1.24 (s, 9H, C(CH3)=C(H)(CMe3)); 2.46 (s, 3H, C(CH3)=C(H)(CMe3); 3.35 (s, lH, C(CH3)=C(H)(CMe3). 13C NMR (benzene-d6): 8 = 12.11, 12.84, 13.96, 13.54 110 (C5Me4H); 88.33 (Zr-C(CH3)=C(H)(CMe3) ); 187.30 (Zr-C(CH3)=C(H)(CMe3) ); 31.56 (Zr-C(CH3)=C(H)(CMe3)); 143.72 (Zr-C(CH3)=C(H)(CMe3)); 18.64 (ZrC(CH3)=C(H)(CMe3)); 98.95, 111.28, 114.82, 116.97, 120.26 (Cp). (11 5-CsMesHT1 5-CsHs)Zr(CH2CH2CH2CH3)(H) (59). 1H NMR (benzene-d6): 8= 1.73 (s, 15H, CsMes); 6.21 (s, lH, ZrH); -0.09 (dd, lH, CH2 CH2CH2CH3); 0.577 (dd, lH, CH2 CH2CH2CH3); 1.92 (m, 2H, CH2 CH2CH2CH3); 0.88 (m, 2H, CH2 CH2CH2CH3); 1.05 (t, 7.3 Hz, 3H, CH2 CH2CH2CH3), 5.91 (s, SH Cp). 13C NMR (benzene-d6): 8 = 12.65 (CsMes); 116.81 (CsMes); 56.71 (CH2CH2CH2CH3); 31.50 (CH2CH2CH2CH3); 24.95 (CH2CH2CH2CH3); 14.33 (CH2CH2CH2CH3); 107.16 (Cp). (T1 5-C5MesHT1 5-CsH3-1,3-(CHMe2h)Zr(CH2CH2CH2CH3)(H) (60). 1H NMR (benzene-d6): 8 = 1.84 (s, 15H, CsMes); 5.38 (s, lH, ZrH); 1.19, 1.24, 1.42, 1.50 (d, 7Hz, 3H, CHMe2); 2.78, 3.20 (sept, 6.5Hz, lH, CHMe2); -0.401 (m, 2H, CH2 CH2CH2CH3); not located (CH2 CH2CH2CH3); 1.06 (m, 2H, CH2 CH2CH2CH3); 0.870 (t, 7.3 Hz, 3H, CH2 CH2CH2CH3); 3.95, 4.88, 5.01 (m, lH, Cp ). (T1 5-CsMe5)(THI)Zr(CH2CH2CH2CH3)(H) (61). 1H NMR (benzene-d6): 8 = 1.86 (s, 15H, CsMes); 5.95 (s, lH, ZrH); -0.501 (m, 2H, CH2 CH2CH2CH3); 1.40 (m, 2H, CH2 CH2CH2CH3); 0.82 (m, 2H, CH2CH2CH2CH3); 1.10 (t, 7.0 Hz, 3H, CH2 CH2CH2CH3), 4.75, 5.02, 5.20 (m, lH, Cp ). 13C NMR (benzene-d6): 8 = 12.15 (CsMes); 117.92 (CsMes); 23.84, 25.01, 25.25, 25.93 (THI); 53.40 (CH2CH2CH2CH3); 47.52 (CH2CH2CH2CH3); 31.73 (CH2CH2CH2CH3); 14.32 (CH2CH2CH2CH3); 107.65, 110.40, 111.60, 125.13, 125.76 (Cp). (T1 5-CsMesHT1 5-C5Me4H)Zr(CH2CH2CH2CH3)(H) (62). 1H NMR (benzene-d6): 8 = 1.88 (s, 15H, CsMes); 1.71, 1.81, 1.91, 2.08 (s, 3H, CsAfe4 H); 4.47 (s, lH, CsMe~); 4.76 (s, lH, ZrH); 0.057 (dd, lH, CH2 CH2CH2CH3); 0.161 (dd, lH, CH2 CH2CH2CH3); not located (CH2CH2CH2CH3); 1.43 (m, 2H, CH2 CH2CH2CH3); 1.08 (t, 6.5 Hz, 3H, CH2CH2CH2CH3). 13C NMR (benzene-d6): 8 = 12.60 (CsMes); 115.71 (CsMes); 11.67; 12.18; 12.30; 13.12 (C5Me4 H); 43.66 (CH2CH2CH2CH3); 27.86 (CH2CH2CH2CH3); 16.09 (CH2CH2CH2CH3); 15.06 (CH2CH2CH2CH3); 105.44; 115.56; 116.47; 116.89; 117.52 (Cp ). 111 h1 5-CsMesHri 5-CsH3-1,3-(CMe3}i)Zr(CH2CH2CH2CH3)(H) (63). 1H NMR (benzene-d6): 3 = 1.72 (s, 15H, CsMes); 1.10, 1.31 (s, 9H, CMe3); 5.51 (s, lH, ZrH); 0.14 (m, 2H, CH2 CH2CH2CH3); 0.652 (m, 2H, CH2CH2CH2CH3); 0.753 (m, 2H, CH2CH2CH2CH3); 943 (t, 7Hz, 3H, CH2CH2CH2CH3); 4.43, 4.60, 4.65 (m, lH, Cp ). 13C NMR (benzene-d6): 3 = 13.06 (CsMes); 113.86 (C5Me5); 32.86 (CMe3); 35.00 (CMe3); 142.62 (CMe3); 140.92 (CMe3); 42.13 (CH2CH2CH2CH3); 31.31 (CH2CH2CH2CH3); 27.38 (CH2CH2CH2CH3); 13.61 (CH2CH2CH2CH3); 100.99; 105.52; 109.05; 110.16; 111.99 (Cp). References. 1. Crabtree, R.H. The Organometallic Chemistry of the Transition Metals, 2nd Ed; Wiley, New York, 1994; Chapters 7, 9. 2. Brintzinger, H.H.; Fischer, D.; Miilhaupt, R.; Rieger, B.; Waymouth, R.M. Angew. Chem. Int. Ed. Engl. 1995, 34, 1143. 3. a) Gilchrist, J.H.; Bercaw, J.E. J. Am. Chem. Soc. 1996, 118, 12021. b) Herzog, T.A.; Zubris, D.L.; Bercaw, J.E. J. Am. Chem. Soc. 1996, 118, 11988 and references therein. 4. Resconi, L.; Camurati, I.; Sudmeijer, 0. Topics In Catalysis 1999, 7, 145. 5. a) Jordan, R.F.; Dasher, W.E.; Echols, S.F. J. Am. Chem. Soc. 1986, 108, 1718. b) Jordan, R.F.; Bajgur, C.S.; Willet, R.; Scott, B. J. Am. Chem. Soc. 1986, 108, 7410. 6. Watson, P.L. J. Am. Chem. Soc. 1982, 104,337. 7. Jeske, G.; Lauke, H.; Mauerman, H.; Swepston, P.N.; Shuman, H.; Marks, T.J. J. Am. Chem. Soc. 1985, 107, 8091. 8. a) Doherty, N.M.; Bercaw, J.E. J. Am. Chem. Soc. 1985, 107, 2670. b) Burger, B.J.; Santarsiero, B.D.; Trimmer, M.S.; Bercaw, J.E. J. Am. Chem. Soc. 1988, 110, 3134. 9. Burger, B.J.; Thompson, M.E.; Cotter, W.D.; Bercaw, J.E. J. Am. Chem. Soc. 1990, 112, 1566. 10. Karl J.; Dahlmann M.; Erker G.; Bergander K. J. Am. Chem. Soc. 1998, 120, 5643. 11. Siedle, A.R.; Lamanna, W.M.; Newmark, R.A.; Schroepfer, J.N. J. Mal. Cat. A 1998, 128, 257. 12. a) Woo, T.K.; Margl, P.M.; Lohrenz, J.C.W.; Blochl, P.E.; Ziegler, T. J. Am. Chem. Soc. 1996, 118, 13021. b) Richardson, D.E.; Alameddin, N.G.; Ryan, M.F.; Hayes, T.; Eyler, J.R.; Siedle, A.R. J. Am. Chem. Soc. 1996 118, 11244. c) .Froese, 112 R.D.J.; Musaev, D.G.; Matsubara, T.; Morokuma, K.J. Organometallics 1997, 16, 2514 and references cited therein. 13. a) Toto, M.; Cavallo, L.; Corradini, P.; Moscardi, G.; Resconi, L.; Guerra, G. Macromolecules 1998, 31, 3431. 14. Chirik, P.J.; Day, M.W.; Bercaw, J.E. Organometallics 1999, 18, 1873. 15. Addition of one equivalent of ethylene to [(CpRn)2ZrH2h results in clean formation of (CpRn)2Zr(CH2CH3)(H). However, addition of excess ethylene results in reductive elimination of ethane and formation of the zirconocyclopentane. McAlister, D.R.; Erwin, D.R.; Bercaw, J.E. J. Am. Chem. Soc. 1978, 100, 5966. 16. Chirik, P.J.; Day, M.W.; Labinger, J.A.; Bercaw, J.E. J. Am. Chem. Soc. 1999, 121, 10308. 17. Lin, Z.; Marks, T.J. J. Am. Chem. Soc. 1990, 112, 5515. 18. Values for cr and cr+ were taken from Isaacs, N.S. Physical Organic Chemistry, John Wiley and Sons: New York, 1986, p. 131. 19. Roddick, D.M.; Fryzuk, M.D.; Seidler, P.F.; Hillhouse, G.L.; Bercaw, J.E. Organometallics 1985, 4, 97. 20. McDade, C.; Bercaw, J.E. J. Organomet. Chem. 1985, 279,281. 21. Brandow, C.G.; Bercaw, J.E. unpublished results. 22. Bercaw, J.E. in Transition Metal Hydrides, Advances in Chemistry Series, Chapter 10. 23. Manriquez, J.M.; McAlister, D.R.; Sanner, R.D.; Bercaw, J.E. J. Am. Chem. Soc. 1978, 100, 2716. 24. Stehling, U.; Diebold, K. R.; Roll, W.; Brintzinger, H.H.; Jungling, S.; Miilhaupt, R.; Langhauser, F. Organometallics 1994, 13, 964. 25. Labinger, J.A. In Comprehensive Organic Synthesis; Trost, B.M.; Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Chapter 3.9. 26. Busico, V.; Cippullo, R. J. Am. Chem. Soc. 1994, 116, 9329. 27. Busico, V.; Caporaso, L.; Cippulo, R.; Landriani, L.; Angelini, G.; Margonelli, A.; Segre, A.L. J. Am. Chem. Soc. 1996, 118, 2105. 28. Nelson, J.E.; Bercaw, J.E.; Labinger, J.A. Organometallics 1989, 8, 2404 and references therein. 113 29. Resconi, L.; Piemontesi, F.; Franciscono, G.; Abis, L.; Fiorani, T. J. Am. Chem. Soc. 1992,114,1025. 30. Veghini, D.; Henling, L.M.; Burkhardt, T.J.; Bercaw, J.E. J. Am. Chem. Soc. 1999, 121,564. 31. Benson, S.W. Thermochemical Kinetics 2nd Ed.; Wiley and Sons, New York, 1976. 32. a) Bryndza, H.E.; Fong, L.K.; Paciello, R.A.; Tam, W.; Bercaw, J.E. J. Am. Chem. Soc. 1987, 109, 1444. b) Labinger, J.A.; Bercaw, J.E. Organometallics 1988, 7, 926. 33. Although.a correlation exists between M-C and C-H bond strengths, it is not absolute, and as a result values may exceed the differences in alkane free energies. 34. Straus, D.A.; Grubbs, R.H. Organometallics 1982, 1, 1658. 35. Schaller, C.P.; Cummins, C.C.; Wolczanski, P.T. J. Am. Chem. Soc. 1996, 118, 591. 36. Burger, B.J.; Bercaw, J.E. In Experimental Organometallic Chemistry; ACS Symposium Series No. 357; Wayda, A.L.; Darensbourg, M.Y. Eds.; American Chemical Society: Washington, DC 1987; Chapter 4. 37. Marvich, R.H.; Brintzinger, H.H. J. Am. Chem. Soc. 1971, 93, 2046. 38. Schock, L.E.; Marks, T.J. J. Am. Chem. Soc. 1988, 110, 7701. 39. Vogel, A.I. Vogel's Textbook of Practical Organic Chemistry 5th Ed.; John Wiley and Sons, New York, 1989 pp. 495-498. 114 Chapter 4 Alkyl Rearrangement Processes in Organozirconium Complexes. Observation of Internal Alkyl Complexes during H ydrozirconation. * 115 Abstract Isotopically labeled alkyl zirconocene complexes of the general formula, (CpRnhZr(CH2CDR'2)(X) (CpRn = alkyl-substituted cyclopentadienyl; R' = H, alkyl group; X = H, D, Me), undergo isomerization of the alkyl ligand as well as exchange with free olefin in solution under ambient conditions. Increasing the substitution on the Cp ring results in slower isomerization reactions, but these steric effects are small. In contrast, changing X has a very large effect on the rate of isomerization. Pure a-bonding ligands such as methyl and hydride promote rapid isomerization, whereas n:-donor ligands inhibit ~-H elimination and hence alkyl isomerization. For (11 5-CsHshZr(R)(Cl), internal alkyl complexes have been observed for the first time. The rate of isomerization depends on the length of the alkyl: longer alkyl chains (heptyl, hexyl) isomerize faster than shorter chains (butyl). The transient intermediate species have been identified by a combination of isotopic labeling and 1H, 2H and l3C NMR experiments. The solid state structure of the zirconocene cyclopentyl-chloride complex, Cp 2Zr(cyclo-C5H 9)(Cl), has been determined by X-ray diffraction. 116 Introduction Alkyl complexes play a central role in organotransition metal chemistry in both catalytic and stoichiometric transformations. 1 The preferences (kinetic and/ or thermodynamic) of a transition metal to bond to a terminal or a internal carbon atom of an alkyl ligand often determine the selectivity and productivity of a system. However, delineation of the factors that govern these preferences is by no means straightforward. The identity of the transition metal, coordination environment and ancillary ligation all influence the relative stabilities for terminal versus internal alkyl complexes.2 Alkyl isomerization has special relevance, both historical and practical, in group 4 metallocene chemistry. The original studies by Schwartz and coworkers3 reported the hydrozirconation of internal olefins with [Cp2Zr(H)(Cl)]n as yielding solely terminal products. This hydrometallation-isomerization protocol allows for functionalization of otherwise unactivated methyl groups and has found widespread synthetic utility. 4 More recently, alkyl isomerization reactions have been found to influence the stereo- and regiochemical outcome of group 4 metallocene-catalyzed olefin polymerizations.5 The degree of isotacticity of the polypropylene produced from a variety of Cz-symmetric zirconocene catalysts has been shown to decrease with decreasing monomer concentration. 6 The explanation for this behavior is an alkyl isomerization process that competes with olefin insertion at low monomer concentrations. Isomerization of a "2,1 "-inserted monomer unit producing a "3,1"-regiomistake has also been identified (eq. 1)? Despite efforts to suppress both of these pathways, the origins of alkyl isomerization and the identity of the mechanisms and their rate limiting steps have remained elusive. CH3 I M-CHCH2P "2, 1" misinsertion . (1) "3,1" misinsertion 117 In this report we describe direct observation of the alkyl isomerization process in several neutral zirconocene complexes of the form (CpRnhZr(CH2CHR' 2)(X) (X = H, Me, Cl; CpRn =. alkyl substituted 11 5-cyclopentadienyl; R' = Hor alkyl). Factors that affect the facility of the isomerization process are disclosed. Additionally, evidence for involvement of free olefin in the mechanism of alkyl isomerization is presented. Results Rearrangement of Labeled Alkyls Obtained from Hydrozirconation of Terminal Olefins. Zirconocene alkyl-hydride complexes are prepared via addition of the appropriate olefin to the zirconocene dihydride. 8,9 This synthetic protocol allows facile incorporation of isotopic labels into the zirconocene alkyl-hydride complex (eq. 2). Rn Rn &P-H Zr....._ + ~ ~ H ► ~-H Zr, ~ CH2CH(CH3h (2) I Rn CpRn = (11 5-CsMes), Cp* (1) CpRn = (11 5-C 5Me 4H) (2) Thus, reaction of substituted zirconocene dideuterides, (CpRnhZrD2 (CpRn = (11 5-CsMes) (Cp*), (11 5-C5Me4H)) with isobutylene in benzene solution affords specifically labeled complexes, (CpRnhZr(CH2CDMe2)(D) in quantitative yield (1H NMR). In benzene solution Cp*2Zr(CH2CDMe 2)(D) undergoes isotopic rearrangement affording both Cp*2Zr(CHDCHMe2)(D) and Cp*2Zr{CH2CH(CH2D)(CH3)}(D) (eq. 3). 10 (11 5-C5Me4H)iZr(CH2CDMe2)(D) exhibits similar behavior. 118 exchange between free olefin and coordinated alkyl. By following the kinetics of these reactions using {l H}2H NMR spectroscopy, a rate constant of 1.0(4) x 10-8 s-1 has been measured for the rearrangement of Cp*2Zr(CH2CDMe2)(D) to Cp*2Zr(CHDCHMe2)(D) and Cp*2Zr{CH2CH(CH2D)(CH3)}(D) at 296K. The corresponding rate constant for (T1 5-C5Me4H)iZr(CH2CDMe2)(D) is 4.3(4) x 10-7 sec-1 at 296 Kin equal amounts. No measureable equilibrium isotope effects was observed. Several other zirconocene isobutyl-deuteride complexes were examined (e. g., Cp*(T1 5-C 5H 4-CMe3)Zr(CH2CDMe2)(D), Cp*CpZr(CH2CDMe2)(D)), but reliable kinetic data could not be obtained. Reaction of (CpRnhZrH2 with one equivalent of 13CH2=CHCH3 results in quantitative formation (1H NMR) of (CpRnhZr( 13CH2CH2CH3)(H). Addition of excess propylene or other a-olefins results in reductive elimination of propane and formation of products derived from the resulting [(CpRnhZr(II)].1 1 Monitoring a benzene-d6 solution of Cp*2Zr( 13CH2CH2CH3)(H) by 13C NMR spectroscopy reveals isomerization affording Cp*2Zr(CH2CH213CH3)(H) (eq. 4) with a k296K = 1.2 x 10-4 s-1. Similar isomerizations are observed for (T1 5-C 5Me4H)zZr( 13CH2CH2CH3)(H) to (T1 5-C5Me4H)zZr(CH2CH213CH3)(H) (k296K = 1.1 x 10-3 s-1) and for Cp*(T1 5-C5H4-CMe3)Zr( 13CH2CH2CH3)(H) to 119 5 13 Cp*(17 -C5H4-CMe3)Zr(CH2CH2 CH3)(H); the rate of the latter is too fast to measure using simple NMR spectral monitoring. ... (4) To determine the effect of the "spectator" ligand (hydride in the examples above) on the rate of alkyl isomerization, several alkyl complexes derived from Schwartz's reagent, [Cp2Zr(H)(Cl)]n12 (3) were prepared. Although 3 is an insoluble polymeric material, its reaction with olefins affords soluble, well-characterized zirconocene alkyl-chloride complexes, Cp 2Zr(R)(Cl).13 Thus reaction of 3 with isobutylene, I-butene, ethylene and propylene affords Cp2Zr(CH2CHMe2)(Cl) (7), Cp2Zr(CH2CH2CH2CH3)(Cl) (4), Cp2Zr(CH2CH3)(Cl) (5) and Cp2Zr(CH2CH2CH3)(Cl) (6). Benzene solutions of Cp2Zr(CH2CHDCH2CH3)(Cl) and Cp2Zr(CH2CH2D)(Cl), prepared from [Cp 2Zr(D)(Cl)]n and the appropriate olefin, display a single peak in the {lH}2H NMR spectrum. No change is observed over the course of one week at 296 K. Thus, there is no evidence for rearrangement of these terminal alkyls via ~-H elimination under these conditions (eq. 5). Likewise, a solution of Cp 2Zr( 13CH2CH2CH3)(Cl) does not undergo isotopic rearrangement at 296 K. 25 °C, days * (5) Furthermore, addition of five equivalents of 13CH2=CHCH3 to a solution of Cp 2Zr(CH2CH2CH3)(Cl) (7) in benzene-d6 resulted in no incorporation of 13 C into the propyl group over the course of one week (eq. 6). 120 25 °C, days * 6 (6) Reaction of [Cp2Zr(CH3)(µ2-H)h 14 with 13CHz=CHCH3 affords Cp2Zr(CH3)(13CH2CH2CH3) in quantitative yield (1H NMR). Over the course of three hours at room temperature, Cp2Zr(CH3)( 13CH2CH2CH 3) isomerizes to Cp2Zr(CH3)(CH2CH213CH3) (eq. 7). hours )Iii (7) 25°C Addition of 13CH2=CHCH3 to a benzene solution of [Cp 2ZrH2]n results in formation of dimeric [CpzZr(13CH2CH2CH3)(µ2-H)h, which undergoes isomerization to [Cp2Zr(CH2CH213CH3)(µ2-H)h over five days at room temperature. Hydrozirconation of internal olefins with [Cp 2Zr(H)(Cl)Jn. Cp 2Zr(cyclo-C5H9)(Cl) (8) and Cp2Zr(cyclo-2-D-C5Hs)(Cl) are obtained from addition of cyclopentene to a solution of 3 or 3-d in either benzene or diethyl ether. The unlabeled complex has been isolated as bright yellow crystals that are stable under vacuum. Cooling an Et2O solution of 8 to -40 °C affords clear yellow crystals suitable for X-ray diffraction. As shown in Figure 1, the cyclopentyl ligand adopts an envelope conformation and is contained in the metallocene wedge. 121 Figure 1. Molecular Structure of Cp2Zr(cyclo-C5H9)(Cl) (8) (50% probability ellipsoids). Selected bond distances (A): Zr-Cent(l), 2.2305(7); Zr-Cent(2), 2.2094(7); Zr-C(ll), 2.276(5); ZrCl, 2.4373(18). Bond angles (deg): Cent(l)-Zr-Cent(2), 130.83(3); C(ll)-Zr-Cl, 93.85(13). Cent(l) is the centroid formed by C(l), C(2), C(3), C(4) and C(5). Cent(2) is the centroid formed by C(6), C(7), C(8), C(9) and C(lO). The {l H} 2H NMR spectrum of a benzene solution of Cp2Zr(cyclo-2-D-C5H3)(Cl) containing a ten-fold excess of cyclopentene initially exhibits only one resonance at 8 = 1.43 ppm, corresponding to deuterium at the 2-position of the cyclopentyl ligand. After 12 hours at 296 K, a new peak appears at 8 = 2.19 ppm that has been identified as free cyclopentene-3-d1. Over a period of five days, deuterium appears in the remaining positions of the Zr-bound cyclopentyl ring and the free cyclopentene. Reaction of 3 with cis-2-butene has also been studied by 1H NMR spectroscopy. After 35 minutes at room temperature, the NMR spectrum displays resonances attributable to Cp 2Zr{CH(CH3)CH2CH3}(Cl) (9) as shown in Figure 2. Over the course of hours at room temperature, the peaks for 9 are replaced by resonances for Cp2Zr(CH2CH2CH2CH3)(Cl) (4) (eq. 8). Changing the solvent from benzene to THF has no discernible effect on the rate of isomerization. During the isomerization of 9 to 4, formation of trans-2-butene is observed by NMR. Furthermore, addition of 1-pentene to a mixture containing 122 only 9 and 4 results in buildup of Cp2Zr(CH2CH2CH2CH2CH3 )(Cl) (10) during the course of isomerization. hours ► 25 °C ~ .,-Cl Zr....._ ./'-.... / ~._,,,- (8) '-../ cis-2-butene C'H1 ~_,.,.Clz 4 Zr~ C2H2 CIH2 c3H2 ~I b 1.8 1.6 1.4 1.2 1.0 0.8 Figure 2. 500-MI-fz 1H NMR spectra of the butyl resonances following hydrozirconation of cis2-butene (a) after 6 hand (b) 3 days. Twenty minutes after reaction of 3-d with cis-2-butene (benzene-d6, 296 K) in benzene solution, the {1H} 2H NMR spectrum displays a singlet at◊= 1.20 ppm, assigned to the ~-deuterium of Cp2Zr{CH(CH3)CHDCH3 }(Cl). Over the course of several hours at this temperature, singlets at 1.31 ppm and 1.47 ppm appear in an approximately 2:1 ratio with gradual disappearance of the resonance at 1.20 ppm. No further change in the 1H NMR spectrum is observed even after weeks at room temperature. The peaks at 1.31 ppm and 1.47 ppm are assigned to the deuterons at position C3 and C2, respectively, of 4 (eq. 9). No signal attributable to deuterium in the terminal positions (C 1 and C4 ) of 4 is observed. 123 j \ ~ ClD [CpzZr(D)(Cl)ln ,. • ~~ hours .... & 25°C ~-c1? . Zr~ ~ Reactions of [Cp2Zr(H)(Cl)Jn (3) with several longer chain olefins have also been examined. Monitoring the reaction of 3 with cis-2-hexene, trans-2-hexene and trans-3-hexene by 1H NMR reveals that internal alkyl complexes are likely present at early conversion times, but the identity and relative amounts of these species could not be definitively established due to the complexity of the 1H NMR spectra. In the expectation that the 13C NMR spectra would be a much more readily interpretable, 1-13C-cis-2-heptene, cis- 13CH3CH=CHCH2CH2CH2CH3, was prepared by addition of 13CH3I to LiC=CCH2CH2CH2CH3 in liquid ammonia, followed by hydrozirconation of the alkyne and quenching with H 20. The 13C NMR spectrum (Figure 3) for the reaction of 3 with ca. 1.3 equivalents of cis- 13CH3CH=CHCH2CH2CH2CH3 in benzene-d6 after 10 minutes at 296 K exhibits a resonance at<> = 23.45 attributable to Cp2Zr{CH( 13CH3)(CH2)4CH3}(Cl) and additional resonances at 8 = 56.0 ppm and 8 = 14.7 ppm, assigned to C1 of Cp2Zr{1 3CH2(CH2)5CH3}(Cl) and C7 of Cp 2Zr{CH2(CH2)513CH3}(Cl), respectively. The resonance due to Cp2Zr{CH( 13CH3)(CH2)4 CH3}(Cl) grows in to a maximum relative intensity of ca. 50% over a period of about 5 hours, then decreases as those attributable to Cp 2Zr{ 13CH2(CH2)5CH3}(Cl) and C7 of Cp2Zr{CH2(CH2)5 13CH3}(Cl) continue to grow until after about 48 hours, they are the only resonances attributable to an organometallic compound. During this period, their ratio remains constant at 85:15 (eq. 10).15 (9) 124 (10) r 3-heptenes cs/tm.,_CH,CH=CH(CH~,'tl, I I j "CH,CH=CH(CH,),CH, .LL_ ~,Cl t=5.5hours _ ~~1 ! . _;.__ _ _ _ _ _ _ _ _ _ __..__ t = 0.2 hours _.....J__ _ _ _ _ _ _ __.___ ss 50 45 io 35 30 __._.__._ _.___..._ ____...,___,_,._,,..._ 25 20 15 PPM Figure 3. 125.77-MHz {1H}1 3c NMR spectra of the heptyl resonances following hydrozirconation of cis-13CH3CH=CHCH2CH2CH2CH3. Conversion of Cp2Zr{CH( 13CH3)(CH2)4CH3}(Cl) to other isomers is observed, predominantly Cp2Zr{ 13CH2(CH2)5CH3}(Cl) and C7 of Cp2Zr{CH2(CH2)s 13CH3}(Cl). For confirmation of these assignments, the hydrozirconation of unlabeled cis-2-heptene was carried out in toluene-d8 for three hours at 296 K, and the reaction was then cooled to -50 °C to prevent further isomerization. The 13C NMR spectrum of the reaction mixture was recorded at this temperature (Figure 125 4). Evident are 14 resonances that correspond to heptyl resonances of two organozirconium complexes, assigned as Cp2Zr{CH2(CH2)5CH3}(Cl) and Cp2Zr{CH(CH3)(CH2)4CH3}(Cl). Perhaps the most informative feature of the spectrum is the region between 50 and 60 ppm, where carbons directly bound to zirconium generally resonate. In this region, only two peaks are observed, one at 8 = 56.0 ppm assigned to C1 of Cp2Zr{CH2(CH2)5CH3}(Cl) and the other at 8 = 59.8 ppm assigned to methine carbon of Cp2Zr{CH(CH3)(CH2)4CH3}(Cl). o = cis-2-heptene 0 0 0 Toluene-d8 n o n n Figure 4. Upfield region of the 125.77 MHz {1H} 13c NMR spectrum obtained at 240 K, following hydrozirconation of cis-2-heptene with 3. In addition to peaks corresponding to Cp2Zr{ 13CH2(CH2)5CH3}(Cl), Cp2Zr{CH2(CH2)s 13CH3}(Cl) and Cp2Zr{CH(13CH3)(CH2)4CH3}(Cl), the 13C NMR spectrum shown in Figure 3 exhibits resonances assigned to terminally 13C-labeled isomeric internal heptenes, based on comparison to authentic samples, along with smaller signals believed to be due to singly 13C-labeled isomeric 3-heptenes (eq. 11). The largest peak at 8 = 18.3 ppm corresponds to both 7_13C-cis-2-heptene and 7_13C-trans-2-heptene. H313C~ [Cp 2Zr(H)(Cl)]n benzene-d6 25°C H313C~ & 13 C labeled 3-heptenes (11) 126 The course of hydrozirconation of cis-2-butene in benzene solution was also followed by quenching with CH30D at various time intervals (eq. 12); results are given in Table 1. 1. [Cp 2Zr(H)(Cl)]n C6D6, 25°C D ~+ ~ (12) D {1H} 2H NMR spectroscopy reveals that at short reaction times (up to about 20 minutes) only 2-deuterobutane is formed, whereas with longer reaction times increasing amounts of 1-deuterobutane is obtained. The time variation of the ratios 1- and 2-deuterated butanes is consistent with the rate of isomerization of Cp2Zr{CH(CH3)CH2CH3}(Cl) to Cp2Zr(CH2CH2CH2CH3)(Cl) as monitored directly by 1H NMR (vide supra). For the hydrozirconation of longer internal olefins such as cis-2-pentene and cis-2-heptene in benzene solution, quenching after one hour with CH30D results in solely terminally deuterated alkane. The 2H{ 1H} NMR spectra of the deuterated alkanes obtained after 1 hour of hydrozirconation are shown in Figure 5. These results suggest that rearrangements of the internal to the primary alkyls are relatively rapid, in contrast to the conclusions obtained by directly monitoring the reaction of 3 with cis- 13CH3CH=CHCH2CH2CH2CH3 by 13C NMR spectroscopy. In an attempt to reconcile this discrepancy, addition of 10 mol percent CH30D was added to the hydrozirconation of cis-2-heptene after 1 hour and the reaction monitored by low temperature 13C NMR spectroscopy; Cp 2Zr{CH2(CH2)5CH3}(Cl) is the only (remaining) heptylzirconium product observed. However, when an identical experiment is performed with cis-2-butene, both internal and terminal organozirconium products are observed in the 13C NMR spectrum, also in agreement with the corresponding quenching experiment. Since after 1 hour the hydrozirconation of cis-2-heptene with insoluble 3 results in relatively low conversion of the olefin to the zirconium alkyl as compared to the hydrozirconation of cis-2-butene, we sought to remove unreacted 3 from the reaction mixture before the addition of methanol. Re·m oval of unreacted 3 can be accomplished by filtration, resulting in a clear 127 yellow solution. Addition of CH3OD to the filtrate, followed by analysis by {l H}2H NMR, reveals that both internally and terminally deuterated heptanes are produced. In order to further demonstrate the effects of unreacted 3 on the quenching of hydrozirconation reactions, addition of cis-2-butene to a twofold excess of 3 followed by quenching with CH3OD after 1 hour results in a substantial increase in the amount of terminally deuterated butane as compared to the stoichiometric reaction. ___l ___ Figure 5. 76.77 MHz {1H} 2H NMR spectra of deuterated alkanes produced by treatment of 3 with cis-2-butene, cis-2-pentene and cis-2-heptene, followed by a CH30D quench. Discussion Rearrangements of isotopically labeled (CpRnhZr(CH2CHR'2)(H). Complexes of the general formula (CpRn)zZr(CH2CHR2')(H) (R, R', R" = alkyl, H) are readily prepared from (CpRn)zZrH2 and the appropriate olefin, CH2=CR'R". We have previously shown that although these complexes are stable in solution at 296 K, they undergo facile, reversible ~-H elimination.9 Using methyl-tert-butylacetylene to rapidly trap (CpRn)zZrH2, rate constants for ~-H elimination have been measured for the (CpRn)zZr(CH2CHR2')(H) (CpRn = (r1 5-C5Mes) (Cp*), (ri 5-C5Me4H)) systems examined here, as well as for several other substituted zriconocenes. 16 Whereas isotopically labeled alkyl complexes undergo rearrangement under the same conditions, the rates of rearrangement are 103 to 104 times slower than ~-H elimination. 128 A proposed mechanism for deuterium migration in Cp*2Zr(CH2CDMe2)D is shown in Scheme 1; similar paths can account for all the isotopic rearrangements observed. Following ~-H elimination and olefin reorientation, either through intramolecular olefin rotation or by dissociation and recoordination in the opposite direction, ~-H migratory insertion affords secondary or tertiary alkyl-hydride species. Since all alkyl-hydride complexes studied undergo very rapid exchange with free olefin, we favor the olefin dissociation pathway, although the presence of an olefin-dihydride intermediate which undergoes olefin rotation faster than dissociation can not be ruled out definitively. The secondary or tertiary alkyl-hydride intermediate then undergoes P-H elimination and readdition to form the primary alkyl with the label in a new position. A mechanism similar to that shown in Scheme 1 has been proposed by Busico to account for the tacticity dependence on monomer concentration in metallocene catalyzed olefin polymerization, where lower propylene pressures result in decreased stereospecificity.6c At low propylene concentrations, epimerization at the methine carbon of the last inserted monomer unit competes with olefin insertion, hence decreasing the isotacticity of the resulting polypropylene. A sequence of P-H elimination and reinsertion steps leads to formation of the tertiary-alkyl intermediate [Zr-C(CH3)2P] (P = polymer chain), which may P-H eliminate from either methyl group to reform the original [ZrCH2CH(CH3)P] or the enantiomeric equivalent. Busico favors the olefin rotation pathway over the free olefin route, since it is commonly accepted that a-olefins undergo insertion at a much greater rate than the corresponding gem-disubstituted olefins.6 The rate of alkyl isomerization is influenced by the degree of substitution on the cyclopentadienyl ligands: more substituted cyclopentadienyl ligands slow the rate of the reaction. 9 For the 13C-labeled propyl-hydride complexes, the relative rate of isotopic rearrangement is [Cp*(T1 5-C5H4-CMe3)Zr] > [(T1 5-C5Me4H)2Zr] > [Cp*2Zr]. Similarly, the rate of deuterium scrambling in the labeled isobutyl-deuteride complexes is [(T1 5-CsMe4H)2Zr] > [Cp*2Zr]. In both cases, the effect of changing the cyclopentadienyl substitution has a relatively modest effect on the rate of isotopic rearrangement. For example, the rate Scheme 1 olefin rotation ? Rn .,~ &JP , ,.......D ~½ ~ D Rn -CH2=C(CH3)i zr~ Zr~D _/ ~CH CD(CH '~C(CH3)2◄ ~ 2 32 ~ C H2 J" ~ ◄ 4P,,D -D ~ ~""CHDCH(CH3) ~ _p:::-::~C(CH3h --~ ~Q)'-.....CHD ~ I ~ ~1 ~ o 4P • Rn ~½ , --D+CH2=C(CH3)i~,.....D Zr ► Zr ..- D _/ ' D ◄ _/ --~CH2 ~ ~C(CH3)i ~ Rn b'z ► _/ &P • ~1 ~ ~ ~ 4fj;l ' ,.....D Zr-H_ \~.i(~LHD CH3)i ~ ~ 4fj;l 'z-D r~ ~ C(CH2D)(CH3 h I I Rn ~ ~ _◄ _ 4P,,o Zr-H +t H ~ 4P,,o ...._ Zr-H Zr_/ ~CH CH(CH D)(CH3) ~ _/ ---- .. 'iC(CH3)(CH2D) ~ _/ ----~CH_2__ 2 2 ~ ~ C H2 ~C(CH3)(CH2D) I Rn I ~ I ~ 1--1 N \0 130 enhancement from removing two methyl groups results in a 40-fold increase in the rate constant at 296 K. Since the rates for olefin insertion and B-H elimination are more than two orders of magnitude faster than isotopic rearrangement, we conclude that the formation of the more substituted alkyl complex (either secondary or tertiary) is the rate determining step in the isomerization process of Scheme 1. This assertion is supported by the failure to observe any intermediate internal alkyl complex in these systems. We have observed similar behavior for the addition of cis-2-butene to Cp*2ZrH2, where the addition of the zirconium hydride bond is much slower than isomerization of the internal alkyl to the final, only observable terminal product, Cp*2Zr(CH2CH2CH2CH3)(H). 9 The rate constant at 296 K for B-H elimination of the isobutyl ligand from Cp*2Zr(CH2CHMe2)(H) is much greater than the rate constant for the isomerization (kf3-H = 2.8 x 10-6 s- 1; kisom = 1.0 x 10-8 s-1; kf3-ttlkisom = 280) for Cp*2Zr(CH2CDCMe2)(D) to Cp*2Zr(CHDCHMe2)(D) and Cp*2Zr(CH2CH(CH2D)(CH3))(D). 9 By comparion, for the related propyl-hydride complex Cp* 2Zr( 13CH2CH2CH3)(H), these rates are much greater and ratio rates less, (kf3-H = 1.1 x 10-3 s-1; kisom = 1.2 x 10-4 s-1; kf3-ttlkisom = 11).9 These data indicate that the isopropyl hydride intermediate is more accessible than the corresponding tert-butyl-hydride intermediate (A in Scheme 1). Apparently, the presence of an additional methyl group in the case of the tert-butyl intermediate sterically disfavors its formation relative to the isopropyl complex, which then in tum decreases the rates of isomerization (as well as B-H elimination). Rearrangements of Cp2Zr(CH2CHR'2)(X) (R' = H, Me, Et; X = H, Me, Cl). Changing the "spectator" ligand in the metallocene wedge from hydride to other one electron ("X-type") ligands has a relatively larger effect on the rates of B-H elimination and alkyl isomerization. Whereas Cp*(C 5H 4-CMe3)Zr(CH2CHR' 2)(H) (R' = H, Me, Et) undergo facile B-H elimination at 296 K, the corresponding compounds Cp2Zr(CH2 CHR' 2)(Cl) (R' = H, Me, Et) are stable to ~-H elimination/ olefin rotation/reinsertion, as demonstrated by the lack of deuterium scrambling and lack of isotopic rearrangement for Cp2Zr( 13CH2CH2CH3)(Cl). The observation that Cp2Zr(CH2CH2CH3)(Cl) does not exchange with 13CH2=CHCH3 also is in 131 agreement with the very stable nature of these alkyl/ chloro complexes. A general lack of ~-H elimination from primary alkyl complexes of the type Cp 2Zr(CH2CHR'2)(Cl) was originally proposed by Schwartz, 18 based on the absence of alkyl exchange with olefins in the related cyclohexylmethyl complex, Cp2Zr(CH2-cyclo-C6H11)(Cl). In order to establish whether this effect is steric or electronic in origin, the labeled propyl-methyl complex Cp2Zr( 13CH2CH2CH3)(CH3) was prepared.1 7 Isotopic rearrangement is observed over the course of three hours at 296 K. Since methyl and chloride are approximately isosteric, the difference in reactivity must therefore be due to electronic properties, most likely then-donating ability of the chloride ligand. Lone electron pair donation from Cl into the la1 zirconocene orbital formally completes the 18-electron zirconocene valence shell, and hence, unlike Cp2Zr(CH2CHR' 2)(X) (X = H, CH3), there is no (strictly) empty orbital for ~-H elimination.18 Moreover, alkyl isomerization initiated by ~-H elimination should be very facile for zirconocene cations, [Cp2Zr(CH2CHR'2)]+, since formally there are two vacant orbitals. 19 We considered the possibility that small, undetectable amounts of the dihydride complex, [Cp 2ZrH2Jn, might promote propyl isomerization for Cp2Zr( 13CH2CH2CH3)(CH3), since preparation of [Cp2Zr(CH3)(H)h involves hydrogenation of Cp 2ZrMe2. [Cp2Zr( 13CH2CH2CH3)(H)]z was therefore prepared via treatment of [CpzZrH2ln with 13CH2=CHCH3. Isotopic rearrangement for [Cp2Zr( 13CH2CH2CH3 )(H)h does occur over the course of 5 days at 296 K, but at a rate much slower than observed for Cp2Zr( 13CH2CH2CH3)(CH3). The slow isomerization rate for [Cp2Zr(13CH2CH2CH3)(H)h is attributed to its dimeric nature in solution. Schwartz20 has previously reported the robust nature of these alkyl-hydride complexes, a result of their strong bridging hydride interactions. Presumably, the dimeric alkyl-hydride must dissociate into the 16-electron monomeric species in order to undergo ~-H elimination, eventually resulting in isotopic scrambling. 132 Hydrozirconation of Internal Olefins and Isomerization of Internal Alkyls. In contrast to primary alkyl complexes of Cp 2Zr(R)(Cl), internal acyclic and cyclic alkyl complexes readily undergo P-H elimination and alkyl isomerization reactions. The formation of terminal products from hydrozirconation of internal olefins was a striking observation in early studies.3,4 It is this behavior that has made hydrozirconation a valuable synthetic tool for a variety of transformations. 4 The order of reactivity based on qualitative observations· is: terminal alkene > internal alkene > exocyclic alkene > cyclic alkene : : : trisubstituted alkene. 4 c For example, only the zirconium-2-cyclohexenylethyl complex is observed upon the hydrozirconation of vinylcyclohexene. 21 Isomerization of the internal alkyl adduct is generally believed to be much faster than its initial formation by reaction of internal olefin with polymeric 3, since no internally substituted products are isolated from treatment of the organozirconium complex with various electrophiles. For example, the hydrozirconation of (Z)-5-decene at 40 °C for 4 hours, followed by addition of D2O, resulted in formation of up to 70% 1-drdecane, with the remaining products identified as internal decenes; no internally deuterated decanes were detected. 22 Tertiary alkylzirconium complexes, e.g., Cp2Zr(CMe3)(Cl), appear to be generally inaccessible even as intermediates. Attempted hydrozirconation of an internal alkene which is capped at both ends with tert-butyl groups yields only isomerized alkene.1 8 Direct analysis of the hydrozirconation of cis-2-butene by high field 1H NMR spectroscopy has now provided the first observation of a transient zirconium internal alkyl complex, Cp2Zr(CH(CH3)CH2CH3)(Cl) (9). 23 The isomerization of 9 to Cp2Zr(CH2CH2CH2CH3)(Cl) (4) occurs over the course of several hours at 296 K, which is slower than the time required for the complete reaction of [Cp 2Zr(H)(Cl)]n (3). Clearly, the rate of alkyl isomerization in the butyl case is not as rapid as previously believed. The hydrozirconation of cis-2-butene with 3-d also confirms the formation of 9. The 2H{lH} NMR spectrum initially displays one peak, attributable to the P-deuterium of Cp 2Zr(CH(CH3)CHDCH3)(Cl). 24 The proposed mechanism for isomerization of Cp2Zr(CH(CH3)CHDCH3)(Cl) to Cp2Zr(CH2CH2CHDCH3)(Cl) and Cp2Zr(CH2CHDCH2CH3)(Cl) is shown in Scheme 2. After addition of Scheme 2 4Jf_c1 Zr~D ~ 3-d /\ • ► &P _/Zr_.Cl ...,. ~ CH(CH3)CHDCH3 ◄ \ ► &P Zr_.Cl \ P-HfromC 1 ~-..H + ~ D 1i tj &P Zr_.Cl &P Zr_.Cl P-H from c3 \ d:s-..H ~ + ~ \ ~ ~'CH2CH2CHDCH3 D tj D &P &P ~-H fro C Zr_.Cl + ~ 'Zr .-Cl ~'CD(CH3)CHzCH3 ◄ m ► ~-..H \ 1 ..I tj &P Zr_.Cl \ ~'CHzCHDCHzCH3 1--l (;J (;J 134 the olefin, the internal alkyl complex can P-H eliminate from either C1 or c 3. If P-H elimination occurs from Ci, [Cp2Zr(H)(Cl)] and 3-di-1-butene are formed, which then undergo insertion to form Cp2Zr(CH2CH2CHDCH3)(Cl). If P-H elimination occurs from C3, liberation of cis- or trans-2-dr2-butene occurs with formation of [Cp2Zr(H)(Cl)]. The 2-butenes then reinsert, forming another internal alkyl complex, now with deuterium on the carbon bound directly to zirconium. This then undergoes P-H elimination from C1 to generate 2-dr 1-butene which then inserts forming Cp2Zr(CH2CHDCH2CH3)(Cl). The ratio of Cp2Zr(CH2CH2CHDCH3)(Cl) to Cp2Zr(CH2CHDCH2CH3)(Cl) is approximately 2:1 during the isomerization reaction, indicating that ~-H elimination from C 1 is favored over elimination from C3. No deuteration in the a or ro positions of 4 is observed, consistent with the static nature of primary alkyls, since those isotopomers are only accessed by further rearrangement of Cp2Zr(CH2CH2CHDCH3)(Cl) or Cp2Zr(CH2CHDCH2CH3)(Cl). The detection of trans-2-butene during isomerization of 9 to 4 suggests the intermediacy of [Cp2Zr(H)(Cl)] and free olefin, rather than olefin-hydride intermediates that undergo intramolecular olefin rotation. This conclusion is further supported by the addition of 1-pentene to a mixture of 9 and 4. By the time 9 is completely gone, the pentyl-chloride complex, Cp2Zr(CH2CH2CH2CH2CH3)(Cl), is observed along with 4 (Scheme 3). Facile olefin exchange is not surprising for a d 0 metal complex that is not capable of stabilizing re-back donation. 135 Scheme 3 41f'_c1 Zr......._, ~H 3t!~ 4 41f'____ c1 Zr~ ~ The isomerization of the deuterium-labeled cyclopentyl-chloride complex Cp2Zr(cyclo-2-D-C 5H 8)(Cl) also supports a free olefin pathway in alkyl isomerization. The fact that deuterium appears in free cyclopentene (cyclopentene-3-d1) before it appears in positions other than the 2 position of 8 demonstrates that P-H elimination and liberation of free cyclopentene is the favored pathway over intramolecular olefin rotation and reinsertion (Scheme 4). Note that the absence of cyclopentene-1-d1 is consistent with Scheme 4, since both the addition and elimination of Zr-H follow strict syn stereochemistry. Alkyl length clearly has a significant effect on the rate of isomerization of internal alkyls. Hydrozirconation of cis- 13CH3CH=CHCH2CH2CH2CH3 demonstrates that alkyl isomerization of the internal heptyl-chloride complex is faster than that of the corresponding butyl complex, since Cp 2Zr{CH( 13CH3)(CH2)4CH3}(Cl) disappears in less than 24 hours whereas 9 persists for several days. Isomerization of Cp 2Zr{CH( 13CH3)(CH2)4CH3}(Cl) produces both Cp 2Zr{ 13CH2(CH2)5CH3}(Cl) and Cp2Zr{CH2(CH2)s 13CH3}(Cl), consistent with isomerization in both directions down the alkyl chain, while 13C 136 NMR spectroscopy reveals that only one internal alkyl complex, Cp2Zr{CH( 13CH3)(CH2)4CH3}(Cl), is formed in appreciable concentration. Formation of Cp2Zr{CH2(CH2)s 13CH3}(Cl) implies the intermediacy of 3- and 4-heptyl zirconium complexes, although we have been unable to detect these complexes spectroscopically. Based on this evidence, we propose that the rate of isomerization for 3- and 4-heptyl complexes is rapid, such that only the 2-isomer can be observed. Unfavorable steric interactions between alkyl chains longer than methyl and the chloride ligand in the 3- and 4-heptyl zirconocene presumably results in destabilization and hence faster rates of isomerization. Although reliable force fields are not available, molecular mechanics25 calculations support this assertion. Of the internal alkyl complexes, Cp2Zr{CH(CH3)(CH2)4CH3}(Cl) was found to be approximately 2 kcal-moi- 1 more stable than Cp2Zr{CH(CH2CH2CH2CH3)(CH2CH3)}(Cl), which in turn is about 3 kcal-moi- 1 more stable than Cp2Zr{CH(CH2CH2CH3)i}(Cl). In addition to directly observing internal alkyl complexes by NMR spectroscopy, we have looked for these species in quenching reactions. Hydrozirconation of cis-2-butene followed by addition of CH30D affords mixtures of internally and terminally deuterated alkanes. For hydrozirconation in the presence of excess cis-2-butene, internally deuterated butanes are observed for up to 48 hours, much longer than previously reported. 4c The ratio of internally to terminally deuterated butanes obtained from the quenching experiments corresponds roughly to the amounts of internal and terminal butyl organozirconium complexes that were detected by direct NMR observation. 137 Scheme 4 3-d 0 ► By contrast, addition of CH3OD to reactions of [Cp 2Zr(H)(Cl)ln with cis-2-pentene or cis-2-heptene results in only terminally deuterated alkanes. These results appear inconsistent with those obtained by monitoring the reaction by NMR spectroscopy. To resolve the discrepancy we first examined the solution obtained from hydrozirconation of cis-2-heptene for one hour followed by addition of 10 mol percent of CH3OD by 13C NMR. Only terminal zirconium heptyl complex was detected, suggesting methanol somehow catalyzes the isomerization of Cp2Zr{CH(CH3)(CH2)4CH3}(Cl) to Cp2Zr{CH2(CH2)5CH3}(Cl). By comparison, after hydrozirconation of cis-2-butene followed by addition of 10 mol percent of methanol, both 9 and 4 are observed by low temperature 13C 138 NMR spectroscopy, so that methanol does not promote isomerization in this case. Why might Cp2Zr{CH(CH3)CH2CH3}(Cl) and Cp2Zr{CH(CH3)(CH2)4CH3}(Cl) behave differently? Qualitative comparison of the relative rates of hydrozirconation reveals that cis-2-butene reacts more rapidly than cis-2-heptene with [Cp2Zr(H)(Cl)Jn (3). This is in accord with previous observations that longer olefins undergo hydrozirconation at a slower rate than their less sterically crowded counterparts.Sc Thus, after one hour there is considerably more unreacted [Cp2Zr(H)(Cl)Jn during the hydrozirconation of cis-2-heptene-than for cis-2-butene. We therefore postulate that methanol might react with the residual 3, forming a small amount of an organozirconium species that catalyzes the isomerization of internal alkyl to terminal complex. To test this hypothesis, we carried out the hydrozirconation of cis-2-heptene for one hour followed by removal of unreacted 3 by filtration and addition of CH3OD to the clear yellow filtrate. In this case {1 H} 2H NMR spectroscopy showed formation of both internally and terminally deuterated heptanes (ca. 40:60, respectively). In the complementary experiment, hydrozirconation of cis-2-butene in the presence of excess 3 followed by quenching with CH3OD results in enrichment of 1-drbutane (Table 1), presumably due to an increased concentration of the (as yet unidentified) isomerization catalyst. These results are consistent with the previous observations for the hydrozirconation of internal olefins yielding only terminally substituted products. This behavior has made 3 a valuable synthetic tool for the functionalization of otherwise unreactive C-H bonds. Typically hydrozirconation reactions are performed using elevated temperatures and / or until a homogenous solution is obtained thus allowing isomerization of all internal alkyl adducts to the more stable terminal organozirconium complex. However, the isomerization of the internal alkyl adduct is not as rapid as previously reported and internally functionalized alkanes can be prepared under the appropriate conditions. Our results demonstrate that in addition to long reaction times, addition of electrophiles such as H+ in the presence of unreacted 3 139 can promote alkyl isomerization. These results in concert offer an explanation for the lack of previous identification of internal alkyl adducts. Experimental General Considerations. All air and moisture sensitive compounds were manipulated using standard vacuum line, Schlenk or cannula techniques or in a dry box under a nitrogen atmosphere as described previously.26 Argon, dinitrogen, dihydrogen and dideuterium gases were purified by passage over columns of MnO on vermiculite and activated molecular sieves. Solvents for air and moisture sensitive reactions were stored under vacuum over titanocene.27 Preparations of Cp*2ZrH2,28 [Cp*(T\ 5-C5H4-CMe3)ZrH2h, (T\ 5-C5Me4H)iZrH2, [Cp2Zr(CH3)(H)]z,14 [Cp2Zr(Cl)(H)]n12, [Cp2Zr(Cl)(D)Jn12, [Cp2ZrH2Jn15 were carried out as described previously. NMR solvents: benzene-d6, toluene-ds and tetrahydrofuran-ds were purchased from Cambridge Isotope Laboratories. Benzene-d6 and toluene-ds were dried over LiAlH4 and sodium and then stored over titanocene. Tetrahydrofuran-ds was dried over CaH2 and stored over sodium / benzophenone ketyl. 13CH2=CHCH3 was purchased from Cambridge Isotope Laboratories and distilled on the vacuum line before use. 13CH3I and CH3OD were purchased from Cambridge Isotope Laboratories and used as received. Ethylene was purchased from Matheson and passed through a trap maintained at -78 °C before use. Isobutene, cis-2-butene and propene were purchased from Aldrich, dried over Al(i-Buh and stored over 4A molecular sieves. 1-Pentene, 1-hexene, cis- and trans-2-hexene, trans-3-hexene and cyclopentene were purchased from Aldrich, distilled from LiAlH4 and stored over CaH2. 2-pentyne was purchased from Lancaster and used as received. NMR spectra were recorded on a Bruker AM500 (500.13 MHz for 1H, 76.77 for 2H, 125.77 MHz for 13C) spectrometer. All chemical shifts are relative to TMS using 1H (residual), 2H or 13C chemical shifts of the solvent as a secondary standard. For 13C NMR experiments, 10 second relaxation delays were used to obtain reliable integration data. Elemental analyses were carried out at the Caltech Elemental Analysis Facility by Fenton Harvey. Many of the alkyl complexes reported either decompose or form oils upon attempted isolation, thereby precluding elemental analysis. 140 Cp*2Zr(CH2CDMe2)(D) (1). In the dry box, a J. Young NMR tube was charged with 0.50 mL of a 0.0488 M stock solution (0.0244 mmol) of Cp* ZrH and 0.094 M Cp Fe in benzene-d6. On the vacuum line, the solution was frozen and 2 2 2 degassed with three freeze-pump-thaw cycles. The tube was then fully submerged in liquid nitrogen and 1 atmosphere of D2 was admitted. The tube was thawed, shaken and rotated at room temperature for 5 minutes after which time the solution was again frozen and the tube evacuated. Via a 6.9 mL calibrated gas volume, 76 Torr (0.028 mmol) of isobutene was added at -196 °C. The tube was then thawed and shaken and monitored by 1H NMR spectroscopy. H NMR (benzene-d 8 = 1.93 (s, 30 H, Cp*), -0.049 (s, 2H, CH CDMe 1.02 (s, 6H, CH2CDMe2). 2H NMR (benzene): 8 = 6.36 (s, 1D, Zr-D), 1.91 (s, 1D, 1 ) : 6 ) , 2 2 CH2CDMe2). In the dry box, a flame-sealable NMR tube was charged with 0.50 mL of a 0.166 M stock solution 1 or 2 containing 10 µL of benzene-d6 in C6H 6 . On the vacuum line, the solution Isomerization of 1 and 2 as monitored by {1 H}2H NMR. was frozen and degassed with three freeze-pump-thaw cycles. The entire tube was then immersed in liquid nitrogen and 1 atmosphere of D2 was admitted. The tube was thawed and rotated. After five minutes, the tube was again frozen and isobutene (230 Torr, 6.9 mL, 0.085 mmol) was added via calibrated gas volume. The tube was then sealed with a torch, thawed and placed in a thermostated bath. Approximately 8-10 spectra were recorded at regular intervals during the course of the reaction and the intensity of each peak was measured by integration versus the internal standard. The rate of the reaction was then plotted as an approach to equilibrium as described previously. 29 <r1 5-C 5Me4 H) 2Zr(CH 2CDMe2)(D) (2). This compound was prepared in the same manner as 1. 1H NMR (benzene-d6): 8 = 2.13 (s, 6H, CsAfe4H), 2.07 (s, 6H, C5Me4H), 1.99 (s, 6H, CsAfe4H), 1.94 (s, 6H, CsAfe4H), 5.11 (s, 2H, C5Me4H), -0.07 (s, 2H, CH2CDMe2), 1.03 (s, 6H, CH2CDMe2). 2H (benzene): 8 = 5.93 (s, 1D, Zr-D), 2.23 (s, 1D, CH2CDMe2). In the dry box, a J. Young NMR tube was charged with 7.0 mg (0.019 mmol) of Cp*2ZrH2 and 0.50 mL benzene-d6 added forming a Cp* 2Zr(CH 2 CH2CH 3)(H). clear solution. On the vacuum line, the tube was degassed with three 141 freeze-pump-thaw cycles. Via 6.9 mL calibrated gas bulb, 52 Torr (0.019 mmol) of CH2=CH2CH3 was added at -196 °C. The solution was then thawed and the tube shaken. With shaking the solution turns from colorless to yellow. lH NMR (benzene-d6): 8 = 1.94 (s, 30 H, Cp*), -0.25 (m, 2H, CH2CH2CH3), 1.86 (m, 2H, CH2CH2CH3), 1.86 (t, ,7Hz, 3H, CH2CH2CH3). Cp* 2Zr(13CH2CH2CH 3)(H). 13C{1H} NMR (benzene-d6): 8 = 55.15 (CH CH CH3), 20.98 (CH CH2CH ). 2 2 2 3 (17 5-C5Me4H)2Zr(CH2CH2CH3)(H). This compound was prepared in the same manner as 1 using 8.0 mg (0.024 mmol) of (17 5-C5Me4H)iZrH2 and 70 Torr (0.026 mmol) of CH2=CH2CH3. 1H NMR (benzene-d6): 8 = 2.26 (s, 6H, C 5Me4H), 2.14 (s, 6H, C5Me4H), 2.08 (s, 6H, CsAfe4H), 1.98 (s, 6H, CsAfe4H), 5.43 (s, 2H, C5Me4H ), -0.60 (m, 2H, CH2CH2CH3), 2.29 (m, 2H, CH2CH2CH3), 0.94 (t, 7 Hz, 3H, CH2CH2CH3). (17 5-C5Me4H)2Zr(13CH2CH2CH3)(H). 13C{1H} NMR (benzene-d6): 8 = 55.74 (CH2CH2CH3), 20.24 (CH2CH2CH3). Isomerization of Cp*2Zr(13CH2CH2CH3)(H) and (175-C 5Me 4H) 2Zr(13CH2CH2CH3)(H) by l3C NMR Analysis. In the dry box, a J. Young NMR tube was charged with 0.50 mL of 0.166 M stock solution of metallocene in benzene-d6. On the vacuum line, the solution was frozen and degassed with three freeze-pump-thaw cycles. While frozen in liquid nitrogen, 13CH2=CHCH3 was added to the tube via 6.9 mL calibrated gas volume. The tube was sealed, rotated several times and then placed in the temperature calibrated NMR probe. Approximately 8-10 spectra were recorded at regular intervals during the course of the reaction. The intensity of each peak was determined by integration and the kinetics plotted as an approach to equilibrium. Cp*(C 5H 4-CMe 3)Zr(CH2CH 2CH3)(H). This compound was prepared in the same manner as 1 using 6.8 mg (0.0196 mmol) of [Cp*(C5H4-CMe3)ZrH2h and 52 Torr (0.0196 mmol) of 13CH2=CHCH3. 1H NMR (benzene-d6): 8 = 1.82 (s, 15H, Cp*), 1.40 (s, 9H, CsH4-CMe3), 5.32, 4.91, 4.88, 4.20 (m, C5H4-CMe3), 5.94 (s, lH, Zr-H), -0.50 (m, 2H, CH2CH2CH3), 2.10 (m, CH2CH2CH3), 1.07 (t, 6 Hz, 3H, CH2CH2CH3).Cp*(C5H4-CMe3)Zr(13 CH2CH2CH 3)(H). 13C{ 1H} NMR (benzene-d6): d = 55.07 (CH2CH2CH3), 21.33 (CH2CH2CH3). 142 Cp2Zr(CH2CHMe2)(Cl). In the dry box, a J. Young NMR tube was charged with 9.0 mg (0.035 mmol) of 3 and benzene-d6 added. On the vacuum line, the tube was frozen in liquid nitrogen and degassed with three freeze-pump-thaw cycles. Via calibrated gas volume, 108 Torr (0.040 mmol) of isobutene was added at -196 °C. The tube was thawed and rotated. With time, dissolution of 3 was observed with formation of a bright yellow solution. 1H NMR (benzene-d6): <> = 6.24 (s, l0H, CsHs), 0.968 (d, 6.4 Hz, 2H, CH2CHMe2), 2.20 (sept., 6.5 Hz, lH, CH2CHMe2), 0.849 (d, 6.5 Hz, 6H, CH2CHMe2). 13C NMR (benzene-d6): <> = 110.94 (CsHs); 50.27 (CH2CHMe2); 38.44 (CH2CHMe2); 13.79 (CH2CHMe2 ). Cp2Zr(CH2CH2CH2CH3)(Cl). In the dry box, a J. Young NMR tube was charged with 15.0 mg (0.058 mmol) of 3 and benzene-d6 added. On the vacuum line, the tube was degassed with three freeze-pump-thaw cycles. Via calibrated gas bulb, 165 Torr (0.061 mmol) of I-butene was added at -196 °C. The solution was then thawed, and the tube shaken. With shaking the white solid dissolves forming a yellow solution. 1H NMR (benzene-d6): <> =5.77 (s, l0H, C5H5), 1.10 (m, 2H, CH2CH2CH2CH3), 1.58 (pent., 7.2 Hz, 2H, CH2CH2CH2CH3), 1.37 (m, 7.3 Hz, 2H, CH2CH2CH2CH3), 1.02 (t, 7.3 Hz, 3H, CH2CH2CH2CH3). 13C NMR (benzene-d6): <> = 112.86 (CsHs), 55.55 (CH2CH2CH2CH3), 37.16 (CH2CH2CH2CH3), 29.72 (CH2CH2CH2CH3), 14.38 (CH2CH2CH2CH3). Cp 2Zr(CH 2CHDCH2CH 3)(Cl). A sample was prepared in an identical manner to that described above with 35.0 mg (0.135) of 3-d. {1H} 2H NMR (benzene): <> = 1.51 (s, 1D, CH2CDHCH2CH2CH3). Cp 2Zr(CH2CH3)(Cl). In the dry box, a J. Young NMR tube was charged with 14.0 mg (0.054 mmol) of 3 and benzene-d6 added. On the vacuum line, the tube was degassed with three freeze-pump-thaw cycles. Via 6.9 mL calibrated gas bulb, 250 Torr (0.092 mmol) of ethylene was added at -196 °C after passage through a -80 °C trap. The solution was then thawed and the tube shaken. With shaking the white solid dissolves forming a yellow solution. 1H NMR (benzene-d6): <> = 5.76 (s, l0H, C5H5 ), 1.09 (q, 7.6 Hz, 2H, CH2CH3), 1.44 (t, 7.65 Hz, CH2CH3). 13C NMR (benzene-d6): <> = 111.57 (C5H5); 56.10 (CH2CH3); 14.70 14.70 (CH2CH3); 143 Cp2Zr(CH2CH2D)(Cl). A sample was prepared in an identical manner to that described above with 57.0 mg (0.220) of 3-d. {1 H} 2H NMR (benzene) 8 = 1.38 (s, 1D, CH2CH2D). Cp2Zr(CH2CH2CH3)(Cl). In the dry box, a J. Young NMR tube was charged with 5.0 mg (0.014 mmol) of 3 and benzene-d6 added. On the vacuum line, the tube was degassed with three freeze-pump-thaw cycles. Via calibrated gas bulb, 60 Torr (0.022 mmol) of CH2=CHCH3 was added at -196 °C. The solution was then thawed and the tube shaken. With shaking the white solid dissolves forming a yellow solution. 1H NMR (benzene-d6): 8 = 5.77 (s, lOH, C5H 5), 1.09 (m, 2H, CH2CH2CH3), 1.50 (m, 2H, CH2CH2CH3), 1.01 (t, 7 Hz, 3H, CH2CH2CH3). Cp2Zr(13 CH2CH2CH3)(Cl). 13C NMR (benzene-d6): 8 = 58.72 (CH2CH2CH3). Cp 2Zr(cyclo-C 5H 9)(Cl). In the dry box, a 25 mL round bottom flask equipped with stir bar was charged with 0.430 g (1.67 mmol) of 3 and a 180° needle valve was attached. On the vacuum line, approximately 10 mL of Et20 was added by vacuum transfer at -78 °C. While at-78 °C, 400 Torr of cyclopentene was added. The reaction was backfilled with argon and warmed to room temperature with stirring. Over the course of several hours, a clear yellow solution forms. The reaction was continued for 12 hours and then all volatiles were removed in vacuo. The reaction flask was transferred onto a swivel frit assembly and the yellow solid extracted with Et20. The Et20 was removed in vacuo leaving a yellow solid. The solid was recrystallized from Et20 at -40 °C in the dry box freezer. Yield of product: 0.350 g (63.5%). 1H NMR (benzene-d6): 8 =5.79 (s, lOH, C5H5), 1.59 (m, lH, C5H9), 1.67 (m, 2H, C5H9), 1.46 (m, 2H, C5H9), 1.45 (m, 2H, C5H9), 1.92 (m, 2H, C5H9). Anal. for C1sH19Zr1Cli: C: 55.27% H: 5.87%. Found C: 54.97%, H: 5.90%. Cp2Zr(CH3)(CH2CH2CH3). In the dry box, a J. Young NMR tube was charged with 5.0 mg (0.021 mmol) of [Cp 2Zr(CH3)(H)h and benzene-d6 added. On the vacuum line, the tube was degassed with three freeze-pump-thaw cycles. Via 6.9 mL calibrated gas bulb, 60 Torr (0.022 mmol) of l3CH2=CHCH3 was added at -196 °C. The solution was then thawed and the tube shaken. With shaking the white solid dissolves forming a yellow solution. The sample was placed in the NMR probe and monitored by 13C and lH NMR spectroscopy. 1H NMR 144 (benzene-d6): 8 =5.71 (s, lOH, CsHs), 0.113 (s, 3H, Zr-CH3), 0.518 (m, 2H, CH2CH2CH3), 1.66 (m, 2H, CH2CH2CH3), 1.03 (t, 6.8 Hz, 3H, CH2CH2CH3). Cp2Zr(CH3)(13CH2CH2CH3). 13C NMR (benzene-d6): 8 = 57.72 (CH 2CH2CH3), 27.34 (CH2CH2CH3). Addition of cis-2-Butene to 3. Identification of 9. In the dry box, a J. Young NMR tube was charged with 14.0 mg (0.054 mmol) of 3 and benzene-d6 added. On the line the tube was degassed with three freeze-pump-thaw cycles. Via calibrated gas volume, 220 torr (0.081 mmol) of cis-2-butene added at -196 °C. The tube was thawed and shaken. With time, the white solid dissolves forming a clear yellow solution. 1H NMR (benzene-d6) 9: 8 =5.78 (s, lOH, C5H 5), 1.27 (d, 6.9 Hz, 3H, CH(CH3)CH2CH3), 1.22 (m, 2H, CH(CH3)CH2CH3), 1.72 (m, lH, CH(CH3)CH2CH3), 0.973 (t, 7.1 Hz, 3H, CH(CH3)CH2CH3). 13C NMR (benzene-d6): 8 = 112.50 (CsHs), 62.86 (CH(CH3)CH2CH3), 33.46 CH(CH3)CH2CH3), 22.74 (CH(CH3)CH2CH3), 15.74 (CH(CH3)CH2CH3). Addition of 1-Pentene to 9. In the dry box, a J. Young NMR tube was charged with 8.0 mg (0.031 mmol) of 3 and benzene-d6 added. On the vacuum line, the tube was degassed with three freeze-pump-thaw cycles. Via calibrated gas volume, 90 Torr (0.033 mmol) of cis-2-butene was added. The tube was sealed and the solution thawed. The tube was rotated for until all solid had dissolved (~3 hours). The NMR spectrum was recorded to verify the disappearance of starting materials. The tube was again placed on the vacuum line and via calibrated gas volume, 90 Torr (0.033 mmol) of 1-pentene was added. The solution was thawed and the tube shaken. 1H NMR spectra were then recorded in several intervals over the course of 24 hours. Preparation of 1-13C-2-heptyne. In the dry box, a 100 mL round bottom flask equipped with stir bar was charged with 2.00 g (22.7 mmol) [Li][C=CCH2CH2CH2CH3] and a 180° needle valve was attached. On the vacuum line, the flask assembly was evacuated and ~30 mL ammonia was condensed onto the white solid at -78 °C. Against an Ar counterflow, 3.18 g (22.7 mmol) 13CH3I was added via syringe with stirring. The reaction mixture was warmed to -50 °C and the clear, colorless solution was stirred forming a white precipitate. The reaction was stirred for 2 hours after which time the reaction was warmed to O °C and the NH3 allowed to escape via an oil bubbler. In air, 10 145 mL of water was added and the organic layer collected. Clear organic layer was dried over MgSO4, followed by CaH2. Product was identified as 1-13C-2-heptyne by comparison to the 1H and 13C NMR spectra of the authentic material. Yield 1.80 g (82.5 %). Preparation of 1-13C-cis-2-heptene. In the dry box, a 100 mL round bottom flask equipped with stir bar was charged with 3.67 g (14.5 mmol) of Cp 2Zr(H)(Cl) and a 180° needle valve was attached. On the vacuum line, approximately 25 mL of Et2O was added by vacuum transfer. Against an Ar counterflow at -80 °C, 1-13C-2-heptyne was added via syringe. The reaction was warmed to room temperature and stirred for 2 days. With time, the white suspension turned into a cloudy yellow solution. The reaction was quenched at O °C by addition of 10 mL H 2O. An additional 50 mL of water was added and the organic layer collected and dried over MgSO4. Ether was removed by atmospheric distillation. The clear, colorless liquid product was then distilled from CaH2 and then vacuum transferred from LiAlH4 . Yield: 0.340 g (24%). The product was characterized by comparison of the 1H and 13C NMR spectra with authentic samples. Reaction of 3 with 1-13 C-cis-2-heptene. In the dry box, a screw-capped NMR tube was charged with 10.0 mg (0.0394 mmol) of 3 and benzene-d6 added. To the tube, 45 µL of a 1.0 M stock solution of 1-13C-cis-2-heptene in benzene-d6 was added. The tube was shaken and placed in the NMR probe. Spectra were recorded over the course of 44 hours. Hydrozirconation of cis-2-butene and cis-2-heptene: CH30D Quench. In the dry box, a J. Young NMR tube was charged ~25 mg of 3, and C 6H 6 and 10 µL of benzene-d6 added. On the vacuum line, the solution was frozen in liquid nitrogen and the tube evacuated. Via calibrated gas volume, olefin was added to the tube at -196 °C. The solution was frozen and rotated continuously at room temperature for the 12 hours. The solution was then frozen in liquid nitrogen and 20 µL of CH3OD was added via microsyringe. The tube was capped, thawed and shaken. The yellow solution turns clear with formation of white precipitate. The {l H}2H NMR spectrum was then recorded and the amount of internally deuterated alkane versus terminally deuterated alkane was determined by integration. 146 Hydrozirconation of cis-2-heptene - CH30D Quench: Identification of Internal Heptanes. An identical procedure to that described above was followed except that after one hour, the reaction mixture was passed through a syringe filter in the dry box to remove any unreacted 3. The clear yellow solution was frozen at-196 °C, CH3OD added and the tube was capped, thawed and shaken and the {1H} 2H NMR spectrum was recorded. Structure Determination for 8. A suitable fragment was cut from a single crystal of 8, attached to a glass fiber and centered on an Enraf-Nonius CAD-4 diffractometer under an 85 K stream of N 2 gas. Unit cell parameters were obtained from the setting angles of 25 high angle reflections. Two equivalent data sets were collected and merged in P2 12121. Three reference reflections were measured every 75 minutes to monitor crystal decay. The structure was solved using direct methods and the difference Fourier maps were used to locate all missing atoms, including hydrogens. 5917 data were refined to R = 0.0287 (GOF = 1.78). Acknowledgments. This work has been supported by USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431) and Exxon Chemicals America. Supplementary Information Available: ORTEP drawings showing the complete atom labeling schemes, cell and crystal packing diagrams, tables of atomic coordinates, complete bond distances and angles and anisotropic diplacement parameters for 8. 30 See any masthead page for ordering or Internet access instructions. References. * The work in this chapter has been published previously. See Chirik, P.J.; Day, M.W.; Labinger, J.A.; Bercaw, J.E. J. Am. Chem. Soc. 1999, 121, 10308. 147 1. Collman, J.P.; Hegedus, L.S.; Norton, J.R.; Finke, R.G. Principles and Applications of Organotransition Metal Complexes: University Science Books, Mill Valley, CA, 1987. 2. For a recent example of phosphine ligand effects on rhodium-catalyzed hydroformylation see: Casey, C.P.; Paulsen, E.L.; Beuttenmueller, E.W.; Proft, B.R.; Matter,. B.A.; Powell, D.R. J. Am. Chem. Soc. 1999, 121, 63. 3. (a) Hart, D.W.; Schwartz, J. J. Am. Chem. Soc. 1974, 96, 8115. (b) Schwartz, J.; Labinger, J.A. Angew. Chem. Int. Ed. Engl. 1976, 15, 333. 4. (a) Negishi, E.; Takahashi, T. Synthesis 1988, 1. (b) Wipf, P.; Takahashi, H.; Zhuang, N. Pure and Appl. Chem. 1998 70, 1077. (c) Labinger, J.A. In Comprehensive Organic Synthesis. Trost, B.M.; Fleming, I. Eds. Pergamon Press, Oxford (1991), Chapter 3.9. 5. Brintzinger, H.H.; Fischer, D.; Miilhaupt, R.; Reiger, B.; Waymouth, R.M. Agnew. Chem. Int. Ed. Engl. 1995, 34, 1143. 6. (a) Busico, V.; Cipullo, R. J. Am. Chem. Soc. 1994, 116, 9329. (b) LeClerc, M.; Brintzinger, H.H. J. Am. Chem. Soc. 1995, 117, 1651. (c) Busico, V.; Caporaso, L.; Cipullo, R.; Landriani, L.; Angelini, G.; Margonelli, A.; Segre, A.L. J. Am. Chem. Soc. 1996, 118, 2105. 7. Busico, V.; Cipullo, R.; Chadwick, J.C.; Modder, J.F.; Sudmeijer, 0. Macromolecules 1994, 27, 7538. 8. Chirik, P.J.; Day, M.W.; Bercaw, J.E. Organometallics, 1999, 18, 1873. 148 9. Chapter 3. 10. Exchange between the hydride ligand and the coordinated alkyl is also observed, producing complexes with two deuterium labels in the isobutyl group and hydrogen on zirconium. 11. McAlister, D.R.; Erwin, D.K.; Bercaw, J.E. J. Am. Chem. Soc. 1978, 100, 5966. 12. Buchwald, S.J.; LaMaire, S.J.; Nielson, R.B.; Watson, B.T.; King, S.M. Tetrahedron.Lett. 1987, 28, 3895. 13. (a) Nelson, J.E.; Bercaw, J.E.; Labinger, J.A. Organometallics 1989, 8, 2404. (b) Erker, G.; Kropp, K.; Atwood, J.L.; Hunter, W.E. Organometallics 1983, 2, 1555. (c) Gibson, T. Organometallics 1987, 6,918. 14. Jordan, R.F.; Bajgur, C.S.; Dasher, W.E.; Rheingold, A.L. Organometallics 1987, 6, 1041. 15. A small amount of Cp2Zr{ (CH(CH3)(CH2)4 13CH3}(Cl) may be formed during the isomerization reaction, but we are unable to detect such a species due to overlapping 13C NMR resonances (see Figure 4). 16. Burger, B.J.; Thompson, M.E.; Cotter, W.D.; Bercaw, J.E. J. Am. Chem. Soc. 1990, 112, 1566. 17. This complex slowly decomposes in solution over the course of several days at room temperature. Access to Zr(II)-derived compounds from dialkyl zirconocenes has been noted previously. See, for example, 149 Negishi, E.I.; Montchamp, J.L. in Metallocenes, Vol. 1; Togni A.; Halterman, R.L., Eds.; VCH: Weinheim, 1998, Chapter 5. 18. Lauher, J.W.; Hoffman, R. J. Am. Chem. Soc. 1976, 98, 1729. 19 Current studies are underway to measure the rates of isomerization in related alkyl zir.conocene cations. Wendt, O.F.; Bercaw, J.E., unpublished results. 20. Gell, K. I.; Posin, B.; Schartz, J.; Williams, G. M. J. Am. Chem. Soc. 1982, 104, 1840. 21. Negishi, E.; Miller, J.A.; Yoshida, T. Tetrahedron Lett. 1984, 25, 3407. 22. Annby, U.; Alvha.11, J.; Gronowitz, S.; Hallberg, A. J. Organomet. Chem. 1989, 377, 75. 23. Secondary alkyls have been observed for styrene and other related aryl substrates: see reference 13a. 24. Relative rates of isomerization suggest that a detectable amount of 13-d2 should form during isomerization to 8-d2 . To date, we have been unable 2 1 to detect such an intermediate by H{ H} NMR. 25. Molecular mechanics calcuations (MM2 level) were performed using CAChe molecular modeling software using the structural parameters obtained from the solid state structure of 11. 150 26. Burger, B.J.; Bercaw, J.E. In Experimental Organometallic Chemistry; ACS Symposium Series No. 357; Wayda, A.L.; Darensbourg, M.Y. Eds.; American Chemical Society: Washington, DC 1987; Chapter 4. 27. Marvich, R.H.; Brintzinger, H.H. J. Am. Chem. Soc. 1971, 93, 2046. 28. Schock, L.E.; Marks, T.J. J. Am. Chem. Soc. 1988, 110, 7701. 29. Moore, J.W.; Pearson, R.G. Kinetics and Mechanism, 3rd Ed; John Wiley & Sons, New York (1981) p. 307. 30. Crystallographic data have been deposited at CCDC, 12 Union Road, Cambridge CB2 lEZ, UK, and copies can be obtained on request free of charge, by quoting the publication citation and the deposition number 114941. 151 Chapter 5 Kinetic Isotope Effects for P-Methyl Elimination. Experimental Observation·of y-Agostic Interactions during the Ziegler-Natta Polymerization of Olefins. 152 Abstract Preparation of isotopically labeled zirconocene-neopentyl methyl complexes of the general formula, (CpRnhZr(CH3)(CH2C(CH3)2CD3) (CpRn = alkyl substituted cyclopentadienyl), has been accomplished via salt metathesis of d3-LiCH2C(CH3)2CD3 with (CpRnhZr(CH3)(Cl). Addition of B(C6Fs)3 to (CpRnhZr(CH3)(CH2C(CH3)zCD3) results in P-methyl elimination forming the ion-pair species, [(CpRnhZrMe][MeB(C6Fs)3], along with isotopomers of isobutene. Comparison of the relative amounts of d3 to do-isobutene affords the kinetic isotope effect for P-methyl elimination. For Cp2Zr(CH3)(CH2C(CH3)zCD3), a kinetic isotope effect of 1.40(2) has been measured at 296 K. Normal secondary kinetic isotope effects have been observed for a total of five metallocenes and the magnitude of these effects is essentially invariant with ligand array. These effects are indicative of y-agostic assistance in the transition state for P-methyl elimination. 153 Introduction Agostic interactions,1 whereby a C-H sigma bond forms a three-center, two electron covalent bond to a transition metal center are now ubiquitous in organometallic chemistry and have been identified in many catalytic reactions.2 In metallocene-catalyzed olefin polymerization, agostic interactions are believed to play a central role in lowering the activation barriers for olefin insertion3 as well as increp.sing degrees of stereospecificity. 4 Experimental observation of aagostic interactions during olefin insertion into a metal carbon bond (Figure 1) was first achieved using isotopic perturbation of stereochemistry5 during the catalytic hydrocyclization of trans-deuterated a, ro--dienes with scandocene and yttrocene catalysts.6,7 More recent studies by Brintzinger have identified aagostic interactions during the hydrodimerization of deuterated 1-hexene8 as well as during the polymerization of (E) and (Z)-propene-d1 with ansazirconocene catalysts. 9 The ~-agostic ground state structure has been identified in a number of group 310 and group 4 metallocenes and is believed to be the catalyst resting state during polymerization. 11 M~ R M~R H H a-agostic ~-agostic :~ R H y-agostic Figure 1. Types of agostic interactions. In addition to these interactions, y-agostic structures have also been proposed in several Ziegler-Natta polymerization systems. Theoretical studies have identified y-agostic alkyls as kinetic products following olefin insertion12 as well as possible resting states for the active species.1 3 Experimental observation of y-agostic interactions has been achieved in the solid state structures of Cp*2YCH(SiMe3)2 (Cp* = C5Me5), Cp*2YN(SiMe3)2,14 and RuCl2(PPh3)(N(SiMe3)C(Ph)(NH(PPh2))) 15 and by NMR chemical shifts in tantalum carborane complexes. 16 154 P-Methyl elimination (eq. 1) is well suited for experimental detection of y- agostic interactions, being the microscopic reverse of olefin insertion into a metal methyl bond and as a result must access the same transition state. Chain termination by P-methyl elimination has been identified in several olefin polymerization systems17 and has also been observed in organoscandium complexes. 18 Horton has described the preparation of [(CpRnhZr(CH2CMe3)][CH3B(C6Fs)3] (CpRn = CsHs, CsMes) which undergoes P-methyl elimination resulting in formation of isobutene and [(CpRnhZr(Me)][MeB(C6fs)3].1 9 Due to their utility in olefin polymerization,20 we felt that isotopic modification of the complexes originally described by Horton would be a logical choice to identify y-agostic interactions in metallocene polymerization catalysts. /CH3 Cp2M + Me \c--Me isobutene insertion ► (1) -•-- c-r H~ H Results and Discussion The strategy employed for the synthesis of isotopically labeled zirconocene neopentyl methyl complexes involved initial preparation of the zirconocene methyl chloride complexes followed by salt metathesis with labeled neopentyl lithium affording the desired zirconocene methyl neopentyl complex. Preparation of Cp2Zr(CH3)(Cl) has been accomplished according to literature procedures21 whereas Cp*2Zr(CH3)(Cl), Cp*(C5Me4)Zr(CH3)(Cl), rac(EBl)Zr(CH3)(Cl) and ThpZr(CH3)(Cl) were prepared via slow addition of one equivalent of HCl to the corresponding dimethyl complex (eq. 2). 22 155 1 HCl (2) Preparation of LiCH2C(CH3)2CD3 proceeded via alkylation of ethyl isobutyrate with CD3I followed by reduction of the ester to the alcohol via addition of lithium aluminum hydride (eq. 3). Conversion of CD3(CH3)2CCH20H to the bromide was accomplished with addition of Ph3PBr2 which is formed in situ by addition of Br2 to triphenylphosphine. Lithiumhalogen exchange in refluxing petroleum ether affords LiCH2C(CH3)2CD3 in modest yield. Addition of LiCH2C(CH3)2CD3 to the zirconocene methylchloride complexes affords the desired dialkyl complexes. In this manner, Cp2Zr(CH2C(CH3)2CD3)(Me) (1), Cp*2Zr(CH2C(CH3)2CD3)(Me) (2), Cp*(CsMe4H)Zr(CH2C(CH3)2CD3)(Me) (3), rac-(EBI)Zr(CH2C(CH3)2CD3)(Me) (4) and ThpZr(CH2C(CH3)2CD3)(Me) (5) have been prepared in >95% isotopic purity. 22 l.LDA 2.CDJ 3. LiAlH 4 4. Br2, PPh3 5. Li Slow cooling of a diethyl ether solution of 1 affords_yellow columns that are suitable for X-ray diffraction. The molecular structure of 1 is shown in Figure 2 and displays a commonly observed coordination mode for zirconocenes. All of the hydrogen atoms have been located in the difference map and have been refined. No ground state y-agostic interactions are observed since the closest zirconium-y-hydrogen distance found in 1 is 3.774 A. 156 Figure 2. Molecular structure of Cp2Zr(CH2CMe3)(CH3) (1) with 50% probability ellipsoids. Selected bond lengths (A): Zr-Cent(l), 2.232; Zr-Cent(2), 2.234; Zr-C(ll), 2.2980(13); Zr-C(12), 2.2719(12). Bond angles (deg): Cent(l)-Zr-Cent(2), 130.6; C(ll)-Zr-C(12), 94.99. Cent(l) is the centroid formed by C(l), C(2), C(3), C(4) and C(S). Cent(2) is the centroid formed by C(6), C(7), C(8), C(9) and C(lO). %- %- %- Total % isobutene- isobutene- isobutene- Conversion do d3 d6 Isobutene (mmol) 2.0 26.7 73.3 < 0.1 2.48 10.0 26.1 73.9 18.0 26.0 26.1 26.2 73.9 <0.1 < 0.1 1.60 X 10-3 1.93 X 10-2 48.6 45.0 27.2 72.5 < 0.1 0.2 3.14 X 10-2 4.10 X 10-2 120.0 33.8 64.4 1.8 4.94 X 10-2 5.14 X 10-2 76.6 79.7 Time (min) 73.8 Table 1. Distribution of isotopomers for the ~-methyl elimination for 1 at 296 K. 29.9 63.6 157 Reaction of 1 with B(C6Fs)3 results in P-methyl elimination initially forming d3 and do-isobutene along with [Cp2ZrMe][MeB(C6Fs)3]. Monitoring the headspace of the reaction by GC / MS allows for quantification of each of the isotopomers produced. Control experiments determining the detector response to different isotopomers of isobutene have been performed. Plots of detector response versus concentration of do and ds-isobutene ranging from 0.5 M to 2.0 M have been constructed in order to determine the isotope effect, if any, on fragmentation. The detector response for do-isobutene (slope = 416 response / M.; R2 = 0.992) is almost identical to that for the ds isotopomer (slope =410 response / M; R? = 0.989). At early reaction times during the P-methyl elimination of 1, only do- and d3-isobutene are detected, but as the reaction progresses d6-isobutene gradually appears (Table 1). Competing reactions such as allylic activation of the isobutene by [Cp2ZrCH3][MeB(C6Fs)3] at longer reaction times complicates the observed values of the kinetic isotope effect (Figure 3).1 9 Likewise, competing insertion of d3-isobutene into [Cp2ZrCD3][MeB(C6Fs)3] followed by P-methyl elimination accounts for formation of the d6 isotopomer (Figure 4). As a result, all kinetic isotope effects reported are from early conversion where the reaction is devoid of these competing processes. Figure 3. Allylic activation of isobutene by zirconocene methyl cations forming zirconocene crotyl complexes. 158 -1- -1- Figure 4. Reversible ~-methyl elimination and olefin insertion to form d6-isobutene. For 1, a normal, secondary kinetic isotope effect (ktt / ko) of 1.40(2) is observed at 296 K. A normal isotope effect is consistent with a transition state y-agostic interaction during C-C bond breaking. Moreover, this transition state effect is consistent with the a-agostic transition state observed for olefin insertion.6 If the y-agostic interaction were to occur primarily in the ground state, an inverse kinetic isotope effect would be expected due to the relative stability of the C-H agostic methyl group versus the C-D fragment. 26 However, a normal secondary isotope effect is not s·ufficient to rule out rapid interconversion between C-H and C-D ground state structures. However, the lack of a substantial ground state interaction is consistent with strong ion-pair formation observed previously by Horton based on 19F NMR chemical shifts.19 It should also be noted that similar, normal secondary hyperconjugative isotope effects have been observed in carbonium ion rearrangements. 23 The effect of temperature on the kinetic isotope effects during the Pmethyl elimination reaction has been studied with 1. As the temperature is raised, the value of the isotope effect decreases. At 5 °C, a ktt / ko = 1.49(6) has been measured whereas at 35 °C, a ktt / ko = 1.35(3) is observed. The 159 temperature dependence of the isotope effect is consistent with a transition state y-agostic interaction.23 Reaction of 2-5 with B(C6Fs)3 also results in ~-methyl elimination and formation of do and d3-isoputene. As with 1, normal kinetic isotope effects are observed at 296 K (Table 2) and at early reaction times. For 1-4, the value of the kinetic isotope effect is essentially invariant with catalyst structure. However, for the doubly-silylene linked 5, a smaller kinetic isotope effect of 1.28(6) is observed. In all cases, d6 -isobutene is observed at longer reaction times indicative of reversible olefin insertion (Figure 3). Complex kHlko (296 K) [Cp2Zr(d3-Np) ][MeB(C6Fs)3] [Cp*(C5Me4H)Zr(d3-Np) ][MeB(C6Fs)3] [Cp*2Zr(d3-Np )][MeB(C6Fs)3] rac-(EBl)Zr(d3-Np)] [MeB(C6Fs)3] THPZr(d3-Np )][MeB(C6Fs)3] 1.40(2) 1.38(2) 1.43(5) 1.49(4) 1.28(6) Table 2. Kinetic isotope effects for ~-methyl elimination with a series of zirconocene catalysts. Con cl us ions In summary, the first experimental observation of a y-agostic interaction has been achieved during the ~-methyl elimination of isotopically labeled isobutene from zirconocene neopentyl cations. From the magnitude of these effects, it appears that these interactions occur primarily in the transition state and are essentially independent of ancillary ligation. Since ~-methyl elimination is the microscopic reverse of olefin insertion, the observed isotope effects are consistent with previous studies that have identified a-agostic interactions in the transition state for olefin insertion. 160 Experimental General Considerations. All air- and moisture-sensitive compounds were manipulated using standard vacuum line, Schlenk, or cannula techniques or in a drybox under a nitrogen atmosphere as described previously. 24 Argon, dinitrogen, dihydrogen, and dideuterium gases were purified over columns of MnO on vermiculite and activated molecular sieves. Solvents for air- and moisture-sensitive reactions were stored under vacuum over titanocene. Benzene-d6 and toluene-ds were purchased from Cambridge Isotope Laboratories. Both solvents were dried over LiAlH4 and sodium and then stored over titanocene. Ethylisobutyrate, lithium diispropylamide and bromine were purchased from Aldrich and used as received. Anhydrous hydrochloric acid was purchased from Aldrich and was subject to three freeze-pump-thaw cycles at -196 °C before use. Lithium turnings were purchased from Strem and stored under argon. Preparation of ds-isobutene was accomplished via dehydration of (CD3)3COD (Cambridge) with phosphoric acid. Preparation of (EBI)ZrMe2,25 Cp2Zr(Me)(Cl),21 Cp*2ZrMe2, Cp*(C5Me4H)ZrMe2,26 THPZrMe227 were prepared as described previously. NMR spectra were recorded on Bruker AM500 (500.13 MHz for 1H, 76.77 for 2H, 125.77 MHz for l3C), JEOL Delta 400 or Varian Inova 500 spectrometers. All lH, 2H and 13C NMR chemical shifts are relative to TMS using lH (residual), 2H or 13C chemical shifts of the solvent as a secondary standard. Elemental analyses were carried out at the Caltech Elemental Analysis Facility by Fenton Harvey. GC-MS isotopic analyses were performed on a Hewlett-Packard 5972 mass spectrometer (Hewlett Packard Co., Palo Alto, California) equipped with a Hewlett Packard model 5980 Series II gas chromatograph. Separations were achieved on a 100% dimethylpolysiloxane capillary column (60 m, 0.32 mm i.d., 5 m film thickness; Rtx®-1 Crossbond, Restek Corporation, Bellefonte, PA). Electronic pressure control was used to maintain a constant column flow of 2 mL/ min. Injections were performed in split mode with a 30:1 split ratio. The column temperature was programmed from 110 °C (2 min hold) to 185 °C at 25 161 °C/min and then to 230 °Cat 50 °C/min for 2 minutes. The second ramp was to clear benzene or toluene from the column. The mass spectrometer was operated in the electron-impact mode with an electron energy of 70 eV at 15 Amperes emission current. The electron multiplier was operated at 2012 volts. The quadrapole was scanned from 100 to 15 m/ z at a rate of 7.85 times per second. The detector response to the isotopomers of isobutene was calibrated by making stock solutions of do and dsisobutene and determining their reponse over a concentration range of 0.5 M to 2.0 M and was found to be identical for both isotopomers. Furthermore, solutions of pure-do and d3-isobutene were mixed and found to have additive responses. Determination of the amounts of do (56 amu), d3 (59 amu) and d6 (62 amu) isobutene were integrated relative to an internal pentane standard (43 amu). Preparation of Ethyl-d3-2,2-Dimethylbutyrate. In the dry box, a three necked round bottom flask equipped with a magnetic stir bar was charged with 11.3 g (0.105 mol) of lithium diisopropylamide. A reflux condensor, inlet valve and an addition funnel were attached to the flask. On the Schlenk line, the flask assembly was purged with Ar for 10 minutes. Approximately 200 mL of THF was added via cannula forming a brown solution. The addition funnel was charged with 12.0 g (0.103 mol) of ethylisobutyrate and 10 mL of THF. The solution of ester was added slowly to the reaction mixture at -78 °Cover the course of 10 minutes. The reaction mixture was stirred at -78 °C for one hour. Into the addition funnel, 14.9 g (0.105 mmol) of CD3I was charged along with 10 mL of THF. The solution was dripped into the reaction mixture over the course of 15 minutes. The reaction mixture was maintained at -78 °C for an additional 30 minutes and then warmed to room temperature and stirred for 8 hours. With time, a milky yellow /white reaction mixture forms. The reaction mixture was poured into 500 mL of brine and the organic layer was collected. The aqueous layer was washed with three 50 mL portions of ether and the organic layers were combined and dried over MgSO4. The ether solution was filtered and the solvent was removed via rotovap. The clear, colorless liquid was distilled at 135 °C and atmospheric pressure yielding 7.03 g (52.4%) of product. The product was identified as d3- ethyl-2,2-dimethylbutyrate by comparison of the 1H and 13C NMR spectra of an authentic sample. 162 Preparation of d3-Neopentyl Alcohol. A three necked, 500 mL round bottom flask equipped with magnetic stir bar was charged with 3.00 g (79 .0 mmol) LiAll-4 and a reflux condensor, addition funnel and a gas inlet were attached. On the Schlenk line, the assembly was purged with Ar for approximately 20 minutes. Via cannula, approximately 200 mL of Et2O was added. Into the addition funnel, 5.50 g (42 mmol) of d3- ethyl-2,2-dimethylbutyrate was charged along with 50 mL of Et2O. The ester solution was slowly dripped into the LiAlfi4 slurry over the course of 30 minutes. The reaction mixture was stirred overnight. The reaction was quenched via slow and careful addition of 3.0 mL of H2O, followed by 15 mL of 15% NaOH and then finally 3 mL of H2O. The organic layer was collected by filtration and was washed three times with H2O. The organic layer was dried over Na2SO4 and the solvent removed by rotovap leaving a clear liquid. The product was purified by atmospheric distillation at 56 °C, yielding 3.40 g (89%) of d3-neopentyl alcohol. The product was identified as d3-neopentyl alcohol by comparison of 1H and 13C NMR spectra with an authentic sample of (CH3)3CCH2OH. Preparation of d3-Neopentyl Bromide. An argon purged 250 mL three necked flask equipped with magnetic stir bar was charged with 9.42 g (35.9 mmol) of PPh3. Approximately 100 mL of dimethylformamide was added by cannula. The flask was cooled to O°C and 5.7 g (35.6 mmol) of Br2 was added slowly via syringe. A white cloudy reaction mixture forms. The reaction mixture was warmed to room temperature and stirred for 30 minutes. Via syringe, a 50 mL solution of 3.00 g (32.9 mmol) of d3-NpOH was added. With addition of alcohol, the solid dissolves forming a yellow solution. The reaction was stirred at room temperature for 16 hours. A distillation head was then attached to the flask and the product was distilled out of the reaction mixture at 150 °C and atmospheric pressure. The product was washed with water three times and dried over Na2SO4 yielding 1.75 g (34.5%) of a clear liquid identified as d3-NpBr by comparison to an authentic sample of (CH3)3CCH2Br. Preparation of d3-NpLi. A 100 mL flask equipped with stir bar was charged with fresh lithium turnings. Via cannula, approximately 50 mL of petroleum ether was added. Against an argon counterflow, 1.50 g (9.74 mmol) d3-NpBr was added via syringe. The reaction mixture was refluxed for one week after which 163 time a milky white slurry formed. The flask was transferred onto a swivel frit assembly and filtered. The petroleum ether was removed in vacuo leaving 0.650 g (82.3 %) of a white powder identified as d3-NpLi based on comparison to an authentic sample of (CH3)3CCH2Li. Preparation of Cp2Zr(d3-Np)(CH3) (1). In the dry box, a 25 mL round bottom flask was charged with 0.466 g (1.71 mmol) of Cp2Zr(CH3)(Cl) and 0.139 g (1.71 mmol) of d3-NpLi and attached to a swivel frit assembly. On the vacuum line, approximately 10 mL of Et2O was added by vacuum transfer. The orange reaction mixture was warmed to room temperature and stirred for 16 hours. The white precipitate was removed by filtration and washed three times with Et2O. The solvent was removed in vacuo leaving an orange oily soild. The oily solid was recrystallized from cold petroleum ether yielding 0.400 g (75.3%) of a yellow powder identified as 1 based on comparision to literature data. 2H{lH} NMR: <> = 1.02 ppm. Preparation of Cp*(C5Me4H)Zr(CH3)(CI). In the dry box, a 25 mL round bottom flask equipped with stir bar was charged with 0.290 g (0.767 mmol) of Cp*(C5Me4H)ZrMe2 and attached to a 43.48 mL calibrated gas volume. On the vacuum line, approximately 10 mL of petroleum ether was added by vacuum transfer. The gas bulb was charged with 330 torr (0.767 mmol) of anhydrous HCL The HCl was added to the solution at room temperature. The reaction mixture was stirred for 13 hours over which time a white precipitate forms. The flask was tranferred onto a swivel frit and the white solid collected by filtration and washed with petroleum ether. Solid dried in vacuo leaving 0.200 g (65.4%) of Cp*(C5Me4H)Zr(CH3)(Cl). 1H NMR (benzene-d6) 8 = 1.81 (s, 15H, CsMes), 2.10 (s, 3H, CsAfe4H), 1.92 (s, 3H, CsAfe4H), 1.76 (s, 3H, CsAfe4H), 1.45 (s, 3H, CsAfe4H), 4.73 (s, 3H, C5Me4ffl, -0.02 (s, 3H, ZrMe) . 13C NMR (benzene-d6) 12.39 (CsMes), 12.04, 12.11, 12.72, 12.82 (C5Me4H), 107.46 (C5Me5), 106.45, 105.59, 119.81 (C5Me4H), 2 peaks not located, 38.06 (ZrMe). Anal. Calcd. for Zri C20H31 Cli: C, 60.34 H, 7.85. Found C, 60.72 H, 8.29. Preparation of Cp*2Zr(Me)(Cl). In the dry box, a 50 mL flask was charged with 0.740 g (1.89 mmol) of Cp*2ZrMe2 and attached to a calibrated gas volume. On the vacuum line, approximately 25 mL of petroleum ether was added by vacuum transfer forming a clear solution. The 104 mL bulb was charged with 340 torr 164 (1.90 mmol) of anhydrous HCl. The gas was added to the flask at room temperature and the reaction stirred for 3 days over which time a white precipitate formed. Flask transferred onto a swivel frit assembly and the solid collected by filtration and washed with petroleum ether. The solid was dried in vacuo affording 0.450 g (58%) of Cp*2Zr(CH3)Cl. 1H NMR (benzene-d6) o= 1.80 (s, 30H, CsMes), 0.00 (s, 3H, ZrMe). Anal. Calcd. for ZriC21H33Cli: C, 61.20 H, 8.07. Found C, 60.94 H, 8.15. Preparation of Cp*2Zr(d3-Np)(CH3) (2). In the dry box a 25 mL round bottom flask was charged with 0.200 g (.485 mmol) of Cp*2Zr(Me)Cl and 0.039 (0.485 rnrnol) d3-NpLi. The flask was then attached to a fine swivel frit assembly. On the vacuum line, toluene was added by vacuum transfer. The reaction was warmed to room temperature and stirred for 2 days. The solvent was removed in vacuo and the resulting yellow solid was extracted with petroleum ether. The solid was recrystallized from petroleum ether at -80 °C affording 0.110 g (50.4%) identified as Cp*2Zr(d3-Np)(CH3) based on literature data.1 9 2H NMR (benzene): 1.09 ppm. Preparation of Cp*(C5Me4H)Zr(d3-Np)(CH3) (3). In the dry box, a 25 mL flask was charged with 0.140 g (0.351 mrnol) of Cp*(C5Me4H)Zr(Me)(Cl) and 0.028 g (0.351 mmol) of d3-NpLi. The flask was attached to a fine swivel frit assembly. On the vacuum line, approximately 10 mL of toluene was added by vacuum transfer. The reaction was warmed to room temperature and stirred for 3 days over which time a yellow solution and white precipitate formed. The toluene was removed in vacuo and petroleum ether added by vacuum transfer. The white precipitate was removed by filtration and the solvent removed in vacuo leaving a yellow oil. Attempts to crystallize the oil by slow cooling of ether or petroleum ether solution were not successful. 1H NMR (benzene-d6) o= 1.80 (s, 15H, Cp*), 2.15 (s, 3H, CsMe4H), 2.09 (s, 3H, C5Me4H), 1.98 (s, 3H, CsMe4H), 1.85 (s, 3H, CsAfe4H), 4.60 (s, 3H, CsMe,¥1), 1.12 (s, 6H, ZrCH2C(CH3)2(CD3)), 0.21 (d, lH, 10 Hz, ZrCH2C(CH3)2(CD3); -0.02 (d, lH, 10 Hz, ZrCH2C(CH3)2(CD3), -0.37 (s, 3H, ZrMe). 2H NMR (benzene) o= 1.10. Isolation as an oil prevented elemental analysis. Preparation of rac-(EBI)Zr(d3-Np)(CH3) (4). In the dry box, a 25 mL round bottom flask was charged with 0.150 g (0.376 mmol) of rac-(EBI)Zr(Me)(Cl) and 165 0.031 g (0.376 mmol) of d3-NpLi. The flask was attached to a medium swivel frit assembly. On the vacuum line, approximately 10 mL of Et2O was added by vacuum transfer and warmed to room temperature. The reaction was stirred for 24 hours over which time an orange solution and white precipitate formed. The white solid was removed by filtration and the solvent removed in vacuo leaving an orange solid. The solid was dried in vacuo affording 0.080 g (49.0%). lH NMR (benzene-d6) 3 = -1.98 (d, 6 Hz, lH, CH2C(CH3)2CD3); -0.02 (d, 6 Hz, lH, CH2C(CH3)2CD3); -0.95 (s, 3H, ZrCH3); 0.87 (s, 6H, ZrCH2C(CH3)2CD3); 2.65 (m, 2H, CH2CH2, EBI); 2.82 (m, 2H, CH2CH2, EBI); 5.55 (m, lH, Cp, EBI); 5.63 (m, lH, Cp, EBI); 5.76 (m, lH, Cp, EBI); 6.40 (m, lH, Cp, EBI); 6.8-7.4 (m, benzo, EBI). 2H NMR (benzene) 3 = 0.85 (ZrCH2C(CH3)2CD3). Anal. Calcd. for ZriC26H30D3Cl1: C, 66.13 H, 7.04. Found C, 65.73 H, 7.26. Preparation of ThpZr(CH3)(Cl). In the dry box, a 25 mL round bottom flask was charged with 0.330 g (.735 mmol) of ThpZrMe2 and the flask attached to a 43.48 mL calibrated gas volume. On the vacuum line, petroleum ether was added by vacuum transfer and the solution warmed to room temperature. The gas bulb was charged with 314 torr (0.735 mmol) of anhydrous HCL The HCl was added at room temperature and the reaction stirred for 3 days over which time a white solid precipitated from solution. The precipitate was collected by filtration and washed with cold ether. The solid was dried in vacuo affording 0.280 g (82%) of a white solid identified as ThpZr(Me)(Cl). 1H NMR (benzene-d6) 3 = 0.348 (s, 3H, Me2Si); 0.549 (s, 3H, Me2Si); 0.791 (s, 3H, Me2Si); 0.814 (s, 3H, Me2Si); 0.161 (s, 3H, ZrMe); 0.840 (d, 7 Hz, 3H, CHMe2); 1.10 (d, 7 Hz, 3H, CHMe2); 1.24 (d, 7 Hz, 3H, CHMe2); 1.39 (d, 7 Hz, 3H, CHMe2); 2.61 (sept, 7 Hz, lH, CHMe2); 2.91 (sept, 7 Hz, lH, CHMe2); 6.31 (m, lH, Cp ); 6.40 (m, lH, Cp ), 6.59 (m, lH, Cp ); 6.69 (m, lH, Cp ). 13C (benzene-d6) 3 = -0.1865, -0.689, 3.59, 3.63 (Me2Si), 31.62 (ZrCH3), 28.82, 28.97, 29.38, 29.60 (CHMe2), 21.23, 21.00 (CHMe2), 104.41, 111.18, 112.27, 114.65, 116.71, 128.68, 132.21, 133.74, 157.27, 160.03 (Cp ). Anal. Calcd. for ZriC21H33Cl1Sii: C, 53.86 H, 7.10. Found C, 52.72 H, 7.49. Preparation of ThpZr(d3-Np)(CH3) (5). In the dry box, a 25 mL round bottom flask equipped with magnetic stir bar was charged with 0.200 g (0.426 mmol) of ThpZr(Me)(Cl) and 0.0345 g (0.426 rnrnol) of d3-NpLi. The flask was attached to a fine swivel frit and on the vacuum line 10 mL of Et2O was added by vacuum transfer. The reaction mixture was warmed to room temperature and stirred for 166 24 hours over which time a yellow solution and white precipitate formed. The precipitate was removed by filtration and washed with several portions of ether. The solvent was removed in vacuo leaving a dark.sticky solid. Recrystallization from cold petroleum ether afforded 0.120 g (51.5 %) of a white solid identified as ThpZr(d3-Np)(Me). 1H NMR (benzene-d6) 8 = 0.093 (s, 3H, Me2Si); 0.378 (s, 3H, Me2Si); 0.516 (s, 3H, Me2Si); 0.528 (s, 3H, Me2Si); 0.5750 (s, 6H, ZrCH2C(CH3)2CD3); 0.127 (s, 2H, ZrCH2C(CH3)2CD3); 0.944 (d, 7 Hz, 3H, CHMe2); 1.07 (d, 7 Hz, 3H, CHMe2); 1.25 (d, 7 Hz, 3H, CHMe2); 1.42 (d, 7 Hz, 3H, CHMe2), 2.62 (sept, 7 Hz, lH, CHMe2), 2.95 (sept, 7 Hz, lH, CHMe2), 6.34 (m, lH, Cp ); 6.45 (m, lH, Cp ); 6.63 (m, lH, Cp ); 6.72 (m, lH, Cp ). Anal. Calcd. for Zri C26Hi1D3Si2: C, 61.59 H, 9.34. Found C, 60.92 H, 9.29. General Procedure for Isotope Effect Measurements. In a typical experiment, 20.0 mg (0.0645 mmol) of 1 was dissolved in 2.0 mL of a stock solution of benzene containing 0.2% (by weight) of pentane. Similarly, 36.0 mg (0.0703 mmol) of B(C6Fs)3 was dissolved in 1.0 mL of stock benzene solution. In the dry box, the zirconium solution was charged into a 50 mL round bottom flask equipped with a side arm and a septum port. The side arm of the flask was charged with the solution of B(C6Fs)3. The flask was placed in a thermostated bath of ethylene glycol and equilibrated to the desired temperature. The B(C6Fs)3 solution was added to the rapidly stirred zirconium solution at which time a canary yellow solution formed. The reaction was monitored by withdrawing 100 µL of gas from the reaction vessel and injecting it into the GC / MS instrument. Structure Determination for 1. A section was cut from a yellow column and mounted on a glass fiber with Paratone-N oil. The data was collected on a Bruker Smart 1000 CCD diffractometer under a stream of N2 gas at 98 K. Three runs of data were collected with 20 second long, -0.20 ° wide ffi-scans at three values of<!> (0, 120 and 240°) with the detector 5 cm (nominal) distant at 0 of -28 °. The initial cell for data reduction was calculated for just under 1000 reflections chosen throughout the data frames. For data processing with SAINT v.602, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to zero, Laue class integration restraints were not used, the model profiles from all nine 167 areas were blended and for the post-integration global least squares refinement, no constraints were applied. The data were corrected with SADABS v. 2.0 (beta) using default parameters except that the scale factor esd was set to a minimum value of 0.001. On the three .raw files the g values converged to 0.0428. No decay correction was needed. The structure was solved using direct methods and the difference Fourier maps were used to locate all missing atoms, including hydrogens. No reflections were specifically omitted from the final processed dataset; 2095 reflections were rejected, with 33 space group-absence violations and 32 inconsistent reflections. Refinement of -F2 was against all reflections. A total of 3299 reflections were refined to R = 0.0219 (GOF = 2.581). References. 1. a) Brookhart, M.; Green, M.L.H. J. Organomet. Chem. 1983, 250,395. b) Brookhart, M.; Green, M.L.H.; Wong, L.L. Prag. Inorg. Chem. 1988, 36, 1. 2. Grubbs, R.H.; Coates, G.W. Acc. Chem. Res. 1996, 29, 85. 3. Prosenc, M.H.; Janiak, C.; Brintzinger, H.H. Organometallics 1992, 11, 4036. 4. Roll, W.; Brintzinger, H.H.; Rieger, B.; Zolk, R. Angew. Chem. Int. Ed. Engl. 1990, 29,279. 5. Clawson, L.; Soto, J.; Buchwald, S.L.; Steigerwald, M.L., Grubbs, R.H. J. Am. Chem. Soc. 1985, 107, 3377. 6. Piers, W.E.; Bercaw, J.E. J. Am. Chem. Soc. 1990, 112, 9406. 7. Burger, B.J.; Cotter, W.D.; Coughlin, E.B.; Chacon, S.T.; Hajela, S.; Herzog, T.; Kohn, R.; Mitchell, J.; Piers, W.E.; Shapiro, P.J.; Bercaw, J.E. In Ziegler Catalysts; Fink, G.; Miilhaupt, R.; Brintzinger, H.H., Eds.; Springer-Verlag: Berlin, 1995; pp. 317-331. 8. Krauledat, H.; Brintzinger, H.H. Agnew. Chem. Int. Ed. Engl. 1990, 29, 1412. 9. LeClerc, M.K.; Brintzinger, H.H. J. Am. Chem. Soc .. 1995, 117, 1651. 10. Burger, B.J.; Thompson, M.E.; Cotter, W.D.; Bercaw, J.E. J. Am. Chem. Soc. 1990, 112, 1566. 11. a) Guo, Z.; Swenson, D.C.; Jordan, R.F. Organometallics 1994, 13, 1424. b) Jordan, R.F.; Bradley, P.K.; Baenziger, N.C.; LaPointe, R.E. J. Am. Chem. Soc. 1990, 112, 1289. 168 12. a) Woo, T.K.; Fan, L.; Ziegler, T. Organometallics 1994, 13, 2252. b) Woo, T.K.; Fan, L.; Ziegler, T. Organometallics 1994, 13,432. c) Fan, L.; Harrison, D.; Woo, T.K.; Ziegler, T. Organometallics 1995, 14, 2018. d) Kawamura-Kuribayashi, H.; Koga, N.; Morokuma, K. J. Am. Chem. Soc. 1992, 114, 8687. e) KawamuraKuribayashi, H.; Koga, N.; Morokuma, K. J. Am. Chem. Soc. 1992, 114, 2359. f) Meier, R.J.; van Doremaele, G.H.J.; Iarlori, S.; Buda, F. J. Am. Chem. Soc. 1994, 116, 7274. g) Yu, Z.; Chien, J.C.W. J. Poly. Sci. Part A: Poly. Chem. 1995, 33, 1085. 13. a) Woo, T.K.; Margl, P.M.; Lohrenz, J.C.W.; Blochl, P.E.; Ziegler, T. J. Am. Chem. Soc. 1996, 118, 13021. b) Lohrenz, J.C.W.; Woo, T.K.; Ziegler, T. J. Am. Chem. Soc. 1995, 117, 12793. 14. den Haan, K.H.; de Boer, J.L.; Teuben, J.H.; Spek, A.L.; Kojic-Prodic, B.; Hays, G.R.; Huis, R. Organometallics 1986, 5, 1726. 15. Wong, W.K.; Jaing, T.; Wong, T.K. J. Chem. Soc. Dalton Trans. 1995, 3087. 16. Boring, E.; Sabat, M.; Finn, M.G.; Grimes, R.N. Organometallics 1998, 17, 3865. 17. Resconi, L.; Piemontesi, F.; Fraciscono, G.; Abis, L.; Fiorani, T. J. Am. Chem. Soc. 1992,114,362. 18. Hajela, S.H.; Bercaw, J.E. Organometallics 1994, 13, 1147. 19. Horton, A.D. Organometallics 1996, 15, 2675. 20. Brintzinger, H.H.; Fischer, D.; Miilhaupt, R.; Rieger, B.; Waymouth, R.M. Angew. Chem. Int. Ed. Engl. 1995, 34, 1143. 21. Surtees, J.R. J. Chem. Soc. Chem. Comm. 1965, 567. 22. EBI = ethylene-bis-indenyl; THP = (Me2Si)2('r1 5-CsH3)('r1 5-CsH-3,5-(CHMe2)2) 23. Isaacs, N.S. Physical Organic Chemistry, John Wiley and Sons: New York, 1986. 24. Burger, B.J.; Bercaw, J.E. In Experimental Organometallic Chemistry; ACS Symposium Series No. 357; Wayda, A.L.; Darensbourg, M.Y. Eds.; American Chemical Society: Washington, DC 1987; Chapter 4. 25. Kim, I.; Jordan, R.F. Macromolecules 1996, 26, 489. 26. Chirik, P.J.; Day, M.D.; Bercaw, J.E. Organometallics 1999, 18, 1873. 27. Veghini, D.; Day, M.D.; Bercaw, J.E. Inorg. Chem. Acta 1998, 280,226. 28. A ground state ~-agostic interaction has been used to explain the observed inverse kinetic isotope effect in the cobalt-catalyzed polymerization of ethylene. Tanner, M.J.; Brookhart, M.; Desimone, J.M. J. Am. Chem. Soc. 1997, 119, 7617. 169 Chapter 6 Preparation and Characterization of Ansa-Tantalocene Derivatives as Transition State Models for Metallocene Olefin Polymerization Catalysts. 170 Abstract Preparation of ansa-tantalocene complexes is described. Reaction of distannylated singly silylene-bridged cyclopentadienyl ligands with TaCls yields tantalocene trichloride complexes of the general formula, Me2Si(ri5-Csf4)(ri5C5H2-R2)TaCl3 (R = H, alkyl). Reduction of the tantalocene trichlorides with LiAlf4 followed by hydrolysis with aqueous ammonium chloride affords the corresponding tantalocene trihydride complexes. Thermolysis of the tantalocene trihydride complexes with phosphines, carbon monoxide and olefins affords the ligand-hydride complexes. The stereochemistry of the resulting products is dependent on both the steric disposition of the ancillary ligation and the incoming ligand, where increased substitution results in higher degrees of selectivity. Reduction of the tantalocene trichloride complexes with zinc dust affords the tantalocene dichloride complexes. Addition of an excess of Grignard reagents of the general form, RCH2CH2MgX (R = H, CH3, C6Hs; X = Cl, Br), affords the tantalocene olefin-hydride complexes. For Me2Si(11 5-Csli,4)(ri 5-C5H3CHMe2)Ta(ri 2-CH2CH2)(H), the predominant isomer (95%) is the one in which the ethylene ligand is coordinated in the open portion of the metallocene wedge. Similar results have been obtained with tantalocene styrene-hydrides and propylene-hydrides. For each metallocene studied, the substitution on the cyclopentadienyl ring directs the coordination of the olefin as to minimize unfavorable steric interactions. The selectivities observed in olefin and phosphine coordination correlate with the specificity of the corresponding zirconocene polymerization catalyst. Both singly and doubly silylene-bridged tantalocene trimethyl complexes have been prepared from reaction of the deprotonated cyclopentadienyl ligand with TaCl2Me3. The singly-bridged, Me2Si(11 5-Csli,4)(ri 5-CsH2-2,4-(CHMe2)2)Ta(CH3)3 displays the expected ri 5, ri 5 coordination of the cyclopentadienyl ligands, whereas for Me2C(ri 5C5lf,4)(Fluorenyl)TaMe3 and Me2C(ri 5-C5If,4)(Fluorenyl)TaMe2F, Tl Lcoordination is observed for the fluorenyl ligand. The doubly silylene-bridged, (Me2Si)2(ri 5CsH2-4-SiMe3)(ri 2-CsH-3,5-(CHMe2)2)Ta(CH3)3 displays an unsual dihapticity for the cyclopentadienyl ligand due to unfavorable steric interactions between the tantalum methyl groups and the dimethylsilylene linkers. 171 Introduction Stereospecific olefin polymerization promoted by group 3 and 4 ansametallocene catalysts represents one of the most enantioselective chemical transformations known.1 Elucidation of the steric and electronic factors that control this remarkable selectivity may aid in the design of new catalysts and also result in the development of new asymmetric transformations. Considerable effort has been devoted toward understanding the nature of the transition state for the C-C bond forming step in metallocene catalysts. From these studies general features common to all metallocene systems have been elucidated. Electronically, it is well accepted that a 14 electron metallocene alkyl with 2 vacant orbitals is required; one orbital is used to accommodate the incoming olefin, while the other allows for a-agostic assistance2 in the transition state for carbon-carbon bond formation (Figure 1).3 M =Sc, Y, lanthanide R' =hydride or alkyl M = Ti, Zr, Hf R' = hydride or alkyl X-= weakly coordinating anion Figure 1. Doubly coordinatively unsaturated, 14 electron metallocene catalysts for olefin polymerization. In addition to electronic effects, considerable effort has been devoted toward understanding the key steric interactions in the olefin insertion transition state. Calculations by Corradini4 demonstrate that the enantiofacial approach of the olefin is determined by the metal alkyl unit, such that the olefin substituent is placed in a trans-relationship with the ~-carbon of the metal alkyl. The metal alkyl is believed to orient itself toward the most open portion of the metallocene framework (Figure 2). The first experimental evidence in support of this model 172 was provided by Pino. 5 Hydrooligomerization of a-olefins with optically pure ethylene bis(4,5,6,7-tetrahydroindenyl) zirconium dichloride (EBTHIZrC12) produced chiral hydrotrimers and hydrotetramers with the predicted absolute configurations. 6 More recently, Gilchrist and Bercaw7 were able to determine the stereoselectivity of yttrium-hydride and yttrium-pentyl additions to carboncarbon double bonds. Optically active deutero-1-pentenes were prepared and used to evaluate the stereoselectivity of olefin insertion into Y-H and Y-pentyl bonds with an optically pure yttrocene. From these studies it was determined that insertions into yttrium-hydride bonds proceed with modest selectivity (34% ee) whereas insertions into yttrium-alkyl bonds proceed with very high levels(> 95% ee) of enantioselectivity. In both the Pino and Bercaw studies, insertion into the metal-hydride occurs with the opposite enantioselectivity of the insertion into the metal alkyl. :j: Figure 2. Model for the olefin insertion transition state in chiral yttrocene catalysts. The stereochemical model developed in the C2-symmetric isospecific systems has since been extended to include C5-symmetric syndiospecific catalysts. 8 In these systems, the favored transition state geometry for two classes of syndiospecific catalysts is shown in Figure 3. In these metallocenes, the growing polymer chain extends away from the less sterically demanding cyclopentadienyl moiety thus forcing the propylene methyl group down toward the more sterically demanding ligand assuming the trans relationship between the coordinated olefin and the growing polymer chain dominates. In both cases shown, the sterically demanding ligand contains an open region to accommodate the methyl substituent on the incoming monomer. 173 ···------~-_.,...,._.....,,. Figure 3. Proposed transition state for syndiospecific metallocene catalysts. Although these proposals have been sucessful in explaining the high levels of stereocontrol observed with C2 and Cs symmetric catalysts, some metallocenes operate with relatively high levels of enantiofacial selectivity that can not be readily explained with current transition state models. One such class of metallocenes are the monosubstituted singly silylene-bridged Me2Si(11 5-CsH4)(11 5-C5H3-3-R)ZrC12 (R = CMe3, CHMe2) complexes originally reported by Miya,9 which polymerize propylene with [mmmm] contents exceeding 70% (Figure 4). MAO Isotactic Polypropylene [mmmm] ~ 70% Figure 4. Isotactic polypropylene produced by C7-symmetric metallocene catalysts. One approach to modeling the carbon-carbon bond forming transition state of a group 4 metallocene catalyst is to prepare the analogous ground state group 5 (M = Nb, Ta) metallocene olefin-alkyl complex. The niobocene and tantalocene complexes can access a formally M(III), d 2 resonance structure (Figure 5) which stabilizes the bound olefin through n-backbonding interactions. Once prepared, conventional NMR and X-ray diffraction experiments may be 174 used to determine the relative disposition of the bound olefin and the metal-alkyl fragment with respect to the ancillary ligation. This approach has been used to elucidate the kinetics and mechanism of olefin insertion into metal-hydride bonds with bis-cyclopentadienyl and bis-pentamethylcyclopentadienyl niobocene and tantalocene olefin-hydride complexes. 10 . M=Nb, Ta R = H, alkyl M(ill) d2 Figure 5. Resonance structures of niobocene and tantalocene olefin hydride complexes. Reports of group 5 ansa metallocenes have been quite limited. Green has reported the synthesis and solution NMR dynamics of a series of carbon-bridged unsubstituted niobocene dichloride and borohydride complexes. 11 Similar silicon-bridged ansa-niobocene dichloride and acetylene-chloride complexes have also been prepared.1 2 Hermann has reported the synthesis ansa-niobocene and ansa-tantalocene amide and imido complexes via traditional salt metathesis and amine elimination methodologies.1 3 Parkin14 has prepared Me2Si(C5Me4)zTaCl3 via tin elimination and was also able to prepare the corresponding tantalocene trihydride complex via reduction of the trichloride with LiAllf4 followed by hydrolysis. Thermolysis of the trihydride in the presence of ethylene afforded Me2Si(C5Me4)zTa(11 2-CH2CH2)(H) which has been characterized by X-ray crystallography. Results and Discussion Tantalum Trihydride Complexes Initially, our synthetic efforts focused on a general route for the preparation of ansa-tantalocene complexes and on the development of methods for further synthetic elaboration of these compounds to the desired olefin- 175 hydride and olefin-alkyl tantalocenes. The first synthetic targets were tantalocene trichloride complexes since Parkin's successful synthesis of Me2Si(C5Me4)2Ta(rt 2-CH2CH2)(H) involved straightforward preparation of the Me2Si(C5Me4)2TaCl3. 14 Reaction of two equivalents of n-Bu3SnCl with Li2[Me2Si(rt 5-Csf4)2] (Li2Sp) affords the distannylated cyclopentadiene derivative, [Me2Si(rt 5-Csf4)2] [SnBu3]2 (1), as a bright yellow oil. Addition of TaCls to a diethyl ether solution of 1 results in precipitation of a red solid identified as Me2Si(rt 5-C5f4)2TaCb (2) based on 1H NMR spectroscopy. Compound 2 is soluble in THF but insoluble in most other common laboratory solvents. Over time, 2 initiates the polymerization of THF so special care should be taken when preparing such solutions. Reduction of 2 with LiAlf4 followed by hydrolysis with saturated Nf4Cl solution affords the tantalum trihydride complex, SpTaH3 (3) (eq. 1). Quenching the reaction mixture with distilled water results in a mixture of products, presumably arising from ligand degradation resulting from hydrolysis of the dimethyl silylene linker. The presence of an acid buffer such as Nf4Cl maintains a minimal concentration of base thus allowing for isolation of a clean product. In addition to the typical ligand resonances, the 1H NMR spectrum of 3 in benzene-d6 displays a triplet at 0.20 ppm for the central tantalum hydride and a doublet at -1.87 ppm for the lateral tantalum hydrides. These values are typical for tantalocene hydride resonances. 15 1 TaC15 /tlfp Me2Si Ta-Cl ~Cl 1. LiAlH 4 2. NH4Cl(aq) /tlf✓H Me2Si~fl (1) 3 2 This synthetic methodology has been extended to include the preparation of more substituted tantalocene trichloride and trihydride complexes. Addition of TaCls to an Et2O solution of [Me2Si(C5f4)(C5H3-3-CHMe2)][SnBu3]2 ([iPrSp] [SnBu3]2), [Me2Si(C5f4)(CsH2-2,4-(CHMe2)2] [SnBu3]2 ([iPr2Sp] [SnBu3]2) and [Me2Si(C5f4)(C5H3-3-CMe3)][SnBu3]2 ([tBuSp ][SnBu3]2) results in precipitation of iPrSpTaCl3 (4), iPr2SpTaCb (5) and tBuSpTaCl3 (6) respectively. 176 As with the parent trichloride complex, 4, 5 and 6 undergo reduction with LiAII-4 followed by subsequent hydrolysis with aqueous NH4Cl to yield iPrSpTaH3 (7), iPr2SpTaH3 (8) and tBuSpTaH3 (9). Each trihydride complex displays upfield lateral hydride resonances(~ -1 to -2 ppm) as well as resonances for the central tantalum hydride (~ 0 to 1 ppm) in the 1H NMR spectrum. ~ 2 Me S i ~ ~ 6 ~ ,,.,H ,,.,H 2 Me S i ~ ~ 7 ~ ,,.,H 2 Me S i ~ ~ 8 Attempts to metallate highly substituted, sterically demanding stannylated cyclopentadienyl ligands have been unsuccessful. No tractable tantalocene trichloride complexes have been obtained from the reaction of [Me2Si(CsHi)(CsH2-(CMe3)2) ][SnBu3]2 {[ tBu2Sp ][Bu3Snh} and [Me2Si(CsH2(CHMe2)2)2][SnBu3]2 {[Ip ][Bu3Snh} with TaCl5. Likewise, indenyl and fluorenyl substituted ligands such as [EBI][SnBu3]2(EBI = ethylene-bis-indenyl) and [Me2C(C5I-4)(fluorenyl)][SnBu3]2 do not produce the desired tantalocene trichloride complexes after stirring with TaCls for several days. The trihydride complexes: 3, 7, 8, and 9 display a wealth of reaction chemistry with a variety of unsaturated organic molecules. Heating a benzened6 solution of 3 to 87 °C under an atmosphere of carbon monoxide results in quantitative formation of the carbonyl hydride complex, SpTa(CO)(H) (10) (eq. 2). The hydride ligand displays a single downfield resonance at -5.68 ppm, substantially shifted from the starting tantalocene trihydride complex. In a similar manner, 7, 8 and 9 react with carbon monoxide over the course of several hours at 87 °C to afford the carbonyl-hydride complexes, iPrSpTa(CO)(H) (11), iPr2SpTa(CO)(H) (12) and tBuSpTa(CO)(H) (13). For 11 and 12, equimolar mixtures of isomers are formed, implying that the linear carbon monoxide molecule is not sufficient in differentiating the steric environments of each side of the metallocene wedge. For 13, a 88:12 ratio of two carbonyl-hydride products is 177 formed, suggesting that the tert-butyl substituted ligand is more sterically conjested than its isopropyl substituted counterparts. /9( ~ • Ta-H Me25 1 ~ H CO (1 atm) 87°C R1 ~,,,co Me2S~H + R1 ~/H Me2S i ~ C O (2) R1 R1 = R2 = H: 3 R1 = CHMe2 , R2 = H: 7 R1 = R2 = CHMe2: 8 R1 = CMe3 , R2 = H: 9 Reaction of 3 with excess ethylene at 87 °C affords the tantalum ethyleneethyl complex, SpTa(1l2-CH2CH2)(CH2CH3) (14), in quantitative yield (eq. 3). Allowing a benzene-d6 solution of 14 to stand at room temperature results in a mixture of 14, SpTa(11 2-CH2CH2)(H) (15) and free ethylene. Formation of 15 arises from loss of ethylene forming a transient Ta(III) ethyl complex which undergoes B-hydrogen elimination. Formation of ethylene-ethyl complexes from thermolysis of Cp2MH3 (M = Nb, Ta) in the presence of ethylene has been observed previously.16 The kinetics of the reaction of 6 with ethylene have been measured at 87 °C. As shown in Table 1, the rate of reaction is independent of the concentration of ethylene (0.196 M to 1.27 M) consistent with rate determining reductive elimination of dihydrogen forming a Ta(l11) monohydride, followed by rapid coordination of ethylene, insertion into the tantalum-hydride and coordination of another ethylene equivalent. For comparison, Me2Si(C5Me4)2TaH3 reacts with ethylene at 90 °C with a rate constant of 9.8(9) x 10-4 sec- 1 forming Me2Si(C5Me4)2Ta(11 2-CH2=CH2)(H).1 4 Similarly, reaction of Cp*2TaH3 (Cp* =11 5-CsMes) with ethylene at 90 °C results in Cp*2Ta(11 2-CH2=CH2)(H) with a rate constant of 2.5 x 10-7 sec- 1 .1 7 These results indicate that the ansa-bridge influences the rate of reductive elimination more than cyclopentadienyl substitution. The effect of an ansa-bridge on rates of reductive elimination has been studied by Parkin.1 4 Reductive elimination from ansa-tantalocene trihydride complexes was found to be approximately 4000 times greater than 178 corresponding unlinked bis-pentamethylcylopentadienyl complexes. The origin of the striking difference is believed to be reduced electron donating capability of the cyclopentadienyl rings in the ansa complex. This results in destabilization of the ground state Ta(V) trihydride with respect to the Ta(III) monohydride intermediate and thus increases the rate of reductive elimination. 6 CH2=CH2 87°C -CH2=CH2 ~_/' • Me2Si~Ta,CH CH ~ 2 3 +CH2=CH2 A/, Me2S 1 ~ H 15 14 [Ethylene] (M) kobs360 K x 104 (sec-1) 0.196 0.635 1.27 1.23(4) 1.26(2) 1.13(6) Table 1. Measured rate constants for the reaction of 6 with ethylene forming 14. Using dynamic NMR techniques, an experimental estimate for the rate of ethylene insertion for 15 can be established. At 85 °C, the dimethylsilylene peaks for 15 coalesce, corresponding to a rate constant of 480(10) sec 1. This rate constant is a composite of the rate of olefin insertion and site interconversion since equivalencing both sides of the metallocene wedge can only be accomplished when both of these processes are occurring. The rate of insertion can, in principle, be measured independently using magnetization transfer or line broadening techinques, but these experiments have not been sucessful. For comparison, the rate constant for ethylene insertion with Me2Si(C5Me4)2Ta(11 2CH2=CH2)(H) has been found to be 1.83 x 103 sec-1 at 100 °C corresponding to a free energy of activation of 16.3 kcal/mol. 14 The corresponding site interconversion barrier has also been measured for Me2Si(C5Me4)2Ta(11 2CH2=CH2)(H) and found to be 0.70 kcal/ mol. The observed insertion rate for the ansa complex is significantly faster than the value of 2.3 sec 1 measured for Cp*2Ta(112-CH2=CH2)(H) at 100 °C. Assuming the barrier for site interconversion is small, it appears that the rate of insertion for 15 is similar to (3) 179 2 that observed for Me2Si(CsMe4)zTa('r1 -CH2=CH2)(H), thus indicating that the rate of olefin insertion is influenced more by the presence of an ansa bridge rather than cyclopentadienyl substitution. Reaction of 7, 8 and 9 with ethylene results in a mixture of isomeric ethylene-ethyl and ethylene-hydride complexes. The lack of symmetry in these molecules coupled with the isomeric products formed has complicated identification of each compound. As a result, the reactivity of the tantalocene trihydride complexes with phosphine ligands has been examined. Through systematic variation in the steric properties of the phosphine, the selectivity for coordination to each side of the metallocene wedge may be determined. Additionally, the resulting tantalocene phosphine-hydride complexes are not expected to undergo further insertion reactions. Thermolysis of 7 with excess PMe3 at 87 °C affords two isomeric phosphine-hydride complexes, iPrSpTa(PMe3)(H) (16a, 16b) (eq. 4). After one hour of heating, the product mixture contains 85% 16a and 15% 16b. The identity of each isomer has been established using NOE difference NMR spectroscopy. For the major isomer, 16a, a strong NOE enhancement in the isopropyl methyl and methine hydrogens of the cyclopentadienyl ligand is observed upon irradiation of the tantalum hydride. Moreover, irradiation of the trimethylphosphine ligand does not result in an NOE enhancement in the isopropyl methine hydrogen thus indicating that the phosphine ligand resides in the open portion of the metallocene wedge. Continued heating of the sample over the course of 19 hours affords solely the major isomer, 16a. Increasing the steric disposition of the phosphine ligand also affects the selectivity of the reaction. Reaction of 7 with PEt3 at 87 °C affords only one isomer of the phosphine-hydride complex, iPrSpTa(PEt3)(H) (17). Contrary to the results with carbon monoxide, phosphine ligands are useful for differentiating the steric disposition of each side of the metallocene wedge. Larger phosphines such as PEt3 are more effective than PMe3 in selectively binding to the more open portion of the metallocene. In both cases, the isopropyl substituent is quite effective in directing the coordination of the phosphine to the tantalum center. 180 (4) 7 87°C 16b 16a The tantalocene trihydride, 8, undergoes clean reaction with trimethylphosphine at 87 °C resulting in a mixture of two isomeric phosphinehydride products, iPr2SpTa(PMe3)(H) (18a, 18b) (eq. 5). At early reaction times (e.g., l hour), an approximately equimolar mixture of the two isomers is present (Table 2). As the reaction progresses, 18b becomes the predominant isomer in solution eventually becoming the only product present. Similar reactivity is observed for the thermolysis of 8 in the presence of PEt3. However, the more bulky triethylphosphine perturbs the product distribution more than PMe3 as evidenced by the 21:79 ratio of 19a:19b at only 30% conversion (Table 2). In both cases, assignments of each isomer are based upon NOE difference NMR spectroscopy. For both phosphines, the preferred isomer is the one in which the phosphine ligand resides on the side of the metallocene wedge with the 4isopropyl substituent. Coordination of the phosphine on the narrow, hence more sterically conjested side of the tantalocene wedge with the 2-isopropyl substituent is disfavored, hence the minor isomer slowly converts to the major with continued heating. 8 ~ ( P R3 PR3 87°C 2 Me S i ~ , i : + ~~H Me2Si~Ta, ~ PR3 R= CH 3 18a 18b R = CH2CH3 19a 19b (5) 181 Phosphine Time (hrs) % Conversion % 18a1 %18b PMe3 1.0 3.0 5.75 26 52 87 100 100 30 78 44 45 39 24 0 21 5 56 55 61 76 100 79 95 10 PEt3 23 1.3 4.5 1. For PEt3, the products are 19a and 19b respectively. Table 2. Reaction of 8 with PR3 at 87 °C. Thermolysis of 9 in the presence of PMe3 affords solely one isomer of tBuSpTa(PMe3)(H) (20). NOE difference NMR spectroscopy reveals that the observed isomer is the one in which the phosphine is coordinated away from the tert-butyl substituent in the metallocene wedge. As with the [iPrSp] ligand system, single substitution with a tert-butyl group is effective in directing the coordination of the phosphine ligand. Preparation of Tantalocene Olefin-Hydride Complexes Due to the recurring problem of over alkylation upon thermolysis of the tantalocene trihydrides with olefins, a cleaner route to the desired olefin-hydride and olefin-alkyl complexes was desired. Previous studies have shown that the Ta(IV) complex, Cp*2TaCli, undergoes clean reaction with a variety of Grignard reagents such as ethylmagnesium bromide and phenethylmagnesium bromide to yield olefin-hydride complexes. 17 For this reason, a route to ansa-Ta(IV) dichloride complexes has been pursued. Addition of zinc dust to a THF solution of 2 results in formation of green solution which thickens over time. Further inspection reveals that polymerization of the THF solvent accompanies the reduction of the tantalum complex. To avoid this complication, the reaction was repeated in dimethoxyethane (DME) and a green powder identified as SpTaCl2 (21) has been isolated in 88% yield (eq. 6). Reduction of 4, 5 and 6 with zinc dust also proceeds 182 smoothly in DME resulting in iPrSpTaCl2 (22), iPr2SpTaCl2 (23) and tBuSpTaCl2 (24) respectively. Each of the tantalum dichloride complexes display a diagnostic eight line (181Ta, 99.99% S = 7/2) EPR spectrum (g = 1.94), consistent with a dl, Ta(IV) complex (Figure 6). [*10" 3] 20.0 17.5 15.0 12.5 10.0 7.5 5.0 2.5 o.o -2.5 -5.0 -7.5 -10.0 -12.5 -15.0 3200 3400 3600 3800 4000 [G] Figure 6. EPR spectrum of 23 in dichloromethane at 296 K. Zn(s) (6) DME R1 = R2 =H: 21 R1 = CHMe2 , R2 = H: 22 R1 = R2 = CHMe2: 23 R1 = CMe3, R2 = H: 24 183 Reaction of 21 with 2.2 equivalents of CH3CH2MgBr affords an orange solution and brown precipitate, consistent with disappearance of the Ta(IV) complex. However, attempts to isolate a tractable product from the reaction mixture have been unsuccessful. Similarly, addition of PhCH2CH2MgBr to 21 results in no tractable product. Addition of 2.2 equivalents of CH3CH2MgBr to a ethereal slurry of 22 also results in formation of an orange solution and brown precipitate. However, in this case a yellow oil identified as iPrSpTa(11 2-CH2CH2)(H) (25) has been isolated (eq. 7). Presumably one equivalent of the ethyl Grignard reagent serves to reduce the tantalum dichloride complex to the Ta(III) chloride which subsequently undergoes alkylation by a second equivalent of Grignard reagent to produce the punative Ta(ill) intermediate, iPrSpTaCH2CH3, which then undergoes ~-hydrogen elimination affording 25 (eq. 7).1 7 (7) 25 The 1H NMR spectrum of 25 indicates that predominantly one isomer of the ethylene-hydride complex forms upon alkylation. A diagnostic upfield resonance (o = -2.70 ppm) is observed for the tantalum hydride of the major isomer. NOE difference NMR experiments confirm that the preferred isomer is the one in which the ethylene ligand resides in the open portion of the metallocene wedge away from the isopropyl substituent. Irradiation of the ethylene resonance at 0.51 ppm results in an NOE enhancement of the tantalum hydride, thus indicating it is the endo ethylene hydrogens.1 8 Selective irradiation of the isopropyl doublets and the isopropyl methine resonances result in a strong NOE to the tantalum hydride and a weak NOE to the endo ethylene peak. These data strongly suggest that the isomer formed is the one in which the ethylene is away from the isopropyl substituent. 184 Heating a benzene-d6 solution of 25 results in broadening of the signals observed for the tantalum-hydride, the cyclopentadienyl hydrogens and the isopropyl methine hydrogen. The broadening of the NMR signals is indicative of olefin insertion and B-hydrogen elimination occurring on the NMR timescale (eq. 8). Attempts to quantify the rate of insertion using magnetization transfer NMR techniques have been unsuccessful. The same isomeric distribution is observed during heating and upon cooling to 25 °C, indicating the observed isomeric preference is indeed thermodynamic and not kinetic products arising from the alkylation procedure. ... Addition of 2.2 equivalents of CH3CH2CH2MgBr to 22 results in formation of four of the eight possible iPrSp('r,2-CH2CHCH3)(H) isomers. The distribution of the propylene-hydride isomers is 63.7% (26a), 20.6% (26b ), 13.0% (26b) and 2.6% (26d). NOE difference spectroscopy indicates that the major isomer is the one in which the propylene is coordinated in an endo fashion on the open side of the metallocene wedge with the methyl group pointed toward the less substituted cyclopentadiene (Figure 7). Figure 7. The major isomer for 26. Similar reactivity is observed upon addition of phenethylmagnesium chloride to 21. Of the 8 styrene-hydride isomers possible, three iPrSpTa(11 2-CH2CHPh)(H) complexes are observed after purification. Two major isomers (27a, 27b) are observed in a 60:40 ratio and constitute 91 % of the product distribution, 185 whereas one trace isomer (27c) forms the remainder of the product mixture. Each of the styrene-hydride isomers displays an upfield tantalum hydride resonance in the 1H NMR spectrum (27a =-1.52 ppm, 27b =-1.69 ppm, 27c = -1.74 ppm). Recrystallization of the reaction mixture affords yellow needles that are suitable for X-ray diffraction. The results of the X-ray diffraction experiment are shown in Figure 8. The 1H NMR spectrum of the single crystals of 27b in benzene-d6 indicate that the crystal structure represents the styrene hydride isomer that constitutes 40% of the product mixture. The benzene-d6 solution of 27b rapidly equilibrates (t1;2 ~ 30 minutes) at 296 K the 60:40 mixture of the major isomers and also contains a trace amount of the minor isomer, 27c. C14 Figure 8. Molecular structure of 27b with 50% probability ellipsoids and atom labeling scheme. The solid state structure for the minor tantalocene styrene-hydride complex, 27b, reveals the expected 11 2-coordination of the styrene ligand. Although the tantalum hydride was not located in the difference map, the orientation of the styrene is clearly on the side of the metallocene wedge away from the isopropyl group (Figure 9). The isopropyl group orients itself such that the methine hydrogen points towards the phenyl group of the coordinated styrene ligand, thus minimizing unfavorable steric interactions between the olefin substituent and the ancillary ligand substitution. The C(16)-C(17) bond 186 distance is 1.4196(89) A which is typical for group V olefin-hydride complexes.IO The phenyl group on the styrene ligand is twisted 6.2 ° from the olefin plane [C(16)-C(17)-C(18)], which is reduced substantially from the 32 ° observed for (rt 5-CsMes)2Nb(rt 2-CH2CHC6Hs)(H). 10 Figure 9. Top view of 27b with 50% probability ellipsoids. Major Isomer (60%) Minor Isomer (40%) Figure 10. The two predominant isomers of 27. NOE difference NMR experiments on the mixture of isomers reveals that the major isomer, 27a, is the one where the styrene is coordinated in the open portion of the metallocene wedge with the phenyl group oriented toward the unsubstituted cyclopentadienyl ring (Figure 10). The major isomers are the same for the propylene-hydride and styrene-hydride complexes thus demonstrating the stereodirecting ability of the isopropyl substituted ligand. Comparing the major and minor isomers of 27 indicates a 20% de for insertion into the tantalumhydride, in accord with previous studies that demonstrate low selectivities for metallocene hydride insertions? Although the enantiofacial preference for olefin 187 coordination is poor, the site selectivity is quite good, where at least 91 % of the olefin coordination occurs away from the isopropyl substituent. The rapid equilibration of the styrene-hydride isomers can take place by three mechanisms (Figure 11). The first pathway involves olefin insertion into the tantalum hydride followed by ~-hydrogen elimination to generate the thermodynamic distribution of isomers. The second pathway generates a tantalum(III) hydride from dissociation of the styrene followed by recoordination thus equilibrating the isomers. Finally, a pathway involving rotation about n:-face of olefin is also possible. This pathway can only generate one other isomer (exo, phenyl substituent towards Cp) in addition to 27b. Since the isomer is not observed, this pathway has been ruled out. )Y M (' ) s· /fll(~ Ta e2 1~...;H Ph TT'l ~ 2~ zz_~ _ _ -styrene n? F'T_ H Me2Siv,£ + styrene ::J:_, 27a 27b 27c ~ - - - - - - ( i i i__ ) _ _/ olefin rotation Figure 11. Possible mechanisms for styrene-hydride isomer interconversion. In an attempt to distinguish between the two remaining pathways shown in Figure 11, olefin exchange experiments have been conducted. Addition of 13CH2=13CH2 to a benzene-d6 solution of 25 results in incorporation of the labeled olefin over the course of three days (eq. 9). Similarly, addition of ethylene to the isomeric mixture of styrene-hydride complexes results in formation of 25 over the course a week at 296 K. The ethylene-hydride isomer 188 formed from addition of ethylene to 27 is the same as the one prepared from the alkylation of 22. Since olefin exchange is slow with respect to isomerization of 27b, the process by which the pure styrene-hydride isomer converts to the thermodynamic mixture appears to be olefin insertion/~-hydrogen elimination (pathway (i), Figure 11). ~~~ +ethylene Me2S1"'~ Ph + styrene Reaction of 2.2 equivalents of CH3CH2MgBr to 23 results in a mixture of ethylene-hydride products, iPr2SpTa(T1 2-CH2CH2)(H) (28a, 28b ), with the major isomer constituting 78% of the product mixture (eq. 10). NOE difference NMR experiments reveal that the major isomer, 28a, is the one where the ethylene ligand resides in the open portion of the metallocene wedge, on the side of the molecule with the 4-isopropyl substituent. These results are consistent with the major isomer in the phosphine-hydride complexes, 18a and 19a. The steric differentiation between the two sides of the metallocene wedge is not as pronounced as with the iPrSp ligand since in this case two ethylene-hydride isomers are formed whereas with the monosubstituted ligand only one ethylene-hydride is observed. These results are consistent with the results obtained from the olefin polymerization experiments, where monosubstituted ligand arrays produce mainly isotactic polypropylene and the disubstituted ligands produce atactic polypropylene. 23 28a, 78 % 28b, 22 % Attempts to prepare clean propylene-hydride complexes with the [iPr2Sp] ligand frame~ork have not been successful. Addition of 2.2 equivalents of CH3CH2CH2MgBr to 23 does result in formation of a yellow oil consistent with formation of an olefin-hydride complex. Although the 1H NMR spectrum in benzene-d6 displays peaks indicative of the desired propylene-hydride complex, the product is not sufficiently pure to allow for definitive assignment. Preparation of the styrene-hydride complex, iPr2SpTa(11 2-CH2CHPh)(H) (29), has been accomplished via addition of phenethylmagnesium chloride to a diethyl ether solution of 23 (eq. 11). Analysis of the product mixture by 1H NMR spectroscopy indicates that four isomers are formed. The isomer distribution consists of two major isomers formed in 55:45 ratio constituting 87% of the styrene-hydride products. Two minor isomers composing 13% of the product mixture are formed in equal amounts. Recrystallization of the reaction mixture from cold petroleum ether affords yellow needles that are suitable for X-ray diffraction. The solid state structure of one isomer of the styrene-hydride complex is shown in Figure 12. Dissolving the crystals in benzene-d6 reveals that the isomer that crystallizes is the major isomer formed. Monitoring the solution over time by lH NMR spectroscopy reveals that the pure 29a undergoes rapid isomerization (~ 30 minutes at 296 K) to the thermodynamic mixture of styrenehydride products. The major isomer, 29a, is the one in which is the styrene ligand resides in the open portion of the metallocene wedge consistent with the major isomer formed in the ethylene-hydride complex and in the phosphinehydride complexes. The phenyl group of the styrene ligand is directed away from the bulky isopropyl groups and towards the unsubstituted cyclopentadienyl ligand. 190 ~~Ph 2 Me Si'\;J~H 23 (11) 29a, 55% 29b, 45% + 2 Minor Styrene-Hydrides (13%) Figure 12. Partially labeled view of the molecular structure of 29a with 50% probability ellipsoids. Hydrogen atoms are omitted for clarity. 191 Figure 13. Top view of 29a with 50% probability ellipsoids. For the 29a, all of the hydrogens, including the tantalum-hydride, have been located in the difference Fourier map. The hydride is coordinated on the side of wedge with the 2-isopropyl substituent. The Ta-H distance of 1.72 A observed in 29a is typical for terminal hydrides of group V metallocenes. For example, a Nb-H distance of 1.75(3) A has been determined for Cp*2Nb(CH2=CHPh)(H) 10b while the Ta-H bond distances in Cp2TaH3 are 1.769(8), 1.775(9), and 1.777(9) A.1 9 As with 27b, the coordinated styrene displays a C(19)-C(20) distance of 1.451(5) A and the plane of the phenyl ring is twisted only 3.2 ° with respect to the olefin framework. The 2-isopropyl substituent is rotated such that the methine hydrogen is oriented towards the dimethylsilylene linker. This conformation places one isopropyl methyl group up toward the metallocene wedge. The 4-isopropyl group, being sufficiently removed from the dimethyl silylene linker, orients its methine hydrogen toward the metallocene wedge thus minimizing steric interactions between the coordinated styrene and the ancillary ligand substitution. Alkylation of 24 with PhCH2CH2MgCl in diethyl ether affords a yellow solid identified as one isomer of tBuSpTa(ri 2-CH2CHPh)(H) (30). Slow cooling of 192 a petroleum ether solution of 30 deposits yellow blades that are suitable for Xray diffraction. The solid state structure of 30, shown in Figures 14 and 15, reveals the isomer formed is the endo isomer where the styrene ligand is on the more open portion of the metallocene wedge with the phenyl ring oriented away from the bulky tert-butyl substituent. The tantalum hydride has been located in the difference map and displays a Ta-H bond length of 1.81 A. The C(17)-C(18) bond length of 1.445(9) A and the 4.2 ° twist to the phenyl ring with respect to the plane of the olefin is consistent with the other ansa-tantalocene styrene hydride complexes. Figure 14. Molecular structure of 30 with 50% probability ellipsoids and atom labeling scheme. The olefin-hydride complexes prepared reveal the effect of ancillary ligand substitution on the stereochemistry of olefin coordination. For [iPrSpTa], the isopropyl group is quite effective in directing coordination of ethylene such that the olefin coordinates away from the alkyl substituent 95% of the time. This result is quite surprising, since minimal steric interaction between the isopropyl substituent and the ethylene ligand would be expected. Similar directing effects are observed in iPrSpTa(11 2-CH2CHC6Hs)(H) complexes. Although only 20% diastereoselectivity is observed, the isopropyl group is effective in directing the styrene toward the open portion of the metallocene wedge. Increasing the steric 193 bulk of the ligand with tBuSpTa(11 2-CH2CHC6Hs)(H) results in even greater selectivity. Since the isopropyl substituent in [iPrSpTa] rotates the methine hydrogen toward the olefin, coordination of the styrene with the phenyl group oriented toward and away from the monosubstituted cyclopentadienyl ring is observed. However, in the [tBuSpTa] case, the tert-butyl group can only position a methyl group toward the olefin substituent and hence only one isomer is formed upon coordination of olefin. Figure 15. Top view of 30 with 50% probability ellipsoids. In the disubstituted, [iPr2SpTa] system, different selectivities for olefin coordination are observed. In this case, styrene-hydride isomers where the phenyl group is oriented away from the isopropyl substituents constitute 87% of the product mixture. Although the selectivity between different sides of the metallocene wedge is poor (55:45), the isopropyl groups are effective in directing the olefin substituent toward the less substituted cyclopentadienyl ring. Interestingly, in all cases studied, endo styrene-hydride products dominate. This contrasts previous results in bis-cyclopentadienyl tantalum and niobium complexes where approximately equal amounts of each isomer are observed. 10 For the ansa-tantalocenes, unfavorable steric interactions between the dimethylsilylene linker and the exo-alkyl substituent disfavor formation of exo-isomers. 194 In combination, the results indicate that ancillary ligand substitution in C1 symmetric tantalocene olefin-hydride complexes is effective in directing the coordination of an olefin. The dimethylsilylene linker is effective in disfavoring the formation of exo-isomers while the cyclopentadienyl substitution directs the olefin toward a particular side of the metallocene wedge. Preparation of Tantalum Trimethyl Complexes Having successfully modeled the transition state geometry for the olefinhydride transition state for C1-symmetric ligands, we turned our attention to the preparation of olefin-alkyl complexes in order to understand the transition state for carbon-carbon bond formation. Based on theoretical predictions and studies with chiral yttrocene and zirconocene catalysts, we anticipate the geometry for the carbon-carbon bond forming transition state to have the opposite enantiofacial preference than the olefin-hydride transition state.4-7 In order to prepare our target molecules, several synthetic strategies have been devised. Previous reports from Schrock and our laboratory have shown that cyclopentadienyl tantalum trimethyl complexes can be converted to the ethylene-methyl complex (Figure 16). 2 Following preparation of the trimethyl complex, abstraction of one methyl group with trityl tetrafluoroborate results in formation of the tantalocene dimethyl cation. Subsequent deprotonation of one of the methyl groups with strong base affords the tantalocene methylidenemethyl complex. Bimolecular decomposition of the methylidene-methyl complex takes place over the course of hours at room temperature liberating an equivalent of an unidentified Ta(ill) compound and generating Cp2Ta(1,2CH2=CH2)(CH3). ° Our group has recently extended this methodology to include ansatantalocene complexes. 21 Conversion of SpTaMe3 to SpTa(17 2-CH2=CH2)(CH3) has been accomplised using the procedure outlined in Figure 16. We therefore decided to prepare ansa-tantalum trimethyl complexes with the hope of being able to convert these compounds to the corresponding olefin-methyl complexes. 195 Figure 16. Synthetic route for the preparation of Cp2Ta(11 2-CH2=CH2)(CH3). Slow addition of a THF solution of Li2[iPr2Sp] to a THF solution of TaCl2Me3 at -80 °C, results in clean formation of the tantalum trimethyl complex, iPr2SpTaMe3 (31), in good yield. 22 Slow cooling of a diethyl ether solution of 31 yields crystals suitable for X-ray diffraction. The solid state structure of 31 is shown in Figures 17 and 18. The tantalocene displays the expected 115 hapticity for both cyclopentadienyl rings. The tantalum methyl groups are located in the plane of the metallocene wedge and display slightly long tantalum-methyl bond lenghts of 2.3253(71) A (Ta-C(19)), 2.2875(66) A (Ta-C(20)) and 2.3730(88) A (TaC(21)). 23 The elongated thermal ellipsoid for C(20) is a result of crystal twinning and may be a ghost image of another tantalum center. The dimethylsilylene linker in 31 is rotated to one side of the metallocene wedge. As with 29a, the 2isopropyl substituent rotates the methine hydrogen toward the dimethylsilylene linker to avoid unfavorable steric interactions. This places one isopropyl methyl group toward the metallocene wedge, thus rotating the tantalum methyl groups toward one side of the metallocene. 196 Figure 17. Molecular structure of 31 with 50% probability ellipsoids with partial atom labeling scheme. Hydrogen atoms omitted for clarity. Figure 18. Top view of the solid state structure of 31 with 50% probability ellipsoids. Hydrogen atoms omitted for clarity. 197 Abstraction of one of the tantalum methyl groups can be accomplished via additon of [Ph3C][BF4] to 31 yielding [iPr2SpTaMe2][BF4] (32) as a bright yellow solid. Deprotonation of one of the methyl groups proceeds readily with addition of LiCH(SiMe3)2 affording only one isomer of the methylidene-methyl complex, iPr2SpTa(CH2)(CH3) (33): Attempts to deprotonate 32 with other bases such as LiCH2SiMe3 and LiN(SiMe3)2 result in formation of 33 although the reaction is not as clean and reproducible as with LiCH(SiMe3)2. The 1H NMR spectrum of 33 in benzene-d6 displays two doublets at 10.22 and 10.30 ppm for the Ta=CH2 fragment. Over the course of 12 hours in solution, 33 converts to one isomer of iPr2SpTa(rt 2-CH2CH2)(CH3) (34) (Figure 19). For comparison, the unsubstituted.complex, SpTa(=CH2)(CH3), converts to the ethylene-methyl complex in minutes at 296 K. The instability of both 33 and 34 has not allowed for characterization of the observed isomer by NOE difference NMR spectroscopy. The increased time required for 33 to convert to 34 is consistent with a bimolecular mechanism proposed by Schrock, since the increased steric disposition of the [iPr2Sp] increases the stability of 33 compared to SpTa(CH2)(CH3). A__,CH3 Me25 1 , H BF43 j LiCH(TMSh ~ ~ C H2 Me2S~~H3 or isomer Figure 19. Preparation of 34. or isomer 198 The synthetic methodology used for the preparation 31 has been extended to include other ligand arrays. The isopropylidene bridged cyclopentadienyl-fluorenyl ligand, Me2C(C5l-i4)(Fluorenyl), when coordinated to zirconium and hafnium results in catalysts that are efficient in producing syndiotactic polypropylene. 24 The proposed mechanism for syndiospecific polymerization requires alternating, stereoregular propylene insertions. In order to evaluate these proposals, we felt that this ligand system would be wellsuited for coordination to tantalum in an attempt to model the transition state for syndiospecific olefin polymerization. Reaction of Li2[Me2C(C5l-i4)(Fluorenyl)] with TaCl2Me3 in toluene affords a golden solid identified as Me2C(C5l-i4)(Fluorenyl)TaMe3 (35) (eq. 12). In a similar manner, reaction of Li2[Ph2C(C5l-i4)(Fluorenyl)] with TaChMe3 yields Ph2C(C5I-i4)(Fluorenyl)TaMe3 (36) (eq. 12). The 1H NMR spectrum of 36 displays 5 inequivalent phenyl resonances indicating restricted rotation about the phenylcarbon bond. Similar solution behavior has been noted in similar zirconocene complexes. 25 Recrystallization of 35 from a cold mixture of CH2Ch/Et2O affords crystals suitable for X-ray diffraction, and the solid state structure is shown in Figure 20. The solid state structure of 35 reveals an 11 1 coordination of the flourenyl ligand. The average carbon-carbon bond distance in the 11 5 coordinated cyclopentadienyl ring is 1.41(1) A whereas the five membered ring in the flourenyl ligand displays long and short carbon-carbon bonds, consistent with 11 1 coordination. For example, the C(9)-C(21) distance of 1.5016(13) A suggests substantial single bond character whereas the 1.4167(45) A and 1.4166(48) Abond distances for C(10)-C(15) and C(16)-C(21) are indicative of carbon-carbon double bonds. The central tantalum methyl group, C(24), is colinear with the centroid formed with the cyclopentadienyl ring and is 2.2095(34) A away from the metal center. 199 Me R Me (12) e R = Me, 35 R = Ph, 36 Figure 20. Molecular structure of 35 with 50% probability ellipsoids and atom labeling scheme. Hydrogens omitted for clarity. 200 Figure 21. Side view of 35 with 50% probability ellipsoids. Hydrogens omitted for clarity. In the batch of yellow crystals of 35, a small amount(~ 5%) of an orange crystalline material suitable for X-ray diffraction was observed. The solid state structure of the orange material (35a) is shown in Figure 22 and reveals a bridged, dinuclear species where one ligand spans two [TaClMe3] fragments. Both the cyclopentadienyl and fluorenyl ligands are coordinated in the expected T\s fashion. The planes of the cyclopentadienyl and fluorenyl rings are oriented 90 ° with respect to each other. Typical tantalum-methyl bond distances {Ta(2)C(25): 2.1877(88) A, Ta(2)-C(26): 2.1678(112) A, Ta(2)-C(27): 2.1890(83) A} and tantalum-chloride bond distances {Ta(2)-Cl(2): 2.3578(5) A} are observed for the fluorenyl portion of the molecule.24 The methyl groups bonded to Ta(l) are slightly disordered with Cl(l) and hence a small ellipsoid and slightly longer bond length (2.2682 A) is observed for C(22). 201 Figure 22. Molecular structure of 35a with atom labeling scheme and 50% probability ellipsoids. Hydrogen atoms omitted for clarity. A more sterically expansive version of the isopropylidene-linked cyclopentadienyl, fluorenyl ligand employing l,1,4,4,7,7,10,10-octamethyll,2,3,4,7,8,9,10-octahydrodibenzo [b,h] fluorene (Oct) has been prepared and has been found to be useful in syndiospecific olefin polymerization. 25 Addition of TaCbMe3 to a THF solution of Li2[Me2C(C5f4)(Oct)] produces a brown solid that has been identified as Me2C(C5f4)(Oct)TaMe3 (37) on the basis of NMR spectroscopy. Unfortunately, single crystals suitable for diffraction have not been obtained and therefore the hapticity of the Oct fragment has not been determined. Addition of HBF4 to 35 at low temperature in toluene solution results in formation of methane and a red solid. A combination of NMR spectroscopy and X-ray crystallography reveal that the product of this reaction is not the desired dimethyl cation, [Me2C(C5f4)(Fluorenyl)TaMe2][BF4], but rather the neutral tantalocene dimethyl fluoride complex, Me2C(C5f4)(Flu)TaMe2F (38), which arises from fluoride abstraction from BF4- by the dimethyl cation (eq. 13). The solid state structure for 38 is shown in Figure 23. Preparation of 38 can also be accomplished via addition of [P~C][BF4] to 35, although the reaction is not as 202 clean as the protonation with HBF4. Abstraction of fluoride from BF4 demonstrates the increased Lewis acidity of the ansa-metallocene with the Tl L fluorenyl ligand as compared to Cp2TaMe3 and 31. 35 HBF4 Me Me (13) F The solid state structure of 38 is analogous to that observed with 35. The flouride ligand is colinear with the tantalum cylopentadienyl centroid and is bonded 1.9133(16) A away from the metal center. As with 35, the five membered portion of the fluorenyl ring displays carbon-carbon bond distances consistent with isolated single {C(9)-C(21): 1.5046(39) A, C(9)-C(10): 1.489(39) A; C(15)-C(16): 1.4527(11) A)} and double bonds {C(10)-C(15): 1.4056(41), C(16)C(21): 1.4148(39) A)}. C19 Figure 23. Molecular structure of 38 with 50% probability ellipsoids and atom labeling scheme. Hydrogen atoms omitted for clarity. 203 Stirring 35 with excess ZnC}i results in formation of a red powder identified as Me2C(C5I-4)(Fluorenyl)TaMe2Cl (39) (eq. 14). Addition of excess ZnCl2 does not chlorinate the remaining tantalum methyl groups. Similar results have been observed by Bazan for reaction of (TBM)TaMe3 (TBM = tribenzylidenemethane) with ZnClz. 26 Preparation of 39 can also be accomplished via addition of one equivalent of anhydrous HCl to 35. Interestingly, addition of excess HCl to 39 does not result in protonation of the lateral tantalum methyl groups but rather protonates the fluorenyl ligand, yielding the piano stool complex, Me2(FluorenylH)(ri 5-C5I-4)TaMe2Cl. Attempts to remove the chloride ligand from 39 with AgBF4, AgOTf or NaBPh4 have been unsuccessful. Me 35 Me Cl (14) In addition to the cyclopentadienyl-fluorenyl ligand system, attempts to prepare doubly silylene-linked ansa tantalocene olefin-hydride and olefin-alkyl products have been pursued. These ligands have been shown to promote syndiotactic polymerization of propylene when coordinated to group 4 metals.8 Reaction of K2[(Me2Si)z(C5H-2,4-(CHMe2)z)(CsH2-4-SiMe3)) (TMSThp) with TaCl2Me3 in Et20 followed by filtration and recrystallization affords the tantalocene trimethyl complex, TMSThpTaMe3 (40), as a light sensitive, golden yellow solid. Slow cooling of an Et20 solution of 40 affords crystals that are suitable for X-ray diffraction. The solid state structure of 40 is shown in Figure 24. 204 Figure 24. Molecular structure of 40 with 50% probability ellipsoids and atom labeling scheme as viewed in the equitorial plane. Selected bond lengths (A): Ta-Cent(l), 2.131; Ta-Cent(2), 2.378. Bond angles (deg): Cent(l)-Ta-Cent(2), 96.9. Cent(l) is the centroid formed by C(l), C(2), C(3), C(lA), C(2A) and Cent(2) is the centroid formed by C(4) and C(4A). Yellow blades of 40 crystallize in the orthorombic space group Pnrna and contain a mirror plane of symmetry containing the tantalum atom, the cyclopentadienyl centroids and the central tantalum methyl group. The metallocene displays an unusual 11 5,11 2 coordination of the cyclopentadienyl groups. The centroid formed by the 115-cyclopentadienyl ring and the central tantalum methyl group (C15) are colinear. No significant deviations (1.40-1.43 A) in the carbon-carbon bond lengths are observed in the two cyclopentadienyl rings. Typical tantalum-methyl group distances are observed, with Ta-C(14) being 2.2026(60) A and Ta-C(15) being 2.2114(90) A. Dihapto coordination of a cyclopentadienyl ring, although rare, has been observed in other transition metal and main group complexes. Green27 has determined the solid state structure of (11 5-C5H5)2Ti(11 2-CsHs) by X-ray diffraction. The dihapto cyclopentadienyl ring has no significant deviations in the carbon-carbon bond distances, each being 1.42-1.44 A. Shapiro has identified a 205 number of cyclopentadienyl aluminum compounds that display 112 cyclopentadienyl ring coordination.28 Molecular structure determinations, NMR spectroscopic measurements and theoretical calculations indicate that in the absence of Lewis bases or 1t-bonding substituents, the 11 2 geometry of the cyclopentadienyl ring is preferred. Figure 25. Side view of 40 with 50% probability ellipsoids. The reactivity of 40 has been briefly explored. Addition of one equivalent of HCl results in protonation of the central methyl group resulting in the Cs symmetric, TMSThpTaMe2Cl (41) (eq. 15). Exposure of 36 to an atmosphere of dihydrogen results in rapid decomposition. Likewise, reaction of [Ph3][BF4] with 36 results in decomposition. Addition of PMe3 produces no reaction even at elevated temperatures. TMS Me,S.~Me Mez"S~e flTMS 1 HCl Me,,s.n~Me Me2'Si~~Me ~ '-1 (15) 206 Reactivity of Olefin-Hydride Complexes Another synthetic approach to the desired olefin-alkyl complexes is to trap a Ta(III) alkyl species with an olefin such as ethylene or propylene. Previous work has demonstrated that reaction of Cp*2Nb(ri 2-CH2=CH2)(H) with carbon monoxide and methylisocyanide results in formation of Cp*2Nb(CH2CH3)(L) (L = CO, CH3NC) 10 thus suggesting that trapping of the punantive M(III) alkyl is synthetically feasible. Tebbe16 has shown that thermolysis of Cp2MH3 (M = Nb, Ta) in the presence of excess ethylene affords Cp2M(CH2CH3)(ri 2-CH2=CH2), demonstrating the ability of ethylene to trap the M(III) intermediate. Addition of ethylene to 25 at room temperature results in slow olefin exhange rather than trapping of a Ta(ill) ethyl species (vide supra). Heating a benzene-d6 solution of 25 in the presence of ethylene does produce one isomer of the desired iPrSpTa(CH2CH3)(ri 2-CH2=CH2) (42). However, upon standing, 42 undergoes loss of ethylene affording a mixture of 42 and 45 thus preventing definitive characterization of the tantalocene olefin alkyl. In a similar experiment, excess styrene(> 15 equivalents) has been added to 30. No reaction is observed at 25 °C after one week. Heating the reaction mixture to 87 °C for several days results in formation of a very small amount (~ 5%) of the desired tantalocene styrene phenylethyl complex (eq. 16). In an attempt to increase the equilibrium concentration of the desired olefin alkyl complex, pentafluorostyrene has been added to 30. It was hypothesized that fluorination of the phenyl ring would lower the energy of the rr* molecular orbital of the C=C double bond which in turn would increase the metal to olefin backbonding interaction thus shifting the equilibrium toward the olefin alkyl complex. Unfortunately, heating 30 with pentafluorostyrene for one week produced no desired product. 207 or isomer 30 trace amounts Since addition of olefin to the tantalocene olefin hydride complexes has not produced· any of the target complexes, addition of other smaller neutral ligands has been attempted. Addition of 15 equivalents of PMe3 to 30 produces no reaction over the course of several days at 25 °C. Heating the reaction mixture to 87 °C results no desired product; only a small amount(~ 5%) of exchange of PMe3 for coordinated styrene is observed (eq. 17). /£{>-Ph Me2Si~H 30 15 PMe3 87°C -styrene A.:--PMe3 2 Me S 1 ~ H (17) 20 (~ 5% conversion) Addition of 1 atmosphere of carbon monoxide to 30 at 87 °C results in formation of 13 and tBuSpTa(CH2CH2Ph)(CO) (eq. 18). The identity of the phenyl ethyl carbonyl has yet to be established by NOE difference NMR spectroscopy. Similar results have been obtained in related permethylniobocene olefin-hydride complexes. (16) 208 30 co (18) or isomer Conclusions A variety of singly silylene-bridged tantalocene trichloride complexes has been prepared via tin elimination from the distannylated cyclopentadienyl ligands. Reduction of the trichloride complexes followed by hydrolysis results in formation of the tantalocene trihydride complexes. At elevated temperatures, the tantalum trihydride complexes undergo clean reaction with a variety of ligands such as phosphines, carbon monoxide and olefins to yield the ligandhydride species, Me2Si(C5H4)(CsH2-R1-R2)Ta(H)(L) (L = PR3, CO, ethylene) species. For C1 -symmetric metallocenes, the isomeric distribution of the product mixture is dependent on both cyclopentadienyl substitution and on the nature of the incoming ligand. In both cases, increased steric bulk results in higher selectivities. Reduction of the tantalocene trichloride complexes with zinc dust results in formation of the Ta(IV) dichloride species. These compounds undergo alkylation with addition of excess Grignard reagents, forming olefin-hydride complexes. For iPrSpTa(ri 2-CH2=CH2)(H), one isomer is observed and has been determined to be the one in which the olefin coordinates to the open side of the metallocene wedge away from the isopropyl substituent. Similar results have been obtained with styrene-hydrides and propylene-hydrides. For each ligand array, the styrene-hydride complexes have been characterized by X-ray crystallography. In the case of iPr2SpTa(11 2-CH2=CHPh)(H) and tBuSpTa(11 2CH2=CHPh)(H) , the major isomer has been crystallized and is the endo isomer in which the phenyl substitutuent orients to avoid interactions with the ligand alkyl groups. For iPrSpTa(ri 2-CH2=CHPh)(H), the minor isomer crystallizes from solution but upon dissolution in benzene converts to the thermodynamic 209 mixture of products. In all cases studied, the ancillary ligand substitution is effective in directing the coordination of the olefin. A variety of singly and doubly bridged ansa-tantalocene trimethyl complexes have been prepared and structurally characterized. For fluorenyl substituted ligands, the fluorenyl ligand adopts an 11 1 hapticity upon coordination to tantalum. For the doubly silylene bridged tantalocene, TMSThpTaMe3, an unusual 11 2 coordinated cyclopentadienyl ring is observed. In one case, iPr2SpTaMe3, the trimethyl complex has been converted to a desired olefin-alkyl complex, iPr2SpTa(11 2-CH2=CH2)(CH3). Experimental Genera.I Considerations. All air- and moisture-sensitive compounds were manipulated using standard vacuum line, Schlenk or cannula techniques or in a drybox under a nitrogen atmosphere as described previously. 29 Argon, dinitrogen and dihydrogen gases were purified by passage over columns of MnO on vermiculite and activated molecular sieves. Toluene and petroleum ether were distilled from sodium and stored under vacuum over titanocene. 30 Tetrahydrofuran, dimethoxyethane and ether were distilled from sodium benzophenone ketyl. Tetrahydrofuran-ds was distilled from sodium benzophenone ketyl and stored over 4A molecular sieves. Dichloromethane-d2 was distilled from CaH2. TaCls, (n-Bu)3SnCl, 1.0 M LiAllf4 in diethyl ether, 3.0 CH3CH2MgBr in diethyl ether, 2.0 M CH3CH2CH2MgCl in diethyl ether, 1.0 M PhCH2CH2MgBr in THF, 54% HBF4 in diethyl ether, PMe3 and PEt3 were purchased from Aldrich and used as received. Carbon monoxide was purchased from Matheson, and anhydrous hydrochloric acid was purchased from Aldrich. Zinc dust and ZnCl2 were purchased from Strem Chemical and dried at 100 °C under high vacuum. Ethylene was purchased from Matheson and passed through a dry ice trap immediately before use. All dilithio salts of ligands were prepared according to standard procedures31 while TaC}iMe3 was prepared according to literature procedures. 20 210 NMR spectra were recorded on a JEOL GX-400 (lH, 399.78 MHz, 13C, 100.53 MHz, 31 P, 161.9 MHz, 19F, 376.1 MHz) or a Varian Inova 500 (lH, 500.13 MHz, 13C, 125.77 MHz) . All chemical shifts are relative to TMS for lH (residual) and 13C (solvent as a secondary standard and H3PO4 for 31P). Nuclear Overhauser Difference experiments were carried out on a Varian Inova 500 MHz spectrometer. Elemental analyses were carried out at the Caltech Analytical Facility by Fenton Harvey or by Midwest Microlab, Indianapolis, Indiana. [Me2Si(C5H4h][n-Bu3Snh (1). In the dry box, a 100 mL round bottom flask was charged with 3.50 g (17.5 mmol) of Li2[Me2Si('r1 5-Cs~)z]. The white solid was slurried in 30 mL of Et2O. Via pipette, 11.97 g (36.8 mmol) of n-Bu3SnCl was added over the course of 15 minutes. The reaction flask was then attached to a swivel frit assembly and stirred for 3 days at room temperature. The yellow Et2O solution was filtered and the white precipitate washed with recycled Et2O. The Et2O was removed in vacuo leaving a 12.5 g (92.5%) of a yellow oil identified as 1. 1H NMR (benzene-d6): o= 0.162 (s, 6H, SiMe2); 0.760 (t, 7 Hz, 18H, SnCH2CH2CH2CH3); 1.10 (m, 12H, SnBu3); 1.13 (m, 12H, SnBu3); 1.41 (m, 12H, SnBu3); 5.96 (m, 4H, Cp ); 6.58 (m, 4H, Cp ). 13C NMR (benzene-d6): o= 0.595 (SiMe2 ); 12.23 (SnBu3); 14.37 (SnBu3); 17.92 (SnBu3); 28.32 (SnBu3); 109.96, 133.24, 133.46 (Cp ). Me2Si('11 5-C5H4}iTaCl3 (2). In the dry box, 5.60 g (7.30 mmol) of 1 was charged into a 100 mL round bottom flask and dissolved in approximately 50 mL of Et2O, forming a clear solution. Small portions of TaCls (2.61 g; 7.30 mmol) were then added slowly to the reaction mixture. A red solid forms upon addition of TaCls. The flask was attached to a swivel frit assembly and the reaction mixture stirred for 12 hours. The solid was collected by filtration and was washed with small portions of Et2O. The red solid was dried in vacuo yielding 2.80 g (81 %) of 2. 1H NMR (THF-ds): o= 0.97 ppm (s, 6H, SiMe2); 6.52 (m, 4H, Cp ); 7.71 (m, 4H, Cp ). 13C NMR (THF-ds): o= 12.38 (SiMe2); 115.21, 134.74, 1 not located (Cp). Me 2Si('r15-C5H4}iTaH3 (3). In the dry box, 1.00 g (2.02 mmol) of 2 is charged into a round bottom flask and attached to a medium swivel frit assembly. On the vacuum line, approximately 15 mL of Et2O was added by vacuum transfer. At -80 °C, 15.0 mL (15 mmol) of 1.0 M LiAl~ solution was added via syringe against an argon counterflow. With addition, a yellow solid forms. The reaction 211 mixture was warmed to room temperature and stirred overnight. Via syringe, 2.0 mL of saturated NI-4Cl solution was added at O 0 C. With addition of the Nlf4Cl solution an exothermic reaction and formation of white precipitate ensued. The reaction mixture was stirred for 1 hour and then filtered. The white solid was washed with Et2O several times. The Et2O was removed in vacuo leaving 0.260 g (33%) of a white solid identified as 3. 1H NMR (benzene-d6): 8 = -1.95 (d, -0.04, 15 Hz, 2H Ta-H); 0.02 (t, 10 Hz, lH, Ta-H); -0.04 (s, 6H, SiMe2); 4.84 (m, 4H, Cp ); 5.36 (m, 4H, Cp ). Me2Si('ri 5-C5H4)(T1 5-C5H3-3-CHMe2)TaCl3 (4). Prepared in an analogous manner to 2 with 4.90 g (6.06 mmol) of [Me2Si(T1 5-Cslf4)(T1 5-C5H3-CHMe2)][Sn(nBu)3]2 and 2.17 g (6.05 mmol) of TaCls affording 2.00 g (64%) of 4. 1H NMR (THF-ds): 0.895 (s, 3H, SiMe2); 0.961 (s, 3H, SiMe2); 1.29 (d, 6.5 Hz, 3H, CHMe2); 1.37 (d, 6.5 Hz, 3H, CHMe2);. 2.87 (sept, 7 Hz, lH, CHMe2); 6.28, 6.56, 6.97, 7.28, 7.35, 7.61, 7.79 (m, lH, Cp ). 13C NMR: (THF-ds): 8 = -5.20 (SiMe2), -5.48 (SiMe2), 20.77 (CHMe2), 24.44 (CHMe2), 30.52 (CHMe2), 115.34, 116.56, 116.78, 135.42, 138.29, 138.47 (Cp). [Me2Si(C5H4)(C5H2-2,4-(CHMez)z)][n-Bu3Sn]z. Prepared in an analogous manner to 1 with 3.80 g (13.6 mmol) of Li2[Me2Si(Cs~)(CsH2-(CHMe2)2] and 9.70 g (29.4 mmol) of n-Bu3SnCl affording 10.5 g (90.5%) of Me2Si(C5H4)(CsH2(CHMe2)2)][n-Bu3Sn]2. 1H NMR(CD2Ch): 8 = 0.02 (s, 3H, SiMe2); 0.30 (s, 3H, SiMe2); 0.81 (t, 7 Hz, 18H, SnBu3); 0.89 (t, 7 Hz, 18H, SnBu3); 1.1-1.6 (rn, SnBu3); 2.60 (sept, 7Hz, lH; CHMe2); 2.69 (sept, 7 Hz, lH; CHMe2); 5.30 (m, lH, Cp ); 5.55 (m, lH, Cp); 5.91 (m, lH, Cp); 6.02 (m, lH, Cp); 6.10 (m, lH, Cp). Me2SHT1 5-C5H4)(T1 5-C5H2-2,4-(CHMe2)z)TaCl3 (5). Prepared in an analogous manner to 2 with 6.50 g (7.58 mmol) of [Me2Si(T1 5-C5H4)(T1 5-CsH2-(CHMe2)2)][nBu3Sn]2 and 2.70 g (7.54 mmol) of TaCls affording 2.54 (60%) of 5. 1H NMR (CD2Ch): 8 = 0.05 (s, 3H, SiMe2); 0.30 (s, 3H, SiMe2); 2.64 (sept; 7H, lH, CHMe2); 2.72 (sept; 7 Hz, lH, CHMe2); 5.31 (m, lH, Cp); 5.57 (m, lH, Cp); 5.92 (m, lH, Cp ); 6.42 (m, lH, Cp ); 6.49 (m, lH, Cp ); 6.58 (m, lH, Cp ). Anal. Cald. for Ta1Si1C1sH26Cb C, 38.76%, H, 4.70%; Found C, 37.96%; H, 4.55%. [Me2Si(C5H4)(C5H3-3-CMe3)][n-Bu3Sn]z. Prepared in an analogous manner to 1 with 3.00 g (11.7 mmol) of Lb[Me2Si(Cs~)(CsH3-3-(CMe3))] and 8.10 g (24.5 212 mmol) of n-Bu3SnCl affording 8.73 g (90%) of [Me2Si(C5li4)(C5H3-3(CMe3))][SnBu3]3. 1H NMR (benzene-d6): 8 = 0.42 (s, 3H, SiMe2); 0.45 (s, 3H, SiMe2); 1.45 (s, 9H, CMe3); 0.90-1.10, 1.30-1.65 (m, SnBu3); 5.75, 5.81, 6.24, 6.56, 6.73, 6.88, 6.92 (m, lH, Cp). 13C NMR (benzene-d6): 11.72, 12.17 (SiMe2); 30.11 (CMe3); 154.45 (CMe3); 14.26, 17.71, 27.45, 28.00, 28.22, 28.55, 29.85, 32.00 (SnBu3); 97.54, 98.67, 103.59, 115.63, 121.51, 126.86, 132.29, 132.98, 2 not located (Cp). Me2Si(ri 5-C5H4)(T] 5-C5H3-3-(CMe3))TaCl3 (6). Prepared in an analogous manner to 2 with 4.55 g (5.47 mmol) of [Me2Si(C5H4)(C5H3-(CMe3)][Sn(n-Bu)3]2 and 1.96 g (5.47 mmol) of TaCls affording 1.50 g (51.7%) of 6. 1H NMR (THF-ds): 8 = 1.113 (s, 3H, SiMe2); 1.17 (s, 3H, SiMe2); 1.40 (s, 9H, CMe3); 6.23, 6.38, 6.69, 7.27, 7.64, 7.80 (s, lH, Cp ). 13C NMR (THF-ds): -1.68, -0.27 (SiMe3); 33.34 (CMe3); 151.71 (CMe3); 109.52, 112.83, 118.90, 120.72, 124.61, 131.82, 144.62, 3 not located (Cp). Anal. Cald. for Ta1Si1C16H22Cl3 C, 36.28%, H, 4.19%; Found C, 35.75%; H, 3.55%. Me2Si(ri 5-C5H4)(T] 5-C5H3-3-CHMe2)TaH3 (7). Prepared in an analogous manner to 3 employing 1.00 g (1.94 mmol) of 4 and 14.5 mL (14.5 mmol) of 1 M LiAlfi4 and quenched with 2.0 mL of saturated Nfi4Cl solution yielding 0.257 g (31.8%) of a white solid identified as 7. 1H (benzene-d6): 8 = -0.002 (s, 3H, SiMe2), -0.05 (s, 3H, SiMe2), 1.2 (d, 6 Hz, 6H, CHMe2), 2.73 (sept, 7 Hz, CHMe2t 4.83, 4.91, 5.03, 5.05, 5.22, 5.28, 5.51 (m, lH, Cpt-1.64 (dd, 11.5 Hz, 12 Hz, lH, TaHt-1.80 (dd, 11 Hz, 12 Hz, lH, TaH), 0.52 (t, 12 Hz, TaH). 13C (benzene-d6): 8 = -5.93 (Me2Sit -4.66 (Me2Si), 24.39 (CHMe2), 25.04 (CHMe2t 28.54 (CHMe2t 88.08, 88.97, 89.21, 90.52, 93.69, 94.27, 97.66, 3 not located (Cp ). Me2Si(ri 5-C5H4)(T] 5-C5H2-2,4-(CHMe2)i)TaH3 (8). Prepared in an analogous manner to 3 employing 0.900 g (1.61 mmol) of 5 and 11.8 mL of 1.0 M LiAlfi4. The reaction was quenched with 1.6 mL of saturated Nfi4Cl solution affording 0.235 g (32.1 %) of 8 as a yellow oil. 1H NMR (benzene-d6): 8 = 0.13 (s, 3H, SiMe2), 0.26 (s, 3H, SiMe2), 1.16 (d, 6 Hz, 3H, CHMe2), 1.29 (d, 6 Hz, 6H, CHMe2), 1.42 (d, 6 Hz, 3H, CHMe2), 2.68 (sept, 7 Hz, lH, CHMe2\ 2.88 (sept, 7 Hz, lH, CHMe2), 4.69, 4.73, 5.11, 5.18, 5.21, 5.70 (bs, lH, Cp ), 0.75 (t, 12 Hz, lH, TaH), -1.76 (m, lH, TaH), -1.48 (m, lH, TaH). 13C NMR (toluene-ds): -3.69 (SiMe2), -3.72 (SiMe2\ 21.06 (CHMe2), 24.13 (CHMe2), 24.65 (CHMe2), 28.24 213 (CHMe2), 29.42 (CHMe2), 30.17(CHMe2), 62.93, 68.04, 86.22, 87.86, 88.74, 92.58, 92.67, 98.51, 126.24, 129.03 (Cp). Me2SHr1 5-C5H4)(J1 5-CsH3-3-(CMe3))TaH3 (9). Prepared in an analogous manner to 3 employing 0.760 g (1.43 mmol) of 6 and 10.2 mL of 1.0 M LiAlH4. The reaction was quenched with 1.75 mL of saturated N~Cl solution affording 0.250 g (37.5 %) of 9. 1H NMR (benzene-d6): 8 = -1.79 (m, lH, Ta-H); -1.88 (m, lH, TaH); 0.276 (t, 11 Hz, lH, Ta-H); -0.027 (s, 3H, SiMe2); -0.001 (s, 3H, SiMe2 ); 1.27 (s, 9H, CMe3); 4.762, 4.766, 4.902, 4.982, 5.187, 5.263, 5.451 (m, lH, Cp ). 13C NMR (benzene-d6): ·8 = -5.604 (SiMe2); -4.776 (SiMe2); 32.661 (CMe3); 138.224 (CMe3); 87.17, 89.23, 89.53, 90.72, 93.24, 94.36, 97.35, 3 not located (Cp). Me2SHT1 5-CsH4)zTa(CO)(H) (10). In the dry box, a J. Young NMR tube was charged with 10.0 mg (0.027 mmol) of 3 and the sample was dissolved in C6D6 forming a clear solution. On the vacuum line, carbon monoxide gas was passed through a trap of liquid nitrogen and 1 atmosphere was charged into the NMR tube. The tube was sealed and heated to 87 °C for 48 hours resulting a red solution and a quantitive yield of 10. Attempts to isolate the material in the solid state have been unsuccessful. 1H NMR (benzene-d6): 8 = -5.72 ppm (s, lH, TaH); -0.29 (s, 3H, SiMe2); -0.18 (s, lH, SiMe2); 4.09, 4.41, 4.74, 5.73 (m, lH, Cp). IR (benzene-d6): 1895.5 cm- 1. Me2Si(T1 5-CsH4)(T1 5-CsH3-3-CHMe2)Ta(CO)(H) (11) . The sample was prepared in an analogous manner to 10 with 10.0 mg (0.024 mmol) of 7 and 1 atmosphere of CO and was heated for 8 hours resulting in quantitative formation of two isomers of 11. 1H NMR (benzene-d6): 8 = -5.32 (s, lH, Ta-H); -5.70 (s, lH, Ta-H); -0.221 (s, 3H, SiMe2); -0.198 (s, 3H, SiMe2); -0.172 (s, 3H, SiMe2); -0.137 (s, 3H, SiMe2); 1.07 (d, 7Hz, 3H, CHMe2); 1.09 (d, 7 Hz, 3H CHMe2); 1.16 (d, 7 Hz, 3H, CHMe2); 1.17 (d, 7 Hz, 3H, CHMe2); 2.42 (sept; 7 Hz, lH, CHMe2); 2.66 (sept; 7 Hz, lH, CHMe2); 3.32, 3.81, 4.10, 4.16, 4.25, 4.70, 4.43, 4.52, 4.60, 4.62, 4.65, 4.69, 4.80, 5.69 (m, lH, Cp). 13C NMR (benzene-d6) : 8 = -6.24, -6.08, -4.50, -4.29 (SiMe2); 24.55, 24.89, 27.13, 28.55 (CHMe2); 29.06, 29.13 (CHMe2); 76.27, 77.41, 77.65, 79.42, 80.50, 81.34, 81.69, 82.82, 83.38, 85.99, 85.99, 89.60, 90.23, 90.99, 101.02, 103.46, 104.26, 121.40, 126.16, 128.84, 138.34 (Ta-CO) not located. IR (benzene-d6): 1901.4 cm- 1 . 214 Me2SH11 5-CsH4)(11 5-C5H2-2,4-(CHMez)z)Ta(CO)(H) (12). The sample was prepared in an analogous manner to 10 with 10.0 mg (0.022 mmol) of 8 and 1 atmosphere of CO and was heated for 8 hours resulting in quantitative formation of two isomers of 12. 1H NMR (benzene-d6): 8 = -5.57 (s, lH, Ta-H); -4.95 (s, lH, Ta-H); -0.13 (s, 3H, SiMe2); -0.08 (s, 3H, SiMe2); 0.12 (s, 3H, SiMe2); 0.20 (s, 3H, SiMe2); 1.12 (d, 7 Hz, 3H, CHMe2); 1.20 (d, 7 Hz, 3H, CHMe2); 1.31 (d, 7 Hz, 3H, CHMe2); 1.41 (d, 7 Hz, 3H, CHMe2); 1.89 (sept, 7 Hz, lH; CHMe2); 2.47 (sept, 7 Hz, lH; CHMe2); 2.50 (sept, 7 Hz, lH, CHMe2); 2.74 (sept, 7 Hz, lH; CHMe2); 3.68, 3.95, 4.34, 4.43, 4.48, 4.53, 4.60, 4.67, 4.72, 4.81, 4.86, 5.59, 5.77, 5.95 (m, lH, Cp). 13C NMR (benzene-d6): 8 = -5.555, -4.303, -3.152, -1.518 (SiMe2); 13.96, 22.44, 24.02, 24.73, 26.91, 28.31, 28.68, 28.85 (CHMe2); 29.01, 30.09, 30.31, 31.49 (CHMe2); 77.62, 79.16, 79.36, 79.96, 80.24, 88.52, 88.71, 89.04, 94.71, 96.17, 96.17, 96.78, 98.89, 101.45, 104.15, 109.21, 112.60, 118.74, 119.94, 2 not located (Cp); 202.04, 203.62 (Ta-CO). IR (benzene-d6): 1895.5 cm-1. Me2SH11 5-C5H4)(r15-CsH3-3-CMe3)Ta(CO)(H) (13). The sample was prepared in an analogous manner to 10 with 10.0 mg (0.021 mmol) of 9 and 1 atmosphere of CO and was heated for 8 hours resulting in quantitative conversion to two isomers of 13. Major Isomer: 1H NMR (benzene-d6): 8 = -5.51 (s, lH, Ta-H); -0.180 (s, 3H, SiMe2); -0.177 (s, 3H, SiMe2); 1.29 (s, 9H, CMe3 ); 3.79, 4.16, 4.29, 4.44, 4.52, 4.79, 5.72 (m, lH, Cp ). 13C NMR (benzene-d6): 8 = -4.82 (SiMe2); -6.43 (SiMe2); 32.04 (CMe3 ); 143.11 (CMe3); 75.94, 77.18, 79.47, 82.23, 85.34, 88.58, 89.69, 103.80, 2 not located (Cp ); 197.80 (Ta-CO). Minor Isomer: 1H NMR (benzene-d6): 8 = -5.43 (s, lH, Ta-H); -0.140 (s, 3H, SiMe2); -0.160 (s, 3H, SiMe2); 1.27 (s, 9H, CMe3 ); 3.80, 4.38, 4.47, 5.04, 5.42, 5.47, 5.76 (m, lH, Cp ). 13C NMR (benzene-d6): 8 = -4.99 (SiMe2); -3.37 (SiMe2); 32.21 (CMe3 ); 142.47 (CMe3); 78.60, 81.27, 83.51, 87.54, 87.73, 91.41, 91.33, 102.37, 2 not located (Cp ); not located (Ta-CO). Me2SH11 5-C5H4)zTa(11 2-CH2CH2)(CH2CH3) (14). In the dry box, a J. Young NMR tube was charged with 10.0 mg (0.0255 mmol) of 3 and the solid dissolved in C6D6. On the vacuum line, the tube was degassed with three freeze-pump- 215 thaw cycles and 0.255 mmol of ethylene added via a calibrated gas volume. The tube was thawed and then heated to 87 °C for three hours. Attempts to isolate this complex in the solid state lead to decomposition. 1H NMR (benzene-d6): -0.02 (s, 3H, SiMe2); 0.10 (s, 3H, SiMe2); 0.78 (t, 11 Hz; 2H; CH2=CH2); 1.75 (t, 11 Hz; 2H; CH2=CH2); 1.35 (q, 7 Hz; 2H; CH2CH3); 1.33 (t, 7 Hz; 3H; CH2CH3); 3.62; 4.81; 5.19; 5.27 (m, lH, Cp ). Me2Si('r1 5-C5H4)zTa(11 2-CH2CH2)(H) (15). Complex 15 has been observed by 1H NMR spectrscopy as component of an equilibrium with 14 and free ethylene. 1H NMR (benzene-d6): o= -2.97 (s, lH, Ta-H) ; 0.01 (s, 3H, SiMe2); 0.12 (s, 3H, SiMe2); 0.48 (t, 11 Hz, 2H, CH2=CH2); 1.08 (t, 11 Hz, 2H, CH2=CH2); 3.34; 4.28; 5.39; 5.82 (m, lH, Cp ). Me2Si(11 5-CsH4)(11 5-C5H3-3-CHMe2)Ta(PMe3)(H) (16a,b). NMR Scale: In the dry box, a J. Young NMR tube was charged with 11.4 mg (0.0276 mmol) of 8 and the sample dissolved in C6D6. On the vacuum line, the tube was frozen in liquid nitrogen and degassed. Via calibrated 7.0 mL gas volume, 260 torr (0.968 mmol) of PMe3 was added. The tube was thawed and shaken and then heated to 87 °C and monitored over time by 1H and 31 P NMR spectroscopy. Preparative Scale: In the dry box, a 25 mL thick-walled glass vessel equipped with a magnetic stirring bar was charged with 70.0 mg (0.170 mmol) of 8. On the vacuum line, the bomb was evacuated and approximately 5 mL of toluene was added by vacuum transfer at -78 °C. The bomb was then attached to a 200 mL calibrated volume and 80 torr (0.850 mmol) of PMe3 was added. The reaction mixture was heated to 87 °c for 36 hours. The contents of the thick-walled vessel were transferred into a swivel frit assembly and the toluene was removed in vacuo leaving a red oil. Attempts to recrystallize the product from petroleum ether or diethyl ether have been unsuccessful. NMR analysis reveals that 16a is the only isomer present. UV-VIS (toluene): 452.1 nm, c ~ 5000 M-1 cm- 1. 16a: lH NMR (benzene-d6): o= -7.89 (d, 21.5 Hz, lH, Ta-H); -0.084 (s, 3H, SiMe2); -0.042 (s, 3H, SiMe2); 1.00 (d, 7.5 Hz, 9H, PMe3); 1.29 (d, 6.5 Hz, 3H, CHMe2); 1.39 (d, 6.5 Hz, 3H, CHMe2); 2.79 (sept, 7 Hz, lH, CHMe2); 4.24, 4.26, 4.37, 4.66, 4.72, 4.80, 5.72 (m, lH, Cp). 13C NMR (benzene-d6): o= -5.35, -3.29 (SiMe2); 25.81, 26.00, 29.47 (CHMe2); 29.47 (CHMe2); 25.27 (d, 20 Hz, PMe3 ); 64.92, 66.58, 75.02, 75.67, 91.25, 92.64, 101.54, 135.25, 2 not located (Cp). 31 P NMR (benzene-d6): o= -26.52. 216 1 16b: H NMR (benzene-d6): 8 = -8.20 (d, 20 Hz, lH, Ta-H); -0.06 (s, 3H, SiMe2); -0.01 (s, 3H, SiMe2); 1.01 (d, 8 Hz, 9H, PMe3); 1.20 (d, 6.5 Hz, 3H, CHMe2); 1.27 (d, 6.5 Hz, 3H, CHMe2); 2.60 (sept, 7 Hz, lH, CHMe2); 4.20; 4.37; 4.84; 5.01; 5.20, 3 not located (m, lH, Cp). 31p NMR (benzene-d6): 8 = -26.10. Me2SH11 5-C5H4)(11 5-CsH3-3-CHMe2)Ta(PEt3)(H) (17). In the dry box, a J. Young NMR tube was charged with 10.0 mg (0.242 mmol) of 8 and the sample was dissolved in C6D6. In the dry box, 15.0 µL (0.158 mmol) of PEt3 was added to the tube via microsyringe. The tube was heated in an 87 °C oil bath and the progress of the reaction monitored by lH and 31p NMR spectroscopy. lH NMR (benzene-d6): •8 = -8.03 (d, 21.5 Hz, lH, Ta-H); -0.028 (s, 3H, SiMe2); 0.012 (s, 3H, SiMe2); 0.779 (m, 9H, PEt3); 0.939 (m, 6H, PEt3); 1.30 (d, 6.5 Hz, 3H, CHMe2); 1.39 (d, 6.5 Hz, 3H, CHMe2); 2.77 (sept, 7 Hz, lH, CHMe2); 3.85; 4.20; 4.24; 4.59; 4.73; 4.80; 5.63 (m, lH, Cp ). 13C NMR (benzene-d6): 8 = -5.35, -3.14 (SiMe2); 24.93, 25.42 (CHMe2); 29.42 (CHMe2); 28.85 (d, 85 Hz, P(CH2CH3)3); 8.46 (P(CH2CH3)3); 66.22, 68.15, 74.07, 74.39, 91.20, 93.32, 101.05, 134.92, 146.12, 150.39. 31p (benzened6): 8 = -17.60. UV-VIS (toluene): 454.6 nm,£~ 5000 M-1 cm-1. Me2SH11 5-C5H4)(11 5-CsH2-2,4-(CHMe2)z)Ta(PMe3)(H) (18a,b). In the dry box, 0.06 mL of a 0.235 M stock solution of 8 in C6D6 was charged into a J. Young NMR tube. On the line, the tube was frozen in liquid nitrogen and degassed. Via 43.48 mL calibrated gas volume, 30 torr of PMe3 was added. The tube was placed in an 87 °Coil bath and monitored by 1H and 31 P NMR spectroscopy. 18a: lH NMR (benzene-d6): 8 = -7.83 (d, 31 Hz; lH, Ta-H) . 31 P (benzene-d6): 8 = -26.92. 18b: lH NMR (benzene-d6): 8 = -8.13 (d, 31 Hz, lH, Ta-H); -0.62 (s, 3H, SiMe2); 0.785 (s, 3H, SiMe2); 1.07 (d, 8 Hz, 9H, PMe3); 1.24, 1.29 (d, 7 Hz, 3H, 4CHMe2 ); 1.37; 1.38 (d, 7 Hz, 3H, 2-CHMe2 ); 2.43 (sept, 6.5 Hz; lH; 2-CHMe2); 2.75 (sept, 6.5 Hz; lH; 4-CHMe2); 4.23, 4.31, 4.46, 4.62, 4.75, 5.22 (m, lH, Cp). 13C (benzene-d6 ): 8 = -3.77, 2.34 (SiMe2); 46.50 (d, 490 Hz, PMe3 ); 24.06; 24.79; 25.53; 29.65; 30.44; 32.56 (CHMe2); 71.59; 71.63; 72.26; 79.75; 80.15; 93.34; 95.30;; 100.33; 100.63; 1 not located (Cp) 31 P (benzene-d6): 8 = -29.09. M e2Si (11S-C5H4)(11 5-CsHz-2,4-(CHMe2)z)Ta(PEt3)(H) (19a,b). In the dry box, 0.05 mL of a 0.235 M stock solution of 8 in C6D6 was charged into a J. Young NMR tube. Via microsyringe, 7.0 mg (0.059 mmol) of PEt3 was added to the tube. The tube was heated to 87 °C and the progress of the reaction monitored by 1H and 217 31 P NMR spectroscopy. 19a: 1H NMR (benzene-d6): 8 = -7.80 (d, 20 Hz, lH, TaH); 19b: 1H NMR (benzene-d6): 8 = -8.25 (d, 20 Hz, lH, Ta-H); -0.05 (s, lH, SiMe2); 0.21 (s, lH, SiMe2); 0.85 (m, 9H, PEt3); 1.16 (m, 6H, PEt3); 1.02, 1.06 (d, 6.5 Hz, 3H, CHMe2); 1.46; 1.50 (d, 6.5 Hz, 3H, CHMe2); 2.62; 2.71 (sept, 7 Hz, lH, CHMe2); 4.28; 4.36; 4.41; 4.63; 4.65; 4.80; 4.92; (m, lH, Cp). 31p (benzene-d6): 8 = -17.65. Me2Si('r1 5-CsH4)('11 5-CsH3-3-CMe3)Ta(PMe3)(H) (20). The sample was prepared in an analogous manner to 16 employing 10.0 mg (0.021 mmol) of 8 and 30 torr of PMe3 was added via a 43.48 mL calibrated gas volume. The tube was placed in an 87 °Coil bath and monitored by lH and 31p NMR spectroscopy. lH NMR (benzene-d6): 8 = -7.960 (d, 20.5 Hz, Ta-H); -0.048 (s, 3H, SiMe2); -0.006 (s, 3H, SiMe2); 1.02 (d, 7 Hz, 9H, PMe3); 1.44 (s, 9H, CMe3); 3.87, 3.92, 4.16, 4.19, 4.66, 4.75, 5.84 (m, lH, Cp ). 13C NMR (benzene-d6): 8 = -5.78 (SiMe2); -3.52 (SiMe2); 32.45 (CMe3); 140.86 (CMe3); 47.12 (d, 695 Hz, PMe3); 64.29, 65.66, 74.21, 75.79, 88.62, 90.47, 101.97 (Cp). 3lp (benzene-d6): 8 = -28.61. Me2SH11 5-CsH4)zTaCI2 (21). In the dry box, a fine swivel frit assembly was charged with 0.716 g (1.51 mmol) of 2 and 0.098 g (1.51 mmol) of Zn dust. On the vacuum line, the frit assembly was evacuated and approximately 25 mL of DME was added by vacuum transfer at-78 °C. The reaction was stirred and slowly warmed to room temperature. After 4 hours, a forest green reaction mixture forms. After stirring for 16 hours, the green DME solution was filtered and the remaining solid was washed three times with recycled solvent. The DME was removed in vacuo leaving a green oily solid. Addition of Et2O afforded a green precipitate that was collected by filtration and dried in vacuo leaving 0.580 g (88%) of 20. EPR (CH2Ch): giso = 1.98; aiso= 101.9 G. Me2Si(11S-C5H4)(11 5-C5H3-3-CHMe2)TaCl2 (22). This compound was prepared in an analogous manner to 21 employing 0.960 g (1.86 mmol) of 4 and 0.121 g (1.86 mmol) of Zn dust affording 0.600 g (67.1 %) of a green solid identified as 22. EPR (CH2Ch): giso = 1.94; aiso = 101.3 G. Me2Si(11S-C5H4)(11 5-C5H2-2,4-(CHMe2)z)TaC}z (23). This compound was prepared in an analogous manner to 21 employing 2.47 g (4.43 mmol) of 5 and 218 0.288 g (4.43 mmol) of Zn dust affording 2.20 g (95.1 %) of a green solid identified as 23. Sublimation at 140 °C and 10-4 torr affords analytically pure material. Anal. Cald. for Ta1Si1C1sH20Clz C, 37.51 %, H, 4.20%; Found C, 37.28%; H, 4.23%. EPR (CH2Clz): giso = 1.94; aiso = 92.9 G. Me2SHT1 5-CsH4)(r1 5-C5H3-3-CMe3)TaCI2 (24). This compound was prepared in an analogous manner to 21 employing 1.00 g (1.73 mmol) of 6 and 0.115 g (1.73 mmol) of Zn dust affording 0.726 g (78.5%) of a green solid identified as 24. Anal. Cald. for Ta1Si1C16H22Clz C, 38.88%, H, 4.49%; Found C, 37.55%; H, 4.36%. EPR (CH2Clz): giso = 1.94; aiso = 101.2 G. Me2SHT1 5-CsH4)(T1 5-C5H3-3-CHMe2)Ta(T1 2-CH2CH2)(H) (25). In the dry box, a fine swivel frit assembly was charged with 0.300 g (0.625 mmol) of 22. On the vacuum line, approximately 25 mL of Et2O was added by vacuum transfer. At -80 °C, against an Ar counterflow, 1.00 mL of a 3.0 M CH3CH2MgBr solution was added by syringe. The reaction mixture was stirred and slowly warmed to room temperature. After 2 hours, an orange solution and brown precipitate form. The reaction mixture was stirred for 16 hours after which time the Et2O was removed and replaced with 10 mL of petroleum ether. The product was extracted several times with petroleum ether. The solvent removed in vacuo leaving a yellow oil identified as 25. 1H NMR (benzene-d6): 8 = -2.72 (s, lH, TaH); 0.19 (s, 3H, SiMe2); 0.30 (s, 3H, SiMe2); 0.51 (m, 2H, CH2=CH2, endo); 1.10 (m, 2H, CH2=CH2, exo); 1.23 (d, 7 Hz, 3H, CHMe2); 1.29 (d, 7 Hz, 3H, CHMe2); 2.90 (sept, 7 Hz, lH, CHMe2); 3.40, 4.32, 4.42, 4.47, 5.35 (2H), 5.94 (m, lH, Cp). 13C NMR (benzene-d6): 8 = -6.92 (SiMe2); -4.10 (SiMe2); 11.87 (CH2=CH2, endo); 30.10 (CH2=CH2, exo); 23.65 (CHMe2); 25.73 (CHMe2); 28.45 (CHMe2); 80.62, 82.38; 91.90; 93.26; 102.10; 104.05; 105.49, 3 not located (Cp ). Me2Si(T1S·C5H4)(T1 5-C5H3-3-CHMe2)Ta(T1 2-CH2CHCH3)(H) (26). In the dry box, a fine swivel frit assembly was charged with 0.225 g (0.514 mmol) of 22. On the vacuum line, approximately 25 mL of Et2O was added by vacuum transfer. At -80 °C, against an Ar counterflow, 2.0 M CH3CH2CH2MgCl solution in diethyl ether was added via syringe. The reaction mixture was stirred and slowly warmed to room temperature. With warming an orange solution and brown precipitate forms. The reaction was stirred for 24 hours and the Et2O was removed in vacuo and replaced with petroleum ether. The product was extracted 219 several times with petroleum ether. The solvent was removed in vacuo leaving a thick orange oil identified as 26. Major Isomer (63.7%) 1H NMR (benzene-d6): 8 = -2.71 (s, lH, Ta-H); 0.04 (s, 3H, SiMe2); 0.12 (s, 3H, SiMe2); 1.23 (d, 7 Hz, 3H; CHMe2); 1.30 (d, 7 Hz, 3H, CHMe2); 2.89 (sept, 6.5 Hz, lH, CHMe2); 0.44 (dd, 10 Hz, 6 Hz, lH, CH2=CHCH3); 0.87 (dd, 10 Hz, 6 Hz, lH; CH2=CHCH3); 1.01 (m, lH, CH2=CHCH3); 2.21 (d, 6.5 Hz, 3H; CH2=CHCH3); 3.37; 3.79; 4.40; 4.56; 5.15; 5.57; 5.59 (m, lH, Cp ). 13C NMR (benzene-d6): 8 = -6.63 (SiMe2); -4.27 (SiMe2); 30.17 (CH2=CHCH3), 28.77 (CH2=CHCH3); 24.23 (CH2=CHCH3); 21 .63 (CHMe2); 21.76 (CHMe2); 29.03 (CHMe2); 81.62; 83.10; 81.31; 91.39; 104.37; 106.70; 106.81; 3 not located (Cp ). Minor Isomer (20.6 %), 1H NMR (benzene-d6): 8 = -2.65 (s, lH, Ta-H); 0.10 (s, 3H, SiMe2); 0.15 (s, 3H, SiMe2); 1.25 (d, 7 Hz, 3H; CHMe2); 1.27 (d, 7 Hz, 3H; CHMe2); 2.80 (sept, 6.5 Hz, lH; CHMe2); 3 propylene resonances not located; 2.25 (d, 6.5 Hz, 3H; CH2=CHCH3); 3.30; 3.65; 4.36; 4.37; 5.18; 5.36; 5.91; (m, lH, Cp ); 13C NMR (benzene-d6): 8 = -7.01 (SiMe2); -3.44 (SiMe2); 29.69 (CH2=CHCH3); 23.85 (CH2=CHCH3); 25.98 (CH2=CHCH3); 21.28 (CHMe2); 22.52 (CHMe2); 27.76 (CHMe2); 79.50; 84.81; 91.02; 94.26; 98.10; 99.34; 107.38; 3 not located (Cp). Me2Si('r1 5-CsH4)(11 5-CsH3-3-CHMe2)Ta(11 2-CH2CHPh)(H) (27) . This compound was prepared in a similar manner to 25 employing 0.400 g (0.914 mmol) of 22 and 2.28 mL of 1.0 M PhCH2CH2MgBr in THF solution. A golden yellow solid (0.120 g) sample of 27 was obtained by slow cooling of a petroleum ether solution followed by filtration. Anal. Cald. for Ta1Si1C23H29 C, 53.69%, H, 5.68%; Found C, 53.12%; H, 5.82%. Major Isomer (54%) 1H NMR: (benzene-d6)= 8 = -1.53 (s, lH, Ta-H); -0.03 (s, 3H, SiMe2); 0.09 (s, 3H, SiMe2); 1.26 (d, 7 Hz, 3H; CHMe2); 1.34 (d, 7 Hz, 3H; CHMe2); 2.92 (sept, 6.5 Hz, lH; CHMe2); 3.56 (m, lH; CH2=CHPh, cis); 3.59 (m, lH; CH2=CHPh, trans); 3.10 (t, 10 Hz. lH; CH2=CHPh); 4.29; 4.33; 5.17; 5.23; 5.28; 5.56; 5.61 (m, lH, Cp ). 13C NMR (benzene-d6): 8 = -6.75 (SiMe2); -4.36 (SiMe2); 13.77 (CH2=CHPh); 30.11 (CH2=CHPh); 21.70 (CMe2) ; 24.26 (CHMe2) ; 29.09 (CHMe2); 83.12; 86.05; 93.46; 95.19; 105.34; 110.55; 4 not located (Cp ). 121.90 (C6Hs, meta); 136.79 (C6Hs, ortho); 154.81 (C6Hs, para) 1 not located (C6Hs, ipso). 220 1 Minor Isomer (36%) H NMR: (benzene-d6): o= -1.69 (s, lH, Ta-H); -0.01 (s, 3H, SiMe2); 0.093 (s, 3H, SiMe2); 1.25 (d, 7 Hz, 3H; CHMe2); 0.76 (d, 7 Hz, 3H; CHMe2); 1.76 (sept, 6.5 Hz, lH; CHMe2); 3.48 (m, lH; CH2=CHPh, cis); 3.48 (m, lH; CH2=CHPh); 3.10 (t, 10 Hz, lH; CH2=CHPh); 4.24; 4.29; 4.32; 5.21; 5.27; 5.62; 6.04 (m, lH, Cp). 13C NMR (benzene-d6): 8 = -6.92 (SiMe2); -4.10 (SiMe2); 14.26 (CH2=CHPh); 28.65 (CH2=CHPh); 24.22 (CMe2); 25.48 (CHMe2); 26.31 (CHMe2); 80.72; 84.27; 94.67; 95.66; 104.79; 106.37; 107.73; 110.34 (Cp), 121.54 (C6Hs, meta); 138.88 (C6Hs, ortho); 153.84 (C6Hs, para); 1 not located (C6Hs, ipso) . Trace Isomer (10%) 1H NMR: (benzene-d6): o= -1.74 (s, lH, Ta-H); -0.04 (s, 3H, SiMe2); 0.06 (s, 3H, SiMe2); 0.92 (d, 7 Hz, 3H; CHMe2); 1.13 (d, 7 Hz, 3H; CHMe2); 2.40 (sept, 6.5 Hz, lH; CHMe2); not located (m, lH; CH2=CHPh, cis); not located (m, lH; CH2=CHPh); 4.12 (t, 10 Hz; lH; CH2=CHPh); 4.67; 4.69; 4.99; 5.34; 5.36; 2 not located (m, lH, Cp ). 13C NMR (benzene-d6): o= -5.20 (SiMe2); -6.02 (SiMe2); 11.90 (CH2=CHPh); 30.61 (CH2=CHPh); 20.28 (CMe2); 22.50 (CHMe2); not located (CHMe2); 87.25; 88.31; 91 .15; 91.59; 93.95; 100.24; 104.60; 110.07, 2 not located (Cp), 123.99 (C6Hs, meta); not located (C6Hs, ortho); not located (C6Hs, para); not located (C6Hs, ipso) . Me2Si(11 5-CsH4)(11 5-CsH2-2,4-(CHMe2)z)Ta(11 2-CH2CH2)(H) (28). This compound was prepared in the similar manner to 25 employing 0.340 g (0.651 mmol) of 23 and 0.477 mL of a 3.0 M CH3CH2MgBr solution in diethyl ether. Extraction with petroleum ether afforded 28 as a yellow oil. Major Isomer 1H NMR (benzene-d6): o= -2.69 (s, lH, Ta-H); 0.15 (s, 3H, SiMe2); 0.29 (s, 3H, SiMe2); 0.42 (m, 2H, CH2=CH2); 0.89 (m, 2H, CH2=CH2); 0.95 (d, 7 Hz, 3H, CHMe2); 0.92 (d, 7 Hz, 3H, CHMe2); 1.26 (d, 7 Hz, 3H, CHMe2); 1.36 (d, 7 Hz, 3H, CHMe2); 2.78 (sept, 7 Hz, lH, CHMe2); 2.47 (sept, 7 Hz, lH, CHMe2); 3.88, 4.45, 4.97, 5.02, 5.26, 5.41. 13C NMR: (benzene-d6): o= -1.86 (SiMe2); 1.36 (SiMe2); 30.55 (CH2=CH2, exo); 8.80 (CH2=CH2, endo); 20.88 (CMe2); 22.72 (CMe2); 27.71 (CMe2); 13.90 (CMe2); 29.70 (CMe2); 30.18 (CMe2); 89.57, 92.60, 96.61, 102.03, 104.22, 123.89, 125.99, 3 not located (Cp). Minor Isomer 1H NMR (benzene-d6): o= -2.78 (s, lH, Ta-H); 0.17 (s, 3H, SiMe2); 0.30 (s, 3H, SiMe2); 0.25 (m, 2H, CH2=CH2); 0.76 (m, 2H, CH2=CH2); 0.97 (d, 7 Hz, 3H, CHMe2); 1.30 (d, 7 Hz, 3H, CHMe2); 2 not located (CHMe2); 2.04 (sept, 7 Hz, 221 lH, CHMe2); 2.23 (sept, 7 Hz, lH, CHMe2); 4.26, 4.33, 4.78, 5.80, 5.10, 5.21. 13C NMR: (benzene-d6): 8 = -4.63 (SiMe2); 1.14 (SiMe2); 30.61 (CH2=CH2, exo); 10.72 (CH2=CH2, endo); 11.31 (CMe2); 16.52 (CMe2); 18.62 (CMe2); not located (CMe2); 26.29 (CMe2); not located (CMe2); 91.12, 94.08, 95.16, 100.82, 100.91, 123.60, 125.73, 3 not located (Cp ). Me2Si(11 5-CsH4) (11 5-CsH3-( CHMe2h)Ta(11 2-CH2CH CH3) (H). An attempt to prepare this compound in a similar manner to 26 was employed with 0.320 g (0.613 mmol) of 23 and 0.700 mL of 2.0 M CH3CH2CH2MgBr solution in diethyl ether. Isolation and analysis of the yellow oil by 1H NMR spectroscopy did not yield any tractible product. Me2Si(11 5-C5H4)(11 5-CsH2-(CHMe2h)Ta(11 2-CH2CHPh)(H) (29) . This compound was prepared in a similar manner to 25 employing 0.385 g (0.737 mmol) of 23 and 1.62 mL of 1.0 M PhCH2CH2MgBr in THF yielding 0.145 g of 29 as a yellow solid. Anal. Cald. for Ta1SiiC26H35 C, 56.11 %, H, 6.34%; Found C, 55.71 %; H, 6.54%. Major Isomer 1H NMR (benzene-d6): 8 = (s, lH, Ta-H); 0.172 (s, 3H, SiMe2); 0.094 (s, 3H, SiMe2); 0.940 (d, 6.5 Hz, 3H, CHMe2); 1.06 (d, 6.5 Hz, 3H, CHMe2); 1.08 (d, 6.5 Hz, 3H, CHMe2); 1.54 (d, 6.5 Hz, 3H, CHMe2); 2.61 (sept, 7 Hz, lH, CHMe2); 2.68 (sept, lH, CHMe2); styrene resonances not located; 4.46, 4.51, 4.75, 4.85, 4.99, 5.23 (m, lH, Cp); 6.90 (t, 5 Hz, lH, C6Hs, para); 7.47 (d, 7 Hz, 2H, C6Hs, ortho); 7.28 (m, 2H, C6Hs, meta). l3C NMR (benzene-d6): 8 = -3.82 (SiMe2); -3.49 (SiMe2);12.48 (CH2=CHPh); 30.73 (CH2=CHPh); 21.47 (CHMe2); 22.79 (CHMe2); 24.24 (CHMe2); 27.28 (CHMe2); 29.28 (CHMe2); 29.64 (CHMe2); 88.69, 92.12, 96.08, 104.54, 109.03, 111.11, 113.58, 3 not located (Cp), 126.33 (C6Hs, para); 136.96 (C6Hs, ortho), 155.99 (C6Hs, meta); 1 not located (C6Hs, ipso). Minor Isomer 1H NMR (benzene-d6): 8 = (s, lH, Ta-H); -0.071 (s, 3H, SiMe2); 0.257 (s, 3H, SiMe2); 1.01 (d, 6.5 Hz, 3H, CHMe2); 1.11 (d, 6.5 Hz, 3H, CHMe2); 1.34 (d, 6.5 Hz, 3H, CHMe2); 1.44 (d, 6.5 Hz, 3H, CHMe2); 2.42 (sept, 7Hz, lH, CHMe2); 2.9l(sept, lH, CHMe2); styrene resonances not located; 4.68, 4.82, 4.92, 5.07 5.17, 5.89 (m, lH, Cp); 6.87 (t, 5 Hz, lH, C6Hs, para); 7.40 (d, 7 Hz, 2H, C6Hs, ortho); 7.27 (m, 2H, C6Hs, meta) . 13C NMR (benzene-d6): 8 = -1.94 (SiMe2); -5.45 (SiMe2); 7.70 (CH2=CHPh); 34.05 (CH2=CHPh); 18.37 (CHMe2); 21.97 (CHMe2); 222 25.78 (CHMe2); 28.24 (CHMe2); not located (CHMe2); not located (CHMe2); 86.32, 88.06, 92.94, 94.23, 103.48, 108.65, 112.78, 3 not located (Cp ), 125.52 (C 6H 5, para); 140.03 (C6Hs, ortho), 2 not located. Me2Si(T1 5-C5H4)(TJ 5-CsH3-3-CMe3)Ta(TJ 2-CH2=CHPh)(H) (30). Prepared in an analogous manner to 25 employing 0.500 g (0.935 mmol) of 24 and 2.10 mL (2.05 mmol) of 1.0 M PhCH2CH2MgBr solution in THF. Cooling a concentrated petroleum ether solution affords 0.120 g (22.5%) of a yellow solid identified as 30. 1H NMR (benzene-d6): 8 = -1.602 (s, lH, Ta-H); -0.0375 (s, 3H, SiMe3); 0.0785 (s, 3H, SiMe3); 1.41 (s, 9H, CMe3); 0.928 (m, lH, CH2=CHPh); 1.54 (m,lH, CH2=CHPh); 3.142 (t, 12.2 Hz, lH, CH2=CHPh); 3.33, 3.46, 4.06, 4.17, 5.27, 5.46, 5.60 (m, lH, Cp). 13C NMR (benzene-d6): 8 = -7.10 (SiMe2); -4.15 (SiMe2); 14.90 (CH2=CHPh); 28.68 (CH2=CHPh); 31.73 (CMe3); 143.59 (CMe3); 72.39, 73.32, 80.52, 84.60, 94.59, 96.27, 102.40, 105.11, 2 not located (Cp); 109.73 (C6Hs, para); 121.96 (C6Hs, ortho), 154.63 (C6Hs, meta); 1 not located (C6Hs, ipso). Me2SHT1 5-C5H4)(TJ 5-CsH2-2,4-(CHMe2h)TaMe3 (31). In the dry box, a 250 mL round bottom flask was charged with 1.01 g (3.55 mmol) of Li2[Me2Si(T\S_ Cs~)(T\ 5-C5H3-(CHMe2)2)]. An addition funnel was charged with 1.00 g (3.55 mmol) of TaC!iMe3 and a 180 ° needle valve attached. On the vacuum line, approximately 100 mL of THF was added to the reaction flask forming a yellow solution. Similarly, the addition funnel was charged with approximately 20 mL of THF. The solution of ligand was added slowly to the tantalum over the course of 30 minutes at -80 °C. With addition, a brown solution forms. The reaction mixture was stirred overnight. The THF was removed in vacuo and replaced with petroleum ether. The reaction mixture was stirred for 30 minutes and then dried. The flask was then attached to a swivel frit assembly and the product extracted with Et2O. The Et2O was removed in vacuo leaving a yellow solid. Recrystallization from petroleum ether afforded 1.30 g (70.6%) of 31 as a yellow solid. 1H NMR (dichloromethane-d2): 8 = -0.456 (s, 3H, Ta-Me); 0.403 (s, 3H, TaMe); 0.6675 (s, 3H, Ta-Me); 0.026 (s, 3H, SiMe2); 0.097 (s, 3H, SiMe2); 0.999 (d, 7 Hz, 3H, CHMe2); 1.14 (d, 7 Hz, 3H, CHMe2); 1.89 (d, 7 Hz, 3H, CHMe2); 1.32 (d, 7 Hz, 3H, CHMe2); 2.46 (sept, 6.5 Hz, lH, CHMe2); 2.84 (sept, 65 Hz, lH, CHMe2); 4.69, 4.91, 5.25, 5.30, 5.50, 5.86 (m, lH, Cp). 13C (dichloromethane-d2): o= -5.37 (SiMe2); -0.019 (SiMe2); 19.75 (TaMe); 20.45 (TaMe); 20.86 (TaMe); 25.11, 25.95, 223 27.62, 28.87 (CHMe2); 30.73, 31.56 (CHMe2); 83.71, 88.16, 97.66, 106.37, 113.55, 117.60, 117.78, 121.46, 122.73, 127.64 (Cp). Anal. Cald. for Ta1Si1C21H35 C, 50.80%, H, 7.10%; Found C, 50.42%; H: 6.85%. [Me2SH11 5-CsH4)(11 5-CsH2-2,4-(CHMe2)z)TaMe2HBF4] (32). In the dry box, a fine swivel frit assembly was charged with 0.203 g (0.392 mmol) of 31 and 0.130 g (0.392 mmol) of [Ph3C][BF4] . On the line, approximately 15 mL of CH2Cl2 was added by vacuum transfer. With addition, a yellow reaction mixture forms. The reaction was stirred at room temperature for 16 hours. The CH2Cli was removed in vacuo and replaced with Et2O precipitating a yellow solid. The solid was collected by filtration and dried in vacuo yielding 0.150 g (65%) of 32. lH NMR (dichloromethane-d2): b = 0.603 (s, 3H, Ta-Me); 0.661 (s, 3H, Ta-Me); 0.491 (s, 3H, SiMe2); 0.724 (s, 3H, SiMe2); 1.15 (d, 7Hz, 3H, CHMe2); 1.28 (d, 7Hz, 3H, CHMe2); 1.38 (d, 7 Hz, 3H, CHMe2); 1.39 (d, 7 Hz, 3H, CHMe2); 2.64 (sept, 6.9 Hz, lH, CHMe2); 2.69 (sept, 6.9 Hz, lH, CHMe2); 5.53, 5.72, 6.02, 7.02, 7.34, 7.54 (m, lH, Cp). 13C NMR (dichloromethane-d2): 6 = -3.13 (SiMe2); -1.79 (SiMe2); 2 not located (TaMe); 20.35, 21.72, 25.43, 29.38 (CHMe2); 29.80, 31.85 (CHMe2); 110.98, 113.81, 116.73, 120.09, 128.99, 143.96, 144.05, 3 not located (Cp). Anal. Cald. for Ta1Si1C20H32B1F4 C, 42.27%, H, 5.68%; Found C, 41.91 %; H: 5.48%. Me2SH11 5-C5H4)(11 5-C5H3-(CHMe2)z)Ta(=CH2)(CH3) (33). In the dry box, a 25 mL round bottom flask was charged with 0.140 g (0.237 mmol) of 32 and 0.040 g (0.239 mmol) of LiCH(TMS)2. The flask was attached to a fine swivel frit assembly. On the vacuum line, petroleum ether was added to the flask. With addition, a yellow slurry forms that turns brown/ orange. The reaction was stirred for one hour and the white precipitate was removed by filtration. The petroleum ether was cooled to -80 °C precipitating a tan solid identified as 33. This compound is both unstable in solution and the solid state and as a result only NMR spectroscopic data could be obtained. 1H NMR (benzene-d6): 6 = 0.091 (s, 3H, SiMe2); -0.198 (s, 3H, SiMe2); 0.243 (s, 3H, TaMe); 10.22 (d, 8 Hz, lH, TaCH2); 10.30 (d, 8 Hz, lH, TaCH2); 1.05 (d, 7 Hz, 3H, CHMe2); 1.13 (d, 7 Hz, 3H, CHMe2); 1.29 (d, 7 Hz, 3H, CHMe2); 1.36 (d, 7 Hz, 3H, CHMe2); 2.43 (sept, 7 Hz, lH, CHMe2); 3.31 (sept, 7 Hz, lH, CHMe2); 4.57, 4.68, 5.35, 5.73, 5.80, 6.01 (m, lH, Cp). 224 Me2Si(ri 5-C5H4)(ri 5-CsH2-2,4-(CHMez)z)Ta(ri 2-CH2CH2)(CH3) (34). This compound was prepared using an analogous procedure to 33 with the exception that the reaction was allowed to stir overnight. Removal of the petroleum ether afforded a tan solid identified as 34. 1H NMR (benzene-d6): 8 = -0.01 (s, 3H, SiMe2); 0.32 (s, 3H, SiMe2); 0.41 (s, 3H, TaMe); 0.83 (m, 2H, CH2=CH2); 1.28 (m, 2H, CH2=CH2); 0.89 (d, 7 Hz, 3H, CHMe2); 0.95 (d, 7 Hz, 3H, CHMe2); 1.10 (d, 7 Hz, 3H, CHMe2); 1.32 (d, 7 Hz, 3H, CHMe2); 1.48 (sept, 7 Hz, lH, CHMe2); 2.72 (sept, 7 Hz, lH, CHMe2); 3.71, 4.42, 4.96, 5.30, 5.34, 5.48 (m, lH, Cp ). Me2C(l1 5-C5H4)(llLFiuorenyl)TaMe3 (35). In the dry box, a 50 mL round bottomed flask was charged with 1.00 g (3.52 mmol) of Li2[Me2C(C5~)(Fluorenyl)] and 1.04 g (3.51 mmol) of TaCbMe3. The reaction mixture was slowly warmed to room temperature and was stirred for 2.5 hours. The yellow solution was filtered from the brown precipitate and the precipitate was exhaustively washed with toluene. The toluene was removed in vacuo leaving 1.05 g (60.0%) of a golden solid identified as 35. 1H NMR (benzene-d6): 8 = 0.478 (s, 6H, TaMe); 0.601 (s, 3H, TaMe); 1.21 (s, 6H, CMe2); 5.17 (s, 4H, Cp ); 5.58 (s, 4H, Cp); 6.87 (d, 8 Hz, 2H, Flu); 7.13 (t, 5 Hz, 2H, Flu); 7.22 (t, 5 Hz, 2H, Flu); 7.87 (d, 8 Hz, 2H, Flu). 13C NMR (benzene-d6): 8 = 29.35 (CMe2); 35.89 (CMe2); 53.84 (TaCH3, lateral); 85.15 (TaCH3 central); 100.69, 117.22, 120.7 (Cp); 125.01, 125.57, 125.78, 140.43, 144.61, 2 not located (Flu) . Anal. Cald for Ta1C24H27 C, 58.07%, H, 5.48%; Found C, 57.49%; H: 5.56%. Ph2C(ll5-C5H4Hr1LF1uorenyl)TaMe3 (36). This compound was prepared using an analogous procedure to 35 employing 1.40 g (3.42 mmol) of Li2[Ph2C(C5~)(Fluorenyl)] and 0.900 g (3.03 mmol) of TaCl2Me3. The reaction was stirred for 4 hours yielding 0.102 g (5.31 %) of a yellow solid identified as 36. lH NMR (benzene-d6): 8 = 0.317 (s, 6H, TaMe); 0.497 (s, 3H, TaMe); 5.40 (s, 4H, Cp); 5.58 (s, 4H, Cp); 6.07 (d, 8 Hz, 2H, Flu); 6.84 (t, 5 Hz, 2H, Flu); 6.92 (t, 5 Hz, 2H, Flu); 8.02 (d, 8 Hz, 2H, Flu); 6.35 (m, lH, CPh2); 6.53 (m, lH, CPh2); 7.02 (m, lH, CPh2); 7.25 (m, lH, CPh2); 7.73 (m, lH, CPh2). Me2C(ri 5-C5H4)(0ct)TaMe3 (37). In the dry box, a round bottom flask was charged with 0.750 g (1.33 mmol) of Li2[Me2C(C5~)(Oct)] . An addition funnel was charged with 0.395 g (1.33 mmol) of TaCl2Me3. On the vacuum line, 150 mL of THF was added to the flask and 25 mL of THF was added to the addition 225 funnel. The yellow tantalum solution was added to the ligand at -80 °c over the course of 30 minutes. The reaction was slowly warmed to room temperature and stirred for 16 hours. The THF was removed from the dark brown solution and replaced with petroleum ether. The petroleum ether was removed in vacuo leaving an oil. In the dry box, the oil was dissolved in 10 mL of petroleum ether and cooled to -30 °C. Over several days, a brown solid precipitates from the solution. The material was collected and dried in vacuo resulting in 0.123 g (12.1 %) of brown solid identified as 37. 1H NMR (benzene-d6): o= 0.528 (s, 6H, TaMe); 0.645 (s, 3H, TaMe); 1.36 (s, 12H, Oct), 1.38 (s, 12H, Oct), 1.40 (s, 6H, CMe2); 1.66 (m, 4H, Oct); 5.33 (s, 2H, Cp); 5.57 (s, 2H, Cp); 6.99 (s, 2H, Flu); 8.14 (s, 2H, Flu). 13C NMR (benzene-d6): o= 28.75 (CMe2); 32.26, 32.55, 32.63, 32.97, 34.06, 34.83, 35.73 (Oct); 35.88 (TaMe); 55.50 (TaMe); 84.50, 100.21 (Cp), 116.53, 117.48, 123.86, 140.86, 141.14, 141.86, 142.24 (Flu). Me2C(T1 5-CsH4)(T1LFluorenyl)TaMe2F (38). In the dry box, a round bottom flask was charged with 0.500 g (1.00 mmol) of 35, and a needle valve was attached. On the vacuum line, toluene was added at -80 °C. Against an Ar counterflow, 125 µL (1 .00 mmol) of 54% wt. solution of HBF4 in Et2O was added at -80 °C. The reaction mixture was stirred for 10 minutes, and the volatiles were then removed in vacuo leaving 0.450 g (80%) of a red powder identified as 38. lH NMR (THF-ds): o= 0.132 (d, 11 H, TaMe); 1.49 (s, 6H, CMe2); 6.06 (s, 4H, Cp); 6.45 (s, 4H, Cp); 7.15 (d, 8 Hz, 2H, Flu); 7.01 (t, 5 Hz, 2H, Flu); 7.18 (t, 5 Hz, 2H, Flu); 7.92 (d, 8 Hz, 2H, Flu). 13C NMR (THF-ds): o= 28.35 (CMe2); 34.63 (CMe2); 46.21 (TaCH3) 100.34, 118.79, 120.72 (Cp); 125.41; 127.27; 129.42; 130.10; 131.89; 142.93; 143.01 (Flu) . 19F NMR (THF-ds): o= 36.40. Me2C(T15-C5H4)(T1LFluorenyl)TaMe2Cl (39). In the dry box, a round bottom flask was charged with 0.650 g (1.30 mmol) of 35 and 0.178 g (1.30 mmol) of ZnCh and then was attached to a swivel frit assembly. On the vacuum line, CH2Cb added at -80 °C. The reaction mixture was stirred at room temperature and a deep red solid forms over time. The reaction mixture was stirred for two days, and the solvent was removed in vacuo and replaced with Et2O. Red solid collected by filtration and dried in vacuo yielding 0.650 g (96%) of 39. 1H NMR (THF-ds): o= 0.56 (s, 6H, TaMe); 1.26 (s, 6H, CMe2); 6.16 (m, 2H, Cp); 6.52 (m, 2H, Cp); 6.98 (d, 8 Hz, 2H, Flu); 7.14 (m, 4H, Flu); 7.84 (d, 8 Hz, 2H, Flu). 13C NMR (THF-ds): o= 28.96 (Me2C); 52.76 (TaMe); 102.05, 118.05, (Cp), 120.28, 226 124.82, 125.56, 126.67 (benzo, fluorenyl); 144.09, 145.81, 1 not located (quaternary centers). [(Me2SD2h1 2-CsH-3,5-(CHMe2)z)(TJ 5-CsH2-4-SiMe3)]TaMe3 (40). In the dry box, a swivel frit assembly was charged with 1.00 g (2.09 mmol) of K2TMSThp and 0.600 g (2.02 mmol) of TaCl2Me3. On the vacuum line, approximately 15 mL of Et2O was added at -80 °C. The reaction mixture was wrapped in foil, stirred and slowly warmed to room temperature. A yellow/ orange solution and a white precipitate forms over time. After 2.5 hours, the reaction mixture was filtered and the white precipitate was washed with several portions of Et2O. Slow cooling of yellow Et2O solution results in formation of a golden solid. The solid was isolated by filtration and dried in vacuo yielding 0.400 g (30.2%) of 40. lH NMR (benzene-d6): b = 0.685 (s, 6H, SiMe2); 0.720 (s, 6H, SiMe2); 0.140 (s, 9H, SiMe3); 1.39 (s, 9H, TaMe3); 3.01 (sept, 2H, CHMe2); 6.24 (s, lH, Cp ); 6.68 (s, 2H, Cp). Anal. Cald. for Ta1Si3C26Hi6 C, 50.06%, H, 7.43%; Found C, 49.82%; H, 7.25%. [(Me2Sih(TJ 2-CsH-3,5-(CHMe2)2)(T} 5-CsH2-4-SiMe3)]TaMe2Cl (41). In the dry box, 10.0 mg (0.016 mmol) of 40 was charged into a J. Young NMR tube and the sample dissolved in benzene-d6 forming a yellow solution. On the vacuum line, the tube was degassed with three-freeze-pump-thaw cycles and 43 torr of anhydrous HCl was added via a 6.9 mL (0.016 mmol) calibrated gas volume at -196 °C. The tube was thawed and shaken and the reaction monitored by lH NMR spectroscopy. 1H (benzene-d6): <3 = 0.15 (s, 9H, SiMe3); 0.65 (s, 6H, SiMe2); 0.75 (s, 6H, SiMe2); 0.97 (d, 7 Hz, 3H, CHMe2); 1.09 (d, 7Hz, 3H, CHMe2); 2.95 (sept, 7 Hz, lH, CHMe2); 1.30 (s, 6H, TaMe); 6.65 (s, lH, Cp); 6.91 (s, 2H, Cp). Kinetic Analysis of 6 with Ethylene. In the dry box, a flame sealable NMR tube was charged with 0.50 mL of 0.244 M stock solution of 6 in benzene-d6. On the vacuum line, the desired amount of ethylene was added via a calibrated gas bulb at -196 °C. The solution was thawed and placed into a preheated NMR probe and approximately 10-15 1H NMR spectra were recorded over regular intervals during the course of the reaction, and the intensity of each peak was measured by integration versus an internal ferrocene standard. The rate of the reaction was then plotted, and the data were fitted using a least-squares analysis. 227 Structure Determinations for 27b, 29a, 31, 40. General Procedure: A suitable crystal was mounted on a glass fiber with Paratone-N oil. The data was collected on a Bruker Smart 1000 CCD diffractometer under a stream of N2 gas at 98 K with the detector 5 cm (nominal) distance at 0 of -28 °. The initial cell for data reduction was calculated for just under 1000 reflections chosen throughout the data frames. For data processing with SAINT v.602, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to zero, Laue class integration restraints were not used, the model profiles from all nine areas were blended and for the post-integration global least squares refinement, no constraints were applied. 27b. Six runs of data were collected with 20 second long, -0.20 ° wide ID-scans at three values of <j> (0, 120,240, 60, 180 and 300°). The data were corrected with SADABS v . 2.0 (beta) using a g-value of 0.0500 and a scale factor of 0.001 (minimum value). No decay correction was needed. The structure was solved using direct methods and the difference Fourier maps were used to locate all missing atoms, including hydrogens. Refinement of F2 was against all reflections. A total of 4617 reflections were refined to R = 0.0837 (GOF = 1.584). 29a. Six runs of data were collected with 20 second long, -0.20 ° wide ID-scans at three values of <j> (0, 120,240, 60, 180 and 300°). The data were corrected with SADABS v. 2.0 (beta) using default parameters except that the scale factor esd was set to a minimum value of 0.001. No decay correction was needed. The structure was solved using direct methods and the difference Fourier maps were used to locate all missing atoms, including hydrogens. Refinement of F2 was against all reflections. A total of 5074 reflections were refined to R = 0.0274 (GOF = 2.191). 30. Six runs of data were collected with 20 second long, -0.20 ° wide ID-scans at three values of <j> (0, 120,240, 60, 180 and 300°). The data were corrected with SADABS v. 2.0 (beta) using default parameters except that the scale factor esd was set to a minimum value of 0.001. No decay correction was needed. The structure was solved using direct methods and the difference Fourier maps were used to locate all missing atoms, including hydrogens. Refinement of F2 was against all reflections. (GOF = 1.291). 228 A total of 4860 reflections were refined to R = 0.0462 31. Three runs of data were collected with 30 second long, -0.25 ° wide ro-scans at three values of <1> (0, 120, and 240°). The data were corrected with SADABS v . 2.0 (beta) using default parameters except that the scale factor esd was set to a minimum value of 0.001. No decay correction was needed. The structure was solved using direct methods and the difference Fourier maps were used to locate all missing atoms, including hydrogens. Refinement of F2 was against all reflections. A total of 4126 reflections were refined to R = 0.0412 (GOF = 1.794). 40. Four runs of data were collected with 20 second long, -0.30 ° wide ro-scans at three values of <j> (0, 120, 240 and 0°) under a dark sheet to protect the crystal from light. The data were corrected with SADABS v. 2.0 (beta) using a g-value of 0.0601 and a scale factor of 0.001 (minimum value). No decay correction was needed. The structure was solved using direct methods and the difference Fourier maps were used to locate all missing atoms, including hydrogens. Refinement of F2 was against all reflections. A total of 3562 reflections were refined to R = 0.0592 (GOF = 7.042). Structure Determinations for 35, 35a, 38. General Procedure: A suitable crystal was attached to a glass fiber and centered on an Enraf-Nonius CAD-4 diffractometer under an 85 K stream of N2 gas. Unit cell parameters were obtained from the setting angles of 25 high-angle reflections. Three reference reflections were measured every 75 minutes to monitor crystal decay. 35. The structure was solved using direct methods and the difference Fourier maps were used to locate the missing atoms, including hydrogens. A total of 4350 data were refined to R = 0.0172 (GOF = 1.560). 35a. The structure was solved using direct methods and the difference Fourier maps were used to locate the missing atoms, including hydrogens. A total of 4439 data were refined to R = 0.0584 (GOF = 1.756). 229 38. The structure was solved using direct methods and the difference Fourier maps were used to locate the missing atoms, including hydrogens. A total of 4709 data were refined to R = 0.0228 (GOF = 1.360). References. 1. For recent reviews see: a) Brintzinger, H.H.; Fischer, D.; Miilhaupt, R.; Reiger, B.; Waymouth, RM. Angew. Chem. Int. Ed. Engl. 1995, 34, 1143. b) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255. 2. a) Piers, W.E.; Bercaw, J.E. J. Am. Chem. Soc. ·1990, 112, 9406. b) Krauledat, H.; Brintzinger, H .H. Angew. Chem. Int. Ed. Engl. 1990, 102, 1412. c) Grubbs, R.H.; Coates, G.W. Acc. Chem. Res. 1996, 29, 85. 3. Jordan, RF. Adv. Organomet. Chem. 1991, 32,325. 4. Guerra, G.; Cavallo, L.; Moscardi, G.; Vacetello, M.; Corradini, P. J. Am. Chem. Soc. 1994,116,2988. 5. Pino, P.; Cioni, P.; Wei, J. J. Am. Chem. Soc. 1987, 109, 6189. 6. Pino, P.; Galimberti, M. J. Organomet. Chem. 1989, 370, 1. 7. Gilchrist, J.H.; Bercaw, J.E. J. Am. Chem. Soc. 1996, 118, 12021. 8. Herzog, T.A.; Zubris, D.L.; Bercaw, J.E. J. Am. Chem. Soc. 1996, 118, 11988. 9 a) Mise, T.; Miya, S.; Yamazaki, H. Chem. Lett. 1989, 1853. b) Zhong, A.H.; Bercaw, J.E. unpublishded results . 10. a) Doherty, N.M.; Bercaw, J.E. J. Am. Chem. Soc. 1985, 107, 2670. b) Burger, B.J.; Santarsiero, B.D.; Trimmer, M.S.; Bercaw, J.E. J. Am. Chem. Soc. 1988, 110, 3134. 11. a) Chernega, A.N.; Green, M.L.H.; Suarez, A.G. Can. J. Chem. 1995, 73, 1157. b) Bailey, N.J.; Cooper, J.A.; Gailus, H.; Green, M.L.H.; James, J.T.; Leech, M.A. J. Chem. Soc. Dalton Trans. 1997, 3579. c) Bailey, N.J.; Green, M.L.H.; Leech, M.A.; Saunders, J.F.; Tidswell, H.M. J. Organomet. Chem. 1997, 538, 111. d) Conway, S.L; Doerrer, L.H.; Green, M.L.H.; Leech, M.A. Organometallics 2000, 19, in press. 12. Antinolo, A.; Martinez-Ripoll, M.; Mugnier, Y.; Otero, A.; Prashar, S.; Rodriguez, A.M. Organometallics 1996, 15, 3241. 13. a) Herrmann, W.A.; Baratta, W. J. Organomet. Chem. 1996, 506,357. b) Herrmann, W.A.; Baratta, W.; Herdtweck, E. Agnew. Chem. Int. Ed. Engl. 1996, 35, 1951. 230 14. Shin, J.H.; Parkin, G. Chem. Comm. 1999, 887. 15. McGrady, N.D.; McDade, C.; Bercaw, J.E. in Organometallic Compounds: Synthesis, Structure and Theory; Shapiro, B.L., Ed.; Texas A&M University Press; College Station, TX, 1983; pp 46-85. 16. Tebbe, F.N .; Parshall, G.W. J. Am. Chem. Soc. 1981, 93, 3793. 17. Gibson, V.C.; Bercaw, J.E.; Bruton, W.J.; Sanner, R.D. Organometallics 1986, 5, 976. • 18. The endo ethylene hydrogens are overlapping. 19. Wilson, R.D.; Koetzle, T.F.; Hart, D.W.; Kvick, A.; Tipton, D.L.; Bau, R. J. Am. Chem. Soc. 1977, 99, 1775. 20. Schrock, R.R.; Sharpe, P.R. J. Am. Chem. Soc. 1978, 100, 2389. 21. Zubris, D.L.; Bercaw, J.E. unpublished results. 22. This preparation is a modification of that reported for the preparation of Me2Si(C5fi4)2TaMe3. Cook, K.S.; Piers, W.E. personal communication. 23. An average tantalum-methyl bond distance is 2.217 A. Orpen, A.G.; Brammer, L.; Allen, F.H.; Kennard, O.; Watson, D.G.; Taylor, R. J. Chem. Soc. Dalton Trans. 1989, Sl. 24. Ewen, J.A.; Jones, R.L; Razavi, A.; Ferrara, J.D. J. Am. Chem. Soc. 1988, 110, 6255. 25. Miller, S.A. Ph.D. Thesis, California Institute of Technology, 2000. 26. Rodriguez, G.; Graham, J.P.; Cotter, W.D.; Sperry, C.K.; Bazan, G.C.; Bursten, B.E. J. Am. Chem. Soc. 1998, 120, 12512. 27. Lucas, C.R.; Green, M.L.H.; Forder, R.A.; Prout, K. J. Chem. Soc. Chem. Comm. 1973, 97. 28. Shapiro, P.J. Coard. Chem. Rev. 1999, 189, l. 29. Burger, B.J.; Bercaw, J.E. In Experimental Organometallic Chemistry; Wayda, A.L.; Darensbourg, M.Y., Eds.; ACS Symposium Series 357; American Chemical Society: Washington, DC, 1987, Chapter 4. 30. Marvich, R.H.; Brintzinger, H.H. J. Am. Chem. Soc. 1971, 93, 2046. 31. Herzog, T.A. Ph.D. Thesis California Institute of Technology, 1997. 231 Appendix A: Select Kinetic Plots 232 1 with Isobutene (296 K) -3.6 . . : . - - - - y = -3.7147 - 0.000~6964x R=j0.99977 -3.8 ·················~·-·· ··············~·······.. ············~··········..·········~·····················~---·············· -4 ................. ,........................................ l ..................... i..................... 1···············.. 'N' -4.2 ::r:: 1--< ·················1·····················1··-·-·. ····:··················1·····················1 ················· N .__, ~ ,_. i i i i i -4.4 ................. , ..................... r ................... , ................ -4.6 ................. r .................... r ................... -4.8 ................. r ................... r ................... r ...................1................ ..f ................ . 0 10 5 10 T.................... ,................. r ..................., .................. ,................. 1 10 1.5 10 2 10 2.5 103 time (sec) 2 with c-2-butene (265 K) -3.5 -4 ,......, N e; -4.5 ::r:: .__, ~ ,_. -5 5 - :.~ 10 0 10 2 10 4 10 6 10 Time (sec) 1 104 233 -9.45 -9.5 Hammett Plot for Olefin Insertion v-..---y = ?-9.5802 - 0;46574x R=:: 0.99724 ····················;··O ······· ....... ;.. •·•·· .. ···············;························;····················· -9.55 -9.6 :: :::::: : : !::: :::.~::::~:~:::: : ::: ::::: r : ::: -9.65 -9.7 :::::r::: :. . .F:: : ; :::J : • -9.75 .................... i....................... i........................ i ................... .. ···················· .--, (/) C ....... ~ .......... C ....... -9.8 ~ . . . . . . . .. . . . . . . . . . . . 1 .. ·····••n••·········· ~···················· .... r.......................r....... .......... -9. 85 ..___.__._____._,__....___..__.___._....._...._....__.__._____._......._...__.__.___.___, -0.2 -0.4 0.2 0.4 0 0.6 sigma Hammett Plot for B-Hydrogen Elimination -7 ,--.---,.---,--r--.--r--r--r--r--r-.--.--.--.--.--r--r--.--.--, . -7.5 ..a .--, ........................ l,,,········· .. ••••• •••••••• (/) I = -7 .5487 •1 1.7959x R= :').99654 ··":"···························i,.,,,,,····························~························· 0 ~ .......... C ....... $ ' I I 1 -0.2 0 0.2 sigma -8 1 -8. 5 L.-L...-L.......JL.......J....,_J....,_J---L---L--L--L--L.--L.-'--'---'---'---'---'-"H---' -0.4 0.4 0.6 234 -11 -11 ~ 6 Eyring Plot for Isobutene with 1 , , y =!4.572~ - 45~9.4x ~= 0.9~998 -11 :::::1:: ::::r:::··:::::;:::::::::r:: ....]... : c::::: i: : -12 ••••••• ..·r··········r····..·····r···· ···~........_····r·········T········.. ···1··········· C: -13 -13 ::::::r;:::::::r::::1:::::;: T :::: -14 ..........r······ ..····r···········r········· ..·r············r············r··········· ••••••• ... -14 ..........~............,.............................._ .........._.._._.......,...........~3 .........- ........ 3.310- .410 .510 3 .610-3:3.710"2:3.8 10-3:3.9 10· 410-3 4.1 10" 1ff Eyring for t-2-butene with 1 -10 ----;...-y = 913446 - f957.81 R= 0.19992 -11 -11 ~ ~ -11 r l- i-! -i· ·i C: -12 ···i-· J·········i-· .;- . J. -13 ·········.. ··: ...............r .............r········ .......:...............r ............r .. ···· ... .. -13 ............ r .............. .; . . . . r...............r··· ..···.......1................,........................... -14 ......................._........................................................................................................................._. 3 3.9 1o-3 4 10· 3 3 3 3 4.1 1o-3 4.2 1o-3 4.3 10" 4.4 10· 4.5 10" 4.6 10- 1ff 235 Reaction of 40 with 37 (296 K) -3.5 . -4 0 . + ••••·•••••••1····••• . . . . 1"··36j\4.·.0T0802~Ra.Q99858 .... T....... ·:............... 1............... 1".............l .............. l........... . -4.5 ............ I.............. -5 ............ 1............... f" ............l..... . . . ............... r.............l .............. ,............ ~ -5.5 ~ ·J· ! ++-: C -6 -6.5 :-1 ........... ❖ .............. c................ -........ ........ y ....... ......................... - ............ ❖ .......... . -7 --1 • • •• • • •••l -1···············1--····l-··············l·······-······· ~ • •• • • -7.5 -5 102 0 5 102 1 1031.5 1022 1022.5 1023 1023.5 103 Time (sec) Reaction of 41 with 37 (270 K) . -3.8 1 :: -3.9 ..-, rl .::!'..-4 ......~ -4.1 4 y = ·3.r915 - 9i4604e·f5x R= 1-9943 I :: o!: I . 0 :: I :: I :: .J . 1--J······L · I I· I :: 1-· ........... 1............... r.............. 1.............. ,..............r ........... !................:............ -4.2 - i :i 10 I ~ 0 I ~ I ~ I ~ I ~ 1 10 2 10 3 10 4 10 Time (sec) Io \ i 236 Appendix B: X-ray Crystallographic Data 237 Table 1. Crystal data and structure refinement for Cp*(11 5-C5H4-CMe3 )ZrC1 2 . Empirical formula C18H26Cl2Zr Formula weight 404.51 Crystallization Solvent Toluene Crystal Habit Block Crystal size 0.26 X 0.25 X 0.18 rnrn3 Crystal color Colorless Data Collection Preliminary Photos Type of diffractometer CAD-4 Wavelength 0.71073 A MoKa Data Collection Temperature 85K Theta range for reflections used in lattice determination 15.5 to 21.7° Unit cell dimensions a = 17.247(3) A b = 6.5860(10) A c = 15.549(2) A Volume 1766.2(5) A3 z 4 Crystal system Orthorhombic Space group Cmcrn Density (calculated) 1.521 Mg/m3 F(000) 832 Theta range for data collection 2.36 to 29. 97° Completeness to theta= 29.97° 99.8% Index ranges -24<=h<=24, 0<=k<=9, -21<=1<=21 Data collection scan type Omega scans Reflections collected 6261 Independent reflections 1371 [Rint= 0.0103; GOFmerge= ] Absorption coefficient 0.917 rnrn-1 Absorption correction Psi scan Max. and min. transmission 0.96and 1.04 Number of standards 3 reflections measured every 75min. Variation of standards -0.12%. a= 90° b=90° g=90° 238 Table 1 (cont.) Structure solution and Refinement Structure solution program SHELXS-97 (Sheldrick, 1990) Primary solution method Direct methods Secondary solution method Direct methods Hydrogen placement Difference Fourier map Structure refinement program SHELXL-97 (Sheldrick, 1997) Refinement method Full matrix least-squares on p2 Data I restraints / parameters 1371 / 0 / 80 Treatment of hydrogen atoms Unrestraj_ned Goodness-of-fit on F2 2.639 Final R indices [I>2s(I)] Rl = 0.0203, wR2 = 0.0617 R indices (all data) Rl = 0.0215, wR2 = 0.0620 Type of weighting scheme used Sigma Weighting scheme used w=l/ s"'2"'(Fo"'2"') Max shift/ error 0.000 Average shift/ error 0.000 Largest diff. peak and hole 0.508 and -0.369 e.A-3 Table 2. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (A2x 103 ) for Cp*(11 5-C5H4-CMe3)ZrCh. U(eq) is defined as the trace of the orthogonalized Uii tensor. X Zr Cl C(l) C(2) C(3) C(4) C(5) 0 0 883(1) 1088(1) 1441(1) 1018(1) 1830(1) y z 578(1) -1860(1) 3548(3) 2410(2) 576(2) 3082(3) -979(3) 2500 3684(1) 2500 3242(1) 2956(1) 4162(1) 3509(1) 6(1) 12(1) 10(1) 9(1) 10(1) 15(1) 17(1) 239 Table 3. Bond lengths [A] and angles [ ] for Cp*(rt 5-CsH4-CMe3)ZrCl2. 0 Zr-Cent Zr-Pln Zr-Cl#l Zr-Cl Zr-C(l) Zr-C(1)#2 Zr-C(2) Zr-C(2)#2 Zr-C(2)#3 Zr-C(2)#1 Zr-C(3)#1 Zr-C(3) Zr-C(3)#2 Zr-C(3)#3 C(l)-C(2)#1 C(l)-C(2) C(l)-H(l) C(2)-C(3) C(2)-C(4) C(3)-C(3)#1 C(3)-C(5) C(4)-H(4A) C(4)-H(4B) C(4)-H(4C) C(5)-H(5A) C(5)-H(5B) C(5)-H(5C) Cent-Zr-Cent Pln-Zr-Pln Cl#l-Zr-Cl Cl#l-Zr-C(l) Cl-Zr-C(l) Cl#l-Zr-C(1)#2 Cl-Zr-C(1)#2 C( 1 )-Zr-C( 1)#2 Cl#l -Zr-C (2) Cl-Zr-C(2) C(l)-Zr-C(2) C(1)#2-Zr-C(2) Cl#l-Zr-C(2)#2 Cl-Zr-C(2)#2 C(l)-Zr-C(2)#2 C(l)#2-Zr-C(2)#2 C(2)-Zr-C(2)#2 Cl#l-Zr-C(2)#3 Cl-Zr-C(2)#3 C (1 )-Zr-C(2 )#3 C(1)#2-Zr-C(2)#3 C(2)-Zr-C(2)#3 C(2)#2-Zr-C(2)#3 2.2271(3) 2.2239(11) 2.4431(5) 2.4431(5) 2.479(2) 2.479(2) 2.5118(14) 2.5118(14) 2.5118(14) 2.5118(14) 2.5834(15) 2.5834(15) 2.5834(15) 2.5834(15) 1.4206(18) 1.4206(18) 0.95(3) 1.4236(19) 1.5013(19) 1.417(3) 1.496(2) 0.95(2) 0.91(2) 0.99(2) 0.95(3) 0.95(3) 0.92(3) 133.84(2) 127.46(6) 97.85(3) 121.23(2) 121.23(2) 121.23(2) 121.23(2) 75.79(9) 131.45(3) 88.25(3) 33.07(4) 94.57(5) 88.25(3) 131.45(3) 94.57(5) 33.07(4) 122.57(7) 131.45(3) 88.25(3) 94.57(5) 33.07(4) 96.68(6) 54.69(6) 240 Cl#l-Zr-C (2 )#1 Cl-Zr-C(2)#1 C(l)-Zr-C(2)#1 C(1)#2-Zr-C(2)#1 C(2)-Zr-C(2)#1 C(2)#2-Zr-C(2)#1 C(2 )#3-Zr-C(2 )#1 Cl#l-Zr-C(3)#1 Cl-Zr-C(3)#1 C(l )-Zr-C(3)#1 C(1)#2-Zr-C(3)#1 C(2)-Zr-C(3)#1 C(2)#2-Zr-C(3)#1 C(2 )#3-Zr-C(3 )#1 C(2)#1-Zr-C(3)#1 Cl#l-Zr-C(3) Cl-Zr-C(3) C(l)-Zr-C(3) C(1)#2-Zr-C(3) C(2)-Zr-C(3) C(2)#2-Zr-C(3) C(2)#3-Zr-C(3) C(2)#1-Zr-C(3) C(3)#1-Zr-C(3) Cl#l-Zr-C(3)#2 Cl-Zr-C(3)#2 C(l)-Zr-C(3)#2 C(1)#2-Zr-C(3)#2 C(2)-Zr-C(3)#2 C(2)#2-Zr-C(3)#2 C(2 )#3-Zr-C(3 )#2 C(2)#1-Zr-C(3)#2 C(3)#1-Zr-C(3)#2 C(3)-Zr-C(3)#2 Cl#l-Zr-C(3)#3 Cl-Zr-C(3)#3 C(l )-Zr-C(3)#3 C(l)#2-Zr-C(3)#3 C(2)-Zr-C(3)#3 C(2)#2-Zr-C(3)#3 C(2)#3-Zr-C(3)#3 C(2)#1-Zr-C(3)#3 C(3)#1-Zr-C(3)#3 C(3)-Zr-C(3)#3 C(3)#2-Zr-C(3)#3 C (2 )#1-C (1 )-C (2) C(2)#1-C(l)-Zr C(2)-C(l )-Zr C(2)#1-C(l)-H(l) C(2)-C(l)-H(l) Zr-C(l)-H(l) C(l)-C(2)-C(3) C(l)-C(2)-C(4) C(3)-C(2)-C(4) 88.25(3) 131.45(3) 33.07(4) 94.57(5) 54.69(6) 96.68(6) 122.57(7) 78.05(3) 101.92(3) 53.82(5) 126.23(5) 53.68(4) 126.35(5) 147.63(5) 32.41(4) 101.92(3) 78.05(3) 53.82(5) 126.23(5) 32.41(4) 147.63(5) 126.35(5) 53.68(4) 31.84(6) 78.05(3) 101.92(3) 126.23(5) 53.82(5) 147.63(5) 32.41(4) 53.68(4) 126.35(5) 148.16(6) 179.95(7) 101.92(3) 78.05(3) 126.23(5) 53.82(5) 126.35(5) 53.68(4) 32.41(4) 147.63(5) 179.95(7) 148.16(6) 31.84(6) 108.62(17) 74.73(10) 74.73(10) 125.66(10) 125.66(10) 119.0(18) 107.46(13) 126.73(13) 125.59(13) 241 C(l)-C(2)-Zr C(3)-C(2)-Zr C(4)-C(2)-Zr C(3)#1-C(3)-C(2) C(3)#1-C(3)-C(5) C(2)-C(3)-C(5) C(3)#1-C(3)-Zr C(2)-C(3)-Zr C(5)-C(3)-Zr C(2)-C(4)-H(4A) C(2)-C(4)-H(4B) H( 4A)-C( 4)-H( 4B) C(2)-C(4)-H(4C) H(4A)-C(4)-H(4C) H(4B)-C(4)-H(4C) C(3)-C(5)-H(5A). C(3)-C(5)-H(5B) H(5A)-C(5)-H(5B) C(3)-C(5)-H(5C) H(5A)-C(5)-H(5C) H(5B)-C(5)-H(5C) 72.21(9) 76.56(8) 121.28(9) 108.22(8) 125.06(9) 126.35(13) 74.08(3) 71.03(8) 126.14(10) 111.3(13) 114.5(13) 109.8(18) 111.0(12) 103.8(17) 105.7(16) 113.9(15) 111.3(15) 105(2) 109.7(16) 109(2) 108(2) Symmetry transformations used to generate equivalent atoms: #1 x,y,-z+l/2 #2-x,y,-z+l/2 #3 -x,y,z 242 Table 4. Crystal data and structure refinement for Cp*(iPr2Cp)ZrC12. Empirical formula C21H32Cl2Zr Formula weight 446.59 Crystallization Solvent Toluene Crystal Habit Rod Crystal size 0.37 X 0.29 X 0.15 mm3 Crystal color Colorless Data Collection Preliminary Photos Type of diffractometer CAD-4 Wavelength 0.71073 A MoK Data Collection Temperature 85K Theta range for reflections used in lattice determination 14.4 to 15.2° Volume a = 13.875(3) A b = 16.059(5) A c = 9.628(2) A 2145.3(9) A3 z 4 Crystal system Orthorhombic Space group Pruna Density (calculated) l.383Mg/m3 F(000) 928 Theta range for data collection 2.5 to 27.5° Completeness to theta = 27.5° 100.0 % Index ranges -18<=h<=18, 0<=k<=20, -12<=1<=12 Data collection scan type Omega scans Reflections collected 8633 Independent reflections 2546 [Rint= 0.022; GOFmerge= ] Absorption coefficient 0.762mm-1 Absorption correction None Number of standards 3 reflections measured every 75min. Variation of standards Within counting statistics, zero%. Unit cell dimensions a= 90° b=90° g=90° 243 Table 4 (cont.) Structure solution and Refinement Structure solution program SHELXS-97 (Sheldrick, 1990) Primary solution method Patterson method Secondary solution method Difference Fourier map Hydrogen placement Difference Fourier map Structure refinement program SHELXL-97 (Sheldrick, 1997) Refinement method Full matrix least-squares on F2 Data / restraints / parameters 2546 Io I 181 Treatment of hydrogen atoms Unrestrai,ned Goodness-of-fit on F2 1.834 Final R indices [I>2s(I)] Rl = 0.0244, wR2 = 0.0548 R indices (all data) Rl = 0.0290, wR2 = 0.0561 Type of weighting scheme used Observed Weighting scheme used w=l/ s"2A(Fo"2") Max shift/ error 0.001 Average shift/ error 0.000 Largest diff. peak and hole 0.666 and -0.409 e.A-3 Table 5. Ato:r.nic coordinates ( x 104) and equivalent isotropic displacement parameters (A2x 10 3) for Cp*(iPr2Cp)ZrCl2. U(eq) is defined as the trace of the orthogonalized Uii tensor. Zr Cl(l) C(l) C(ll) C(2) C(22) C(3) C(33) C(5) C(6) C(68) C(66) C(67) C(7) X y z U(eq) 409(1) -715(1) 1628(2) 2705(3) 1050(2) 1374(5) 117(1) -703(3) 1861(1) 1120(1) 1362(2) 939(1) 1348(2) 635(2) 2500 3659(1) 2500 2500 3208(1) 4105(3) 2935(1) 3472(2) 2947(1) 3222(1) 4184(1) 4096(1) 4763(1) 2500 1917(1) 2245(1) -20(3) 86(4) -210(2) -177(3) -599(2) -1076(3) 3186(2) 4073(2) 6039(2) 4575(2) 3622(2) 4559(2) 10(1) 18(1) 34(1) 99(3) 28(1) 88(2) 20(1) 54(1) 13(1) 13(1) 27(1) 18(1) 26(1) 14(1) 244 Table 6. Bond lengths [A] and angles [ ] for Cp*(iPr2Cp)ZrCl2. 0 Zr-Plnl Zr-Pln2 Zr-Centl Zr-Cent2 Zr-Cl(l)#l Zr-Cl(l) Zr-C(5) Zr-C(5)#1 Zr-C(2)#1 Zr-C(2) Zr-C(l) Zr-C(3)#1 Zr-C(3) Zr-C(7) Zr-C(6) Zr-C(6)#1 C(l)-C(2) C(l)-C(2)#1 C(l)-C(ll) C(ll )-H(llA) C(ll)-H(llB) C(2)-C(3) C(2)-C(22) C(22)-H(22A) C(22)-H(22B) C(22)-H(22C) C(3)-C(3)#1 C(3)-C(33) C(33)-H(33A) C(33)-H(33B)° C(33)-H(33C) C(5)-C(6) C(5)-C(5)#1 C(5)-H(5) C(6)-C(7) C(6)-C(66) C(68)-C(66) C(68)-H(68A) C(68)-H(68B) C(68)-H(68C) C(66)-C(67) C(66)-H(66) C(67)-H(67A) C(67)-H( 67B) C(67)-H(67C) C(7)-C(6)#1 C(7)-H(7) Plnl-Zr-Pln2 Centl-Zr-Cent2 Cl(l)#l-Zr-Cl(l) 2.225(1) 2.204(1) 2.2262(5) 2.2217(4) 2.4478(6) 2.4478(6) 2.4632(16) 2.4632(16) 2.5059(18) 2.5059(18) 2.519(3) 2.5537(17) 2.5537(17) 2.562(2) 2.5737(16) 2.5737(16) 1.404(3) 1.404(3) 1.498(4) 0.97(4) 0.75(3) 1.416(3) 1.508(4) 0.74(5) 0.98(4) 0.96(3) 1.397(4) 1.500(3) 0.95(3) 0.92(3) 0.99(3) 1.407(2) 1.434(3) 0.944(19) 1.420(2) 1.507(2) 1.533(3) 1.02(2) 0.94(2) 1.00(2) 1.520(3) 0.95(2) 1.00(2) 0.94(2) 0.96(2) 1.420(2) 0.96(3) 126.87(8) 131.49(2) 98.94(3) 245 Cl(l)#l-Zr-C(5) Cl(l)-Zr-C(5) Cl(l )#1-Zr-C(5)#1 Cl(l)-Zr-C(5)#1 C(5)-Zr-C(5)#1 Cl(l )#l-Zr-C(2)#1 Cl(l)-Zr-C(2)#1 C(5)-Zr-C(2)#1 C(5)#1-Zr-C(2)#1 Cl(l)#l-Zr-C(2) Cl(l )-Zr-C(2) C(5)-Zr-C(2) C(5)#1-Zr-C(2) C(2)#1-Zr-C(2) Cl(l)#l-Zr-C(l) Cl(l)-Zr-C(l) C(5)-Zr-C(l) C(5)#1-Zr-C(l) C(2)#1-Zr-C(l) C(2)-Zr-C(l) Cl(l )#l-Zr-C(3)#1 Cl(l)-Zr-C(3)#1 C(5)-Zr-C(3)#1 C(5)#1-Zr-C(3)#1 C(2)#1-Zr-C(3)#1 C(2)-Zr-C(3)#1 C(l)-Zr-C(3)#1 Cl(l)#l-Zr-C(3) Cl(l )-Zr-C(3) C(5)-Zr-C(3) C(5)#1-Zr-C(3) C(2)#1-Zr-C(3) C(2)-Zr-C(3) C(l)-Zr-C(3) C(3)#1-Zr-C(3) Cl(l)#l-Zr-C(7) Cl(l )-Zr-C(7) C(5)-Zr-C(7) C(5)#1-Zr-C(7) C(2 )#1-Zr-C(7) C(2)-Zr-C(7) C(l)-Zr-C(7) C(3)#1-Zr-C(7) C(3)-Zr-C(7) Cl(l)#l-Zr-C(6) Cl(l)-Zr-C(6) C(5)-Zr-C(6) C(5)#1-Zr-C(6) C(2)#1-Zr-C(6) C(2)-Zr-C(6) C(l)-Zr-C(6) C(3)#1-Zr-C(6) C(3)-Zr-C(6) C(7)-Zr-C(6) 132.73(4) 103.66(4) 103.66(4) 132.73(4) 33.84(8) 89.21(5) 132.55(4) 104.30(6) 89.01(6) 132.55(4) 89.22(5) 89.01(6) 104.30(6) 53.99(10) 121.55(3) 121.55(3) 79.49(7) 79.49(7) 32.45(6) 32.45(6) 79.24(4) 103.25(4) 132.81(6) 121.35(6) 32.50(6) 53.49(6) 53.39(7) 103.25(4) 79.24(4) 121.35(6) 132.81(6) 53.49(6) 32.50(6) 53.39(7) 31.76(8) 87.15(4) 87.15(4) 53.67(6) 53.67(6) 140.15(6) 140.15(6) 130.76(8) 163.94(4) 163.94(4) 118.87(4) 78.37(4) 32.35(5) 54.37(5) 136.65(6) 108.56(6) 109.84(6) 161.59(5) 134.62(5) 32.10(4) 246 Cl(l)#l-Zr-C(6)#1 Cl(l)-Zr-C(6)#1 C(5)-Zr-C(6)#1 C(5)#1-Zr-C(6)#1 C(2)#1-Zr-C(6)#1 C(2)-Zr-C(6)#1 C(l)-Zr-C(6)#1 C(3)#1-Zr-C(6)#1 C(3)-Zr-C(6)#1 C(7)-Zr-C( 6 )#1 C(6)-Zr-C(6)#1 C(2 )-C(l )-C(2 )#1 C(2)-C(l)-C(ll) C(2)#1-C(l)-C(ll) C(2)-C(l)-Zr C(2)#1-C(l)-Zr C(ll)-C(l)-Zr C(l)-C(ll)-H(llA) C(l)-C(ll)-H(llB) H(l lA)-C(l 1)-H(l lB) C(l)-C(2)-C(3) C(l)-C(2)-C(22) C(3)-C(2)-C(22) C(l )-C(2)-Zr C(3)-C(2)-Zr C(22)-C(2)-Zr C(2)-C(22)-H(22A) C(2)-C(22)-H(22B) H(22A)-C(22)-H(22B) C(2)-C(22)-H(22C) H(22A)-C(22)-H(22C) H(22B)-C(22)-H(22C) C(3)#1-C(3)-C(2) C(3)#1-C(3)-C(33) C(2)-C(3)-C(33) C(3)#1-C(3)-Zr C(2)-C(3)-Zr C(33)-C(3)-Zr C(3)-C(33)-H(33A) C(3)-C(33)-H(33B) H(33A)-C(33)-H(33B) C(3)-C(33)-H(33C) H(33A)-C(33)-H(33C) H(33B)-C(33)-H(33C) C( 6 )-C(5)-C(5)#1 C(6)-C(5)-Zr C(5)#1-C(5)-Zr C(6)-C(5)-H(5) C(5)#1-C(5)-H(5) Zr-C(5)-H(5) C(5)-C( 6 )-C(7) C(5)-C(6)-C(66) C(7)-C(6)-C(66) C(5)-C(6)-Zr 78.37(4) 118.87(4) 54.37(5) 32.35(5) 108.56(6) 136.65(6) 109.84(6) 134.62(5) 161.59(5) 32.10(4) 53.53(7) 108.2(2) 125.40(12) 125.40(12) 73.26(13) 73.26(13) 128.3(2) 107(2) 116(2) 115(2) 107.80(17) 126.9(3) 125.0(3) 74.29(13) 75.61(10) 121.48(17) 112(4) 110(2) 119(4) 107.0(19) 105(4) 103(3) 108.04(11) 125.10(17) 126.6(2) 74.12(4) 71.90(10) 124.60(14) 112(2) 112.9(18) 98(3) 109.8(16) 114(3) 110(2) 108.31(9) 78.15(9) 73.08(4) 127.0(12) 124.5(12) 118.8(12) 106.86(15) 127.52(15) 125.20(15) 69.50(9) 247 C(7)-C(6)-Zr C( 66 )-C( 6 )-Zr C(66)-C(68)-H(68A) C(66)-C(68)-H(68B) H(68A)-C(68)-H(68B) C(66)-C(68)-H(68C) H(68A)-C(68)-H(68C) H(68B)-C(68)-H(68C) C(6)-C(66)-C(67) C(6)-C(66)-C(68) C(67)-C(66)-C(68) C(6)-C(66)-H(66) C(67)-C(66)-H(66) C(68)-C(66)-H(66) C(66)-C(67)-H(67A) C(66)-C(67)-H(67B) H(67 A)-C(67)-H(67B) C( 66 )-C( 67)-H( 67C) H(67A)-C(67)-H(67C) H(67B)-C(67)-H(67C) C(6)#1-C(7)-C(6) C( 6 )#l -C(7)-Zr C( 6)-C(7)-Zr C(6)#1-C(7)-H(7) C(6)-C(7)-H(7) Zr-C(7)-H(7) 73.50(11) 127.94(11) 110.2(12) 107.8(13) 108.3(18) 110.5(13) 110.9(17) 109.0(19) 113.62(15) 108.47(14) 110.34(16) 108.5(12) 108.7(12) 107.0(12) 109.5(11) 111.9(13) 107.3(17) 112.1(13) 107.6(17) 108.2(18) 109.4(2) 74.40(11) 74.40(11) 125.26(11) 125.26(11) 119.7(18) Symmetry transformations used to generate equivalent atoms: #1 x,-y+l/2,z 248 Table 7. Crystal data and structure refinement for (tBu2CphZrCl 2. Empirical formula C26H42Cl2Zr Formula weight 516.72 Crystallization Solvent Toluene Crystal Habit Blade Crystal size 0.44 X 0.15 X 0.08 mm3 Crystal color Colorless Data Collection Preliminary Photos Type of diffractometer CAD-4 Wavelength 0.71073 AMoKa Data Collection Temperature 85(2) K Theta range for reflections used in lattice determination 10.3 to 12.6° Volume a = 21.110(19) A b = 6.575(5) A c = 19.132(9) A 2648(3) A3 z 4 Crystal system Monoclinic Space group C2/c Density (calculated) l.296Mg/m3 F(000) 1088 Theta range for data collection 1.9 to 25.0° Completeness to theta = 25.0° 99.7% Index ranges -24<=h<=24, 0<=k<=7, -22<=1<=22 Data collection scan type scans Reflections collected 5947 Independent reflections 2330 [Rmt= 0.026; GOFmerge= ] Absorption coefficient 0.627mm- 1 Absorption correction scan Max. and min. transmission 1.16 and 0.85 Number of standards 3 reflections measured every 75 min. Variation of standards -0.19%. Unit cell dimensions a= 90° b= 94.17(7) 0 g=90° 249 Table 7 (cont.) Structure solution and Refinement Structure solution program SHELXS-97 (Sheldrick, 1990) Primary solution method Direct methods Secondary solution method Hydrogen placement Structure refinement program Refinement method Data / restraints / parameters Treatment of hydrogen atoms Goodness-of-fit on F2 Final R indices [I> 2s(I)] R indices (all data) Type of weighting scheme used Weighting scheme used Max shift/ error Average shift/ error Largest diff. peak ·and hole Difference Fourier map Difference Fourier map SHELXL-97 (Sheldrick, 1997) Full matrix least-squares on F2 2330 Io I 216 Unresti::ained 2.036 Rl = 0.0358, wR2 = 0.0743 Rl = 0.0438, wR2 = 0.0756 Sigma w=l/[ A2A(FoA2/\) 0.000 0.000 1.154 and -1.461 e.A-3 Table 8. Atm;,nic coordinates ( x 104) and equivalent isotropic displacement parameters (A2x 103 ) for (tBu2CphZrCl2. U(eq) is defined as the trace of the orthogonalized Uii tensor. X Zr Cl(l) C(l) C(2) C(3) C(4) C(5) C(ll) C(12) C(13) C(14) C(15) C(16) C(17) C(18) 0 -261(1) -731(2) -620(1) -944(1) -1211(1) -1106(1) -1126(1) -610(2) -1722(2) -1295(2) -1446(1) -1778(2) -993(2) -1948(2) y z -3313(1) -5834(1) -381(5) -911(5) -2736(5) -3397(5) -1913(5) -3539(5) -3144(6) -2319(6) -5792(5) -1730(5) -3693(6) -1069(6) -59(7) -2500 -1633(1) -2566(2) -3269(2) -3436(2) -2818(2) -2289(2) -4171(2) -4676(2) -4423(2) -4168(2) -1611(2) -1432(2) -998(2) -1751(2) ueq 11(1) 16(1) 15(1) 14(1) 13(1) 15(1) 15(1) 16(1) 20(1) 21(1) 22(1) 19(1) 26(1) 22(1) 33(1) 250 Table 9. Bond lengths [A] and angles [0 ] for (tBu2Cp)zZrC1 2. Zr-Pln(l) Zr-Pln(2)#1 Zr-Cent(l) Zr-Cent(2)#1 Zr-Cl(l)#l Zr-Cl(l) Zr-C(l)#l Zr-C(l) Zr-C(2)#1 Zr-C(2) Zr-C(5)#1 Zr-C(5) Zr-C(4) Zr-C(4)#1 Zr-C(3)#1 Zr-C(3) C(l)-C(5) C(l)-C(2) C(l)-H(l) C(2)-C(3) C(2)-H(2) C(3)-C(4) C(3)-C(ll) C(4)-C(5) C(4)-H(4) C(5)-C(15) C(ll)-C(14) C(l 1)-C(12) C(ll)-C(13) C(12)-H(12A) C(12)-H(12B) C(12)-H(12C) C(13)-H(13A) C(13)-H(13B) C(13)-H(13C) C(14)-H(11A) C(14)-H(llB) C(14)-H(11C) C(15)-C(16) C(15)-C(17) C(15)-C(18) C(16)-H(16A) C(16)-H(16B) C(16)-H(16C) C(17)-H(17A) C(17)-H(17B) C(17)-H(17C) C(18)-H(18A) C(18)-H(18B) C(18)-H(18C) 2.231(3) 2.231(3) 2.238(3) 2.238(3) 2.4364(14) 2.4364(14) 2.467(3) 2.467(3) 2.468(3) 2.468(3) 2.568(3) 2.568(3) 2.585(4) 2.585(4) 2.609(4) 2.609(4) 1.408(4) 1.425(4) 0.91(3) 1.406(4) 0.98(3) 1.415(4) 1.524(4) 1.412(4) 0.96(3) 1.531(4) 1.524(5) 1.530(4) 1.540(5) 0.94(3) 1.00(3) 0.93(4) 0.95(4) 1.01(3) 1.00(4) 1.02(4) 0.90(4) 0.95(3) 1.520(5) 1.523(5) 1.537(5) 0.96(4) 1.00(4) 0.99(4) 0.98(4) 1.02(3) 0.88(4) 1.04(4) 0.96(4) 0.97(4) 251 Pln(l)-Zr-Pln(2)#1 Cent(l )-Zr-Cent(2)#1 Cl( 1 )#1-Zr-Cl(l) Cl(l)#l-Zr-C(l)#l Cl(l)-Zr-C(l)#l Cl(l)#l-Zr-C(l) Cl(l)-Zr-C(l) C(l)#l-Zr-C(l) Cl(l)#l-Zr-C(2)#1 Cl(l)-Zr-C(2)#1 C(l)#l-Zr-C(2)#1 C(l)-Zr-C(2)#1 Cl(l )#1-Zr-C(2) Cl(l )-Zr-C(2) C(l)#l-Zr-C(2) C(l )-Zr-C(2) C(2 )#1-Zr-C(2) Cl(l )#1-Zr-C(5)#1 Cl(l)-Zr-C(5)#1 C(l)#l-Zr-C(5)#1 C(l )-Zr-C(5)#1 C(2)#1-Zr-C(5)#1 C(2)-Zr-C(5)#1 Cl(l)#l-Zr-C(5) Cl(l )-Zr-C(5) C(l)#l-Zr-C(5) C(l }-Zr-C(5) C(2)#1-Zr-C(5) C(2)-Zr-C(5) C(5)#1-Zr-C(5) Cl(l)#l-Zr-C(4) Cl(l )-Zr-C( 4) C(l)#l-Zr-C(4) C(l)-Zr-C(4) C(2)#1-Zr-C( 4) C(2)-Zr-C(4) C(5)#1-Zr-C(4) C(5)-Zr-C(4) Cl(l)#l-Zr-C(4)#1 Cl(l)-Zr-C(4)#1 C(l)#l-Zr-C(4)#1 C(l)-Zr-C(4)#1 C(2)#1-Zr-C(4)#1 C(2)-Zr-C( 4)#1 C(5)#1-Zr-C(4)#1 C(5)-Zr-C( 4)#1 C(4)-Zr-C(4)#1 Cl(l)#l -Zr-C(3)#1 Cl(l)-Zr-C(3)#1 C(l)#l-Zr-C(3)#1 C(l)-Zr-C(3)#1 C(2)#1-Zr-C(3)#1 C(2)-Zr-C(3)#1 C(5)#1-Zr-C(3)#1 121.1(1) 129.7(1) 94.28(7) 113.26(9) 131.94(8) 131.94(8) 113.26(9) 77.19(17) 134.81(9) 99.55(9) 33.56(10) 80.38(12) 99.55(9) 134.81(9) 80.38(12) 33.56(10) 100.42(16) 83.33(9) 127.16(8) 32.39(10) 106.49(12) 54.23(10) 97.21(12) 127.16(8) 83.33(9) 106.49(12) 32.39(10) 97.21(12) 54.23(10) 137.97(15) 95.38(9) 82.95(9) 129.26(11) 53.17(11) 128.80(11) 53.18(11) 149.89(10) 31.81(10) 82.95(9) 95.38(9) 53.17(11) 129.26(11) 53.18(11) 128.80(11) 31.81(10) 149.89(10) 177.56(15) 111.57(8) 80.24(8) 53.66(10) 111.40(11) 32.01(10) 131.42(11) 53.01(10) 252 C(5)-Zr-C(3)#1 C(4)-Zr-C(3)#1 C(4)#1-Zr-C(3)#1 Cl(l)#l-Zr-C:(3) Cl(l)-Zr-C(3) C(l)#l-Zr-C(3) C(l)-Zr-C(3) C(2)#1-Zr-C(3) C(2)-Zr-C(3) C(5)#1-Zr-C(3) C(5)-Zr-C(3) C(4)-Zr-C(3) C(4)#1-Zr-C(3) C(3)#1-Zr-C(3) C(5)-C(l)-C(2) C(5)-C(l)-Zr C(2)-C(l)-Zr C(5)-C(l)-H(l) C(2)-C(l)-H(l) Zr-C(l)-H(l) C(3)-C(2)-C(l) C(3)-C(2)-Zr C(l )-C(2)-Zr C(3)-C(2)-H(2) C(l )-C(2 )-H(2) Zr-C(2)-H(2) C(2)-C(3)-C( 4) C(2)-C(3)-C(ll) C(4)-C(3)-C(ll) C(2)-C(3)-Zr C(4)-C(3)-Zr C(ll)-C(3)-Zr C(5)-C( 4)-C(3) C(5)-C(4)-Zr C(3)-C(4)-Zr C(5)-C(4)-H(4) C(3)-C(4)-H(4) Zr-C(4)-H(4) C(l )-C(5)-C( 4) C(l )-C(5)-C(15) C( 4)-C(5)-C(15) C(l)-C(5)-Zr C( 4)-C(5)-Zr C(15)-C(5)-Zr C(3)-C(ll)-C(14) C(3)-C(ll)-C(12) C(14)-C(ll)-C(12) C(3)-C(ll)-C(13) C(14)-C(ll)-C(13) C(12)-C(ll)-C(13) C(ll)-C(12)-H(12A) C(l 1)-C(12)-H(12B) H(12A)-C(12)-H(12B) C(ll)-C(12)-H(12C) 119.82(10) 149.06(10) 31.62(10) 80.24(8) 111.57(8) 111.40(11) 53.66(10) 131.42(11) 32.01(10) 119.82(10) 53.01(10) 31.62(10) 149.06(10) 163.25(14) 108.4(3) 77.76(19) 73.26(18) 127.8(19) 123.7(19) 118.4(18) 108.3(3) 79.52(18) 73.19(18) 128.5(18) 123.0(18) 117.7(17) 106.7(3) 126.3(3) 125.1(3) 68.47(17) 73.28(18) 135.4(2) 109.6(3) 73.43(18) 75.10(18) 123.5(19) 126.7(19) 121.7(18) 106.7(3) 125.0(3) 127.0(3) 69.85(18) 74.76(18) 130.4(2) 112.1(3) 112.4(3) 110.2(3) 104.7(3) 108.7(3) 108.5(3) 114(2) 110.7(18) 108(3) 107(2) 253 H(12A)-C(12)-H(12C) H(12B)-C(12)-H(12C) C(l 1)-C(13)-H(13A) C(l 1)-C(13)-H(13B) H(13A)-C(13)-H(13B) C(ll)-C(13)-H(13C) H(13A)-C(13)-H(13C) H(13B)-C(13)-H(13C) C(ll)-C(14)-H(l1A) C(ll)-C(14)-H(11B) H(l 1A)-C(14)-H(l 1B) C(ll)-C(14)-H(l1C) H(llA)-C(14)-H(llC) H(l 1B)-C(14)-H(11C) C(16)-C(15)-C(17) C(16)-C(15)-C(5) . C(l 7)-C(15)-C(5) C(16)-C(15)-C(18) C(17)-C(15)-C(18) C(5)-C(15)-C(18) C(15)-C(16)-H(16A) C(15)-C(16)-H(16B) H(16A)-C(16)-H(16B) C(15)-C(16)-H(16C) H(16A)-C(16)-H(16C) H(16B)-C(16)-H(16C) C(15)-C(17)-H(17A) C(15)-C(17)-H(17B) H(17 A)-C(17)-H(17B) C(15)-C(l 7)-H(l 7C) H(17 A)-C(17)-H(17C) H(17B)-C(17)-H(17C) C(15)-C(18)-H(18A) C(15)-C(18)-H(18B) H(18A)-C(18)-H(18B) C(15)-C(18)-H(18C) H(18A)-C(18)-H(18C) H(18B)-C(18)-H(18C) 107(3) 109(3) 112(2) 113.2(19) 108(3) 111.1(19) 111(3) 100(3) 113(2) 112(2) 99(3) 110.4(19) 117(3) 104(3) 110.1(3) 112.1(3) 111.6(3) 108.8(3) 108.4(3) 105.7(3) 111(2) 114(2) 110(3) 109(2) 101(3) 112(3) 116(2) 110.7(18) 101(3) 107(2) 108(3) 114(3) 111(2) 113(2) 107(3) 112(2) 102(3) 111(3) Symmetry transformations used to generate equivalent atoms: #l -x,y,-z-1/2 Table 10. Crystal data and structure refinement for Cp*2HfH2 Empirical formula Formula weight Crystallization Solvent Petroleum ether Crystal Habit Fragment Crystal size 0.38 X 0.15 X 0.08 mm3 Crystal color Colorless 254 Data Collection Preliminary Photos Type of diffractometer CAD-4 Wavelength 0.71073 A MoKa Data Collection Temperature 85K Theta range for reflections used in lattice determination 10.6 to 11.3° Unit cell dimensions a= 15.733(4) A b =15.366(4) A c =16.401(4) A Volume 3740.3(1.6) A3 z 8 Crystal system Monoclinic Space group p2(1)/ C Density (calculated) 1.602Mg/m3 F(000) 1792 Theta range for data collection 1.9 to 25.0° Completeness to theta =25.0° 84.9% Index ranges -18<==h<==17, -18<=k<=18, -19<=1<=19 Data collection scan type Omega scans Reflections collected 16022 Independent reflections 6559 [Rint= 0.031; GOFmerge= ] Absorption coefficient 5.572 mm- 1 Absorption correction Psi scan Max. and min. transmission l.lOand0.87 Number of standards 3 reflections measured every 75min. Variation of standards Within counting statistics, zero %. a= 90° b= 109.38(2)° g == 90° Structure solution and Refinement Structure solution program Primary solution method Secondary solution method Hydrogen placement Structure refinement program Refinement method SHELXS-97 (Sheldrick, 1990) Direct methods Difference Fourier map Geometric positions SHELXL-97 (Sheldrick, 1997) Full matrix least-squares on F2 255 Data/ restraints / parameters Treatment of hydrogen atoms Goodness-of-fit on F2 Final R indices [I>2s(I)] R indices (all data) Type of weighting scheme used Weighting scheme used Max shift/ error Average shift/ error Largest diff. peak and hole 5570 I 252 I 419 Restrained to Geometric positions 1.354 Rl = 0.0418, wR2 = 0.0679 Rl = 0.0595, wR2 = 0.0715 Sigma w=l/[A2A(FoA2) 0.286 0.004 1.384 and -0.846 e.A-3 256 Table 11. Bond lengths [A] and angles [0 ] for Cp*2 H£H2 HfA-Cent(lA) HfA-Cent(2A) HfA-Pln(lA) HfA-Pln(2A) HfA-C(9A) HfA-C(lOA) HfA-C(3A) HfA-C(8A) HfA-C(2A) HfA-C(4A) HfA-C(6A) HfA-C(7A) HfA-C(lA) HfA-C(5A) C(1A)-C(2A) C(1A)-C(5A) C(lA)-C(l lA) C(2A)-C(3A) C(2A)-C(12A) C(3A)-C(4A) C(3A)-C(13A) C(4A)-C(SA) C(4A)-C(14A) C(5A)-C(15A) C(llA)-H(llA) C(llA)-H(llB) C(llA)-H(llC) C(12A)-H(12A) C(12A)-H(12B) C(12A)-H(12C) C(13A)-H(13A) C(13A)-H(13B) C(13A)-H(13C) C(14A)-H(14A) C(14A)-H(14B) C(14A)-H(14C) C(15A)-H(15A) C(15A)-H(15B) C(15A)-H(15C) C(6A)-C(7A) C(6A)-C(10A) C(6A)-C(16A) C(7A)-C(8A) C(7A)-C(17A) C(8A)-C(9A) C(8A)-C(18A) C(9A)-C(10A) C(9A)-C(19A) C(10A)-C(20A) C(16A)-H(16A) C(16A)-H(16B) 2.192(3) 2.175(3) 2.192(3) 2.175(3) 2.493(7) 2.483(8) 2.479(7) 2.482(8) 2.515(8) 2.486(7) 2.490(7) 2.497(7) 2.516(7) 2.515(7) 1.418(11) 1.421(11) 1.506(10) 1.440(10) 1.476(11) 1.389(10) 1.519(10) 1.426(10) 1.495(10) 1.508(11) 0.9398 0.9398 0.9398 0.8775 0.8775 0.8775 0.9571 0.9571 0.9571 0.9379 0.9379 0.9379 0.9622 0.9622 0.9622 1.434(11) 1.426(11) 1.509(10) 1.411(10) 1.492(11) 1.403(11) 1.519(11) 1.435(11) 1.495(11) 1.505(11) 0.8652 0.8652 257 C(16A)-H(16C) C(17A)-H(17A) C(17A)-H(17B) C(17A)-H(17C) C(18A)-H(18A) C(18A)-H(18B) C(18A)-H(18C) C(19A)-H(19A) C(19A)-H(19B) C(19A)-H(19C) C(20A)-H(20A) C(20A)-H(20B) C(20A)-H(20C) HfB-Cent(lB) HfB-Cent(2B) HfB-Pln(lB) HfB-Pln(2B) HfB-C(9B) HfB-C(l0B) HfB-C(4B) HfB-C(8B) HfB-C(3B) HfB-C(5B) HfB-C(2B) HfB-C(6B) HfB-C(lB) HfB-C(7B) C(1B)-C(2B) C(1B)-C(5B) C(lB)-C(l lB) C(2B)-C(3B) C(2B)-C(12B) C(3B)-C(4B) C(3B)-C(13B) C(4B)-C(5B) C(4B)-C(14B) C(5B)-C(15B) C(llB)-H(llD) C(llB)-H(llE) C(llB)-H(llF) C(12B)-H(12D) C(12B)-H(12E) C(12B)-H(12F) C(13B)-H(13D) C(13B)-H(13E) C(13B)-H(13F) C(14B)-H(14D) C(14B)-H(14E) C(14B)-H(14F) C(15B)-H(15D) C(15B)-H(15E) C(15B)-H(15F) C(6B)-C(10B) C(6B)-C(7B) 0.8652 0.9582 0.9582 0.9582 0.8480 0.8480 0.8480 0.9897 0.9897 0.9897 0.9523 0.9523 0.9523 2.175(3) 2.168(3) 2.175(3) 2.168(3) 2.481(7) 2.486(7) 2.500(7) 2.476(7) 2.491(7) 2.488(7) 2.486(7) 2.483(6) 2.489(7) 2.482(7) 1.421(9) 1.424(10) 1.490(10) 1.448(10) 1.509(9) 1.414(10) 1.496(10) 1.427(10) 1.474(10) 1.505(10) 0.9381 0.9381 0.9381 0.8323 0.8323 0.8323 0.9018 0.9018 0.9018 0.9711 0.9711 0.9711 0.8643 0.8643 0.8643 1.442(10) 1.398(10) 258 C(6B)-C(16B) C(7B)-C(8B) C(7B)-C(17B) C(8B)-C(9B) C(8B)-C(18B) C(9B)-C(10B) C(9B)-C(19B) C(10B)-C(20B) C(16B)-H(16D) C(16B)-H(16E) C(16B)-H(16F) C(17B)-H(17D) C(17B)-H(17E) C(17B)-H(17F) C(18B)-H(18D) C(18B)-H(18E) C(18B)-H(18F) C(19B)-H(19D) C(19B)-H(19E) C(19B)-H(19F) C(20B)-H(20D) C(20B)-H(20E) C(20B)-H(20F) Cent(lA )-HfA-Cen t(2A) Pln(lA)-HfA-Pln(2A) C(9A)-HfA-C(lOA) C(9A)-HfA-C(3A) C(lOA)-HfA-C(3A) C(9A)-HfA-C(8A) C(l0A)-HfA-C(8A) C(3A)-HfA-C(8A) C(9A)-HfA-C(2A) C(lOA)-HfA-C(2A) C(3A)-HfA-C(2A) C(8A)-HfA-C(2A) C(9A)-HfA-C(4A) C(l0A)-HfA-C(4A) C(3A)-HfA-C(4A) C(8A)-HfA-C(4A) C(2A)-HfA-C(4A) C(9A)-HfA-C(6A) C(lOA)-HfA-C(6A) C(3A)-HfA-C(6A) C(8A)-HfA-C(6A) C(2A)-HfA-C(6A) C(4A)-HfA-C(6A) C(9A)-HfA-C(7A) C(lOA)-HfA-C(7 A) C(3A)-HfA-C(7 A) C(8A)-HfA-C(7A) C(2A)-HfA-C(7 A) C(4A)-HfA-C(7 A) C(6A)-HfA-C(7A) 1.514(10) 1.412(10) 1.527(10) 1.425(11) 1.514(10) 1.421(10) 1.495(10) 1.502(10) 0.9272 0.9272 0.9272 0.9195 0.9195 0.9195 0.9950 0.9950 0.9950 0.8138 0.8138 0.8138 0.9535 0.9535 0.9535 144.1(2) 145.2(2) 33.5(3) 158.7(2) 162.4(2) 32.8(3) 54.2(2) 143.4(2) 153.7(3) 149.4(3) 33.5(2) 121.0(3) 151.5(2) 130.0(2) 32.5(2) 175.5(2) 54.6(2) 55.9(2) 33.3(2) 145.1(2) 54.8(2) 116.5(3) 127.1(2) 55.4(2) 54.9(3) 136.5(2) 32.9(2) 103.4(3) 145.9(2) 33.4(3) 259 C(9A)-HfA-C(lA) C(l0A)-HfA-C(lA) C(3A)-HfA-C(lA) C(8A)-HfA-C(lA) C(2A)-HfA-C(lA) C( 4A)-HfA-C(lA) C(6A)-HfA-C(lA) C(7 A)-HfA-C(lA) C(9A)-HfA-C(5A) C(l0A)-HfA-C(5A) C(3A)-HfA-C(5A) C(8A)-HfA-C(5A) C(2A)-HfA-C(5A) C(4A)-HfA-C(5A) C(6A)-HfA-C(5A) C(7 A)-HfA-C(5A) C(lA)-HfA-C(5A) C(2A)-C( lA )-C( 5A) C(2A)-C(1A)-C(l 1A) C(5A)-C(1A)-C(l 1A) C(2A)-C(lA)-HfA C(5A)-C(lA)-HfA C(llA)-C(lA)-HfA C(1A)-C(2A)-C(3A) C(1A)-C(2A)-C(12A) C(3A)-C(2A)-C(12A) C(lA)-C(2A)-HfA C(3A)-C(2A)-HfA C(12A)-C(2A)-HfA C( 4A)-C(3A)-C(2A) C(4A)-C(3A)-C(13A) C(2A)-C(3A)-C(13A) C(4A)-C(3A)-HfA C(2A)-C(3A)-HfA C(13A)-C(3A)-HfA C(3A)-C( 4A)-C(5A) C(3A)-C(4A)-C(14A) C(5A)-C( 4A)-C(14A) C(3A)-C(4A)-HfA C(5A)-C(4A)-HfA C(14A)-C(4A)-HfA C( 4A)-C(5A)-C(1A) C(4A)-C(5A)-C(15A) C(1A)-C(5A)-C(15A) C(4A)-C(5A)-HfA C(lA)-C(5A)-HfA C(15A)-C(5A)-HfA C(lA)-C(l lA)-H(l lA) C(lA)-C(l lA)-H(l lB) H(llA)-C(llA)-H(llB) C(lA)-C(llA)-H(llC) H(l lA)-C(l lA)-H(l lC) H(llB)-C(l lA)-H(l lC) C(2A)-C(12A)-H(12A) 145.1(2) 119.4(2) 54.9(2) 122.5(2) 32.7(2) 54.9(2) 90.2(2) 92.2(2) 144.3(3) 110.9(3) 54.3(2) 146.7(2) 54.2(3) 33.1(2) 95.7(2) 113.9(2) 32.8(2) 107.7(7) 125.7(7) 125.3(7) 73.6(4) 73.5(4) 128.9(5) 107.4(7) 126.4(7) 126.2(7) 73.7(4) 71.9(4) 120.7(5) 108.5(6) 126.6(7) 124.7(7) 74.0(4) 74.6(4) 121.3(5) 108.2(6) 127.4(7) 123.8(7) 73.5(4) 74.5(4) 125.1(5) 108.1(7) 124.4(7) 127.2(7) 72.3(4) 73.6(4) 124.4(5) 109.5 109.5 109.5 109.5 109.5 109.5 109.5 260 C(2A)-C(12A)-H(12B) H(12A)-C(12A)-H(12B) C(2A)-C(12A)-H(12C) H(12A)-C(12A)-H(12C) H(12B)-C(12A)-H(12C) C(3A)-C(13A)-H(13A) C(3A)-C(13A)-H(13B) H(13A)-C(13A)-H(13B) C(3A)-C(13A)-H(13C) H(13A)-C(13A)-H(13C) H(13B)-C(13A)-H(13C) C(4A)-C(14A)-H(14A) C(4A)-C(14A)-H(14B) H(14A)-C(14A)-H(14B) C(4A)-C(14A)-H(14C) H(14A)-C(14A)-H(14C) H(14B)-C(14A)-H(14C) C(5A)-C(15A)-H(15A) C(5A)-C(15A)-H(15B) H(15A)-C(15A)-H(15B) C(5A)-C(15A)-H(15C) H(15A)-C(15A)-H(15C) H(15B)-C(15A)-H(15C) C(7 A)-C(6A)-C(10A) C(7 A)-C(6A)-C(16A) C(10A)-C(6A)-C(16A) C(7 A)-C(6A)-HfA C(l0A)-C(6A)-HfA C(16A)-C(6A)-HfA C(6A)-C(7A)-C(8A) C(6A)-C(7 A)-C(17A) C(8A)-C(7 A)-C(17A) C(6A)-C(7 A)-HfA C(8A)-C(7 A)-HfA C(17A)-C(7 A)-HfA C(9A)-C(8A)-C(7A) C(9A)-C(8A)-C(18A) C(7A)-C(8A)-C(18A) C(9A)-C(8A)-HfA C(7 A)-C(8A)-HfA C(18A)-C(8A)-HfA C(8A)-C(9A)-C(10A) C(8A)-C(9A)-C(19A) C(10A)-C(9A)-C(19A) C(8A)-C(9A)-HfA C(lOA)-C(9A)-HfA C(19A)-C(9A)-HfA C(9A)-C(10A)-C(6A) C(9A)-C(10A)-C(20A) C(6A)-C(10A)-C(20A) C(9A)-C(l0A)-HfA C(6A)-C(l0A)-HfA C(20A)-C(lOA)-HfA C(6A)-C(16A)-H(16A) 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 106.9(6) 128.0(7) 124.1(7) 73.5(4) 73.0(4) 127.8(5) 107.0(7) 126.9(7) 125.6(7) 73.0(4) 72.9(4) 126.1(5) 111.1(7) 126.2(7) 122.4(7) 74.1(4) 74.1(4) 123.9(5) 105.6(7) 127.8(7) 126.5(7) 73.2(4) 72.9(4) 121.0(5) 109.4(7) 127.4(7) 123.2(7) 73.6(4) 73.6(4) 120.3(5) 109.5 261 C(6A)-C(16A)-H(16B) H(16A)-C(16A)-H(16B) C(6A)-C(16A)-H(16C) H(16A)-C(16A)-H(16C) H(16B)-C(16A)-H(16C) C(7 A)-C(17A)-H(17A) C(7 A)-C(17A)-H(17B) H(17A)-C(17A)-H(17B) C(7A)-C(17A)-H(17C) H(17A)-C(1 7A)-H(17C) H(17B)-C(17A)-H(17C) C(8A)-C(18A)-H(18A) C(8A)-C(18A)-H(18B) H(18A)-C(18A)-H(18B) C(8A)-C(18A)-H(18C) H(18A)-C(18A)-H(18C) H(18B)-C(18A)-H(18C) C(9A)-C(19A)-H(19A) C(9A)-C(19A)-H(19B) H(19A)-C(19A)-H(19B) C(9A)-C(19A)-H(19C) H(19A)-C(19A)-H(19C) H(l 9B)-C(l 9A)-H(l 9C) C(10A)-C(20A)-H(20A) C(10A)-C(20A)-H(20B) H(20A)-C(20A)-H(20B) C(10A)-C(20A)-H(20C) H(20A)-C(20A)-H(20C) H (20B )-C (20A )-H (20C) Cent(lB)-HfB-Cent(2B) Pln (1B)-HfB-Pln (2B) C(9B)-HfB-C(l0B) C(9B)-HfB-C(4B) C(l0B)-HfB-C( 4B) C(9B)-HfB-C(8B) C(l0B)-HfB-C(8B) C(4B)-HfB-C(8B) C(9B)-HfB-C(3B) C(lOB)-HfB-C(3B) C(4B)-HfB-C(3B) C(8B)-HfB-C(3B) C(9B)-HfB-C(5B) C(l0B)-HfB-C(5B) C(4B)-HfB-C(5B) C(8B)-HfB-C(5B) C(3B)-HfB-C(5B) C(9B)-HfB-C(2B) C(lOB)-HfB-C(2B) C(4B)-HfB-C(2B) C(8B)-HfB-C(2B) C(3B)-HfB-C(2B) C(5B)-HfB-C(2B) C(9B)-HfB-C(6B) C(lOB)-HfB-C(6B) 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 145.0(2) 145.9(2) 33.3(2) 156.2(2) 140.4(2) 33.4(3) 55.0(2) 164.5(2) 153.8(2) 172.6(2) 32.9(2) 131.7(2) 150.6(2) 117.8(2) 33.2(2) 153.0(3) 54.9(2) 147.2(2) 145.1(3) 55.2(2) 113.8(2) 33.8(2) 54.8(2) 55.5(2) 33.7(2) 262 C(4B)-HfB-C(6B) C(8B)-HfB-C(6B) C(3B)-HfB-C(6B) C(5B)-HfB-C( 6B) C(2B)-HfB-C( 6B) C(9B)-HfB-C(lB) C(l0B)-HfB-C(lB) C(4B)-HfB-C(lB) C(8B)-HfB-C(lB) C(3B)-HfB-C(lB) C(5B)-HfB-C(lB) C(2B)-HfB-C(lB) C(6B)-HfB-C(lB) C(9B)-HfB-C(7B) C(lOB)-HfB-C(7B) C(4B) -HfB-C(7B) C(8B)-HfB-C(7B) C(3B)-HfB-C(7B) C(5B)-HfB-C(7B) C(2B)-HfB-C(7B) C(6B)-HfB-C(7B) C(lB)-HfB-C(7B) C(2B)-C(1B)-C(5B) C(2B)-C(lB)-C(llB) C(5B)-C(l B)-C(l lB) C(2B)-C(lB)-HfB C(5B)-C(lB)-HfB C(llB)-C(lB)-HfB C(3B)-C(2B)-C(lB) C(3B)-C(2B)-C(12B) C(1B)-C(2B)-C(12B) C(3B)-C(2B)-HfB C(lB)-C(2B)-HfB C(12B)-C(2B)-HfB C( 4B)-C(3B)-C(2B) C( 4B)-C(3B)-C(l3B) C(2B)-C(3B)-C(13B) C(4B)-C(3B)-HfB C(2B)-C(3B)-HfB C(13B)-C(3B)-HfB C(3B)-C(4B)-C(5B) C(3B)-C(4B)-C(14B) C(5B)-C(4B)-C(14B) C(3B)-C(4B)-HfB C(5B)-C( 4B)-HfB C(14B)-C( 4B)-HfB C( 4B)-C(5B)-C(l B) C(4B)-C(5B)-C(15B) C(l B)-C(5B)-C(15B) C(4B)-C(5B)-HfB C(lB)-C(5B)-HfB C(15B)-C(5B)-HfB C(lB)-C(l lB)-H(llD) C(lB)-C(l lB)-H(llE) 136.7(2) 54.9(2) 144.4(2) 103.6(2) 111.4(2) 145.1(2) 119.4(2) 55.5(2) 122.8(3) 55.7(2) 33.3(2) 33.2(2) 90.4(2) 55.3(2) 55.0(2) 147.9(2) 33.1(2) 128.1(2) 120.0(3) 96.7(2) 32.7(2) 92.6(2) 107.2(6) 125.4(7) 125.9(6) 73.3(4) 73.3(4) 129.6(5) 108.3(6) 123.9(6) 127.6(7) 73.3(4) 73.5(4) 123.1(5) 107.7(6) 126.7(7) 125.2(6) 73.9(4) 72.9(4) 124.0(5) 107.8(6) 125.9(7) 126.3(7) 73.2(4) 72.9(4) 121.3(5) 109.1(6) 126.1(7) 124.7(7) 73.9(4) 73.4(4) 122.1(5) 109.5 109.5 263 H(llD)-C(llB)-H(llE) C(lB)-C(llB)-H(l lF) H(l 1D)-C(l lB)-H(l lF) H(llE)-C(llB)-H(llF) C(2B)-C(12B)-H(12D) C(2B)-C(12B)-H(12E) H(12D)-C(12B)-H(12E) C(2B)-C(12B)-H(12F) H(12D)-C(12B)-H(12F) H(12E)-C(12B)-H(12F) C(3B)-C(13B)-H(13D) C(3B)-C(13B)-H(13E) H(13D)-C(13B)-H(13E) C(3B)-C(13B)-H(13F) H(13D)-C(13B)-H(13F) H(13E)-C(13B)-H(13F) C(4B)-C(14B)-H(14D) C( 4B)-C(14B)-H(14E) H(14D)-C(14B)-H(14E) C(4B)-C(14B)-H(14F) H(14D)-C(14B)-H(14F) H(14E)-C(14B)-H(14F) C(5B)-C(15B)-H(15D) C(5B)-C(l5B)-H(15E) H(15D)-C(15B)-H(15E) C(5B)-C(15B)-H(15F) H(15D)-C(15B)-H(15F) H(15E)-C(15B)-H(15F) C(10B)-C(6B)-C(7B) C(10B)-C(6B)-C(16B) C(7B)-C(6B)-C(16B) C(lOB)-C(6B)-HfB C(7B)-C(6B)-HfB C(16B)-C(6B)-HfB C(8B)-C(7B)-C( 6B) C(8B)-C(7B)-C(l 7B) C(6B)-C(7B)-C(17B) C(8B)-C(7B)-HfB C(6B)-C(7B)-HfB C(17B)-C(7B)-HfB C(9B)-C(8B)-C(7B) C(9B)-C(8B)-C(18B) C(7B)-C(8B)-C(18B) C(9B)-C(8B)-HfB C(7B)-C(8B)-HfB C(18B)-C(8B)-HfB C(8B)-C(9B)-C(10B) C(8B)-C(9B)-C(l 9B) C(10B)-C(9B)-C(l 9B) C(8B)-C(9B)-HfB C(10B)-C(9B)-HfB C(19B)-C(9B)-HfB C(9B)-C(10B)-C( 6B) C(9B)-C(10B)-C(20B) 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 107.7(6) 122.4(6) 129.1(7) 73.2(4) 73.6(4) 126.8(5) 108.8(6) 123.1(7) 127.1(7) 73.3(4) 73.7(4) 128.3(5) 108.4(6) 125.9(7) 125.4(7) 73.5(4) 73.7(4) 123.3(5) 107.3(6) 127.5(7) 125.2(7) 73.1(4) 73.5(4) 119.3(5) 107.7(6) 125.5(7) 264 C(6B)-C(10B)-C(20B) C(9B)-C(10B)-HfB C(6B)-C(10B)-HfB C(20B)-C(10B)-HfB C(6B)-C(16B)-H(16D) C(6B)-C(16B)-H(16E) H(16D)-C(16B)-H(16E) C(6B)-C(16B)-H(16F) H(16D)-C(16B)-H(16F) H(16E)-C(16B)-H(16F) C(7B)-C(17B)-H(17D) C(7B)-C(17B)-H(17E) H(17D)-C(17B)-H(17E) C(7B)-C(17B)-H(17F) H(17D)-C(17B)-H(17F) H(17E)-C(17B)-H(17F) C(8B)-C(18B)-H(18D) C(8B)-C(18B)-H(18E) H(18D)-C(18B)-H(18E) C(8B)-C(18B)-H(18F) H(18D)-C(18B)-H(18F) H(18E)-C(18B)-H(18F) C(9B)-C(l 9B)-H(l 9D) C(9B)-C(19B)-H(19E) H(l 9D)-C(l 9B)-H(l 9E) C(9B)-C(l 9B)-H(l 9F) H(19D)-C(19B)-H(19F) H(19E)-C(l 9B)-H(l 9F) C(10B)-C(20B)-H(20D) C(10B)-C(20B)-H(20E) H(20D)-C(20B)-H(20E) C(10B)-C(20B)-H(20F) H(20D)-C(20B)-H(20F) H(20E)-C(20B)-H(20F) 126.6(6) 73.2(4) 73.0(4) 123.3(5) 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 Symmetry transformations used to generate equivalent atoms: 265 Table 12. Crystal data and structure refinement for meso-DpZrMe2. Empirical formula C22H36SiZr Formula weight 419.82 Crystallization Solvent Petroleum ether Crystal Habit Chunk Crystal size 0.296 X 0.185 X 0.074 mm3 Crystal color Pale yellow Data Collection Preliminary Photos Type of diffractometer CAD-4 Wavelength 0.71073 A MoKa Data Collection Temperature 85 K Theta range for reflections used in lattice determination 11.5 to 12.2° Unit cell dimensions a= 19.899(4) A b = 16.667(6) A c = 13.417(5) A Volume 4438(2) A3 z 8 Crystal system Monoclinic Space group P2(1)/c Density (calculated) l.257Mg/m3 F(000) 1776 Theta range for data collection 1.60 to 24.97° Completeness to theta = 24.97° 81.2 % Index ranges -22<=h<=22, -18<=k<=18, 0<=1<=14 Data collection scan type Omega scans Reflections collected 13928 Independent reflections 6332 [Rint= 0.0318; GOFmerge= ] Absorption coefficient 0.551 mm- 1 Absorption correction None Number of standards 3 reflections measured every 75min. Variation of standards -0.75%. a= 90° b= 94.16(2) 0 g=90° 266 Table 12 (cont.) Structure solution and Refinement Structure solution program Primary solution method Secondary solution method Hydrogen placement Structure refinement program Refinement method Data/ restraints / parameters Treatment of hydrogen atoms Goodness-of-fit on F2 Final R indices [I> 2s(I)] R indices (all data) Type of weighting scheme used Weighting scheme used Max shift/ error Average shift/ error Largest diff. peak and hole SHELXS-97 (Sheldrick, 1990) Direct methods Difference Fourier map Difference Fourier map SHELXL-97 (Sheldrick, 1997) Full matrix least-squares on F2 6332 IO/ 721 Unrestrained 1.304 Rl = 0.0342, wR2 = 0.0585 Rl = 0.0535, wR2 = 0.0634 Sigma w=l/sA2A(FoA2A) 1.268 0.002 0.427 and -0.378 e.A-3 Table 13. Bond lengths [A] and angles [0 ] for meso-DpZrMez. ZrA-Cent(lA) ZrA-Cent(2A) ZrA-Pln(lA) ZrA-Pln(2A) ZrA-C(22A) ZrA-C(21A) ZrA-C(6A) ZrA-C(lA) ZrA-C(2A) ZrA-C(7A) ZrA-C(5A) ZrA-C(lOA) ZrA-C(3A) ZrA-C(8A) ZrA-C(4A) ZrA-C(9A) SiA-C(lA) SiA-C(19A) SiA-C(6A) SiA-C(20A) C(1A)-C(5A) 2.2447(6) 2.2459(7) 2.235(2) 2.241(2) 2.275(4) 2.273(4) 2.470(3) 2.476(3) 2.469(3) 2.467(3) 2.543(3) 2.552(3) 2.582(3) 2.601(3) 2.657(3) 2.685(3) 1.873(3) 1.849(4) 1.868(3) 1.851(4) 1.418(5) 267 C(1A)-C(2A) C(2A)-C(3A) C(2A)-H(2A) C(3A)-C(4A) C(3A)-H(3A) C(4A)-C(5A) C(4A)-C(11A) C(5A)-H(5A) C(6A)-C(10A) C(6A)-C(7A) C(7A)-C(8A) C(7A)-H(7A) C(8A)-C(9A) C(8A)-H(8A) C(9A)-C(10A) C(9A)-C(15A) C(lOA)-H(lOA) C(l 1A)-C(13A) C(11A)-C(14A) C(l 1A)-C(12A) C(12A)-H(12A) C(12A)-H(12A) C(12A)-H(12A) C(13A)-H(13A) C(13A)-H(13A) C(13A)-H(13A) C(14A)-H(14A) C(14A)-H(14A) C(14A)-H(14A) C(15A)-C(18A) C(15A)-C(16A) C(15A)-C(17A) C(16A)-H(16A) C(16A)-H(16A) C(16A)-H(16A) C(17A)-H(17A) C(17A)-H(17A) C(17A)-H(17A) C(18A)-H(18A) C(18A)-H(18A) C(18A)-H(18A) C(19A)-H(19A) C(19A)-H(19A) C(19A)-H(19A) C(20A)-H(20A) C(20A)-H(20A) C(20A)-H(20A) C(21A)-H(21A) C(21A)-H(21A) C(21A)-H(21A) C(22A)-H(22A) C(22A)-H(22A) C(22A)-H(22A) ZrB-Cent(lB) 1.430(5) 1.403(5) 0.92(3) 1.409(5) 0.89(3) 1.411(5) 1.522(5) 0.88(3) 1.429(4) 1.429(5) 1.397(5) 0.88(3) 1.409(5) 0.89(3) 1.414(4) 1.518(4) 0.87(3) 1.530(5) 1.537(5) 1.530(5) 1.01(3) 0.96(3) 0.97(3) 0.95(3) 0.99(4) 0.96(4) 0.94(3) 0.97(4) 1.00(4) 1.526(5) 1.538(5) 1.535(5) 0.98(3) 0.91(3) 0.92(4) 0.93(3) 0.94(3) 0.98(3) 0.97(3) 0.86(3) 0.97(3) 0.86(4) 0.95(4) 0.97(4) 0.92(3) 0.93(3) 0.93(4) 0.98(3) 0.94(4) 0.90(4) 0.94(4) 0.84(3) 0.90(4) 2.2403(7) 268 ZrB-Cent(2B) ZrB-Pln(lB) ZrB-Pln(2B) ZrB-C(21B) ZrB-C(22B) ZrB-C(6B) ZrB-C(7B) ZrB-C(lB) ZrB-C(2B) ZrB-C(5B) ZrB-C(lOB) ZrB-C(8B) ZrB-C(3B) ZrB-C(4B) ZrB-C(9B) SiB-C(6B) SiB-C(20B) SiB-C(19B) SiB-C(lB) C(l B)-C(5B) C(1B)-C(2B) C(2B)-C(3B) C(2B)-H(2B) C(3B)-C(4B) C(3B)-H(3B) C(4B)-C(5B) C( 4B)-C(l 1B) C(5B)-H(5B) C(6B)-C(10B) C(6B)-C(7B) C(7B)-C(8B) C(7B)-H(7B) C(8B)-C(9B) C(8B)-H(8B) C(9B)-C(10B) C(9B)-C(15B) C(lOB)-H(l0B) C(l 1B)-C(12B) C(11B)-C(14B) C(l l B)-C(13B) C(13B)-H(13B) C(13B)-H(13B) C(13B)-H(13B) C(12B)-H(12B) C(12B)-H(12B) C(12B)-H(12B) C(14B)-H(14B) C(14B)-H(14B) C(14B)-H(14B) C(15B)-C(16B) C(15B)-C(18B) C(15B)-C(l 7B) C(16B)-H(16B) C(16B)-H(16B) 2.2513(5) 2.242(2) 2.231(2) 2.264(4) 2.273(4) 2.472(3) 2.461(3) 2.484(3) 2.487(3) 2.533(3) 2.537(3) 2.579(3) 2.596(4) 2.663(3) 2.654(3) 1.869(3) 1.850(4) 1.854(4) 1.874(3) 1.413(4) 1.433(5) 1.407(5) 0.89(3) 1.417(5) 0.91(3) 1.414(4) 1.517(4) 0.89(3) 1.414(5) 1.418(5) 1.401(5) 0.89(3) 1.416(5) 0.87(3) 1.408(5) 1.529(5) 0.83(3) 1.532(5) 1.524(5) 1.543(5) 0.98(3) 0.99(4) 0.91(4) 0.97(4) 1.00(4) 0.92(3) 0.92(3) 1.02(3) 0.88(4) 1.526(5) 1.530(5) 1.522(5) 1.00(4) 0.99(3) 269 C(l6B)-H(l6B) C(l7B)-H(l7B) C(l7B)-H(l7B) C(l7B)-H(l7B) C(l8B)-H(l8B) C(l8B)-H(l8B) C(l8B)-H(l8B) C(l9B)-H(l9B) C(l9B)-H(l9B) C(l9B)-H(l9B) C(20B)-H(20B) C(20B)-H(20B) C(20B)-H(20B) C(21B)-H(21B) C(21B)-H(21B) C(21B)-H(21B) C(22B)-H(22B) C(22B)-H(22B) C(22B)-H(22B) Cent(lA)-ZrA-Cent(2A) Pln(lA)-ZrA-Pln(2A) C(22A)-ZrA-C(21A) C(22A)-ZrA-C(6A) C(21A)-ZrA-C(6A) C(22A)-ZrA-C(lA) C(21A )-Zr A-C( lA) C(6A)-ZrA-C(lA) C (22A )-Zr A-C (2A) C(21A)-ZrA-C(2A) C(6A)-ZrA-C(2A) C(lA)-ZrA-C(2A) C(22A)-ZrA-C(7A) C(21A)-ZrA-C(7A) C(6A)-ZrA-C(7A) C(lA)-ZrA-C(7A) C(2A)-ZrA-C(7A) C(22A)-ZrA-C(5A) C(21A)-ZrA-C(5A) C( 6A)-ZrA-C(5A) C(lA)-ZrA-C(5A) C(2A)-ZrA-C(5A) C(7 A)-ZrA-C(5A) C(22A)-ZrA-C(l0A) C(21A)-ZrA-C(l0A) C(6A)-ZrA-C(lOA) C(lA)-ZrA-C(lOA) C(2A)-ZrA-C(lOA) C(7 A)-ZrA-C(lOA) C(5A)-ZrA-C(l0A) C(22A)-ZrA-C(3A) C(21A)-ZrA-C(3A) C(6A)-ZrA-C(3A) C(lA)-ZrA-C(3A) 0.90(3) 0.99(3) 0.89(4) 0.91(3) 0.88(4) 1.00(4) 1.03(3) 0.99(3) 0.96(4) 0.86(4) 0.99(3) 0.99(4) 0.95(4) 0.95(3) 0.97(4) 0.90(4) 0.91(4) 0.91(4) 0.91(4) 126.86(2) 116.34(13) 99.63(15) 112.85(14) 131.49(13) 112.48(12) 130.30(12) 68.83(11) 135.22(13) 97.40(13) 84.40(11) 33.61(11) 134.84(14) 98.25(14) 33.64(11) 85.38(11) 82.28(12) 83.40(12) 126.32(13) 93.46(11) 32.77(10) 53.52(12) 117.17(11) 83.38(13) 128.46(13) 33.01(10) 93.21(10) 116.33(11) 53.44(12) 105.19(11) 113.25(13) 78.90(13) 116.34(11) 54.24(11) 270 C(2A)-ZrA-C(3A) C(7A)-ZrA-C(3A) C(5A)-ZrA-C(3A) C(lOA)-ZrA-C(3A) C(22A)-ZrA-C(8A) C(21A)-ZrA-C(8A) C( 6A)-ZrA-C(8A) C(lA)-ZrA-C(8A) C(2A)-ZrA-C(8A) C(7A)-ZrA-C(8A) C(5A)-ZrA-C(8A) C(lOA)-ZrA-C(8A) C(3A)-ZrA-C(8A) C(22A)-ZrA-C(4A) C(21A)-ZrA-C(4A) C(6A)-ZrA-C(4A) C(lA)-ZrA-C( 4A) C(2A)-ZrA-C( 4A) C(7A)-ZrA-C( 4A) C(5A)-ZrA-C( 4A) C(l0A)-ZrA-C( 4A) C(3A)-ZrA-C( 4A) C(8A)-ZrA-C( 4A) C(22A)-ZrA-C(9A) C(21A)-ZrA-C(9A) C(6A)-ZrA-C(9A) C(lA)-ZrA-C(9A) C(2A)-ZrA-C(9A) C(7A)-ZrA-C(9A) C(5A)-ZrA-C(9A) C(lOA)-ZrA-C(9A) C(3A)-ZrA-C(9A) C(8A)-ZrA-C(9A) C( 4A)-ZrA-C(9A) C(lA)-SiA-C(19A) C(lA)-SiA-C(6A) C(19A)-SiA-C(6A) C(lA)-SiA-C(20A) C(19A)-SiA-C(20A) C(6A)-SiA-C(20A) C(5A)-C(1A)-C(2A) C(5A)-C(lA)-SiA C(2A)-C(lA)-SiA C(5A)-C(lA)-ZrA C(2A)-C(lA)-ZrA SiA-C(lA)-ZrA C(3A)-C(2A)-C(1A) C(3A)-C(2A)-ZrA C(lA)-C(2A)-ZrA C(3A)-C(2A)-H(2A) C(1A)-C(2A)-H(2A) ZrA-C(2A)-H(2A) C( 4A)-C(3A )-C(2A) C( 4A)-C(3A)-ZrA 32.14(11) 110.73(11) 52.20(11) 146.75(11) 112.55(13) 80.93(13) 54.12(11) 116.93(11) 110.87(12) 31.85(11) 147.06(11) 51.90(11) 132.24(11) 84.50(12) 95.10(13) 122.05(10) 53.80(10) 52.86(11) 134.49(11) 31.39(10) 136.13(10) 31.15(10) 162.88(11) 84.19(13) 97.45(12) 53.79(10) 121.84(10) 133.91(11) 52.49(11) 135.89(11) 31.20(10) 162.50(11) 30.88(11) 164.33(10) 111.04(18) 96.68(14) 111.31(17) 112.41(16) 114.13(18) 109.97(16) 104.9(3) 129.0(2) 121.2(2) 76.21(18) 72.91(18) 96.45(13) 109.1(3) 78.4(2) 73.48(18) 124.4(19) 126.5(19) 115.2(18) 108.9(3) 77.37(19) 271 C(2A)-C(3A)-ZrA C(4A)-C(3A)-H(3A) C(2A)-C(3A)-H(3A) ZrA-C(3A)-H(3A) C(3A)-C( 4A)-C(5A) C(3A)-C(4A)-C(11A) C(5A)-C( 4A)-C(l 1A) C(3A)-C( 4A)-ZrA C(5A)-C(4A)-ZrA C(l lA)-C( 4A)-ZrA C(1A)-C(5A)-C( 4A) C(lA)-C(5A)-ZrA C( 4A)-C(5A)-ZrA C(1A)-C(5A)-H(5A) C( 4A)-C(5A)-H(5A) ZrA-C(5A)-H(5A) C(10A)-C(6A)-C(7A) C(lOA )-C( 6A )-SiA C(7 A)-C(6A)-SiA C(lOA)-C(6A)-ZrA C(7A)-C(6A)-ZrA SiA-C(6A)-ZrA C(8A)-C(7A)-C(6A) C(8A)-C(7A)-ZrA C(6A)-C(7 A)-ZrA C(8A)-C(7 A)-H(7 A) C(6A)-C(7A)-H(7 A) ZrA-C(7 A)-H(7 A) C(7A)-C(8A)-C(9A) C(7A)-C(8A)-ZrA C(9A)-C(8A)-ZrA C(7A)-C(8A)-H(8A) C(9A)-C(8A)-H(8A) ZrA-C(8A)-H(8A) C(8A)-C(9A)-C(10A) C(8A)-C(9A)-C(15A) C(10A)-C(9A)-C(15A) C(8A)-C(9A)-ZrA C(lOA)-C(9A)-ZrA C(15A)-C(9A)-ZrA C(9A)-C(10A)-C(6A) C(9A)-C(lOA)-ZrA C(6A)-C(lOA)-ZrA C(9A)-C(l0A)-H(lOA) C(6A)-C(lOA)-H(l0A) ZrA-C(lOA)-H(l0A) C( 4A)-C(llA)-C(13A) C(4A)-C(11A)-C(l4A) C(13A)-C(l 1A)-C(14A) C( 4A)-C(l 1A)-C(12A) C(13A)-C(l 1A)-C(12A) C(14A)-C(l 1A)-C(12A) C(l 1A)-C(12A)-H(12A) C(l 1A)-C(l2A)-H(12A) 69.47(19) 127.1(19) 123.9(19) 121.1(18) 106.2(3) 124.8(3) 128.1(3) 71.48(18) 69.84(18) 131.9(2) 110.8(3) 71.02(18) 78.77(19) 125.2(19) 124(2) 122.0(19) 104.4(3) 127.9(2) 123.3(2) 76.68(18) 73.09(19) 96.80(13) 109.7(3) 79.3(2) 73.27(19) 125(2) 125(2) 114(2) 109.2(3) 68.8(2) 77.9(2) 125(2) 126(2) 123.3(19) 106.0(3) 124.8(3) 128.6(3) 71.26(19) 69.23(18) 131.3(2) 110.7(3) 79 .57(19) 70.31(18) 123(2) 126(2) 115(2) 111.4(3) 106.8(3) 108.1(3) 112.2(3) 109.9(3) 108.3(3) 111.9(18) 109.7(18) 272 H(12A)-C(12A)-H(12A) C(l 1A)-C(12A)-H(12A) H(12A)-C(12A)-H(12A) H(12A)-C(12A)-H(12A) C(11A)-C(13A)-H(13A) C(11A)-C(13A)-H(13A) H(13A)-C(13A)-H(13A) C(11A)-C(13A)-H(13A) H(13A)-C(13A)-H(l3A) H(13A)-C(13A)-H(13A) C(11A)-C(14A)-H(14A) C(11A)-C(14A).-H(14A) H(14A)-C(14A)-H(14A) C(l 1A)-C(14A)-H(14A) H(14A)-C(14A)-H(14A) H(14A)-C(14A)-H(14A) C(9A)-C(15A)-C(18A) C(9A)-C(15A)-C(16A) C(18A)-C(15A)-C(16A) C(9A)-C(15A)-C(17A) C(18A)-C(15A)-C(17A) C(16A)-C(15A)-C(17A) C(15A)-C(16A)-H(16A) C(15A)-C(16A)-H(16A) H(16A)-C(16A)-H(16A) C(15A)-C(16A)-H(16A) H(16A)-C(16A)-H(16A) H(16A)-C(16A)-H(16A) C(15A)-C(17A)-H(17 A) C(15A)-C(17A)-H(17A) H(17A)-C(17A)-H(17A) C(15A)-C(17A)-H(17A) H(17A)-C(17A)-H(17A) H(17A)-C(17A)-H(17 A) C(15A)-C(18A)-H(18A) C(15A)-C(18A)-H(18A) H(18A)-C(18A)-H(18A) C(15A)-C(18A)-H(18A) H(18A)-C(18A)-H(18A) H(18A)-C(18A)-H(18A) SiA-C(19A)-H(19A) SiA-C(19A)-H(19A) H(19A)-C(19A)-H(19A) SiA-C(19A)-H(19A) H(l 9A)-C(19A)-H(19A) H(19A)-C(l9A)-H(19A) SiA-C(20A)-H(20A) SiA-C(20A)-H(20A) H(20A)-C(20A)-H(20A) SiA-C(20A)-H(20A) H(20A)-C(20A)-H(20A) H(20A)-C(20A)-H(20A) ZrA-C(21A)-H(21A) ZrA-C(21A)-H(21A) 107(3) 109.3(18) 109(2) 110(2) 115(2) 111(2) 106(3) 112(2) 108(3) 105(3) 107.4(19) 114(2) 112(3) 109(2) 109(3) 105(3) 112.1(3) 107.5(3) 108.1(3) 111.5(3) 109.4(3) 108.1(3) 110.4(19) 112(2) 106(3) 107(2) 112(3) 110(3) 109.8(19) 108.8(19) 108(3) 112(2) 115(3) 104(3) 114.3(19) 112(2) 103(3) 110.5(18) 109(3) 108(3) 111(2) 113(2) 107(3) 114(2) 101(3) 110(3) 110(2) 113(2) 111(3) 111(2) 107(3) 105(3) 112.3(18) 111(2) 273 H(21A)-C(21A)-H(21A) ZrA-C(21A)-H(21A) H(21A)-C(21A)-H(21A) H(21A)-C(21A)-H(21A) ZrA-C(22A)-H(22A) ZrA-C(22A)-H(22A) H(22A)-C(22A)-H(22A) ZrA-C(22A)-H(22A) H(22A)-C(22A)-H(22A) H (22A )-C(22A )-H (22A) Cent(1B)-ZrB-Cent(2B) Pln(lB)-ZrB-Pln(2B) C(21B)-ZrB-C(22B) C(21B)-ZrB-C(6B) C(22B)-ZrB-C(6B) C(21B)-ZrB-C(7B.) C(22B)-ZrB-C(7B) C(6B)-ZrB-C(7B) C(21B)-ZrB-C(lB) C(22B)-ZrB-C(lB) C(6B)-ZrB-C(lB) C(7B)-ZrB-C(lB) C(21B)-ZrB-C(2B) C(22B)-ZrB-C(2B) C( 6B)-ZrB-C(2B) C(7B)-ZrB-C(2B) C(1B)-ZrB-C(2B) C(21B)-ZrB-C(5B) C(22B)-ZrB-C(5B) C( 6B)-ZrB-C(5B) C(7B)-ZrB-C(5B) C(1B)-ZrB-C(5B) C(2B)-ZrB-C(5B) C(21B)-ZrB-C(10B) C(22B)-ZrB-C(10B) C(6B)-ZrB-C(10B) C(7B)-ZrB-C(10B) C(lB)-ZrB-C(l0B) C(2B)-ZrB-C(10B) C(5B)-ZrB-C(10B) C(21B)-ZrB-C(8B) C(22B)-ZrB-C(8B) C(6B)-ZrB-C(8B) C(7B)-ZrB-C(8B) C(1B)-ZrB-C(8B) C(2B)-ZrB-C(8B) C(5B)-ZrB-C(8B) C(l0B)-ZrB-C(8B) C(21 B)-ZrB-C(3B) C(22B)-ZrB-C(3B) C(6B)-ZrB-C(3B) C(7B)-ZrB-C(3B) C(1B)-ZrB-C(3B) C(2B)-ZrB-C(3B) 106(3) 106(2) 110(3) 111(3) 117(2) 109(2) 108(3) 111(2) 106(3) 107(3) 126.66(2) 116.34(14) 97.20(16) 129.31(13) 116.24(13) 96.21(14) 135.79(13) 33.40(11) 131.00(14) 115.07(14) 68.41(10) 85.71(11) 97.81(15) 135.25(14) 84.65(11) 83.73(11) 33.50(11) 129.14(14) 85.01(14) 92.55(11) 117.10(11) 32.70(10) 53.35(12) 128.18(14) 85.88(13) 32.77(11) 53.40(12) 91.65(11) 115.82(11) 102.68(11) 79.32(14) 111.18(13) 54.20(11) 32.16(11) 117.42(11) 112.93(11) 146.57(11) 52.28(12) 80.69(14) 111.33(13) 116.43(11) 112.34(11) 54.23(11) 32.05(10) 274 C(5B)-ZrB-C(3B) C(lOB)-ZrB-C(3B) C(8B)-ZrB-C(3B) C(21 B)-ZrB-C( 4B) C(22B)-ZrB-C(4B) C(6B)-ZrB-C(4B) C(7B)-ZrB-C( 4B) C(l B)-ZrB-C( 4B) C(2B)-ZrB-C(4B) • C(5B)-ZrB-C( 4B) C(lOB)-ZrB-C(4B) C(8B)-ZrB-C(4B) C(3B)-ZrB-C( 4B) C(21B)-ZrB-C(9B) C(22B)-ZrB-C(9B) C(6B)-ZrB-C(9B) . C(7B)-ZrB-C(9B) C(lB)-ZrB-C(9B) C(2B)-ZrB-C(9B) C(5B)-ZrB-C(9B) C(lOB)-ZrB-C(9B) C(8B)-ZrB-C(9B) C(3B)-ZrB-C(9B) C( 4B)-ZrB-C(9B) C(6B)-SiB-C(20B) C(6B)-SiB-C(19B) C(20B)-SiB-C(l 9B) C(6B)-SiB-C(lB) C(20B)-SiB-C(lB) C(19B)-SiB-C(lB) C(5B)-C(1B)-C(2B) C(5B)-C(lB)-SiB C(2B)-C(lB)-SiB C(5B)-C(lB)-ZrB C(2B)-C(l B)-ZrB SiB-C(lB)-ZrB C(3B)-C(2B)-C(1B) C(3B)-C(2B)-ZrB C(lB)-C(2B)-ZrB C(3B)-C(2B)-H(2B) C(1B)-C(2B)-H(2B) ZrB-C(2B)-H(2B) C(2B)-C(3B)-C(4B) C(2B)-C(3B)-ZrB C( 4B)-C(3B)-ZrB C(2B)-C(3B)-H(3B) C( 4B)-C(3B)-H(3B) ZrB-C(3B)-H(3B) C(5B)-C(4B)-C(3B) C(5B)-C( 4B)-C(l 1B) C(3B)-C( 4B)-C(l 1B) C(5B)-C(4B)-ZrB C(3B)-C(4B)-ZrB C(11B)-C(4B)-ZrB 52.28(11) 145.53(11) 134.73(11) 98.00(13) 83.53(13) 121.45(10) 135.57(11) 53.80(10) 52.74(11) 31.46(10) 133.57(11) 165.23(11) 31.23(10) 97.28(14) 83.64(13) 53.81(10) 52.92(11) 120.99(10) 135.30(10) 133.23(11) 31.36(10) 31.36(11) 165.02(11) 161.13(10) 113.57(17) 110.63(18) 111.20(19) 96.22(14) 114.40(16) 109.95(17) 104.7(3) 130.9(3) 119.8(2) 75.55(19) 73.36(19) 97.21(13) 109.4(3) 78.3(2) 73.14(19) 127(2) 123(2) 119(2) 108.6(3) 69.7(2) 77.0(2) 126(2) 125.1(19) 120.5(19) 105.9(3) 129.1(3) 123.9(3) 69.18(18) 71.78(19) 132.5(2) 275 C(l B)-C(5B)-C( 4B) C(lB)-C(5B)-ZrB C( 4B)-C(SB)-ZrB C(1B)-C(5B)-H(5B) C(4B)-C(5B)-H(5B) ZrB-C(5B)-H(5B) C(10B)-C(6B)-C(7B) C(lOB)-C(6B)-SiB C(7B)-C(6B)-SiB C(lOB)-C(6B)-ZrB C(7B)-C(6B)-ZrB SiB-C(6B)-ZrB C(8B)-C(7B)-C(6B) C(8B)-C(7B)-ZrB C(6B)-C(7B)-ZrB C(8B)-C(7B)-H(7B) C(6B)-C(7B)-H(7B) ZrB-C(7B)-H(7B) C(7B)-C(8B)-C(9B) C(7B)-C(8B)-ZrB C(9B)-C(8B)-ZrB C(7B)-C(8B)-H(8B) C(9B)- C(8B)-H(8B) ZrB-C(8B)-H(8B) C(8B)-C(9B)-C(10B) C(8B)-C(9B)-C(15B) C(10B)-C(9B)-C(15B) C(8B)-C(9B)-ZrB C(l0B)-C(9B)-Zr B C(15B)-C(9B)-ZrB C( 6B)-C(10B)-C(9B) C( 6B)-C(lOB)-ZrB C(9B)-C(lOB)-ZrB C(6B)-C(lOB)-H(lOB) C(9B)-C(l0B)-H(l0B) ZrB-C(l0B)-H(lOB) C( 4B)-C(l 1B)-C(12B) C( 4B)-C(l 1B)-C(14B) C(12B)-C(11B)-C(14B) C( 4B)-C(l 1B)-C(13B) C(12B)-C(l 1B)-C(13B) C(14B)-C(llB)-C(13B) C(11B)-C(13B)-H(13B) C(l 1B)-C(13B)-H(13B) H(13B)-C(l3B)-H(13B) C(l 1B)-C(13B)-H(13B) H(13B)-C(13B)-H(13B) H(13B)-C(13B)-H(13B) C(l 1B)-C(12B)-H(12B) C(l 1B)-C(12B)-H(12B) H(12B)-C(12B)-H(12B) C(l 1B)-C(l2B)-H(12B) H(12B)-C(12B)-H(12B) H(12B)-C(12B)-H(12B) 111.3(3) 71.75(18) 79.36(19) 125(2) 123(2) 115(2) 105.0(3) 128.5(3) 122.2(2) 76.11(19) 72.84(18) 97.74(13) 109.6(3) 78.6(2) 73.76(18) 127(2) 123(2) 112.9(19) 108.5(3) 69.25(19) 77.2(2) 127(2) 125(2) 118(2) 105.9(3) 124.7(3) 128.4(3) 71.39(19) 69.70(19) 132.2(2) 111.0(3) 71.11(19) 78.9(2) 127(2) 122(2) 117(2) 106.6(3) 112.2(3) 108.6(3) 112.3(3) 107.4(3) 109.5(3) 107.8(19) 109(2) 109(3) 109(2) 115(3) 107(3) 107(2) 111(2) 108(3) 110(2) 109(3) 112(3) 276 C(l 1B)-C(14B)-H(14B) C(llB)-C(14B)-H(14B) H(14B)-C(14B)-H(14B) C(11B)-C(14B)-H(14B) H(14B)-C(14B)-H(14B) H(14B)-C(14B)-H(14B) C(16B)-C(15B)-C(9B) C(16B)-C(15B)-C(18B) C(9B)-C(15B)-C(18B) C(16B)-C(15B)-C(17B) C(9B)-C(15B)-C(l 7B) C(18B)-C(15B)-C(17B) C(l5B)-C(16B)-H(16B) C(15B)-C(16B)-H(16B) H(16B)-C(16B)-H(16B) C(15B)-C(16B)-H(16B) H(16B)-C(16B)-H(16B) H(16B)-C(16B)-H(16B) C(15B)-C(17B)-H(17B) C(15B)-C(17B)-H(17B) H(l 7B)-C(17B)-H(l 7B) C(15B)-C(17B)-H(17B) H(17B)-C(17B)-H(17B) H(17B)-C(17B)-H(17B) C(15B)-C(18B)-H(18B) C(15B)-C(18B)-H(18B) H(18B)-C(18B)-H(18B) C(15B)-C(18B)-H(18B) H(18B)-C(18B)-H(18B) H(18B)-C(18B)-H(18B) SiB-C(19B)-H(19B) SiB-C(19B)-H(19B) H(l 9B)-C(l 9B)-H(l 9B) SiB-C(l 9B)-H(l 9B) H(l 9B)-C(l 9B)-H(l 9B) H(l 9B)-C(l 9B)-H(l 9B) SiB-C(20B )-H(20B) SiB-C (20B )-H(20B) H(20B)-C(20B)-H(20B) SiB-C(20B)-H(20B) H(20B)-C(20B)-H(20B) H(20B)-C(20B)-H(20B) ZrB-C(21B)-H(21B) ZrB-C(21B)-H(21B) H(21B)-C(21B)-H(21B) ZrB-C(21B)-H(21B) H(21B)-C(21B)-H(21B) H(21B)-C(21 B)-H(21B) ZrB-C(22B)-H(22B) ZrB-C(22B)-H(22B) H(22B)-C(22B)-H(22B) ZrB-C(22B)-H(22B) H(22B)-C(22B)-H(22B) H(22B)-C(22B)-H(22B) 112(2) 109.4(18) 105(3) 114(2) 105(3) 111(3) 111.3(3) 108.9(3) 106.2(3) 110.5(3) 111.8(3) 108.0(3) 112(2) 113.4(18) 106(3) 110(2) 103(3) 112(3) 111.5(19) 108(2) 107(3) 110(2) 113(3) 106(3) 112(2) 113(2) 104(3) 113.5(19) 109(3) 104(3) 110(2) 115(2) 104(3) 112(2) 106(3) 109(3) 110.2(18) 112(2) 103(3) 115(2) 109(3) 108(3) 107.4(19) 113(2) 102(3) 112(2) 108(3) 114(3) 104(2) 118(2) 103(3) 113(2) 106(3) 112(3) 277 Symmetry transformations used to generate equivalent atoms: Table 14. Crystal Data and Structure Analysis Details for meso-[DpZrHzh. Empirical formula C40H62Si2Zt2 Formula weight 781.52 Crystallization solvent toluene Crystal habit plate Crystal size 0.08 X 0.07 X 0.04 mm Crystal color colorless Data Collection Preliminary photograph(s) rotation Type of diffractometer Bruker SMART 1000 ccd Wavelength 0.71073 A MoKa Data collection temperature 98K Theta range for 2846 reflections used in lattice determinatii:m 2.2 to 21.9° Volume a = 10.0511(11) A b = 14.2131(16) A c = 15.3334(17) A 2026.1(4) A3 z 2 Crystal system triclinic Space group P' l (#2) Density (calculated) 1.281 g/cm3 F(000) 820 Theta range for data collection 1.35 to 25.00° Completeness to theta = 25.00° 99.8 % Index ranges -11 £ h £ 11, -16 £ k £ 16, -18 £ 1 £ 18 Data collection scan type w scans at 4 fixed f values Reflections collected 20564 Independent reflections 7112 [Rint= 0.0851] Absorption coefficient 0.598 mm- 1 Absorption correction empirical Max. and min. transmission 1.00 and 0.93 Number of standards first scans recollected at end of runs Unit cell dimensions a= 82.573(2) 0 b= 79.502(2) 0 g = 70.609(2) 0 278 Variation of standards within counting statistics Structure Solution and Refinement Primary solution method direct methods Secondary solution method difference map Hydrogen placement calculated Refinement method full-matrix least-squares on F2 Data I restraints / parameters 7112 Io I 397 Treatment of hydrogen atoms not refined; Diso's set at 120% Ueq of attached atom Goodness-of-fit on F2 1.734 Final R indices [l>2s(I), 4312 reflections] Rl = 0.0610, wR2 = 0.1160 R indices (all data) Rl = 0.1217, wR2 = 0.1273 Type of weighting scheme used sigma Weighting scheme used 2 2 w=l/s (Fo ) Max shift/ error 0.010 Average shift/ error 0.001 Largest diff. peak and hole 1.745 and -0.673 e.A-3 Programs Used Cell refinement Bruker SAINT v6.02 Data collection Bruker SMART vS.054 Data reduction Bruker SAINT v6.02 Absorption correction SADABS V2.0 beta Structure solution SHELXS-97 (Sheldrick, 1990) Structure refinement SHELXL-97 (Sheldrick, 1997) Special Refinement Details A tiny, colorless irregular plate was mounted on a glass fiber with Paratone-N oil. Four runs of data were collected with 90 second long, -0.2000 wide w-scans at four values of j (0, 120, 240 and 30000) with the detector 5 cm (nominal) distant at a q of -28 00 . The initial cell for data reduction was calculated from just under 1000 reflections chosen from throughout the data frames. For data processing with SAINT v6.02, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to zero, no Laue class integration restraints were used, the model profiles from all nine areas were blended, and for the post-integration global least squares refinement, no 279 constraints were applied. The data were corrected with SADABS v. 2.0 (beta) using default parameters except that the scale factor esd was set to 0. No decay correction was needed. No reflections were specifically omitted from the final processed dataset; the data were truncated at a 2q of 50 4369 reflections were rejected, and there were 11 inconsistent equivalents. Refinement of F2 was against all reflections. The weighted R-factor (wR) and 00, goodness of fit (S) are based on F2, conventional R-factors (R) are based on F, with F set to zero 2 for negative F2. The threshold expression of F2 > 2s( F ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. There are two, dimers in the unit cell; each sits on a center of symmetry so that the asymmetric unit consists of two independent half-dimers. The bridging hydride atoms were not located in difference-maps and so were excluded from the refinement. There are three peaks in the final difference map greater than 111 e◊A-3 : 1.74 eOA-3 at2.21 A from H14A, 1.53 e◊A-3 at(_,_,_) 1.75 A from ZrA and 1.10 eOA-3 at 2.20 A from H18D. Table 15. Bond lengths [A] and angles [0] for meso-[DpZrH2]2 ZrA-CplA ZrA-Cp2A ZrA··PlnlA ZrA··Pln2A ZrA-ClA ZrA-C6A ZrA-C7A ZrA-C2A ZrA-C5A ZrA-ClOA ZrA-C8A ZrA-C3A ZrA-C9A ZrA-C4A ZrA-ZrA 10 SiA-CllA SiA-C6A SiA-C12A SiA-ClA C1A-C2A C1A-C5A C2A-C3A C2A-H2A C3A-C4A C3A-H3A C4A-C5A C4A-C13A C5A-H5A C6A-C7A C6A-ClOA C7A-C8A C7A-H7A C8A-C9A 2.222 2.215 2.213(3) 2.207(3) 2.443(7) 2.447(7) 2.469(7) 2.482(7) 2.493(7) 2.509(7) 2.554(7) 2.572(7) 2.621(7) 2.635(7) 3.4922(15) 1.816(8) 1.849(8) 1.849(7) 1.863(8) 1.403(10) 1.424(10) 1.420(10) 1.0000 1.408(9) 1.0000 1.414(10) 1.495(10) 1.0000 1.415(10) 1.447(10) 1.392(10) 1.0000 1.395(9) 280 C8A-H8A C9A-ClOA C9A-C17A ClOA-HlOA CllA-HllA CllA-HllB CllA-HllC C12A-H12A C12A-H12B C12A-Hl2C C13A-C16A C13A-C15A C13A-C14A C14A-H14A C14A-H14B C14A-H14C C15A-H15A C15A-H15B C15A-H15C C16A-H16A C16A-H16B C16A-H16C C17A-C20A C17A-Cl8A C17A-C19A C18A-H18A C18A-Hl8B C18A-Hl8C C19A-H19A C19A-Hl9B C19A-H19C C20A-H20A C20A-H20B C20A-H20C ZrB-CplB ZrB-Cp2B ZrB---PlnlB ZrB···Pln2B ZrB-ClB ZrB-C5B ZrB-C6B ZrB-C7B ZrB-C2B ZrB-ClOB ZrB-C3B ZrB-C8B ZrB-C4B ZrB-C9B ZrB-ZrBu;; SiB-CllB SiB-C12B SiB-ClB SiB-C6B C1B-C2B 1.0000 1.427(10) 1.509(10) 1.0000 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 1.522(10) 1.530(10) 1.535(11) 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 1.520(10) 1.524(10) 1.546(10) 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 2.204 2.229 2.197(3) 2.223(3) 2.432(7) 2.458(7) 2.471(7) 2.487(7) 2.494(6) 2.515(7) 2.563(7) 2.576(7) 2.598(7) 2.611(7) 3.4498(15) 1.822(8) 1.839(8) 1.867(7) 1.867(7) 1.420(9) 281 C1B-C5B C2B-C3B C2B-H2B C3B-C4B C3B-H3B C4B-C5B C4B-C13B C5B-H5B C6B-C7B C6B-C10B C7B-C8B C7B-H7B C8B-C9B C8B-H8B C9B-C10B C9B-C17B ClOB-HlOB C11B-H11D C11B-H11E CllB-H11F C12B-H12D C12B-H12E C12B-H12F C13B-C16B C13B-C14B C13B-C15B C14B-H14D C14B-H14E C14B-H14F C15B-H15D C15B-H15E C15B-H15F C16B-H16D C16B-H16E C16B-H16F C17B-C20B C17B-C19B C17B-C18B C18B-H18D C18B-H18E C18B-H18F C19B-H19D C19B-H19E C19B-H19F C20B-H20D C20B-H20E C20B-H20F CplA-ZrA-Cp2A Pln1A- .. Pln2A C 11A-SiA-C6A CllA-SiA-C12A C6A-SiA-C12A CllA-SiA-ClA C6A-SiA-ClA 1.421(9) 1.382(9) 1.0000 1.410(10) 1.0000 1.420(9) 1.495(9) 1.0000 1.409(9) 1.438(9) 1.412(9) 1.0000 1.410(9) 1.0000 1.405(9) 1.518(9) 1.0000 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 1.532(10) 1.545(10) 1.558(10) 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 1.496(9) 1.519(10) 1.539(10) 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 125.1 62.4(3) 112.2(4) 115.2(4) 110.6(4) 109.9(4) 96.5(3) 282 Cl2A-SiA-ClA C2A-ClA-C5A C2A-ClA-SiA C5A-ClA-SiA ClA-C2A-C3A ClA-C2A-H2A C3A-C2A-H2A C4A-C3A-C2A C4A-C3A-H3A C2A-C3A-H3A C3A-C4A-C5A C3A-C4A-Cl3A C5A-C4A-Cl3A C4A-C5A-ClA C4A-C5A-H5A ClA-C5A-H5A . C7A-C6A-Cl0A C7 A-C6A-SiA ClOA-C6A-SiA C8A-C7A-C6A C8A-C7A-H7A C6A-C7A-H7A C7A-C8A-C9A C7A-C8A-H8A C9A-C8A-H8A C8A-C9A-ClOA C8A-C9A-Cl7A ClOA-C9A-Cl7A C9A-ClOA-C6A C9A-ClOA-HlOA C6A-ClOA-HlOA SiA-CllA-HllA SiA-CllA-HllB HllA-CllA-HllB SiA-CllA-HllC HllA-CllA-HllC HllB-CllA-HllC SiA-Cl2A-Hl2A SiA-Cl2A-Hl2B Hl2A-Cl2A-Hl2B SiA-Cl2A-Hl2C Hl2A-Cl2A-Hl2C Hl2B-Cl2A-Hl2C C4A-Cl3A-Cl6A C4A-Cl3A-Cl5A Cl6A-Cl3A-Cl5A C4A-Cl3A-Cl4A Cl6A-Cl3A-Cl4A Cl5A-Cl3A-Cl4A Cl3A-Cl4A-Hl4A Cl3A-Cl4A-Hl4B Hl4A-Cl4A-Hl4B Cl3A-Cl4A-Hl4C Hl4A-Cl4A-Hl4C 110.9(4) 104.7(7) 128.1(6) 122.1(6) 109.6(7) 124.9 124.9 108.9(7) 125.3 125.3 105.2(7) 126.0(7) 128.2(7) 111.6(7) 123.9 123.9 103.9(7) 128.0(6) 122.9(6) 110.3(7) 124.5 124.5 109.8(7) 124.9 124.9 105.7(7) 127.3(7) 126.3(7) 110.2(7) 124.6 124.6 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 106.8(7) 112.9(6) 108.5(7) 111.4(6) 107.5(7) 109.6(7) 109.5 109.5 109.5 109.5 109.5 283 H14B-C14A-H14C C13A-C15A-H15A C13A-C15A-H15B H15A-C15A-H15B C13A-C15A-H15C H15A-C15A-H15C H15B-C15A-H15C C13A-C16A-H16A C13A-C16A-H16B H16A-C16A-H16B C13A-C16A-H16C H16A-C16A-H16C H16B-C16A-H16C C9A-C17A-C20A C9A-C17A-C18A C20A-C17A-C18A C9A-C17A-C19A C20A-C17A-C19A C18A-C17A-C19A C17A-C18A-H18A C17A-C18A-H18B H18A-C18A-H18B C17A-C18A-Hl8C H18A-C18A-H18C H18B-C18A-H18C C17A-C19A-H19A C17A-C19A-H19B H19A-C19A-H19B C17A-C19A-H19C H19A-C19A-H19C H19B-C19A-H19C C17A-C20A-H20A C17A-C20A-H20B H20A-C20A-H20B C17A-C20A-H20C H20A-C20A-H20C H20B-C20A-H20C CplB-ZrB-Cp2B Pln1B···Pln2B CllB-SiB-C12B CllB-SiB-ClB C12B-SiB-ClB CllB-SiB-C6B C12B-SiB-C6B ClB-SiB-C6B C2B-C1B-C5B C2B-ClB-SiB C5B-ClB-SiB C3B-C2B-C1B C3B-C2B-H2B C1B-C2B-H2B C2B-C3B-C4B C2B-C3B-H3B C4B-C3B-H3B 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 114.3(6) 110.6(6) 110.1(6) 106.1(6) 107.8(7) 107.7(6) 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 10 124.6 62.8(3) 112.9(4) 111.1(3) 111.9(4) 113.9(4) 109.4(3) 96.5(3) 104.7(6) 129.0(5) 121.2(6) 109.8(7) 124.9 124.9 109.6(7) 125.0 125.0 284 C3B-C4B-C5B C3B-C4B-C13B C5B-C4B-C13B C4B-C5B-C1B C4B-C5B-H5B C1B-C5B-H5B C7B-C6B-C10B C7B-C6B-SiB C10B-C6B-SiB C6B-C7B-C8B C6B-C7B-H7B C8B-C7B-H7B C9B-C8B-C7B C9B-C8B-H8B C7B-C8B-H8B C10B-C9B-C8B C10B-C9B-C17B C8B-C9B-C17B C9B-C10B-C6B C9B-C10B-H10B C6B-C10B-H10B SiB-CllB-HllD SiB-CllB-HllE HllD-CllB-HllE SiB-CllB-HllF HllD-CllB-HllF HllE-Cl lB-HllF SiB-C12B-H12D SiB-C12B-H12E H12D-C12B-H12E SiB-C12B-H12F H12D-C12B-H12F H12E-C12B-H12F C4B-C13B-C16B C4B-C13B-C14B C16B-C13B-Cl4B C4B-C13B-C15B C16B-C13B-C15B C14B-C13B-C15B C13B-C14B-H14D C13B-C14B-H14E H14D-C14B-H14E C13B-C14B-H14F H14D-C14B-H14F H14E-C14B-H14F C13B-C15B-H15D C13B-C15B-H15E H15D-C15B-H15E C13B-C15B-H15F H15D-C15B-H15F H15E-C15B-H15F C13B-C16B-H16D C13B-C16B-H16E H16O-C16B-H16E 105.3(7) 125.1(7) 129.1(7) 110.5(7) 124.3 124.3 104.6(6) 125.0(6) 124.2(5) 109.8(6) 124.7 124.7 108.7(6) 125.5 125.5 106.2(6) 127.5(7) 125.2(6) 110.8(7) 124.3 124.3 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 108.8(6) 113.3(6) 106.3(7) 111.5(6) 107.4(7) 109.2(6) 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 285 C13B-C16B-H16F 109.5 H16D-C16B-H16F 109.5 H16E-C16B-H16F 109.5 C20B-Cl 7B-C9B 111.5(6) C20B-C17B-C19B 109.1(7) C9B-C17B-C19B 107.3(6) C20B-C17B-C18B 108.9(6) C9B-Cl 7B-C18B 111.0(6) C19B-C17B-C18B 109.0(7) C17B-C18B-H18D 109.5 C17B-C18B-H18E 109.5 H18D-C18B-H18E 109.5 C17B-C18B-H18F 109.5 H18D-C18B-H18F 109.5 H18E-C18B-H18F 109.5 C17B-C19B-H19D 109.5 C17B-C19B-H19E 109.5 H19D-C19B-H19E 109.5 C17B-C19B-H19F 109.5 H19D-C19B-H19F 109.5 Hl 9E-Cl 9B-Hl 9F 109.5 C17B-C20B-H20D 109.5 Cl 7B-C20B-H20E 109.5 H20D-C20B-H20E 109.5 C17B-C20B-H20F 109.5 H20D-C20B-H20F 109.5 H20E-C20B-H20F 109.5 Symmetry transformations used to generate equivalent atoms: n' -x+ 1,-y+1,-z+1 n" -x+2,-y+2,-z 286 C22 C26 C2 @ C25 i3 Labeled view of BpZr(µ2-N2)ZrBp. 287 Table 16. Crystal Data and Structure Analysis Details for BpZrN2ZrBp. Empirical formula C59H 1ooN2Si6Zr2 Formula weight 1188.39 Crystallization solvent toluene Crystal habit wedge Crystal size 0.33 X 0.26 X 0.19 mm Crystal color trichroic - pale yellow / rose / dark brown Data Collection Preliminary photograph(s) rotation Type of diffractometer Bruker SMART 1000 ccd Wavelength 0.71073 A MoKa Data collection temperature 98K Theta range for 7518 reflections used in lattice determination 2.2 to 28.4° Unit cell dimensions a = 16.7641(9) A b = 10.7439(6) A c = 18.3696(10) A Volume 3250.4(3) A3 z 2 Crystal system monoclinic Space group P 2/n (#13) Density (calculated) 1.214g/cm3 F(000) 1264 Theta range for data collection 1.51 to 28.73° Completeness to theta = 28.73° 92.3% Index ranges -21 £ h £ 22, -14 £ k £ 14, -24 £ 1 £ 23 Data collection scan type w scans at 3 fixed f values Reflections collected 31707 Independent reflections 7795 [Rint= 0.0479] Absorption coefficient 0.466mm-1 Absorption correction empirical Max. and min. transmission 1.00 and 0.90 Number of standards first scans recollected at end of runs Variation of standards within counting statistics a= 90° b= 100.7580(10)0 g=90° 288 Structure Solution and Refinement Primary solution method direct methods Secondary solution method difference map Hydrogen placement calculated Refinement method full-matrix least-squares on F2 Data I restraints / parameters 7795 Io I 520 Treatment of hydrogen atoms all parameters refined Goodness-of-fit on F2 2.286 Final R indices [I>2s(i), 6406 reflections] Rl =0.0458, wR2 = 0.0828 R indices (all data) Rl = 0.0:586, wR2 = 0.0853 Type of weighting scheme used sigma Weighting scheme used w=l/s2(Fo ) Max shift/ error 0.024 Average shift/error 0.001 Largest diff. peak and hole 0.822 and -1.687 e.A-3 2 Programs Used Cell refinement Bruker SAINT v6.02 Data collection Bruker SMART vS.054 Data reduction Bruker SAINT v6.02 Absorption correction SADABS V2.0 beta Structure solution SHELXS-97 (Sheldrick, 1990) Structure refinement SHELXL-97 (Sheldrick, 1997) 289 Special Refinement Details A fragment of an incredibly trichroic (pale yellow / rose / dark brown) tabular crystal was mounted on a glass fiber with Paratone-N oil. Three runs of data were collected with 20 second long, -0.2° wide co--scans at three values of <p (0, 120, and 240°) with the detector 5 cm (nominal) distant at a 0 of -28°. The initial cell for data reduction was calculated from just under 1000 reflections chosen from throughout the data frames. For data processing with SAINT v6.02, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to zero, no Laue class integration restraints were used, the model profiles from all nine areas were blended, and for the post-integration global least squares refinement, no constraints were applied. The data were corrected with SADABS v. 2.0 (beta) using default parameters except that the scale factor esd was set to 0. No outlier reflections were omitted from the final processed dataset; 1000 reflections were rejected, there were 38 inconsistent equivalents and 4 systematic absence violations. Refinement of F2 was against all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F2, conventional R-factors (R) are based on F, with F set to zero for negative F2. The 2 threshold expression of F2 > 2a( F ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. There is _ of the Zr complex in the asymmetric unit; the dimer lies on a two-fold axis which passes through both atoms of the bridging dinitrogen. There is also _ of a toluene in the asymmetric unit, which also lies on a twofold axis passing through the methyl carbon and bisecting the phenyl ring. All parameters were refined on all hydrogen atoms including the half hydrogen atoms of the solvent. The two peaks in the final difference map greater than 111 e-A-3 are-1.69 e-A-3 (0.91 A from Zr) and -1.33 e-A-3 (0.95 A from Zr). Table 17. Bond lengths [A] and angles [0 ] for BpZrN2ZrBp. Zr-Cpl Zr-Cp2 Zr···Plnl Zr···Pln2 Zr---zr<iJ Zr-N2 Zr-Nl Zr-C6 Zr-Cl Zr-CS Zr-ClO Zr-C7 Zr-C2 Zr-C3 Zr-C9 Zr-C4 Zr-CS Sil-Cl2 Sil-Cll Sil-C6 Sil-Cl 2.242 2.244 2.238(1) 2.237(1) 4.366 2.2680(8) 2.2717(8) 2.485(2) 2.500(2) 2.512(2) 2.513(2) 2.515(2) 2.526(2) 2.577(2) 2.585(2) 2.626(2) 2.647(2) 1.860(3) 1.863(3) 1.875(2) 1.875(2) Si2-C15 Si2-C13 Si2-C14 Si2-C2 Si3-C26 Si3-C25 Si3-C24 Si3-C10 Nl-N2 Nl-Zrr;J N2-z/iJ Cl-CS Cl-C2 C2-C3 C3-C4 C3-H3 C4-C5 C4-C16 CS-HS C6-C7 C6-C10 1.863(3) 1.866(3) 1.868(3) 1.882(2) 1.868(2) 1.868(2) 1.869(3) 1.882(2) 1.245(4) 2.2717(8) 2.2680(8) 1.417(3) 1.442(3) 1.435(3) 1.405(3) 0.98(2) 1.420(3) 1.518(3) 0.95(2) 1.422(3) 1.441(3) 290 C7-C8 C7-H7 C8-C9 C8-C20 C9-C10 C9-H9 Cll-HllA Cll-HllB Cll-HllC C12-H12A C12-H12B C12-H12C C13-H13A C13-H13B C13-H13C Cl4-H14A C14-H14B C14-H14C C15-H15A C15-H15B C15-H15C C16-C17 C16-C19 C16-C18 C17-H17A C17-H17B C17-H17C C18-H18A C18-H18B C18-H18C C19-H19A C19-H19B C19-H19C C20-C21 C20-C23 C20-C22 C21-H21A C21-H21B C21-H21C C22-H22A C22-H22B C22-H22C C23-H23A C23-H23B C23-H23C C24-H24A C24-H24B C24-H24C C25-H25A C25-H25B C25-H25C C26-H26A C26-H26B C26-H26C 1.420(3) 0.91(2) 1.403(3) 1.517(3) 1.434(3) 0.96(2) 0.95(3) 0.97(3) 0.91(3) 0.99(2) 0.91(3) 0.96(2) 0.90(3) 0.95(3) 0.94(3) 0.99(3) 0.94(3) 0.99(3) 0.94(3) 0.94(3) 0.93(3) 1.528(3) 1.529(3) 1.535(3) 0.95(3) 0.96(2) 0.99(2) 1.02(3) 0.93(3) 0.92(3) 0.88(3) 0.98(3) 0.97(3) 1.514(4) 1.521(3) 1.531(4) 0.86(4) 0.96(3) 1.00(3) 0.94(3) 0.99(3) 0.96(4) 0.96(3) 0.92(3) 1.00(4) 0.97(3) 0.92(2) 0.94(3) 0.93(3) 0.98(3) 0.98(3) 0.93(3) 0.92(3) 0.99(3) C27-C28 1m C27-C28 C27-H27 C28-C29 C28-H28 C29-C30 C29-H29 C30-C29 1m C30-C31 C31-H31A C31-H31B C31-H31C 1.369(3) 1.369(3) 0.97(3) 1.377(4) 0.91(3) 1.385(3) 0.90(2) 1.385(3) 1.492(5) 1.08(5) 0.96(5) 1.04(6) Cp1-Zr-Cp2 Cpl-Zr-Nl Cpl-Zr-N2 Cp2-Zr-Nl Cp2-Zr-N2 Plnl·· ·Pln2 N2-Zr-Nl N2-Nl-Zr N2-Nl-Zrw Zr-Nl-Zrw Nl-N2-Zrw Nl-N2-Zr Zr 1;J_N2-Zr C12-Sil-Cll C12-Sil-C6 Cll-Sil-C6 C12-Sil-Cl Cll-Sil-Cl C6-Sil-Cl C15-Si2-C13 C15-Si2-C14 C13-Si2-C14 C15-Si2-C2 C13-Si2-C2 C14-Si2-C2 C26-Si3-C25 C26-Si3-C24 C25-Si3-C24 C26-Si3-C10 C25-Si3-C10 C24-Si3-C10 C5-Cl-C2 CS-Cl-Sil C2-Cl-Sil C3-C2-Cl C3-C2-Si2 Cl-C2-Si2 C4-C3-C2 C4-C3-H3 C2-C3-H3 125.8 110.2 122.7 121.9 109.7 61.75(9) 31.83(9) 73.92(7) 73.92(7) 147.84(14) 74.25(7) 74.25(7) 148.50(14) 107.84(12) 109.45(11) 117.07(11) 117.46(11) 109.93(11) 95.09(9) 108.76(13) 108.74(13) 106.08(13) 116.09(12) 109.43(11) 107.27(11) 106.04(12) 107.48(13) 110.35(12) 107.99(11) 106.81(11) 117.58(11) 106.75(19) 117.37(15) 131.44(17) 106.02(19) 121.95(16) 129.11(17) 110.91(19) 124.8(12) 124.1(12) 291 C3-C4-C5 C3-C4-C16 C5-C4-C16 Cl-C5-C4 Cl-C5-H5 C4-C5-H5 C7-C6-C10 C7-C6-Sil C10-C6-Sil C8-C7-C6 C8-C7-H7 C6-C7-H7 C9-C8-C7 C9-C8-C20 C7-C8-C20 C8-C9-C10 C8-C9-H9 C10-C9-H9 C9-C10-C6 C9-C10-Si3 C6-C10-Si3 Sil-Cll-HllA Sil-Cll-HllB HllA-Cll-HllB Sil-Cll-HllC HllA-Cll-HllC HllB-Cll-HllC Sil-C12-H12A Sil-C12-H12B H12A-C12-H12B Sil-C12-H12C H12A-C12-H12C H12B-C12-H12C Si2-C13-H13A Si2-C13-H13B H13A-C13-H13B Si2-C13-H13C H13A-C13-H13C H13B-C13-H13C Si2-C14-H14A Si2-C14-H14B H14A-C14-H14B Si2-C14-H14C H14A-C14-H14C H14B-C14-H14C Si2-C15-H15A Si2-C15-H15B H15A-C15-H15B Si2-C15-H15C H15A-C15-H15C H15B-C15-H15C C4-C16-C17 C4-C16-C19 C17-C16-C19 105.42(19) 128.13(19) 125.4(2) 110.83(19) 125.0(14) 124.1(14) 106.58(19) 116.90(15) 132.56(17) 110.5(2) 125.5(15) 123.9(15) 105.8(2) 128.3(2) 124.8(2) 110.6(2) 124.6(13) 124.4(13) 106.40(19) 121.54(16) 128.33(16) 109.4(15) 108.9(14) 111(2) 113.1(16) 108(2) 106(2) 107.2(12) 114.5(18) 112(2) 111.3(14) 108.1(19) 103(2) 105.7(18) 112.3(19) 105(2) 114.4(16) 108(2) 110(2) 110.5(14) 111.1(15) 107(2) 110.2(14) 109(2) 110(2) 108.6(16) 113.3(17) 108(2) 111.6(18) 107(2) 108(2) 111.4(2) 111.99(19) 109.6(2) C4-C16-C18 C17-C16-C18 C19-C16-C18 C16-C17-H17A C16-C17-H17B H17A-C17-H17B C16-C17-H17C H17A-C17-H17C H17B-C17-H17C C16-C18-H18A C16-Cl8-H18B H18A-C18-H18B C16-C18-H18C H18A-C18-H18C H18B-C18-H18C C16-C19-H19A C16-Cl 9-Hl 9B H19A-C19-H19B C16-C19-H19C H19A-C19-H19C H19B-C19-H19C C21-C20-C8 C21-C20-C23 C8-C20-C23 C21-C20-C22 C8-C20-C22 C23-C20-C22 C20-C21-H21A C20-C21-H21B H21A-C21-H21B C20-C21-H21C H21A-C21-H21C H21B-C21-H21C C20-C22-H22A C20-C22-H22B H22A-C22-H22B C20-C22-H22C H22A-C22-H22C H22B-C22-H22C C20-C23-H23A C20-C23-H23B H23A-C23-H23B C20-C23-H23C H23A-C23-H23C H23B-C23-H23C Si3-C24-H24A Si3-C24-H24B H24A-C24-H24B Si3-C24-H24C H24A-C24-H24C H24B-C24-H24C Si3-C25-H25A Si3-C25-H25B H25A-C25-H25B 106.34(19) 108.6(2) 108.8(2) 113.7(15) 107.7(13) 110(2) 112.9(14) 107(2) 105.1(18) 112.5(14) 109.5(15) 108(2) 115.9(16) 103(2) 108(2) 111.0(18) 113.2(15) 106(2) 110.2(14) 108(2) 109(2) 111.7(2) 109.9(3) 111.1(2) 109.3(3) 106.8(2) 107.8(2) 112(3) 112(2) 113(4) 109.2(17) 110(3) 100(3) 112.6(18) 110.3(16) 110(2) 108(2) 106(3) 109(2) 108.4(17) 109.8(16) 111(2) 114(2) 110(3) 104(3) 110.1(14) 108.2(14) 108(2) 111.3(16) 106(2) 113(2) 109.4(17) 110.5(14) 108(2) 292 Si3-C25-H25C H25A-C25-H25C H25B-C25-H25C Si3-C26-H26A Si3-C26-H26B H26A-C26-H26B Si3-C26-H26C H26A-C26-H26C H26B-C26-H26C 111.9(14) 112(2) 105(2) 111.4(15) 113.0(17) 111(2) 112.0(15) 104(2) 105(2) C28(ii!-C27-C28 119.7(4) 120.17(18) 120.1(3) 120.2(16) 119.5(16) 121.4(3) 119.2(16) 119.4(16) 117.3(3) 121.33(16) 109(3) 106(3) 108(3) 111(3) 110(3) 113(4) C28-C27-H27 C27-C28-C29 C27-C28-H28 C29-C28-H28 C28-C29-C30 C28-C29-H29 C30-C29-H29 c29iii! -C30-C29 C29-C30-C31 C30-C31-H31A C30-C31-H31B H31A-C31-H31B C30-C31-H31C H31A-C31-H31C H31B-C31-H31C 293 Table 18. Crystal data and structure refinement for [RpZrfa(µ3-Hh(µz-H)3. Empirical formula C42H59Si6Zr3 Formula weight 1006.11 Crystallization Solvent Benzene Crystal Habit Prism Crystal size 0.52 X 0.26 X 0.10 mm3 Crystal color Dichroic, dark brown-green / colorless Data Collection Preliminary Photos Type of diffractometer CAD-4 Wavelength 0.71073 A MoKa Data Collection Temperature 84K Theta range for reflections used in lattice determination 15 to 17° Unit cell dimensions a= 15.804(4) A b = 15.804(4) A c = 17.018(3) A Volume 4250.5(17) A3 z 4 Crystal system Tetragonal Space group P4(3)2(1)2 Density (calculated) 1.572Mg/m3 F(000) 2060 Theta range for data collection 1.5 to 25° Completeness to theta = 25° 100.0 % Index ranges 0<=h<=18, -18<=k<=l8, 0<=1<=20 Data collection scan type scans Reflections collected 13292 Independent reflections 3746 [Rint= 0.0206; GOFmerge= ] Absorption coefficient 0.921 mm- 1 Absorption correction None Number of standards 3 reflections measured every 75min. Variation of standards 0, within experimental error%. a= 90° b=90° g=90° 294 Structure solution and Refinement Structure solution program SHELXS-97 (Sheldrick, 1990) Primary solution method direct Secondary solution method difmap Hydrogen placement difmap Structure refinement program SHELXL-97 (Sheldrick, 1997) Refinement method Full-matrix least-squares on p2 Data / restraints / parameters 3746 / 0 / 349 Treatment of hydrogen atoms all Goodness-of-fit on p2 1.627 Final R indices [I>2s(I)] Rl =0.0163, wR2 =0.0403 R indices (all data) Rl =0.0168, wR2 = 0.0405 Type of weighting scheme used calc Weighting scheme used calc w=l//\2/\(fo/\2/\) Max shift/ error 0.043 Average shift/ error 0.002 Absolute structure parameter 0.00(2) Largest diff. peak and hole 0.252 and -0.308 e.A-3 Table 19. Bond lengths [A] and angles [0 ] for [RpZrl3(µ3-H)2(µ2-H)3. Zrl-CplC Zrl-Cp2C Zrl-CplP Zrl-Cp2P Zrl-Zr2 Zrl-Zrl#l Zrl-H0 Zrl-Hl Zrl-H2 H0-H0#l Zrl-Cl Zrl-C2 Zrl-C3 Zrl-C4 Zrl-C5 Zrl-C6 Zrl-C7 Zrl-C8 Zrl-C9 Zrl-ClO Zr2-Cp3C Zr2-Cp3P 2.2593 2.2622 2.2543(11) 2.2591(11) 3.2687(9) 3.3443(9) 2.17(2) 1.93(2) 1.96(1) 1.85(4) 2.520(2) 2.504(2) 2.564(2) 2.635(2) 2.589(2) 2.521(2) 2.532(2) 2.578(2) 2.625(2) 2.570(2) 2.2726 2.2690(10) 295 Zr2-Zrl#l Zr2-H0 Zr2-Hl Zr2-C15 Zr2-C16 Zr2-C17 Zr2-C18 Zr2-C19 Sil-Cll Sil-C12 Sil-C6 Sil-Cl Si2-C14 Si2-C13 Si2-C2 Si2-C7 Si3-C21 Si3-C20 Si3-C15 Si3-C19#1 Cl-CS Cl-C2 C2-C3 C3-C4 C3-H3 C4-C5 C4-H4 CS-HS C6-C10 C6-C7 C7-C8 C8-C9 C8-H8 C9-C10 C9-H9 ClO-HlO Cll-HllA Cll-HllB Cll-HllC C12-H12A C12-H12B C12-H12C C13-Hl3A C13-H13B C13-H13C C14-H14A Cl4-Hl4B C14-H14C C15-C16 C15-C19 C16-Cl7 C16-H16 C17-C18 C17-H17 3.2687(9) 2.04(2) 1.95(2) 2.525(2) 2.573(2) 2.634(2) 2.597(2) 2.537(2) 1.862(2) 1.869(2) 1.871(2) 1.882(2) 1.858(2) 1.868(2) 1.871(2) 1.879(2) 1.862(2) 1.865(2) 1.873(2) 1.877(2) 1.422(3) 1.447(3) 1.431(3) 1.410(3) 0.88(2) 1.402(3) 0.83(2) 0.97(2) 1.432(3) 1.444(3) 1.422(3) 1.412(3) 0.91(2) 1.404(3) 0.95(3) 0.95(2) 0.86(2) 0.94(3) 0.91(3) 0.92(3) 0.83(3) 0.85(3) 0.93(3) 1.00(3) 0.85(3) 0.88(3) 0.88(3) 0.92(3) 1.425(3) 1.443(3) 1.404(3) 0.94(2) 1.401(3) 0.89(2) 296 C18-C19 C18-Hl8 C19-Si3#1 C20-H20A C20-H20B C20-H20C C21-H21A C21-H21B C21-H21C Cp1C-Zr1-Cp2C Cp1C-Zrl-Zr2 Cp2C-Zrl-Zr2 CplC-Zrl-Zrl#l Cp2C-Zr1-Zrl#l Zr2-Zr1-Zr1#1 CplC-Zrl-H0 Cp2C-Zr1-H0 Zr2-Zrl-H0 Zrl#l-Zrl-H0 CplC-Zrl-Hl Cp2C-Zrl-H1 Zr2-Zrl-H1 Zrl#l-Zrl-Hl H0-Zrl-Hl Cp1C-Zr1-H2 Cp2C-Zr1-H2 Zr2-Zrl-H2 Zrl#l-Zr1-H2 H0-Zrl-H2 H1-Zr1-H2 Cp1P-?-Cp2P Cp3C-Zr2-Zrl#1 Cp3C-Zr2-Zr1 Zrl#l-Zr2-Zrl Cp3C-Zr2-H0 Zr1#1-Zr2-H0 Zrl-Zr2-H0 Cp3C-Zr2-H1 Zr1#1-Zr2-Hl Zrl-Zr2-H1 H0-Zr2-Hl Cp3P#l-?-Cp3P C11-Si1-C12 C11-Sil-C6 C12-Sil-C6 Cll-Sil-Cl C12-Sil-Cl C6-Sil-Cl C14-Si2-C13 C14-Si2-C2 C13-Si2-C2 C14-Si2-C7 C13-Si2-C7 1.426(3) 0.90(2) 1.877(2) 0.88(3) 0.90(3) 0.92(3) 0.87(3) 0.95(3) 1.00(3) 116.630(17) 122.217(10) 113.452(9) 111.566(10) 121.781(13) 59.232(4) 96.4(6) 146.8(6) 37.6(6) 38.8(6) 110.0(7) 100.3(6) 32.8(6) 91.9(6) 63.0(8) 95.9(4) 111.7(3) 90.8(7) 31.6(7) 64.9(8) 123.5(9) 70.12(6) 114.354(8) 119.931(8) 61.536(8) 148.8(6) 39.6(7) 40.5(7) 111.2(6) 93.7(6) 32.3(6) 65.1(10) 70.46(6) 107.82(11) 108.87(10) 116.01(10) 112.66(10) 117.83(11) 92.95(9) 110.17(11) 111.37(11) 112.94(10) 110.60(10) 117.83(10) 297 C2-Si2-C7 C21-Si3-C20 C21-Si3-C15 C20-Si3-C15 C21-Si3-Cl 9#1 C20-Si3-Cl 9#1 C15-Si3-Cl 9#1 CS-Cl-C2 CS-Cl-Sil C2-Cl-Sil C3-C2-Cl C3-C2-Si2 Cl-C2-Si2 C4-C3-C2 C4-C3-H3 C2-C3-H3 CS-C4-C3 CS-C4-H4 C3-C4-H4 C4-CS-Cl C4-CS-HS Cl-CS-HS C10-C6-C7 C10-C6-Sil C7-C6-Sil C8-C7-C6 C8-C7-Si2 C6-C7-Si2 C9-C8-C7 C9-C8-H8 C7-C8-H8 C10-C9-C8 C10-C9-H9 C8-C9-H9 C9-Cl0-C6 C9-C10-H10 C6-C10-H10 Sil-Cll-HllA Sil-Cll-HllB HllA-Cll-HllB Sil-Cll-HllC HllA-Cll-HllC HllB-Cll-HllC Sil-C12-H12A Sil-C12-H12B H12A-C12-H12B Sil-C12-H12C H12A-C12-H12C H12B-C12-H12C Si2-C13-H13A Si2-C13-H13B H13A-C13-H13B Si2-C13-H13C H13A-C13-H13C 92.91(9) 107.35(11) 111.48(10) 115.63(11) 109.93(11) 118.91(11) 93.04(9) 106.76(18) 124.75(16) 123.07(15) 106.87(18) 127.32(16) 121.29(15) 108.91(19) 129.4(14) 121.7(14) 107.82(19) 126.2(17) 125.9(17) 109.64(19) 127.0(12) 123.4(12) 107.25(18) 125.13(16) 122.37(15) 106.81(18) 125.38(16) 122.19(15) 109.14(19) 127.4(14) 123.5(14) 108.14(19) 127.9(15) 123.9(15) 108.64(18) 122.7(14) 128.7(14) 111.7(15) 109.0(17) 100(2) 110.0(17) 117(2) 108(2) 110.8(18) 113(2) 107(3) 111(2) 108(3) 106(3) 112.0(18) 109.9(15) 104(2) 111.1(17) 114(2) 298 H13B-C13-H13C Si2-C14-H14A Si2-C14-H14B H14A-C14-H14B Si2-C14-H14C H14A-C14-H14C H14B-C14-H14C C16-C15-C19 C16-C15-Si3 C19-C15-Si3 C17-C16-C15 C17-C16-H16 C15-C16-H16 C18-C17-C16 C18-C17-H17 C16-C17-H17 C17-C18-C19 C17-Cl8-H18 C19-C18-H18 C18-C19-C15 C18-C19-Si3#1 C15-Cl 9-Si3#1 Si3-C20-H20A Si3-C20-H20B H20A-C20-H20B Si3-C20-H20C H20A-C20-H20C H20B-C20-H20C Si3-C21-H21A Si3-C21-H21B H21A-C21-H21B Si3-C21-H21C H21A-C21-H21C H21B-C21-H21C 106(2) 110(2) 109.4(17) 104(2) 114(2) 118(3) 101(2) 107.2(2) 125.97(17) 121.67(17) 108.9(2) 125.6(14) 125.6(14) 108.08(18) 125.6(12) 126.3(12) 109.3(2) 125.6(14) 125.0(14) 106.5(2) 123.93(17) 124.05(17) 108.7(17) 114.4(19) 108(3) 108.7(17) 99(2) 117(3) 112.9(19) 109.3(16) 111(2) 109.7(15) 108(2) 106(2) Symmetry transformations used to generate equivalent atoms: #1-y+l,-x+l,-z+l/2 Table 19. Crystal Data and Structure Refinement for Cp2Zr(CH2CMe3)(CH3). Empirical formula Formula weight 307.57 Crystallization solvent diethyl ether Crystal habit column Crystal size 0.40 X 0.30 X 0.23 mm3 Crystal color yellow Data Collection Preliminary photograph(s) rotation Type of diffractometer Bruker SMART 1000 ccd 299 Wavelength 0.71073 A MoKa Data collection temperature 98K Theta range for 6370 reflections used in lattice determination 2.5 to 28.6° Unit cell dimensions a = 8.0303(3) A b = 16.5205(7) A c = 21.9315(9) A Volume 2909.5(2) A3 z 8 Crystal system orthorhombic Space group Pbca Density (calculated) l.404g/cm3 F(000) 1280 Theta range for data collection 1.86 to 28.77° Completeness to theta = 28.77° 95.5 % Index ranges -l0<=h<=lO, -21<=k<=21, -29<=1<=28 Data collection scan type w scans at 3 fixed f values Reflections collected 27381 Independent reflections 3612 [l\nt= 0.0374] Absorption coefficient 0.734mm·l Absorption correction SADABS v2.0 (beta) Max. and min. transmission 1.000 and 0.895 Number of standards first 90 scans recollected at end of runs Variation of standards within counting statistics a= 90° b=90° g=90° Structure Solution and Refinement Structure solution program SHELXS-97 (Sheldrick, 1990) Primary solution method direct methods Secondary solution method difference map Hydrogen placement calculated Structure refinement program SHELXL-97 (Sheldrick, 1997) Refinement method full-matrix least-squares on F2 Data / restraints / parameters 3612 / 0 / 250 Treatment of hydrogen atoms all parameters refined Goodness-of-fit on F2 2.581 Final R indices [I>2s(I), 3299 reflections] Rl = 0.0219, wR2 = 0.0502 R indices (all data) Rl = 0.0247, wR2 = 0.0508 300 Type of weighting scheme used sigma Weighting scheme used w=l/s2(Fo2) Max shift/ error 0.065 Average shift/ error 0.003 Largest di££. peak and hole 0.506 and -0.372 e.A-3 Special Refinement Details A section was cut from a yellow column and mounted on a glass fiber with Paratone-N oil. Three runs of data were collected with 20 second long, -0.20° wide ro-scans at three values of <p (0, 120, and 240°) with the detector 5 cm (nominal) distant at a 0 of -28°. The initial cell for data reduction was calculated from just under 1000 reflections chosen from throughout the data frames. For data processing with SAINT v6.02, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to zero, no Laue class integration restraints were used, the model profiles from all nine areas were blended, and for the post-integration global least squares refinement, no constraints were applied. The data Were corrected with SADABS v. 2.0 (beta) using default parameters except that the scale factor esd was set to 0. On the three .raw files the g value converged to 0.0428. No decay correction was needed. There is one molecule in the asymmetric unit. No reflections were specifically omitted from the final processed dataset; 2095 reflections were rejected, with 33 space group-absence violations and 32 inconsistent equivalents. Refinement of F2 was against ALL reflections. The weighted R-factor (wR) and goodness of fit 2 (S) are based on F2, conventional R-factors (R) are based on F, with F set to zero for negative F • The threshold expression of F2 > 2cr( F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. Table 20. Bond lengths [.A.] and angles [0 ] for Cp2Zr(CH2CMe3)(CH3). Zr-Cpl Zr-Cp2 Zr···Plnl Zr···Pln2 Zr-C12 Zr-C11 Zr-Cl Zr-CS Zr-CIO Zr-C9 Zr-C7 Zr-C8 Zr-C6 Zr-C2 Zr-C4 Zr-C3 Cl-C2 Cl-CS 2.232 2.234 2.3209(6) 2.2335(5) 2.2719(12) 2.2980(13) 2.4990(13) 2.5067(13) 2.5184(13) 2.5311(12) 2.5391(13) 2.5400(13) 2.5400(13) 2.5424(12) 2.5507(13) 2.5638(12) 1.4091(19) 1.413(2) 301 Cl-Hl C2-C3 C2-H2 C3-C4 C3-H3 C4-C5 C4-H4 C5-H5 C6-C7 C6-C10 C6-H6 C7-C8 C7-H7 C8-C9 C8-H8 C9-C10 C9-H9 ClO-HlO Cll-HllA Cll-HllB Cll-HllC C12-Cl3 C12-H12A C12-H12B C13-C15 C13-Cl6 C13-C14 C14-H14A C14-H14B C14-H14C C15-H15A C15-H15B C15-H15C C16-H16A C16-H16B C16-H16C Cpl-Zr-Cp2 Cpl-Zr-Cll Cpl-Zr-C12 Plnl-Pln2 C12-Zr-Cll C12-Zr-Cl Cll-Zr-Cl C12-Zr-C5 Cll-Zr-C5 Cl-Zr-CS C12-Zr-C10 Cll-Zr-ClO Cl-Zr-ClO C5-Zr-C10 C12-Zr-C9 Cll-Zr-C9 Cl-Zr-C9 0.922(16) 1.399(2) 0.956(15) 1.4089(18) 0.895(16) 1.4035(19) 0.922(16) 0.945(16) 1.400(2) 1.411(2) 0.923(15) 1.4097(19) 0.951(15) 1.3999(19) 0.962(16) 1.409(2) 0.950(15) 0.942(15) 0.933(16) 0.940(16) 0.912(17) 1.5418(17) • 0.989(14) 0.964(14) 1.5280(18) 1.5285(18) 1.5354(18) 0.960(15) 0.961(16) 0.911(17) 0.931(16) 0.960(14) 0.979(15) 1.053(15) 0.951(15) 0.939(15) 130.6 103.4 107.8 51.42(5) 94.99(5) 108.70(5) 130.53(5) 135.63(4) 102.33(5) 32.78(5) 135.08(4) 89.68(5) 101.45(5) 86.00(5) 105.67(5) 77.53(5) 131.79(5) 302 C5-Zr-C9 C10-Zr-C9 C12-Zr-C7 Cll-Zr-C7 Cl-Zr-C7 C5-Zr-C7 C10-Zr-C7 C9-Zr-C7 C12-Zr-C8 Cll-Zr-C8 C1-Zr-C8 C5-Zr-C8 C10-Zr-C8 C9-Zr-C8 C7-Zr-C8 C12-Zr-C6 Cll-Zr-C6 C1-Zr-C6 C5-Zr-C6 C10-Zr-C6 C9-Zr-C6 C7-Zr-C6 C8-Zr-C6 C12-Zr-C2 Cll-Zr-C2 C1-Zr-C2 C5-Zr-C2 C10-Zr-C2 C9-Zr-C2 C7-Zr-C2 C8-Zr-C2 C6-Zr-C2 C12-Zr-C4 Cll-Zr-C4 Cl-Zr-C4 C5-Zr-C4 C10-Zr-C4 C9-Zr-C4 C7-Zr-C4 C8-Zr-C4 C6-Zr-C4 C2-Zr-C4 C12-Zr-C3 Cll-Zr-C3 Cl-Zr-C3 C5-Zr-C3 C10-Zr-C3 C9-Zr-C3 C7-Zr-C3 C8-Zr-C3 C6-Zr-C3 C2-Zr-C3 C4-Zr-C3 C2-Cl-C5 117.79(4) 32.41(5) 92.17(4) 130.35(4) 92.39(4) 106.12(5) 53.43(4) 53.32(4) 81.94(5) 100.75(5) 124.62(4) 132.66(4) 53.38(5) 32.05(4) 32.23(4) 123.99(4) 122.08(5) 79.28(4) 79.55(4) 32.40(5) 53.44(4) 32.01(4) 53.20(4) 82.05(4) 117.53(5) 32.45(4) 53.69(4) 133.85(5) 162.92(5) 112.11(4) 139.49(4) 109.56(4) 119.26(4) 76.95(5) 53.59(4) 32.21(4) 105.34(4) 129.56(4) 138.29(5) 158.72(4) 109.72(4) 53.07(4) 88.21(4) 86.00(5) 53.31(4) 53.29(4) 136.71(4) 159.18(5) 143.37(4) 168.47(5) 130.43(4) 31.79(4) 31.98(4) 107.83(12) 303 C2-Cl-Zr CS-Cl-Zr C2-Cl-Hl C5-Cl-Hl Zr-Cl-Hl C3-C2-Cl C3-C2-Zr Cl-C2-Zr C3-C2-H2 Cl-C2-H2 Zr-C2-H2 C2-C3-C4 C2-C3-Zr C4-C3-Zr C2-C3-H3 C4-C3-H3 Zr-C3-H3 C5-C4-C3 C5-C4-Zr C3-C4-Zr C5-C4-H4 C3-C4-H4 Zr-C4-H4 C4-C5-Cl C4-C5-Zr Cl-CS-Zr C4-C5-H5 Cl-CS-HS Zr-CS-HS C7-C6-C10 C7-C6-Zr C10-C6-Zr C7-C6-H6 C10-C6-H6 Zr-C6-H6 C6-C7-C8 C6-C7-Zr C8-C7-Zr C6-C7-H7 C8-C7-H7 Zr-C7-H7 C9-C8-C7 C9-C8-Zr C7-C8-Zr C9-C8-H8 C7-C8-H8 Zr-C8-H8 C8-C9-C10 C8-C9-Zr C10-C9-Zr C8-C9-H9 C10-C9-H9 Zr-C9-H9 C9-C10-C6 75.47(8) 73.91(8) 124.2(9) 128.0(9) 117.9(9) 108.03(12) 74.94(7) 72.08(7) 126.3(10) 125.6(10) 116.7(9) 108.28(12) 73.26(7) 73.50(7) 128.8(10) 122.9(10) 116.7(10) 107.95(12) 72.17(7) 74.52(7) . 126.3(9) 125.8(9) 117.3(10) 107.91(12) 75.62(7) 73.31(8) 126.2(9) 125.9(9) 117.0(9) 107.92(12) 73.96(7) 72.96(8) 127.3(9) 124.7(9) 119.5(9) 108.08(12) 74.03(8) 73.92(8) 126.7(9) 125.2(9) 119.9(9) 108.14(12) 73.63(7) 73.85(7) 126.8(9) 125.0(9) 116.9(8) 107.97(12) 74.33(7) 73.30(7) 126.5(9) 125.5(9) 118.4(9) 107.88(12) 304 C9-C10-Zr C6-C10-Zr C9-Cl0-H10 C6-C10-H10 Zr-ClO-HlO Zr-Cll-HllA Zr-Cll-HllB HllA-Cll-HllB Zr-Cll-HllC HllA-Cll-HllC HllB-Cll-HllC C13-C12-Zr C13-C12-H12A Zr-C12-H12A C13-C12-H12B Zr-C12-H12B H12A-C12-H12B C15-C13-C16 C15-C13-C14 C16-C13-C14 C15-C13-C12 C16-C13-C12 C14-C13-C12 C13-C14-H14A C13-C14-H14B Hl4A-Cl4-Hl4B C13-C14-H14C H14A-Cl4-H14C H14B-C14-H14C C13-C15-H15A C13-C15-H15B H15A-C15-H15B C13-C15-H15C H15A-C15-H15C H15B-C15-H15C C13-C16-H16A C13-Cl6-H16B H16A-C16-H16B C13-C16-H16C H16A-C16-H16C H16B-C16-H16C 74.29(7) 74.64(7) 124.5(9) 127.5(9) 114.9(8) 112.6(10) 109.8(9) 105.6(13) 109.9(10) 108.8(15) 110.0(13) 141.94(9) 108.2(8) 96.8(8) 109.2(8) 91.6(8) 103.7(11) 108.62(11) 108.62(10) 107.61(11) 110.72(10) 111.48(10) 109.69(11) 110.2(9) 112.1(9) 110.8(12) 110.2(9) 105.7(13) 107.6(13) 112.7(10) 109.1(8) 106.9(13) 110.2(9) 111.3(12) 106.3(12) 110.8(8) 111.5(9) 107.2(12) 112.6(9) 104.7(12) 109.7(12) Table 21. Crystal Data and Structure Analysis Details for iPrSpTa(112CH2CHC6H5)(H). Empirical formula C23H29SiTa Formula weight 514.50 Crystallization solvent petroleum ether Crystal habit needle Crystal size 0.12 X 0.08 X 0.04 mm 305 Crystal color yellow Data Collection Preliminary photograph( s) rotation Type of diffractometer Bruker SMART 1000 ccd Wavelength 0.71073 A MoKa Data collection temperature 98K Theta range for 6300 reflections used in lattice determination 2.8 to 24.6° Unit cell dimensions a = 14.5277(9) A b = 6.6809(4) A c = 21.0147(12) A Volume 2012.7(2) A3 z 4 Crystal system monoclinic Space group Density (calculated) P2/n (#13) 1.698 g/cm3 F(000) 1016 Theta range for data collection 1.59 to 27.50° Completeness to theta = 27.50° 99.7% Index ranges -18 £ h £ 18, -8 £ k £ 8, -27 £ 1 £ 27 Data collection scan type w scans at 6 fixed f values Reflections collected 34421 Independent reflections 4617 [Rint= 0.1013] Absorption coefficient 5.524mm-1 Absorption correction empirical Max. and min. transmission 1.00 and 0.79 Number of standards first scans recollected at end of runs Variation of standards within counting statistics a= 90° b= 99.3310(10) 0 g=90° Structure Solution and Refinement Primary solution method direct methods Secondary solution method difference map Hydrogen placement calculated Refinement method full-matrix least-squares on p2 Data / restraints / parameters 4617 / 0 / 226 306 not refined; Uiso's set at 120% Ueq of the Treatment of hydrogen atoms attached atom Goodness-of-fit on F2 1.584 Final R indices [I>2s(I), 3186 reflections] Rl = 0.0420, wR2 = 0.0655 R indices (all data) Rl = 0.0837, wR2 = 0.0719 Type of weighting scheme used sigma Weighting scheme used w=l/s2(Fa2) Max shift/ error 0.024 Average shift/ error 0.001 Largest diff. peak and hole 1.920 and -1.842 e.A-3 Programs Used Cell refinement Bruker SAINT v6.02 Data collection Bruker SMART v5.054 Data reduction Bruker SAINT v6.02 Absorption correction SADABS V2.0 beta Structure solution SHELXS-97 (Sheldrick, 1990) Structure refinement SHELXL-97 (Sheldrick, 1997) Special Refinement Details A small fragment extracted from a yellow rosette was mounted on a glass fiber with ParatoneN oil. Six runs of data were collected with 20 second long, -0.20° wide Or-scans at six values of <p (0, 120,240, 60, 180 and 300°) with the detector 5 cm (nominal) distant at a 0 of -28°. The initial cell for data reduction was calculated from just under 1000 reflections chosen from throughout the data frames. There were a number of unindexed reflections, possibly indicating a twin. For data processing with SAINT v6.02, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to zero, no Laue class integration restraints were used, the model profiles from all nine areas were blended, and for the post-integration global least squares refinement, no constraints were applied. The data were corrected with SADABS v. 2.0 (beta) using default parameters except that the scale factor esd was set to 0. No decay correction was needed. There is one molecule in the asymmetric unit. No reflections were specifically omitted from the final processed dataset; the dataset was truncated at a 20 of 55°, 2289 reflections were rejected, with 2 space group-absence violations and O inconsistent equivalents. Refinement of F2 was against all reflections. The weighted Rfactor (wR) and goodness of fit (S) are based on F2, conventional R-factors (R) are based on F, 2 2 with F set to zero for negative F2. The threshold expression of F > 2cr( F ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. 307 There is one molecule in the asymmetric unit. The hydride atom was not located in a difference map and was excluded from the refinement. There are numerous large peaks in the final difference map; the first twenty are greater than 111 e-A-3 with the two largest being 1.92 e-A-3 (1.23 A from H13) and-1.84 e-A-3 (1.77 A from H16). Table 22. Bond lengths [A] and angles [0 ] for iPrSpTa('r12-CH2CHC6Hs)(H). ----------------------------------------------------C13-C15 Ta-Cpl• 2.071 Ta-Cp2b Ta-Cenc Ta···Plnl ct Ta···Pln2e Ta-C16 Ta-C17 Ta-C6 Ta-ClO Ta-CS Ta-C2 Ta-C7 Ta-Cl Ta-C9 Ta-C4 Ta-C3 Ta-CS Si-Cll Si-C12 Si-C6 Si-Cl Cl-CS Cl-C2 C2-C3 C2-H2 C3-C4 C3-H3 C4-CS C4-H4 CS-HS C6-C10 C6-C7 C7-C8 C7-H7 C8-C9 C8-C13 C9-C10 C9-H9 ClO-HlO Cll-HllA Cll-HllB Cll-HllC C12-H12A C12-H12B C12-H12C C13-C14 2.066 2.173 2.068(3) 2.061(3) 2.274(7) 2.298(7) 2.344(6) 2.347(6) 2.352(6) 2.354(6) 2.359(6) 2.371(6) 2.436(6) 2.437(6) 2.449(6) 2.482(6) 1.826(7) 1.844(7) 1.867(7) 1.868(7) 1.419(9) 1.432(8) 1.412(9) 1.0000 1.371(9) 1.0000 1.417(9) 1.0000 1.0000 1.417(8) 1.433(8) 1.422(8) 1.0000 1.404(9) 1.498(9) 1.434(8) 1.0000 1.0000 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 1.515(8) C13-H13 C14-Hl4A C14-H14B C14-H14C ClS-HlSA ClS-HlSB ClS-HlSC C16-C17 C16-H16A C16-H16B C17-C18 C17-H17 C18-C23 Cl8-C19 C19-C20 C19-H19 C20-C21 C20-H20 C21-C22 C21-H21 C22-C23 C22-H22 C23-H23 Cpl-Ta-Cp2 Cpl-Ta-C16 Cpl-Ta-C17 Cp2-Ta-C16 Cp2-Ta-C17 Cpl-Ta-Cen Cp2-Ta-Cen Plnl· ··Pln2 C16-Ta-C17 Cll-Si-C12 Cll-Si-C6 C12-Si-C6 Cll-Si-Cl C12-Si-Cl C6-Si-Cl CS-Cl-C2 CS-Cl-Si C2-Cl-Si C3-C2-Cl C3-C2-H2 Cl-C2-H2 1.538(8) 1.0000 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 1.420(9) 0.9900 0.9900 1.474(9) 1.0000 1.389(9) 1.412(9) 1.373(10) 0.9500 1.373(11) 0.9500 1.383(11) 0.9500 1.383(9) 0.9500 0.9500 132.8 105.5 112.3 105.6 113.9 109.9 110.8 54.1(3) 36.2(2) 113.2(3) 113.5(3) 110.8(3) 112.2(3) 112.2(3) 93.5(3) 104.5(6) 126.6(5) 121.8(5) 110.0(6) 124.7 124.7 308 C4-C3-C2 C4-C3-H3 C2-C3-H3 C3-C4-C5 C3-C4-H4 C5-C4-H4 C4-C5-Cl C4-C5-H5 Cl-C5-H5 C10-C6-C7 C10-C6-Si C7-C6-Si C8-C7-C6 C8-C7-H7 C6-C7-H7 C9-C8-C7 C9-C8-C13 C7-C8-C13 C8-C9-C10 C8-C9-H9 C10-C9-H9 C6-C10-C9 C6-C10-H10 C9-C10-H10 Si-Cll-HllA Si-Cll-HllB HllA-Cll-HllB Si-Cll-HllC HllA-Cll-HllC HllB-Cll-HllC Si-C12-H12A Si-C12-H12B H12A-C12-H12B Si-C12-H12C H12A-C12-H12C H12B-C12-H12C C8-C13-C14 C8-C13-C15 C14-C13-C15 C8-C13-H13 C14-C13-H13 C15-C13-H13 C13-C14-Hl4A C13-C14-H14B H14A-C14-H14B C13-C14-H14C H14A-C14-H14C H14B-C14-H14C C13-C15-H15A C13-C15-H15B H15A-C15-H15B C13-Cl5-H15C H15A-C15-H15C H15B-C15-H15C 107.2(6) 126.3 126.3 109.2(6) 125.4 125.4 108.9(6) 125.1 125.1 105.8(5) 126.4(5) 122.2(5) 110.3(6) 124.5 124.5 106.2(6) 124.9(6) 128.7(6) 109.2(6) 125.3 125.3 108.5(6) 125.4 125.4 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 113.0(6) 109.3(5) 110.2(6) 108.1 108.1 108.1 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 C17-C16-Ta C17-C16-H16A Ta-C16-H16A C17-C16-H16B Ta-C16-H16B H16A-C16-H16B C16-C17-C18 C16-C17-Ta C18-C17-Ta C16-C17-H17 C18-C17-H17 Ta-C17-H17 C23-Cl8-Cl 9 C23-Cl8-C17 C19~Cl8-C17 C20-C19-C18 C20-C19-H19 Cl8-C19-H19 Cl 9-C20-C21 Cl 9-C20-H20 C21-C20-H20 C20-C21-C22 C20-C21-H21 C22-C21-H21 C23-C22-C21 C23-C22-H22 C21-C22-H22 C22-C23-C18 C22-C23-H23 C18-C23-H23 72.8(4) 116.3 116.3 116.3 116.3 113.3 125.8(7) 71.0(4) 120.2(4) 111.3 111.3 111.3 116.7(7) 122.9(7) 120.3(7) 121.4(7) 119.3 119.3 120.9(8) 119.6 119.6 118.6(8) 120.7 120.7 121.0(8) 119.5 119.5 121.2(8) 119.4 119.4 309 • Cpl is the centroid of atoms Cl, C2, C3, C4 and CS b Cp2 is the centroid of atoms C6, C7, C8, C9 and ClO c Cen is the centroid of atoms Cl6 and Cl7 ct Plnl is the best plane through atoms Cl, C2, C3, C4 and CS e Pln.2 is the best plane through atoms C6, C7, C8, C9 and ClO 310 C17 H16 C24 C '""o H19A ~--- C2 '~ <'.~-?--- Top view of iPr2SpTa(T1 2-CH2CHC6Hs)(H) with selected distances. 311 Table 23. Crystal data and structure refinement for iPr2SpTa('r12CH2CHPh)(H). Empirical formula C26 H35 Si Ta Formula weight 556.58 Crystallization Solvent Petroleum ether Crystal Habit Thick blade Crystal size 0.33 X 0.18 X 0.14 mm3 Crystal color Yellow Data Collection Preliminary Photos Type of diffractometer CCD area detector Wavelength 0.71073 A MoKa Data Collection Temperature 95K Theta range for 4398 reflections used in lattice determination 2.34 to 28.19° Unit cell dimensions a= 9.2305(8) A b = 10.1700(9) A c = 12.9218(12) A Volume 1155.05(18) A3 z 2 Crystal system Triclinic Space group P-1 Density (calculated) 1.600Mg/m3 F(000) 556 Data collection program Bruker SMART Theta range for data collection 2.04 to 28.23° Completeness to theta = 28.23° 88.8% Index ranges -ll<=h<=12, -13<=k<=13, -17<=1<=16 Data collection scan type phi and omega scans Data reduction program Bruker SAINT v6.2 Reflections collected 10310 Independent reflections 5071 [Rint= 0.0256; GOFmerge= ] Absorption coefficient 4.819mm-1 Absorption correction SADABS Max. and min. transmission 1.000 and 0.688 Number of standards ? reflections measured every ?min. Variation of standards within counting statistics a= 90.3360(10) 0 b= 104.1870(10) 0 g = 100.4140(10)0 312 Structure solution and Refinement Structure solution program SHELXS-97 (Sheldrick, 1990) Primary solution method Patterson method Secondary solution method Difference Fourier map Hydrogen placement Difference Fourier map Structure refinement program SHELXL-97 (Sheldrick, 1997) Refinement method Full matrix least-squares on F2 Data I restraints / parameters 5071 Io I 389 Treatment of hydrogen atoms Unrestrained (see special details) Goodness-of-fit on F2 2.191 Final R indices [I>2s(I)] Rl = 0.0259, wR2 = 0.0503 R indices (all data) Rl = 0.0274, wR2 = 0.0504 Type of weighting scheme used Sigma Weighting scheme used w=l/ s"2"(Fo"2") Max shift/ error 0.015 Average shift/ error 0.002 Largest diff. peak and hole 2.328 and -1.763 e.A-3 Table 24. Bond lengths [A] and angles [0 ] for iPr2SpTa(sty)(H). Ta-C(19) Ta-C(20) Ta-C(6) Ta-C(7) Ta-C(l) Ta-C(2) Ta-C(5) Ta-C(lO) Ta-C(4) Ta-C(3) Ta-C(9) Ta-C(8) Ta-H Si-C(ll) Si-C(12) Si-C(l) Si-C(6) C(l)-C(5) C(l)-C(2) C(2)-C(3) C(2)-H(2) C(3)-C(4) C(3)-H(3) C(4)-C(5) 2.253(4) 2.276(4) 2.355(3) 2.374(3) 2.377(4) 2.380(4) 2.385(3) 2.408(3) 2.414(3) 2.436(4) 2.442(3) 2.454(3) 1.7236 1.852(5) 1.858(5) 1.873(4) 1.875(4) 1.421(5) 1.435(5) 1.406(6) 0.96(4) 1.407(5) 0.90(5) 1.416(6) 313 C(4)-H(4) C(5)-H(5) C(6)-C(10) C(6)-C(7) C(7)-C(8) C(7)-H(7) C(8)-C(9) C(8)-C(13) C(9)-C(10) C(9)-H(9) C(10)-C(16) C(l 1)-H(l lA) C(ll)-H(llB) C(ll)-H(llC) C(12)-H(12A) C(12)-H(12B) C(12)-H(12C) C(13)-C(15) C(13)-C(14) C(13)-H(13) C(14)-H(14A) C(14)-H(14B) C(14)-H(14C) C(15)-H(15A) C(15)-H(15B) C(15)-H(15C) C(16)-C(17) C(16)-C(18) C(16)-H(16) C(17)-H(17A) C(17)-H(17B) C(17)-H(17C) C(18)-H(18A) C(18)-H(18B) C(18)-H(18C) C(19)-C(20) C(19)-H(19A) C(19)-H(19B) C(20)-C(21) C(20)-H(20) C(21)-C(22) C(21)-C(26) C(22)-C(23) C(22)-H(22) C(23)-C(24) C(23)-H(23) C(24)-C(25) C(24)-H(24) C(25)-C(26) C(25)-H(25) C(26)-H(26) 0.98(3) 0.92(4) 1.436(5) 1.441(5) 1.396(5) 1.05(4) 1.422(5) 1.519(5) 1.415(5) 0.85(4) 1.513(5) 0.76(5) 1.06(4) 0.99(6) 1.15(4) 0.87(5) 0.79(6) 1.511(5) 1.533(5) 0.98(4) . 0.99(5) 1.10(4) 1.08(4) 0.91(4) 0.83(4) 0.96(4) 1.520(6) 1.540(6) 1.07(3) 0.93(4) 1.02(4) 0.96(4) 0.99(5) 1.06(5) 0.95(4) 1.451(5) 0.93(4) 0.90(4) 1.478(5) 0.93(4) 1.389(5) 1.409(5) 1.400(5) 0.85(4) 1.379(5) 1.00(4) 1.386(5) 0.95(4) 1.387(5) 1.01(4) 0.94(4) C(19)-Ta-C(20) C(19)-Ta-C(6) 37.37(13) 139.59(13) 314 C(20)-Ta-C(6) C(19)-Ta-C(7) C(20)-Ta-C(7) C(6)-Ta-C(7) C(19)-Ta-C(l) C(20)-Ta-C(l) C(6)-Ta-C(l) C(7)-Ta-C(l) C(l 9)-Ta-C(2) C(20)-Ta-C(2) C(6)-Ta-C(2) C(7)-Ta-C(2) . C(l)-Ta-C(2) C(l 9)-Ta-C(5) C(20)-Ta-C(5) C(6)-Ta-C(5) C(7)-Ta-C(5) C(l)-Ta-C(5) C(2)-Ta-C(5) C(l 9)-Ta-C(l0) C(20)-Ta-C(10) C(6)-Ta-C(10) C(7)-Ta-C(10) C(l )-Ta-C(l0) C(2)-Ta-C(10) C(5)-Ta-C(10) C(19)-Ta-C( 4) C(20)-Ta-C(4) C(6)-Ta-C(4) C(7)-Ta-C(4) C(l)-Ta-C(4) C(2)-Ta-C(4) C(5)-Ta-C(4) C(lO)-Ta-C( 4) C(l 9)-Ta-C(3) C(20)-Ta-C(3) C(6)-Ta-C(3) C(7)-Ta-C(3) C(l)-Ta-C(3) C(2)-Ta-C(3) C(5)-Ta-C(3) C(10)-Ta-C(3) C( 4)-Ta-C(3) C(l 9)-Ta-C(9) C(20)-Ta-C(9) C(6)-Ta-C(9) C(7)-Ta-C(9) C(l )-Ta-C(9) C(2)-Ta-C(9) C(5)-Ta-C(9) C(10)-Ta-C(9) C( 4)-Ta-C(9) C(3)-Ta-C(9) C(l 9)-Ta-C(8) 139.78(12) 108.78(13) 131.88(13) 35.49(12) 138.38(14) 143.05(12) 71.45(12) 84.71(12) 106.68(14) 131.84(13) 88.02(13) 80.33(13) 35.10(13) 123.66(14) 109.65(13) 96.09(12) 118.42(13) 34.72(12) 56.88(13) 121.69(14). 105.50(13) 35.08(12) 57.40(12) 99.00(13) 122.67(13) 109.22(13) 89.81(14) 86.26(13) 128.29(13) 136.72(13) 57.90(13) 56.68(13) 34.32(13) 141.81(13) 80.89(14) 98.27(13) 121.86(13) 109.39(13) 57.59(13) 33.92(14) 56.37(13) 155.65(14) 33.72(13) 89.00(13) 84.72(12) 57.22(12) 55.82(13) 128.57(12) 136.15(13) 142.65(13) 33.91(12) 166.62(12) 158.24(13) 81.67(13) 315 C(20)-Ta-C(8) C(6)-Ta-C(8) C(7)-Ta-C(8) C(l )-Ta-C(8) C(2)-Ta-C(8) C(5)-Ta-C(8) C(10)-Ta-C(8) C( 4)-Ta-C(8) C(3)-Ta-C(8) C(9)-Ta-C(8) C(19)-Ta-H C(20)-Ta-H C(6)-Ta-H C(7)-Ta-H C(l)-Ta-H C(2)-Ta-H C(5)-Ta-H C(lO)-Ta-H C(4)-Ta-H C(3)-Ta-H C(9)-Ta-H C(8)-Ta-H C(l 1 )-Si-C(12) C( 11 )-Si-C( 1) C(12)-Si-C(l) C(ll )-Si-C( 6) C(12)-Si-C(6) C(l)-Si-C(6) C(5)-C(l)-C(2) C(5)-C(l )-Si C(2)-C(l)-Si C(S)-C(l)-Ta C(2)-C(l)-Ta Si-C(l)-Ta C(3)-C(2)-C(l) C(3)-C(2)-Ta C(l)-C(2)-Ta C(3)-C(2)-H(2) C(l)-C(2)-H(2) Ta-C(2)-H(2) C(4)-C(3)-C(2) C( 4 )-C(3 )-Ta C(2)-C(3)-Ta C(4)-C(3)-H(3) C(2)-C(3)-H(3) Ta-C(3)-H(3) C(3)-C(4)-C(5) C(3)-C(4)-Ta C(5)-C(4)-Ta C(3)-C(4)-H(4) C(5)-C(4)-H(4) Ta-C(4)-H(4) C(4)-C(5)-C(l) C( 4)-C(5)-Ta 98.34(12) 57.94(12) 33.58(12) 118.25(12) 106.96(12) 151.67(13) 57.07(12) 158.54(12) 124.94(13) 33.76(11) 106.5 69.2 90.2 121.6 98.0 130.0 73.7 64.7 87.3 121.0 80.3 114.0 112.0(3) 110.1(2) 111.9(2) 110.76(19) 115.93(19) 95.00(16) 105.3(3) 124.6(3) 123.0(3) 72.9(2) 72.6(2) 95.69(14) 109.5(3) 75.2(2) 72.3(2) 126(2) 124(2) 123(2) 108.0(4) 72.3(2) 70.9(2) 131(3) 121(3) 121(3) 107.5(3) 74.0(2) 71.72(19) 117.7(19) 134.8(19) 119.7(19) 109.7(3) 74.0(2) 316 C(l )-C(5)-Ta C(4)-C(5)-H(5) C(l)-C(5)-H(5) Ta-C(5)-H(5) C(10)-C(6)-C(7) C(10)-C(6)-Si C(7)-C( 6 )-Si C(10)-C(6)-Ta C(7)-C(6)-Ta Si-C(6)-Ta C(8)-C(7)-C(6) C(8)-C(7)-Ta C(6)-C(7)-Ta C(8)-C(7)-H(7) C( 6 )-C(7)-H(7) Ta-C(7)'-H(7) C(7)-C(8)-C(9) C(7)-C(8)-C(13) C(9)-C(8)-C(13) C(7)-C(8)-Ta C(9)-C(8)-Ta C(13)-C(8)-Ta C(10)-C(9)-C(8) C(10)-C(9)-Ta C(8)-C(9)-Ta C(10)-C(9)-H(9) C(8)-C(9)-H(9) Ta-C(9)-H(9) C(9)-C(10)-C(6) C(9)-C(10)-C(16) C(6)-C(10)-C(16) C(9)-C(10)-Ta C( 6 )-C(lO)-Ta C(16)-C(10)-Ta Si-C(ll)-H(llA) Si-C(ll)-H(llB) H(llA)-C(ll)-H(l lB) Si-C(ll)-H(llC) H(llA)-C(ll)-H(llC) H(llB)-C(ll)-H(llC) Si-C(12)-H(12A) Si-C(12)-H(12B) H(12A)-C(12)-H(12B) Si-C(12)-H(12C) H(12A)-C(12)-H(12C) H(12B)-C(12)-H(12C) C(15)-C(13)-C(8) C(15)-C(13)-C(14) C(8)-C(13)-C(14) C(15)-C(13)-H(13) C(8)-C(13)-H(13) C(14)-C(13)-H(13) C(13)-C(14)-H(14A) C(13)-C(14)-H(14B) 72.35(19) 128(2) 122(2) 115(2) 105.9(3) 131.7(3) 116.7(3) 74.50(19) 73.0(2) 96.39(14) 110.4(3) 76.4(2) 71.54(19) 128(2) 122(2) 123(2) 106.3(3) 126.2(3) 126.6(3) 70.06(19) 72.67(19) 130.7(2) 110.0(3) 71.74(18) 73.6(2) 119(3) 131(3) 122(3) 107.4(3) 125.2(3) 126.7(3) 74.36(19) 70.42(19) 128.3(2) 114(4) 119(2) 105(4) 112(3) 116(5) 89(4) 109(2) 117(3) 113(4) 111(4) 92(5) 112(5) 112.4(3) 110.9(3) 108.1(3) 108(2) 106(2) 111(2) 113(3) 112(2) 317 H(14A)-C(14)-H(14B) C(13)-C(14)-H(14C) H(14A)-C(14)-H(14C) H(14B)-C(14)-H(14C) C(13)-C(15)-H(15A) C(13)-C(15)-H(15B) H(15A)-C(15)-H(15B) C(13)-C(15)-H(15C) H(15A)-C(15)-H(15C) H(15B)-C(15)-H(15C) C(10)-C(16)-C(17) C(10)-C(16)-C(18) C(17)-C(16)-C(18) C(10)-C(16)-H(16) C(17)-C(16)-H(16) C(18)-C(16)-H(16) C(16)-C(17)-H(17A) C(16 )-C(l 7)-H(l 7B) H(17 A)-C(17)-H(17B) C(16)-C(17)-H(17C) H(17 A)-C(17)-H(17C) H(17B)-C(17)-H(17C) C(16)-C(18)-H(18A) C(16)-C(18)-H(18B) H(18A)-C(18)-H(18B) C(16)-C(18)-H(18C) H(18A)-C(18)-H(18C) H(18B)-C(18)-H(18C) C(20)-C(l 9)-Ta C(20)-C(l9)-H(19A) Ta-C(19)-H(19A) C(20)-C(l 9)-H(l 9B) Ta-C(l 9)-H(l 9B) H(19A)-C(19)-H(19B) C(19)-C(20)-C(21) C(l 9)-C(20)-Ta C(21)-C(20)-Ta C(19)-C(20)-H(20) C(21)-C(20)-H(20) Ta-C(20)-H(20) C(22)-C(21 )-C(26) C(22)-C(21 )-C(20) C(26)-C(21)-C(20) C(21)-C(22)-C(23) C(21)-C(22)-H(22) C(23)-C(22)-H(22) C(24 )-C(23 )-C(22) C(24 )-C(23 )-H (23) C(22)-C(23)-H(23) C (23 )-C (24 )-C(25) C(23)-C(24)-H(24) C(25)-C(24)-H(24) C(26 )-C(25)-C(24) C(26)-C(25)-H(25) 112(3) 104(2) 108(3) 108(3) 110(2) 114(3) 119(4) 109(2) 105(3) 99(4) 114.0(3) 107.9(3) 110.7(4) 107.4(18) 112.1(18) 104.1(18) 99(3) 115(2) 118(3) 109(2) 118(4) 99(3) 111(3) 115(2) 106(4) 103(2) 120(4) 103(3) 72.2(2) 116(2) 122(2) 116(2) 118(2) 109(3) 124.5(3) 70.5(2) 122.2(2) 116(2) 112(2) 104(2) 116.7(3) 123.9(3) 119.3(3) 121.5(4) 116(3) 123(3) 120.8(4) 123(2) 116(2) 118.6(3) 124(2) 118(2) 120.7(3) 122(2) 318 C(24)-C(25)-H(25) C(25)-C(26)-C(21) C(25)-C(26)-H(26) C(21)-C(26)-H(26) 117(2) 121.5(3) 122(2) 117(2) Symmetry transformations used to generate equivalent atoms: 319 Table 25. Crystal data and structure refinement for tBuSpTa(sty)(H). Empirical formula C24 H31 Si Ta Formula weight 528.53 Crystallization Solvent Petroleum ether Crystal Habit Stacked plates Crystal size 0.26 X 0.15 X 0.03 mm3 Crystal color Yellow Data Collection Preliminary Photos Type of diffractometer CCD area detector Wavelength 0.71073 AMoKa Data Collection Temperature 93K Theta range for 6528 reflections used in lattice determination 2.77 to 28.25° Unit cell dimensions a = 10.2246(18) A b = 10.5009(18) A c = 11.1345(19) A Volume 1058.5(3) A3 z 2 Crystal system Triclinic Space group P-1 Density (calculated) l.658Mg/m3 F(00O) 524 Data collection program Bruker SMART Theta range for data collection 1.90 to 28.25° Completeness to theta = 28.25° 92.9% Index ranges -13<=h<=13, -13<=k<=13, -14<=1<=14 Data collection scan type phi and omega scans Data reduction program Bruker SAINT v. 6.2 Reflections collected 19961 Independent reflections 4860 [Rint= 0.2215; GOFmerge= ] Absorption coefficient 5.254mm-1 Absorption correction Analytical Max. and min. transmission 0.8571 and 0.2775 Number of standards ? reflections measured every ?min. Variation of standards ?%. a= 74.140(3) 0 b= 84.118(3) 0 g = 66.993(2) 0 320 Structure solution and Refinement Structure solution program SHELXS-97 (Sheldrick, 1990) Primary solution method Patterson method Secondary solution method Difference Fourier map Hydrogen placement Calculated (see Special Details) Structure refinement program SHELXL-97 (Sheldrick, 1997) Refinement method Full matrix least-squares on F2 Data / restraints / parameters 4860 Io I 257 Treatment of hydrogen atoms Mixed (~ee Special Details) Goodness-of-fit on p2 1.291 Final R indices [I>2s(I), 4347 reflections] Rl = 0.0469, wR2 = 0.1119 R indices (all data) Rl = 0.0524, wR2 = 0.1141 Type of weighting scheme used Sigma Weighting scheme used w=l/s"2"(Fo"2") Max shift/ error 0.001 Average shift/ error 0.000 Largest diff. peak and hole 3.625 and -3.292 e.A-3 Table 26. Bond lengths [A] and angles [0 ] for tBuSpTa(sty)(H). Ta-Cent(l) Ta-Cent(2) Ta-Pln(l) Ta-Pln(2) Ta-C(17) Ta-C(18) Ta-C(6) Ta-C(l) Ta-C(lO) Ta-C(7) Ta-C(2) Ta-C(5) Ta-C(4) Ta-C(9) Ta-C(3) Ta-C(8) Ta-H Si-C(6) Si-C(ll) Si-C(12) Si-C(l) C(l)-C(5) C(l)-C(2) 2.068(5) 2.084(5) 2.081(3) 2.062(3) 2.267(9) 2.307(7) 2.334(5) 2.359(6) 2.358(5) 2.367(7) 2.381(8) 2.375(7) 2.419(7) 2.449(6) 2.466(6) 2.476(7) 1.8669 1.858(7) 1.856(9) 1.850(8) 1.876(6) 1.409(12) 1.429(9) 321 C(2)-C(3) C(2)-H(2) C(3)-C(4) C(3)-H(3) C(4)-C(5) C(4)-H(4) C(5)-H(5) C(6)-C(10) C(6)-C(7) C(7)-C(8) C(7)-H(7) C(8)-C(9) C(8)-C(13) C(9)-C(10) C(9)-H(9) C(10)-H(10) C(11)-H(11A) C(11)-H(11B) C(11)-H(11C) C(12)-H(12A) C(12)-H(12B) C(12)-H(12C) C(13)-C(16) C(13)-C(14) C(13)-C(15) C(14)-H(14A) C(14)-H(14B) C(14)-H(14C) C(15)-H(15A) C(15)-H(15B) C(15)-H(15C) C(16)-H(16A) C(16)-H(16B) C(16)-H(16C) C(17)-C(18) C(17)-H(17A) C(17)-H(17B) C(18)-C(19) C(18)-H(18) C(19)-C(20) C(19)-C(24) C(20)-C(21) C(20)-H(20) C(21)-C(22) C(21)-H(21) C(22)-C(23) C(22)-H(22) C(23)-C(24) C(23)-H(23) C(24)-H(24) Cent(1)-Ta-Cent(2) Pln(1)-Ta-Pln(2) C(17)-Ta-C(18) 1.401(10) 0.8711 1.387(12) 1.0994 1.380(8) 0.9300 0.9978 1.421(11) 1.433(10) 1.434(9) 1.0524 1.398(12) 1.510(9) 1.442(8) 0.7546 0.9396 0.9312 0.9312 0.9312 0.9587 0.9587 0.9587 1.528(9) 1.519(11) 1.538(10) 1.0447 1.0447 1.0447 0.9807 0.9807 0.9807 0.7188 0.7188 0.7188 1.445(9) 0.9739 0.9739 1.483(7) 0.7398 1.384(12) 1.381(10) 1.398(8) 0.9300 1.377(12) 0.8784 1.361(13) 1.0306 1.380(8) 0.7862 0.8519 131.94(1) 125.2(3) 36.8(2) 322 C(17)-Ta-C(6) C(18)-Ta-C(6) C(17)-Ta-C(l) C(18)-Ta-C(l) C(6)-Ta-C(l) C(17)-Ta-C(10) C(18)-Ta-C(10) C(6)-Ta-C(10) C(l)-Ta-C(l0) C(17)-Ta-C(7) C(18)-Ta-C(7) C(6)-Ta-C(7) C(l )-Ta-C(7) C(10)-Ta-C(7) C(17)-Ta-C(2) C(18)-Ta-C(2) C(6)-Ta-C(2) C(l)-Ta-C(2) C(10)-Ta-C(2) C(7)-Ta-C(2) C(l 7)-Ta-C(5) C(18)-Ta-C(5) C(6)-Ta-C(5) C(l)-Ta-C(5) C(10)-Ta-C(5) C(7)-Ta-C(5) C(2)-Ta-C(5) C(17)-Ta-C(4) C(18)-Ta-C(4) C(6)-Ta-C(4) C(l)-Ta-C(4) C(l0)-Ta-C( 4) C(7)-Ta-C( 4) C(2)-Ta-C( 4) C(5)-Ta-C(4) C(17)-Ta-C(9) C(18)-Ta-C(9) C(6)-Ta-C(9) C(l )-Ta-C(9) C(10)-Ta-C(9) C(7)-Ta-C(9) C(2)-Ta-C(9) C(5)-Ta-C(9) C( 4)-Ta-C(9) C(17)-Ta-C(3) C(18)-Ta-C(3) C(6)-Ta-C(3) C(l )-Ta-C(3) C(10)-Ta-C(3) C(7)-Ta-C(3) C(2)-Ta-C(3) C(5)-Ta-C(3) C( 4)-Ta-C(3) C(9)-Ta-C(3) 113.8(2) 136.9(2) 114.8(3) 140.5(3) 70.7(2) 81.0(2) 102.3(2) 35.2(3) 95.5(2) 135.6(2) 131.9(2) 35.5(2) 87.4(2) 57.9(3) 135.4(3) 134.3(2) 88.6(2) 35.1(2) 122.2(2) 85.0(3) 82.3(3) 106.4(3) 94.1(2) 34.6(3) 102.7(2) 120.1(2) 57.0(3) 80.4(3) 86.5(3) 125.7(2) 56.6(2) 134.3(2) 140.0(3) 55.8(3) 33.45(19) 80.4(3) 82.1(2) 58.0(2) 127.74(19) 34.9(2) 56.5(3) 141.2(3) 136.2(2) 159.7(3) 109.7(3) 100.9(2) 121.8(2) 56.68(19) 152.2(2) 114.6(3) 33.5(2) 55.6(3) 33.0(3) 166.8(3) 323 C(17)-Ta-C(8) C(18)-Ta-C(8) C(6)-Ta-C(8) C(l)-Ta-C(8) C(10)-Ta-C(8) C(7)-Ta-C(8) C(2)-Ta-C(8) C(5)-Ta-C(8) C(4)-Ta-C(8) C(9)-Ta-C(8) C(3 )-Ta-C(8) C(17)-Ta-H C(18)-Ta-H C(6)-Ta-H C(l)-Ta-H C(l0)-Ta-H C(7)-Ta-H C(2)-Ta-H C(5)-Ta-H C(4)-Ta-H C(9)-Ta-H C(3)-Ta-H C(8)-Ta-H C(6)-Si-C(ll) C(6)-Si-C(l2) C(l 1 )-Si-C(12) C(6)-Si-C(l) C(ll)-Si-C(l) C(12)-Si-C(l) C(5)-C(l)-C(2) C(5)-C(l)-Si C(2)-C(l )-Si C(5)-C(l)-Ta C(2)-C(l)-Ta Si-C(l)-Ta C(3)-C(2)-C(l) C(3)-C(2)-Ta C(l)-C(2)-Ta C(3)-C(2)-H(2) C(l)-C(2)-H(2) Ta-C(2)-H(2) C(4)-C(3)-C(2) C(4)-C(3)-Ta C(2)-C(3)-Ta C(4)-C(3)-H(3) C(2)-C(3)-H(3) Ta-C(3)-H(3) C(3)-C( 4)-C(5) C(3)-C(4)-Ta C(5)-C(4)-Ta C(3)-C(4)-H(4) C(5)-C(4)-H(4) Ta-C(4)-H(4) C(l)-C(5)-C(4) 110.2(3) 97.6(2) 58.0(2) 121.6(2) 57.0(2) 34.4(2) 114.3(3) 151.91(19) 167.0(3) 33.0(3) 134.1(3) 112.4 76.3 125.4 113.1 136.5 90.2 78.1 119.6 89.2 104.2 64.5 79.9 110.0(4) 113.3(4) 113.1(4) 93.2(3) 113.6(3) 112.1(3) 106.2(5) 124.3(5) 123.6(6) 73.3(4) 73.3(4) 97.0(3) 108.2(8) 76.6(5) 71.6(4) 125.9 125.9 117.8 107.4(6) 71.6(4) 69.9(4) 126.3 126.3 123.8 109.5(7) 75.4(4) 71.5(4) 125.2 125.2 119.5 108.5(7) 324 C(l)-C(5)-Ta C( 4)-C(5)-Ta C(l)-C(5)-H(5) C(4)-C(5)-H(5) Ta-C(5)-H(5) C(10)-C(6)-C(7) C(10)-C(6)-Si C(7)-C( 6 )-Si C(10)-C(6)-Ta C(7)-C(6)-Ta Si-C(6)-Ta C(6)-C(7)-C(8) C(6)-C(7)-Ta C(8)-C(7)-Ta C(6)-C(7)-H(7) C(8)-C(7)-H(7) Ta-"C(7)-H(7) C(9)-C(8)-C(7) C(9)-C(8)-C(13) C(7)-C(8)-C(13) C(9)-C(8)-Ta C(7)-C(8)-Ta C(13)-C(8)-Ta C(8)-C(9)-C(10) C(8)-C(9)-Ta C(10)-C(9)-Ta C(8)-C(9)-H(9) C(10)-C(9)-H(9) Ta-C(9)-H(9) C(6)-C(10)-C(9) C(6)-C(10)-Ta C(9)-C(10)-Ta C(6)-C(10)-H(10) C(9)-C(10)-H(10) Ta-C(l0)-H(lO) Si-C(ll)-H(llA) Si-C(ll)-H(l lB) H(l lA)-C(ll)-H(l lB) Si-C(ll)-H(llC) H(llA)-C(ll)-H(llC) H(l lB)-C(ll)-H(llC) Si-C(12)-H(12A) Si-C(l2)-H(12B) H(12A)-C(12)-H(12B) Si-C(12)-H(12C) H(12A)-C(12)-H(12C) H(12B)-C(12)-H(12C) C(8)-C(13)-C(16) C(8)-C(13)-C(14) C(16)-C(13)-C(14) C(8)-C(13)-C(15) C(16 )-C(13)-C(15) C(14)-C(13)-C(15) C(13 )-C(l 4)-H(14A) 72.1(4) 75.0(4) 125.7 125.7 119.0 106.7(6) 127.0(6) 121.2(6) 73.3(3) 73.5(3) 98.4(3) 109.1(7) 71.0(4) 77.0(4) 125.5 125.5 118.4 107.3(6) 127.0(7) 124.5(8) 72.4(4) 68.7(4) 133.6(3) 108.7(7) 74.6(4) 69.1(3) 125.6 125.6 122.3 108.2(7) 71.4(3) 76.0(3) 125.9 125.9 118.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 105.7(5) 113.7(6) 110.2(7) 109.7(7) 107.7(6) 109.6(5) 109.5 325 C(13)-C(14)-H(14B) H(14A)-C(14)-H(14B) C(13)-C(14)-H(14C) H(14A)-C(14)-H(14C) H(14B)-C(14)-H(14C) C(13)-C(15)-H(15A) C(13)-C(15)-H(15B) H(15A)-C(15)-H(15B) C(13)-C(15)-H(15C) H(15A)-C(15)-H(15C) H(15B)-C(15)-H(15C) C(13)-C(16)-H(16A) C(13)-C(16)-H(16B) H(16A)-C(16)-H(16B) C(13)-C(16)-H(16C) H(16A)-C(16)-H(16C) H(16B)-C(16)-H(16C) C(18)-C(17)-Ta C(18)-C(17)-H(17A) Ta-C(17)-H(17A) C(18)-C(17)-H(17B) Ta-C(17)-H(17B) H(17A)-C(17)-H(17B) C(l 7)-C(18)-C(l 9) C(17)-C(18)-Ta C(19)-C(18)-Ta C(l 7)-C(18)-H(18) C(l 9)-C(18)-H(18) Ta-C(18)-H(18) C(20)-C(19)-C(24) C(20)-C(l 9)-C(18) C(24)-C(19)-C(18) C(19)-C(20)-C(21) C(l 9)-C(20)-H(20) C(21 )-C(20)-H (20) C(22)-C(21 )-C(20) C(22)-C(21)-H(21) C(20)-C(21)-H(21) C(23)-C(22)-C(21) C(23)-C(22)-H(22) C(21)-C(22)-H(22) C(22 )-C(23 )-C(24) C(22)-C(23)-H(23) C(24)-C(23)-H(23) C(l 9)-C(24)-C(23) C(19)-C(24)-H(24) C(23)-C(24)-H(24) 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 73.1(5) 116.2 116.2 116.2 116.2 113.2 126.9(7) 70.1(4) 120.8(5) 116.5 116.5 79.0 117.2(6) 123.2(7) 119.4(7) 121.8(7) 119.1 119.1 119.0(8) 120.5 120.5 119.7(6) 120.1 120.1 120.9(8) 119.5 119.5 121.2(8) 119.4 119.4 Symmetry transformations used to generate equivalent atoms: 326 C21 C14 Labeled view of iPr2SpTaMe3. 327 Table 27. Crystal Data and Structure Analysis Details for iPr2SpTaMe3. Empirical formula C21H35SiTa Formula weight 496.53 Crystallization solvent ether Crystal habit rounded plate Crystal size 0.22 X 0.22 X 0.07 mm Crystal color brown Data Collection Preliminary photograph( s) rotation . Type of diffractometer Bruker SMART 1000 ccd Wavelength 0.71073 A MoKa Data collection temperature 98K Theta range for 1137 reflections used in lattice determination 2.7 to 8.2° Unit cell dimensions a= 7.9023(14) A b = 10.4850(19) A c = 13.295(2) A Volume 997.1(3) A3 z 2 Crystal system triclinic Space group P 1 (#2) Density (calculated) l.654g/cm3 F(000) 496 Theta range for data collection 2.10 to 28. 70° Completeness to theta = 28.70° 80.1 % Index ranges -10 £ h £ 10, -12 £ k £ 13, -17 £ 1 £ 17 Data collection scan type w scans at 3 fixed f values Reflections collected 7045 Independent reflections 4126 [Rint= 0.0506] Absorption coefficient 5.571 mm-1 Absorption correction empirical Max. and min. transmission 1.0 and 0.4 Number of standards first scans recollected at end of runs Variation of standards within counting statistics Structure Solution and Refinement a= 88.009(5) 0 b= 78.408(7) 0 g = 67.670(6) 0 328 Primary solution method direct methods Secondary solution method difference map Hydrogen placement calculated Refinement method full-matrix least-squares on F2 Data I restraints / parameters 4126 Io I 208 Treatment of hydrogen atoms not refined Goodness-of-fit on F2 1.792 Final R indices [I>2s(I), 3825 reflections] Rl = 0.0398, wR2 = 0.0800 R indices (all data) Rl = 0.0417, wR2 = 0.0803 Type of weighting scheme used sigma Weighting scheme used w=l/s2(Fo2) Max shift/ error 0.880 Average shift/ error 0.061 Largest diff. peak and hole 3.491 and -1.534 e.A-3 Programs Used Cell refinement Bruker SAINT v6.02 Data collection Bruker SMART v5.054 Data reduction Bruker SAINT v6.02 Absorption correction SADABS V2.0 beta Structure solution SHELXS-97 (Sheldrick, 1990) Structure refinement SHELXL-97 (Sheldrick, 1997) Special Refinement Details A small brown crystal which could not be satisfactorily indexed on a CAD-4 diffractometer was some time later transferred to the ccd on a glass fiber with Paratone-N oil. Three runs of data were collected with 30 second long, -0.25° wide ro-scans at three values of <p (0, 120, and 240°) with the detector 5 cm (nominal) distant at a 0 of -28°. A short fourth run was not used. The initial cell for data reduction was calculated from just under 1000 reflections chosen from throughout the data frames; over a third were discarded as ill-fitting. For data processing with SAINT v6.02, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to zero, no Laue class integration restraints were used, the model profiles from all nine areas were blended, and for the post-integration global least squares refinement, no constraints were applied. The data were corrected with SADABS v. 2.0 (beta) using default parameters except that the scale factor esd was set to 0. One outlier reflection (0 -11) was omitted from the final processed dataset; there were 136 inconsistent equivalents. Refinement of F2 was against all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F2, conventional R-factors (R) are based on F, with F set 329 to zero for negative F The threshold expression of F > 2cr( F is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. 2 2 • 2 ) There is one molecule in the asymmetric unit. The structure is normal except for the elongated displacement ellipsoid of the central methyl carbon C20. No chemically reasonable disorder model could be found to account for this peculiarity. Some undetermined twinning is a possible explanation. There are numerous large excursions in the final difference map; all are near the Ta atom, except three in the vicinity of C20, the largest (1.58 e-A-3 ) is 0.46 A distant. Table 28. Bond lengths [A.] and angles [0 ] for iPr2SpTaMe3. ----------------------------------------------------C12-H12B Ta-Cpl• 2.120 Ta-Cp2b Ta···Plnlc Ta···Pln2d Ta-C20 Ta-C19 Ta-C21 Ta-C6 Ta-CS Ta-C7 Ta-Cl Ta-C2 Ta-ClO Ta-C3 Ta-CS Ta-C4 Si-C12 Si-Cll Si-Cl Si-C6 Cl-CS Cl-C2 C2-C3 C2-H2 C3-C4 C3-H3 C4-C5 C4-H4 CS-HS C6-Cl0 C6-C7 C7-C8 C7-H7 C8-C9 C8-C13 C9-Cl0 C9-H9 C10-C16 Cll-HllA Cll-HllB Cll-HllC C12-Hl2A 2.125 2.118(3) 2.121(2) 2.288(7) 2.325(7) 2.373(9) 2.392(5) 2.394(6) 2.407(6) 2.422(5) 2.439(6) 2.440(5) 2.475(6) 2.480(5) 2.480(6) 1.863(6) 1.875(5) 1.889(5) 1.904(6) 1.419(9) 1.434(8) 1.442(8) 1.0000 1.426(10) 1.0000 1.411(8) 1.0000 1.0000 1.406(8) 1.436(8) 1.442(8) 1.0000 1.399(8) 1.526(7) 1.428(7) 1.0000 1.533(7) 0.9800 0.9800 0.9800 0.9800 C12-H12C C13-C14 C13-C15 C13-H13 C14-H14A Cl4-H14B Cl4-H14C C15-H15A C15-H15B C15-H15C C16-C18 C16-C17 C16-H16 C17-H17A C17-H17B C17-H17C Cl8-H18A C18-H18B C18-H18C C19-H19A C19-H19B C19-H19C C20-H20A C20-H20B C20-H20C C21-H21A C21-H21B C21-H21C Cpl-Ta-Cp2 Cpl-Ta-C19 Cpl-Ta-C20 Cpl-Ta-C21 Cp2-Ta-C19 Cp2-Ta-C20 Cp2-Ta-C21 Plnl ···Pln2 C20-Ta-C19 C20-Ta-C21 C19-Ta-C21 C12-Si-Cll 0.9800 0.9800 1.521(9) 1.530(9) 1.0000 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 1.489(10) 1.541(8) 1.0000 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 129.9 100.9 115.3 95.7 103.4 113.1 97.4 54.9(2) 74.4(4) 60.2(5) 134.5(3) 112.4(3) 330 C12-Si-Cl Cll-Si-Cl C12-Si-C6 Cll-Si-C6 Cl-Si-C6 CS-Cl-C2 CS-Cl-Si C2-Cl-Si Cl-C2-C3 Cl-C2-H2 C3-C2-H2 C4-C3-C2 C4-C3-H3 C2-C3-H3 CS-C4-C3 C5-C4-H4 C3-C4-H4 C4-CS-Cl C4-CS-HS Cl-CS-HS C10-C6-C7 C10-C6-Si C7-C6-Si C6-C7-C8 C6-C7-H7 C8-C7-H7 C9-C8-C7 C9-C8-C13 C7-C8-C13 C8-C9-Cl0 C8-C9-H9 C10-C9-H9 C6-Cl0-C9 C6-Cl0-C16 C9-C10-C16 Si-Cll-HllA Si-Cll-HllB HllA-Cll-HllB Si-Cll-HllC HllA-Cll-HllC HllB-Cll-HllC Si-C12-H12A Si-C12-H12B H12A-C12-H12B Si-C12-H12C H12A-Cl2-H12C H12B-C12-H12C C14-C13-C8 C14-C13-C15 C8-C13-C15 C14-C13-H13 C8-C13-H13 C15-C13-Hl3 C13-C14-H14A 109.3(3) 113.0(3) 111.3(3) 115.4(3) 94.1(2) 107.8(5) 124.9(4) 120.1(4) 106.8(6) 126.2 126.2 108.4(5) 125.6 125.7 107.4(6) 126.2 126.2 109.3(5) 124.9 124.8 107.8(5) 125.8(4) 121.1(4) 107.7(5) 125.8 125.8 107.3(5) 127.4(5) 124.9(5) 109.1(5) 125.4 125.4 108.1(5) 126.1(5) 124.2(5) 109.5 109.5 109.5 109.5 109.5 109.5 109.4 109.5 109.5 109.5 109.5 109.5 110.2(5) 110.8(6) 111.3(5) 108.2 108.2 108.2 109.5 C13-C14-H14B H14A-C14-H14B C13-C14-Hl4C H14A-C14-H14C H14B-C14-H14C C13-C15-H15A C13-C15-H15B HlSA-ClS-HlSB C13-C15-H15C HlSA-ClS-HlSC HlSB-ClS-HlSC C18-C16-Cl0 C18-C16-C17 Cl0-C16-C17 crn~c16-H16 C10-C16-H16 C17-C16-H16 C16-C17-H17A C16-C17-H17B H17A-C17-H17B C16-C17-H17C H17A-C17-H17C H17B-C1 7-H17C C16-C18-H18A C16-C18-H18B H18A-C18-H18B C16-C18-H18C H18A-C18-H18C H18B-C18-H18C Ta-C19-H19A Ta-C19-H19B H19A-C19-H19B Ta-C19-H19C H19A-C19-H19C H19B-C19-H19C Ta-C20-H20A Ta-C20-H20B H20A-C20-H20B Ta-C20-H20C H20A-C20-H20C H20B-C20-H20C Ta-C21-H21A Ta-C21-H21B H21A-C21-H21B Ta-C21-H21C H21A-C21-H21C H21B-C21-H21C 109.5 109.5 109.4 109.5 109.5 109.5 109.4 109.5 109.5 109.5 109.5 113.6(5) 109.6(6) 107.6(5) 108.6 108.7 108.7 109.5 109.5 109.5 109.4 109.5 109.5 109.5 109.4 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.4 109.5 109.5 109.5 109.6 109.5 109.4 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 331 a Cpl is the centroid of atoms Cl, C2, C3, C4 and CS b Plnl is the best plane through atoms Cl, C2, C3, C4 and CS c Cp2 is the centroid of atoms C9, ClO, Cl5, C16 and C21 ct Pln2 is the best plane through atoms C9, ClO, Cl5, C16 and C21 Table 29. Crystal Data and Structure Analysis Details for (Ewen)TaMe3. Empirical formula Formula weight Crystallization solvent dichloromethane Crystal habit yellow Crystal size 0.33 X 0.33 X 0.26 mm Crystal color irregular block Data Collection Preliminary photograph(s) none Type of diffractometer CAD-4 Wavelength 0.71073 A MoKa Data collection temperature 84K Theta range for 25 reflections used in lattice determination 15 to 17° Volume a = 8.717(2) A b = 13.796(4) A c = 15.763(4) A 1895.7(9) A3 z 4 Crystal system orthorhombic Space group P212121 (#19) Density (calculated) 1.739 g/ cm3 F(000) 976 Theta range for data collection 1.5 to 27.5° Completeness to theta = 27.5° 99.9 % Index ranges 0 £ h £ 11, -17 £ k £ 17, -20 £ 1 £ 20 Data collection device CAD-4 Data collection scan type w-scan Reflections collected 12266 Independent reflections 4350 [Rint= 0.0259; GOFmerge= 1.57] Absorption coefficient 5.801 mm-1 Unit cell dimensions a= 90° b=90° g=90° 332 Absorption correction y-scan Max. and min. transmission 1.14 and 0.76 Number of standards 3 reflections measured every 75 min Decay of standards 0.6% Structure Solution and Refinement Primary solution method direct methods Secondary solution method difference map Hydrogen placement calculated Refinement method full-matrix least-squares on F2 Data / restraints ./ parameters 4350 Io I 308 Treatment of hydrogen atoms coordinates refined; Uiso's fixed at 120% Ueq of attached atom Goodness-of-fit on F2 1.561 Final R indices [I>2s(I), 4292 reflections] Rl = 0.0169, wR2 = 0.0406 R indices (all data) Rl = 0.0172, wR2 = 0.0407 Type of weighting scheme used sigma Weighting scheme used w=l/s\Fo ) Max shift/ error 0.068 Average shift/ error 0.002 Absolute structure parameter -0.014(8) Extinction coefficient 0.00076(9) Largest diff. peak and hole 0.972 and -0.668 e.A-3 2 Programs Used Cell refinement CAD-4 Software (Enraf-Nonius, 1989) Data collection CAD-4 Software (Enraf-Nonius, 1989) Data reduction CRYM (Duchamp, 1964) Structure solution SHELXS-97 (Sheldrick, 1990) Structure refinement SHELXL-97 (Sheldrick, 1997) 333 Special Refinement Details An irregular yellow block was carved from a yellow rosette and mounted on a glass fiber with Paratone-N oil. Data were collected with loo w-scans. The individual measured backgrounds were replaced by a background function of 2q derived from weak reflections. The GOFmerge was 1.57 (4352 multiples) in point group 222; Rmerge was 0.015 for 2993 duplicates with F0 > 0. Yscan data were used for the absorption correction. There was minimal decay. Two outlier reflections (101,011) were omitted from the refinement. A small extinction correction was included. 2 Weights ware calculated as 11s2(F0 ); variances (s2(F 0 2)) were derived from counting statistics plus an additional term, (0.0141)2; variances of the merged data were obtained by propagation of error plus another additional term, (0.014<1> )2. The refinement of F2 is as always against all reflections. The weighted R-factor wR and goodness of fit Sare based on F2, conventional R-factors Rare based on F, with F set to zero for negative F2 . The threshold expression of F2 > 2s(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. The asymmetric unit contains one Ta complex. P212121 is a chiral, non-polar spacegroup. Although the molecule is not chiral; the structure is. The Flack parameter was not included in the full matrix least squares. Table 30. Bond lengths [.A.] and angles [0 ] for (Ewen)TaMe3. ----------------------------------------------------Ta-Cpa C7-H7B 2.118 Ta···Plnb Ta-C23 Ta-C22 Ta-C24 Ta-C9 Ta-Cl Ta-CS Ta-C2 Ta-C4 Ta-C3 Cl-C2 Cl-CS Cl-C6 C2-C3 C2-H2 C3-C4 C3-H3 C4-C5 C4-H4 CS-HS C6-C7 C6-C8 C6-C9 C7-H7A 2.114(2) 2.188(4) 2.194(4) 2.210(3) 2.294(3) 2.389(3) 2.390(3) 2.406(3) 2.484(4) 2.505(4) 1.411(5) 1.421(5) 1.511(5) 1.423(6) 0.85(4) 1.390(6) 0.86(5) 1.417(6) 0.81(5) 0.94(4) 1.527(5) 1.541(5) 1.575(4) 0.91(4) C7-H7C C8-H8A C8-H8B C8-H8C C9-C10 C9-C21 ClO-Cll ClO-ClS Cll-C12 Cll-Hll C12-C13 C12-H12 C13-C14 Cl3-Hl3 C14-C15 C14-H14 C15-C16 C16-C17 C16-C21 C17-C18 C17-H17 Cl8-C19 C18-H18 C19-C20 0.97(5) 0.94(4) 0.98(4) 0.97(4) 0.92(5) 1.493(4) 1.502(4) 1.400(4) 1.417(4) 1.388(5) 0.91(4) 1.385(5) 0.83(4) 1.395(5) 0.93(4) 1.395(5) 0.92(4) 1.448(4) 1.393(4) 1.417(5) 1.396(5) 1.00(4) 1.394(5) 0.96(4) 1.388(5) 334 C19-H19 C20-C21 C20-H20 C22-H22A C22-H22B C22-H22C C23-H23A C23-H23B C23-H23C C24-H24A C24-H24B C24-H24C Cp-Ta-C9 Cp-Ta-C22 Cp-Ta-C23 Cp-Ta-C24 C23-Ta-C22 C23-Ta-C24 C22-Ta-C24 C23-Ta-C9 C22-Ta-C9 C24-Ta-C9 C2-Cl-C5 C2-Cl-C6 C5-Cl-C6 Cl-C2-C3 Cl-C2-H2 C3-C2-H2 C4-C3-C2 C4-C3-H3 C2-C3-H3 C3-C4-C5 C3-C4-H4 C5-C4-H4 C4-C5-Cl C4-C5-H5 Cl -CS-HS Cl-C6-C7 Cl-C6-C8 C7-C6-C8 Cl-C6-C9 C7-C6-C9 C8-C6-C9 C6-C7-H7A C6-C7-H7B H7A-C7-H7B C6-C7-H7C H7A-C7-H7C H7B-C7-H7C C6-C8-H8A C6-C8-H8B H8A-C8-H8B C6-C8-H8C 0.76(4) 1.408(5) 0.97(4) 1.07(4) 0.92(5) 1.10(4) 0.87(5) 1.07(4) 0.98(4) 0.99(4) 0.88(4) 1.02(4) 90.7 102.5 101.6 177.5 115.38(14) 78.58(14) 79.64(14) 117.93(13) 120.69(13) 87.01(12) 105.9(3) 125.2(3) 124.2(3) 109.3(3) 130(3) 121(3) 107.6(4) 123(3) 129(3) 108.1(4) 119(3) 133(3) 109.0(3) 128(3) 123(3) 111.5(3) 111.8(3) 106.2(3) 98.7(3) 114.6(3) 114.1(3) 108(3) 112(3) 104(4) 116(3) 105(4) 111(4) 107(3) 119(3) 113(4) 107(3) H8A-C8-H8C H8B-C8-H8C C10-C9-C21 C10-C9-C6 C21-C9-C6 C10-C9-Ta C21-C9-Ta C6-C9-Ta Cll-Cl0-C15 Cll-C10-C9 C15-C10-C9 Cl2-Cll-C10 C12-Cll-Hll ClO-Cll-Hll Cl3-C12-Cll C13-C12-H12 Cll-C12-H12 C12-C13-C14 C12-C13-H13 C14-C13-H13 C15-Cl4-C13 C15-C14-H14 C13-C14-H14 C14-C15-C10 C14-C15-C16 C10-C15-C16 C17-C16-C21 C17-C16-C15 C21-C16-C15 C16-C17-C18 C16-C17-H17 C18-C17-H17 C19-Cl8-C17 C19-C18-H18 C17-C18-H18 C20-C19-C18 C20-C19-H19 C18-C19-H19 C19-C20-C21 Cl 9-C20-H20 C21-C20-H20 C20-C21-C16 C20-C21-C9 C16-C21-C9 Ta-C22-H22A Ta-C22-H22B H22A-C22-H22B Ta-C22-H22C H22A-C22-H22C H22B-C22-H22C Ta-C23-H23A Ta-C23-H23B H23A-C23-H23B Ta-C23-H23C 106(4) 103(4) 102.9(3) 120.0(3) 120.4(3) 103.0(2) 107.1(2) 101.6(2) 118.6(3) 131.2(3) 110.1(3) 119.7(3) 118(2) 123(2) 121.7(3) 125(3) 113(3) 119.7(3) 121(3) 119(3) 119.4(3) 120(2) 121(2) 121.0(3) 130.1(3) 108.7(3) 122.0(3) 129.6(3) 108.1(3) 118.9(3) 120(2) 121(2) 119.7(3) 118(2) 122(2) 121.8(3) 119(3) 119(4) 119.6(3) 117(2) 123(2) 118.0(3) 131.5(3) 110.2(3) 106(2) 117(3) 116(3) 106(2) 96(3) 113(4) 105(3) 109(2) 107(3) 116(3) 335 H23A-C23-H23C H23B-C23-H23C Ta-C24-H24A Ta-C24-H24B H24A-C24-H24B Ta-C24-H24C H24A-C24-H24C H24B-C24-H24C 116(4) 103(3) 119(2) 111(3) 108(4) 105(2) 107(3) 106(4) 336 a Cp is the centroid of atoms Cl, C2, C3, C4 and CS b Pln is the best plane through atoms Cl, C2, C3, C4 and CS Table 31. Crystal Data and Structure Analysis Details for Flyover. Empirical formula C27H36Cl2Ta2 Formula weight 793.36 Crystallization solvent dichloromethane Crystal habit plate Crystal size 0.33 X 0.26 X 0.04 mm Crystal color orange Data Collection Preliminary photograph(s) none Type of diffractometer CAD-4 Wavelength 0.71073 A MoKa Data collection temperature 84K Theta range for 25 reflections used in lattice determination 11 to 14° Volume a= 8.999(4) A b = 11.960(3) A c =13.128(5) A 1261.3(8) A3 z 2 Cry~tal system triclinic Space group p 1 (#2) Density (calculated) 2.089 g/cm3 F(000) 756 Theta range for data collection 1.5 to 25° Completeness to theta = 25° 100.0 % Index ranges -10 £ h £ 10, -12 £ k £ 14, -13 £ 1 £ 15 Data collection device CAD-4 Data collection scan type w-scan Reflections collected 10000 Independent reflections 4439 [Rint= 0.0399; GOFmerge= 1.20 ] Absorption coefficient 8.894mm-l Absorption correction y-scan Max. and min. transmission 1.33 and 0.30 Unit cell dimensions a= 64.92(3) 0 b= 80.99(3) 0 g =82.85(3) 0 337 Number of standards 3 reflections measured every 75 min Variation of standards within counting statistics Structure Solution and Refinement Primary solution method direct methods Secondary solution method difference map Hydrogen placement calculated Refinement method full-matrix least-squares on p2 Data / restraints / parameters 4439 Io I 147 Treatment of hydrogen atoms not refined Goodness-of-fit on p2 1.756 Final R indices [I>2s(I), 3627 reflections]Rl = 0.0409, wR2 = 0.0744 R indices (all data) Rl = 0.0584, wR2 = 0.0782 Type of weighting scheme used sigma Weighting scheme used 2 2 w=l/s (Fo ) Max shift/ error 0.021 Average shift/error 0.001 Largest di££. peak and hole 1.942 and -2.234 e-A-3 Programs Used Cell refinement CAD-4 Software (Enraf-Nonius, 1989) Data collection CAD-4 Software (Enraf-Nonius, 1989) Data reduction CRYM (Duchamp, 1964) Structure solution SHELXS-97 (Sheldrick, 1990) Structure refinement SHELXL-97 (Sheldrick, 1997) Special Refinement Details This material is present as a small quantity of impurity in PJC17. Unwanted by its creator, a lonely orange triangular plate languished in Paratone-N on a glass slide during data collection for PJC17 and slowly turned colorless around the edges until it was finally mounted on a glass fiber with Paratone-N oil. Data were collected with 1.75 w-scans as the peaks were broad. The individual measured backgrounds were replaced by a background function of 2q derived from weak reflections. The GOFmerge was 1.20 (4439 multiples) in point group'l; Rmerge was 0.031 for 3662 duplicates with F0 > 0. Y-scan data were used for the absorption correction. There was no decay. No outlier reflections were omitted from the refinement. 00 Weights w are calculated as 1/ s2(F0 2); variances (s2(F/)) were derived from counting statistics plus an additional term, (0.0141)2; variances of the merged data were obtained by 338 propagation of error plus another additional term, (0.014<1> )2. The refinement of F2 is as always against all reflections. The weighted R-factor wR and goodness of fit Sare based on F2, conventional R-factors Rare based on F, with F set to zero for negative F2 . The threshold 2 expression of F > 2s(F2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. This is not a high-quality structure. Only the Ta and Cl atoms were refined anisotropically; all other non-hydrogen atoms were refined isotropically and hydrogen atoms were placed at calculated positions with Uiso's set at 120% of the Uiso's of the attached atoms. There may be some confusion among the Cl's and several of the methyl groups; it is not possible to tell with this dataset. There are many large peaks in the final difference map; the four greater than 121 eoA-3 (-2.23, -2.11, -2.11 and -2.01) are all within 1.16A of Tal or Ta2; 1.52 e0A-3 (1.26A from ClO) and -1.35 e◊A-3 (1.19A from H8C) are the largest .positive and negative excursions not near a Ta or Cl atom. Table 32. Bond lengths [A] and angles [0 ] for Flyover. Tal-Cpl• Tal···Plnlb Tal-C24 Tal-C23 Tal-C22 Tal-Cll Tal-C3 Tal-C4 Tal-CS Tal-C2 Tal-Cl Ta2-Cp2c Ta2···Pln2d Ta2-C26 Ta2-C27 Ta2-C25 Ta2-Cl2 Ta2-C9 Ta2-C10 Ta2-C21 Ta2-C16 Ta2-C15 Cl-CS Cl-C2 Cl-C6 C2-C3 C2-H2 C3-C4 C3-H3 C4-C5 C4-H4 CS-HS C6-C9 C6-C7 C6-C8 2.111 2.109(4) 2.181(10) 2.207(9) 2.268(7) 2.355(2) 2.401(8) 2.405(9) 2.417(9) 2.422(9) 2.482(9) 2.164 2.156(4) 2.168(11) 2.189(8) 2.190(9) 2.358(2) 2.377(8) 2.475(8) 2.476(9) 2.546(9) 2.555(8) 1.405(12) 1.420(11) 1.522(11) 1.381(12) 0.9800 1.412(12) 0.9800 1.408(12) 0.9800 0.9800 1.533(11) 1.534(11) 1.540(11) C7-H7A C7-H7B C7-H7C C8-H8A C8-H8B C8-H8C C9-C21 C9-C10 ClO-Cll Cl0-C15 Cll-C12 Cll-Hll C12-C13 C12-H12 C13-C14 C13-H13 C14-C15 C14-H14 C15-C16 C16-C21 C16-C17 C17-C18 C17-H17 C18-C19 C18-H18 C19-C20 C19-H19 C20-C21 C20-H20 C22-H22A C22-H22B C22-H22C C23-H23A C23-H23B C23-H23C 0.9600 0.9600 0.9600 0.9600 0.9600 0.9600 1.458(11) 1.466(11) 1.419(11) 1.422(11) 1.355(12) 0.9300 1.414(12) 0.9300 1.348(12) 0.9300 1.410(12) 0.9300 1.443(11) 1.414(12) 1.439(11) 1.356(12) 0.9300 1.391(13) 0.9300 1.369(12) 0.9300 1.445(11) 0.9300 0.9600 0.9600 0.9600 0.9600 0.9600 0.9600 339 C24-H24A C24-H24B C24-H24C C25-H25A C25-H25B C25-H25C C26-H26A C26-H26B C26-H26C C27-H27A C27-H27B C27-H27C 0.9600 0.9600 0.9600 0.9600 0.9600 0.9600 0.9600 0.9600 0.9600 0.9600 0.9600 0.9600 Cpl-Tal-Cll Cpl-Tal-C22 Cpl-Tal-C23 Cpl-Tal-C24 C24-Tal-C23 C24-Tal-C22 C23-Tal-C22 C24-Tal-Cll C23-Tal-Cll C22-Tal-Cll Cp2-Ta2-Cl2 Cp2-Ta2-C25 Cp2-Ta2-C26 Cp2-Ta2-C27 C26-Ta2-C27 C26-Ta2-C25 C27-Ta2-C25 C26-Ta2-Cl2 C27-Ta2-Cl2 C25-Ta2-Cl2 CS-Cl-C2 C5-Cl-C6 C2-Cl-C6 C3-C2-Cl C3-C2-H2 Cl-C2-H2 C2-C3-C4 C2-C3-H3 C4-C3-H3 C5-C4-C3 CS-C4-H4 C3-C4-H4 Cl-C5-C4 Cl-CS-HS C4-CS-HS Cl-C6-C9 Cl-C6-C7 C9-C6-C7 Cl-C6-C8 C9-C6-C8 C7-C6-C8 119.6 115.1 106.0 110.6 76.7(4) 132.1(3) 77.8(3) 83.9(2) 134.3(2) 85.91(18) 124.5 116.8 103.2 111.6 78.0(4) 79.4(4) 129.9(4) 132.1(3) 80.2(3) 83.0(2) 106.3(7) 126.9(7) 126.3(8) 107.8(8) 125.7 125.7 110.3(8) 124.7 124.7 105.1(8) 127.0 127.0 110.3(8) 124.6 124.6 110.5(6) 109.4(7) 112.3(7) 108.9(7) 106.8(7) 108.9(6) C6-C7-H7A C6-C7-H7B H7A-C7-H7B C6-C7-H7C H7A-C7-H7C H7B-C7-H7C C6-C8-H8A C6-C8-H8B H8A-C8-H8B C6-C8-H8C H8A-C8-H8C H8B-C8-H8C C21-C9-C10 C21-C9-C6 C10-C9-C6 Cll-Cl0-C15 Cll-Cl0-C9 C15-C10-C9 C12-Cll-C10 C12-Cll-Hll ClO-Cll-Hll Cll-C12-C13 Cll-C12-H12 C13-C12-H12 C14-C13-C12 C14-C13-H13 C12-C13-H13 C13-C14-C15 C13-C14-H14 C15-C14-Hl4 C14-C15-C10 C14-C15-C16 Cl0-C15-C16 C21-C16-C17 C21-C16-C15 C17-C16-C15 C18-C17-C16 C18-C17-H17 C16-C17-H17 C17-C18-C19 C17-Cl8-H18 C19-C18-H18 C20-C19-C18 C20-C19-H19 Cl8-C19-H19 C19-C20-C21 C19-C20-H20 C21-C20-H20 C16-C21-C20 C16-C21-C9 C20-C21-C9 H22A-C22-H22B H22A-C22-H22C H22B-C22-H22C 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 104.7(7) 128.9(7) 122.0(6) 117.6(8) 132.8(8) 109.6(7) 119.5(8) 120.3 120.3 122.0(8) 119.0 119.0 120.6(9) 119.7 119.7 118.7(8) 120.6 120.6 121.6(7) 130.8(8) 107.4(7) 123.2(8) 108.3(7) 128.4(8) 116.3(9) 121.9 121.9 122.1(8) 118.9 118.9 123.1(9) 118.5 118.5 118.2(9) 120.9 120.9 117.0(7) 109.7(7) 133.1(8) 109.5 109.5 109.5 340 H23A-C23-H23B H23A-C23-H23C H23B-C23-H23C H24A-C24-H24B H24A-C24-H24C H24B-C24-H24C H25A-C25-H25B H25A-C25-H25C H25B-C25-H25C H26A-C26-H26B H26A-C26-H26C H26B-C26-H26C H27A-C27-H27B H27A-C27-H27C H27B-C27-H27C 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 341 • Cpl is the centroid of atoms Cl, C2, C3, C4 and CS b Plnl is the best plane through atoms Cl, C2, C3, C4 and CS c Cp2 is the centroid of atoms C9, ClO, C15, C16 and C21 <l Pln2 is the best plane through atoms C9, ClO, Cl5, C16 and C21 Table 33. Crystal Data and Structure Analysis Details for (Ewen)TaMe2F. Empirical formula C33.5H36FTa Formula weight 638.60 Crystallization solvent CH2Cl4/PE Crystal habit tabular fragment Crystal size 0.30 X 0.30 X 0.22 mm Crystal color yellow [C23H24FTa • l_C7H3] [500.39 · l_ (92.14)] Data Collection Preliminary photograph(s) none Type of diffractometer CAD-4 Wavelength 0.71073 A MoKa Data collection temperature 84K Theta range for 25 reflections used in lattice determination 14 to 16° Volume a = 13.505(3) A b = 12.465(3) A c = 16.034(4) A 2682.0(11) A3 z 4 Crystal system monoclinic Space group P21/n (#14) Density (calculated) 1.581 g/cm3 F(000) 1276 Theta range for data collection 1.5 to 25° Completeness to theta = 25° 100.0 % Index ranges -16 £ h £ 15, -14 £ k £ 14, 0 £ 1 £ 19 Data collection device CAD-4 Data collection scan type w-scan Reflections collected 11341 Unit cell dimensions a= 90° b= 96.47(2) 0 g=90° 342 Independent reflections 4709 [Rint= 0.0203; GOFmerge= 1.05] Absorption coefficient 4.125mm-1 Absorption correction y-scan Max. and min. transmission 1.06 and 0.85 Number of standards 3 reflections measured every 75 min Variation of standards within counting statistics Structure Solution and Refinement Primary solution method direct methods Secondary solution method difference map Hydrogen placement calculated Refinement method full-matrix least-squares on p2 Data / restraints / parameters 4709 Io I 448 Treatment of hydrogen atoms coordinates refined; Uiso's fixed at 120% Ueq of attached atom Goodness-of-fit on F2 1.363 Final R indices [l>2s(I), 4339 reflections] Rl = 0.0193, wR2 = 0.0415 R indices (all data) Rl = 0.0228, wR2 = 0.0425 Type of weighting scheme used sigma Weighting scheme used 2 w=l/s2(Fo ) Max shift / error 0.061 Average shift/ error 0.002 Largest di££. peak and hole 0.797 and -0.482 e.A-3 Programs Used Cell refinement CAD-4 Software (Enraf-Nonius, 1989) Data collection CAD-4 Software (Enraf-Nonius, 1989) Data reduction CRYM (Duchamp, 1964) Structure solution SHELXS-97 (Sheldrick, 1990) Structure refinement SHELXL-97 (Sheldrick, 1997) Special Refinement Details 343 A pale yellow tabular fragment was mounted on a glass fiber with Paratone-N oil. Data were collected with 1.200 w-scans, as the peaks wereslightly broad. The individual measured backgrounds were replaced by a background function of 2q derived from weak reflections. The GOFmerge was 1.05 (4708 multiples) in point group 2/m; Rmerge was 0.015 for 4195 duplicates with F0 > 0. Y-scan data were used for the absorption correction. There was no decay. No outlier reflections were omitted from the refinement. Weights ware calculated as 1!s2(Fi); variances (s2 (F 0 2)) were derived from counting statistics plus an additional term, (0.0141)2; variances of the merged data were obtained by propagation of error plus another additional term, (0.014<1> )2. The refinement of F2 is as always against all reflections. The weighted R-factor wR and goodness of fit Sare based on F2, conventional R-factors Rare based on F, with F set to zero for negative F2 . The threshold expression of F2 > 2s(F2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. The asymmetric unit contains one Ta complex and l_ molecules of toluene. The toluene is disordered over a center of symmetry; the _ carbon atoms were refined anisotropically and the hydrogen atoms placed at calculated positions. All hydrogen atoms were given fixed Uiso's. Table 34. Bond lengths [A] and angles [0 ] for (Ewen)TaMe2F. Ta-cp• Ta···Plnb Ta-F Ta-C23 Ta-C22 Ta-C9 2.104 2.100(2) 1.9133(16) 2.173(3) 2.173(3) 2.290(3) Ta-C5 2.385(3) Ta-Cl Ta-C2 Ta-C4 Ta-C3 Cl-C2 Cl-CS Cl-C6 C2-C3 C2-H2 C3-C4 C3-H3 C4-C5 C4-H4 CS-HS C6-C7 C6-C8 C6-C9 C7-H7A C7-H7B C7-H7C C8-H8A C8-H8B 2.385(3) 2.389(3) 2.476(3) 2.479(3) 1.413(4) 1.415(4) 1.518(4) 1.417(4) 0.91(3) 1.403(5) 0.93(3) 1.421(4) 0.93(3) 0.90(3) 1.530(4) 1.530(4) 1.573(4) 0.85(4) 0.93(3) 0.96(3) 0.98(4) 0.95(3) C8-H8C C9-C10 C9-C21 ClO-Cll ClO-ClS Cll-C12 Cll-Hll C12-C13 C12-H12 C13-C14 C13-Hl3 C14-C15 C14-H14 C15-C16 C16-C17 C16-C21 C17-C18 C17-H17 C18-C19 C18-H18 C19-C20 C19-H19 C20-C21 C20-H20 C22-H22A C22-H22B C22-H22C C23-H23A C23-H23B 0.91(4) 1.499(4) 1.505(4) 1.395(4) 1.406(4) 1.391(5) 0.95(3) 1.381(5) 1.01(4) 1.390(5) 0.88(4) 1.391(4) 0.96(3) 1.453(4) 1.395(4) 1.415(4) 1.381(5) 0.83(3) 1.376(5) 0.89(3) 1.392(4) 0.94(3) 1.405(4) 0.96(3) 0.92(4) 0.81(4) 1.00(4) 1.01(3) 0.88(4) 344 C23-H23C 0.98(3) C24-C25 C24-C29 C24-H24 C25-C26 C25-H25 C26-C27 C26-H26 C27-C28 C27-H27 C28-C29 C28-H28 C29-C30 C30-H30A C30-H30B C30-H30C 1.358(6) 1.416(5) 0.92(4) 1.406(6) 1.01(4) 1.364(6) 0.98(4) 1.394(5) 1.07(4) 1.372(5) 1.05(4) 1.490(5) 1.08(4) 1.00(4) 1.03(4) C31-C36 C31-C32 C31-H31 C32-C33 C32-H32 C33-C34 C33-H33 C34-C35 C34-H34 C35-C36 C35-H35 C36-C37 C37-H37A C37-H37B C37-H37C 1.42(3) 1.48(3) 0.9300 1.20(2) 0.9300 1.32(3) 0.9300 1.43(4) 0.9300 1.48(2) 0.9300 1.476(18) 0.9600 0.9600 0.9600 Cp-Ta-F Cp-Ta-C9 Cp-Ta-C22 Cp-Ta-C23 F-Ta-C23 F-Ta-C22 C23-Ta-C22 F-Ta-C9 C23-Ta-C9 C22-Ta-C9 C2-Cl-C5 C2-Cl-C6 C5-Cl-C6 Cl-C2-C3 Cl-C2-H2 C3-C2-H2 C4-C3-C2 C4-C3-H3 C2-C3-H3 C3-C4-C5 173.3 90.2 102.4 102.9 81.43(10) 80.59(10) 110.96(14) 83.10(9) 120.07(12) 122.86(12) 106.7(3) 124.3(3) 124.3(3) 108.8(3) 126(2) 125(2) 108.1(3) 125(2) 127(2) 107.5(3) C3-C4-H4 C5-C4-H4 Cl-C5-C4 Cl-CS-HS C4-C5-H5 Cl-C6-C7 Cl-C6-C8 C7-C6-C8 Cl-C6-C9 C7-C6-C9 C8-C6-C9 C6-C7-H7A C6-C7-H7B H7A-C7-H7B C6-C7-H7C H7A-C7-H7C H7B-C7-H7C C6-C8-H8A C6-C8-H8B H8A-C8-H8B C6-C8-H8C H8A-C8-H8C H8B-C8-H8C C10-C9-C21 C10-C9-C6 C21-C9-C6 C10-C9-Ta C21-C9-Ta C6-C9-Ta Cll-ClO-ClS Cll-Cl0-C9 C15-C10-C9 C12-Cll-Cl0 C12-Cll-Hll ClO-Cll-Hll C13-C12-Cl 1 C13-C12-H12 Cll-C12-H12 C12-C13-C14 C12-C13-H13 C14-C13-H13 C13-C14-C15 C13-C14-H14 C15-C14-H14 C14-C15-C10 C14-C15-C16 C10-C15-C16 C17-C16-C21 C17-C16-C15 C21-C16-C15 C18-C17-C16 C18-C17-H17 C16-C17-H17 C19-C18-C17 125(2) 127(2) 108.9(3) 127(2) 124(2) 111.2(2) 111.9(2) 106.8(3) 97.6(2) 115.0(2) 114.3(2) 107(2) 110(2) 105(3) 114.9(19) 113(3) 107(3) 112.4(19) 116.1(19) 108(3) 106(2) 107(3) 108(3) 103.1(2) 120.0(2) 119.7(2) 103.72(18) 106.00(17) 102.51(17) 118.5(3) 131.1(3) 110.2(2) 119.4(3) 120(2) 121(2) 121.4(3) 121(2) 117(2) 120.2(3) 122(2) 118(2) 118.5(3) 122(2) 120(2) 121.8(3) 129.6(3) 108.5(2) 120.8(3) 130.5(3) 108.6(2) 119.0(3) 122(2) 119(2) 120.9(3) 345 C19-C18-H18 C17-C18-H18 C18-C19-C20 C18-C19-H19 C20-C19-H19 C19-C20-C21 C19-C20-H20 C21-C20-H20 C20-C21-C16 C20-C21-C9 C16-C21-C9 Ta-C22-H22A Ta-C22-H22B H22A-C22-H22B Ta-C22-H22C H22A-C22-H22C H22B-C22-H22C Ta-C23-H23A Ta-C23-H23B H23A-C23-H23B Ta-C23-H23C H23A-C23-H23C H23B-C23-H23C 124(2) 115(2) 121.4(3) 124(2) 115(2) 118.9(3) 120.5(19) 120.6(19) 118.9(3) 131.4(3) 109.5(2) 106(2) 101(3) 114(3) 124.5(19) 107(3) 105(3) 102.3(19) 128(2) 114(3) 105.1(19) 104(3) 102(3) C25-C24-C29 C25-C24-H24 C29-C24-H24 C24-C25-C26 C24-C25-H25 C26-C25-H25 C27-C26-C25 C27-C26-H26 C25-C26-H26 C26-C27-C28 C26-C27-H27 C28-C27-H27 C29-C28-C27 C29-C28-H28 C27-C28-H28 C28-C29-C24 C28-C29-C30 C24-C29-C30 C29-C30-H30A C29-C30-H30B H30A-C30-H30B C29-C30-H30C H30A-C30-H30C H30B-C30-H30C C36-C31-C32 C36-C31-H31 C32-C31-H31 C33-C32-C31 C33-C32-H32 C31-C32-H32 120.2(4) 125(2) 115(2) 121.0(4) 120(2) 119(2) 118.9(4) 124(2) 117(2) 120.4(4) 124(2) 115(2) 121.1(4) 121(2) 117(2) 118.3(4) 121.4(4) 120.3(4) 111(2) 102(2) 118(3) 110(2) 112(3) 103(3) 103(2) 128.6 128.6 134(2) 112.8 112.8 C32-C33-C34 C32-C33-H33 C34-C33-H33 C33-C34-C35 C33-C34-H34 C35-C34-H34 C34-C35-C36 C34-C35-H35 C36-C35-H35 C31-C36-C37 C31-C36-C35 C37-C36-C35 C36-C37-H37A C36-C37-H37B H37A-C37-H37B C36-C37-H37C H37A-C37-H37C H37B-C37-H37C 124(3) 118.2 118.2 117(2) 121.7 121.7 116.3(14) 121.8 121.8 106.5(15) 126.2(13) 127.2(17) 109.5 109.5 109.5 109.5 109.5 109.5 346 a Cp is the centroid of atoms Cl, C2, C3, C4 and CS b Pln is the best plane through atoms Cl, C2, C3, C4 and CS Table 35. Crystal Data and Structure Analysis Details for TMSThpTaMe3. Empirical formula C26H47Si3Ta Formula weight 624.86 Crystallization solvent Diethyl ether Crystal habit prism Crystal size 0.31 X 0.26 X 0.23 mm Crystal color orange Data Collection Preliminary photograph(s) rotation Type of diffractometer Bruker SMART 1000 ccd Wavelength 0.71073 A MoKa Data collection temperature 98K Theta range for 7823 reflections used in lattice determination 2.4 to 28.5° a= 90° b=90° g=90° Unit cell dimensions a= 17.205(4) A b = 16.270(3) A c = 9.995(2) A Volume 2798.0(10) A3 z 4 Crystal system orthorhombic Space group Density (calculated) Pnma (#62) l.483g/cm3 F(000) 1272 Theta range for data collection 2.36 to 28.62° Completeness to theta = 28.62° 95.9 % Index ranges -22 £ h £ 22, -21 £ k £ 21, -13 £ 1 £ 13 Data collection scan type w scans at 4 fixed f values Reflections collected 34549 Independent reflections 3562 [Rint= 0.0385] Absorption coefficient 4.068mm-1 Absorption correction none Number of standards first scans recollected at end of runs Variation of standards within counting statistics 347 Structure Solution and Refinement Primary solution method direct methods Secondary solution method difference map Hydrogen placement calculated Refinement method full-matrix least-squares on F2 Data I restraints / parameters 3562 / 0 / 157 Treatment of hydrogen atoms not refined; Uiso's set at 120% Ueq of the attached atom Goodness-of-fit on F2 7.041 Final R indices [I>2s(I), 3358 reflections] Rl = 0.0556, wR2 = 0.1222 R indices (all data) Rl = 0.0592, wR2 = 0.1227 Type of weighting scheme used sigma Weighting scheme used 2 w=l/s2(Fo ) Max shift/ error 0.015 Average shift/ error 0.001 Largest diff. peak and hole 11.952 and -6.111 e.A-3 Programs Used Cell refinement Bruker SAINT v6.02 Data collection Bruker SMART v5.054 Data reduction Bruker SAINT v6.02 Structure solution SHELXS-97 (Sheldrick, 1990) Structure refinement SHELXL-97 (Sheldrick, 1997) Special Refinement Details Data for this material were previously collected on a CAD-4 diffractometer (PJC13); however the compound is light sensitive and there was a large decrease in the check reflections (>35%). For this dataset on the ccd, the terminated cap was cut from an orange prism and mounted on a glass fiber with Paratone-N oil. The ccd enclosure was covered in black plastic as a precaution. Four runs of data were collected with 20 second long, -0.3° wide O}-Scans at three values of <p (0, 120,240 and 0°) with the detector 5 cm (nominal) distant at a 0 of -28°. The initial cell for data reduction was calculated from just under 1000 reflections chosen from throughout the data frames. For data processing with SAINT v6.02, all defaults were used, except: box size optimization was enabled, periodic orientation matrix updating was disabled, the instrument error was set to zero, no Laue class integration restraints were used, the model profiles from all nine areas were blended, and for the post-integration global least squares refinement, no constraints were applied. No SADABS manipulations were employed. No decay correction was needed. 348 No reflections were specifically omitted from the final processed dataset; 1783 reflections were rejected, with 84 space group-absence violations and 28 inconsistent equivalents. Refinement of F2 was against all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F2, conventional R-factors (R) are based on F, with F set to zero for negative F2. 2 2 The threshold expression of F > 2cr( F ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. The molecule lies on a mirror plane. The t-butyl group is disordered across this plane and modeled with two orientations (50:50 by symmetry). (Similar disorder occurs in at least one isostructural compound.) The goodness-of-fit is extraordinarily high and there are many extremely large peaks in the final difference map; the three greater than 121 e-A-3 (11.95, -6.11 and -2.76) are all within 0.79 A of the Ta atom. Nonetheless, this is a reasonable structure as evidenced by the R-indices, displacement ellipsoids and geometric parameters. This was a strongly diffracting crystal [3358 of 3562 reflections greater than 2cr(I)] and the sigmas are not correct, especially for the intense reflections. Table 36. Bond lengths [A] and angles [0 ] for TMSThpTaMe3 ----------------------------------------------------C9A-H9C 2.131 Ta-Cp Ta ···Pln Ta-Cen Ta-C14 Ta-C15 Ta-Cl Ta-C2 Ta-C4 Ta-C3 Sil-Cl Sil-CS Sil-C7 Sil-C4 Si2-C9A Si2-C10 Si2-C3 Si2-C9B Cl-C2 Cl-Clw C2-C3 C2-H2 C4-C5 C4-C4w C5-C6 C5-Cll C6-H6 C7-H7A C7-H7B C7-H7C C8-H8A C8-H8B C8-H8C C9A-H9A C9A-H9B 2.126(3) 2.378 2.203(6) 2.211(9) 2.402(5) 2.461(5) 2.492(5) 2.538(8) 1.861(5) 1.864(7) 1.872(6) 1.874(6) 1.795(17) 1.833(14) 1.874(8) 1.915(15) 1.413(8) 1.459(10) 1.433(7) 0.9500 1.415(8) 1.489(10) 1.404(7) 1.524(7) 0.9500 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 C9B-H9D C9B-H9E C9B-H9F ClO-HlOA ClO-HlOB ClO-HlOC Cll-C12 Cll-C13 Cll-Hll C12-H12A C12-H12B C12-H12C C13-H13A C13-H13B C13-H13C C14-H14A C14-H14B C14-H14C C15-H15A C15-H15B Cp-Ta-C4 Cp-Ta-C14 Cp-Ta-C15 Cp-Ta-Cen Cen-Ta-C14 Cen-Ta-C15 C14r;i_Ta-C14 C14-Ta-C15 C15-Ta-C4w c14<i1-Ta-C4 C14-Ta-C4 C15-Ta-C4 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 1.526(8) 1.530(8) 1.0000 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9800 0.9613 0.9608 96.6 103.1 178.2 96.9 119.3 85.0 110.9(4) 75.9(2) 85.2(3) 135.5(2) 102.8(2) 85.2(3) 349 Cl-Sil-C8 Cl-Sil-C7 C8-Sil-C7 Cl-Sil-C4 C8-Sil-C4 C7-Sil-C4 C9A-Si2-C3 C10-Si2-C3 C3-Si2-C9Bw C9Am-Si2-Cl0 C10-Si2-C9B C9Aw-Si2-C9B C2-Cl-Cl 1;1 C2-Cl-Sil Clm-Cl-Sil Cl-C2-C3 Cl-C2-H2 C3-C2-H2 C2m-C3-C2 C2m-C3-Si2 C2-C3-Si2 C5-C4-C4w C5-C4-Sil C4 1;1-C4-Sil C5-C4-Ta cl0-C4-Ta Sil-C4-Ta C6-C5-C4 C6-C5-Cll C4-C5-Cll C5m-C6-C5 c5<i>-C6-H6 C5-C6-H6 Sil-C7-H7A Sil-C7-H7B H7A-C7-H7B Sil-C7-H7C H7A-C7-H7C H7B-C7-H7C Sil-C8-H8A Sil-C8-H8B H8A-C8-H8B Sil-C8-H8C H8A-C8-H8C H8B-C8-H8C 107.9(3) 115.5(3) 106.8(4) 93.5(2) 116.1(3) 116.7(3) 107.6(6) 113.4(5) 106.8(5) 109.9(11) 105.3(8) 113.8(12) 106.3(3) 124.5(4) 123.41(16) 112.0(5) 124.0 124.0 103.5(6) 128.1(3) 128.1(3) 106.1(3) 129.0(4) 122.62(17) 116.7(4) 72.62(12) 93.0(2) 109.6(5) 125.4(5) 125.0(5) 108.2(7) 125.9 125.9 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 Si2-C9A-H9A Si2-C9A-H9B H9A-C9A-H9B Si2-C9A-H9C H9A-C9A-H9C H9B-C9A-H9C Si2-C9B-H9D Si2-C9B-H9E H9D-C9B-H9E Si2-C9B-H9F H9D-C9B-H9F H9E-C9B-H9F Si2-Cl0-H10A Si2-Cl0-H10B Hl0A-ClO-HlOB Si2-Cl0-H10C HlOA-Cl0-HlOC HlOB-ClO-HlOC C5-Cll-C12 C5-Cll-C13 C12-Cll-C13 C5-Cll-Hll C12-Cll-Hll C13-Cll-Hll Cll-C12-H12A Cll-C12-H12B H12A-C12-H12B Cll-C12-H12C H12A-C12-H12C H12B-C12-H12C Cll-C13-H13A Cll-Cl3-H13B H13A-Cl3-H13B Cll-C13-H13C H13A-C13-H13C H13B-C13-H13C Ta-C14-Hl4A Ta-C14-H14B H14A-Cl4-H14B Ta-Cl4-H14C H14A-C14-H14C H14B-Cl4-H14C Ta-C15-H15A Ta-C15-H15B H15A-C15-H15B Symmetry transformations used to generate equivalent atoms: m x,-y+l/2,z 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 111.5(5) 112.7(5) 109.1(5) 107.8 107.8 107.8 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.5 109.8 109.3 109.5