Synthesis and Reactivity of Titanocene Methylene Complexes and Bis(η⁵-Cyclopentadienyl) Titanacyclobutenes Citation Meinhart, James Douglas (1987) Synthesis and Reactivity of Titanocene Methylene Complexes and Bis(η⁵-Cyclopentadienyl) Titanacyclobutenes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/16dt-2465. https://resolver.caltech.edu/CaltechTHESIS:10212019-165401033 Abstract Syntheses of several bis(η 5 -cyclopentadienyl) titanium methylene phosphine complexes are reported. The titanium methylene phosphine complexes are generated from themolysis of titanacyclobutanes in the presence of excess phosphine. Spectral data and reactivity are consistent with a methylene phosphine complex rather than an ylide complex. Bis(η 5 -cyclopentadienyl) titanacyclobutenes are readily synthesized by treatment of sources of "Cp 2 TiCH 2 " with disubstituted alkynes. A variety of stable titanacyclobutenes were synthesized containing aryl, alkyl, and etherial substituents. Titanacyclobutenes, unlike the related titanacyclobutanes, do not reform "Cp 2 TiCH 2 " thermally. Titanacyclobutenes insert carbon monoxide, forming an acyl intermediate which rearranges to a titanocene vinyl ketene complex. A trimethylphosphine adduct of one of the ketene complexes was characterized by x-ray diffraction techniques. The carbonylation mechanism involves insertion of carbon monoxide into the more accessible titanium-carbon bond, followed by intra-molecular attack of the vinyl group to the acyl. Insertion of t-butyl isocyanide into a titanacyclobutene yields a cyclic imino-acyl complex, which was also characterized by x-ray diffraction. The vinyl ketene complexes react with many unsaturated substrates (alkynes, ethylene, and aldehydes) to form new organotitanium species. Titanacyclobutenes react with ketones and aldehydes via 1,2-addition to yield titanium oxacyclohexenes. Aldehydes form both titanium-oxygen and titanium-carbon regioisomers. The organic ligand may be removed from the titanium to give homo-allylic alcohols in good yield. Nitriles also insert into titancyclobutenes to roduce titanium imidocyclohexenes. 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): Grubbs, Robert H. Thesis Committee: Dervan, Peter B. (chair) Grubbs, Robert H. Goddard, William A., III Bercaw, John E. Defense Date: 26 November 1986 Additional Information: Thesis title listed in 1987 commencement program varies from actual thesis: Synthesis and Reactivity of Titanocene Methylene Complexes and Bis(Cyclopentadienyl) Titanacyclobutenes. Funders: Funding Agency Grant Number Earl C. Anthony Fellowship UNSPECIFIED NSF UNSPECIFIED Record Number: CaltechTHESIS:10212019-165401033 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:10212019-165401033 DOI: 10.7907/16dt-2465 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 11837 Collection: CaltechTHESIS Deposited By: Mel Ray Deposited On: 22 Oct 2019 00:10 Last Modified: 16 Apr 2021 22:12 Thesis Files Preview PDF - Final Version See Usage Policy. 44MB Repository Staff Only: item control page

Synthesis and Reactivity of Titanocene Methylene Complexes and Bis(77 5 -Cyclopentadienyl) Titanacyclobutenes Thesis by Jam.es Douglas Meinhart In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy California Institute of Technology Pasadena, California 1987 (Submitted November 26, 1986) 11 © 1987 James Douglas Meinhart iii ACKNOWLEDGMENTS During my time at Caltech it has been my good fortune to be associated with a large number of very fine people. First among these is my advisor, Bob Grubbs, who fosters a superior environment for doing research. His willingness to delegate responsibility has provided an invaluable education. I owe a great deal to members of the Grubbs' research group, both past and present. Many thanks to those who took the time to discuss research, lend advice, or have a beer. Many thanks to Bob Waymouth, who managed early morning rounds of golf. Special thanks to the other NMR GLA's, Eric Anslyn and Dave Wheeler, who helped keep the instruments in excellent condition. I also want to thank the NMR users who took the time to learn something about the technique, treated the instruments gently, and didn't call me at 3 a.m. when they committed an "operator error." The x-ray crystallographic work in this thesis was done in collaboration with Dr. Bernard Santarsiero; my thanks for his expertise. I would also like to acknowledge an Earl C. Anthony fellowship from the California Institute of Technology and financial support from the National Science Foundation. Lastly, I thank my wife, Carol, to whom this thesis is dedicated. lV ABSTRACT Syntheses of several bis(77 5-cyclopentadienyl) titanium methylene phosphine complexes are reported. The titanium methylene phosphine complexes are generated from themolysis of titanacyclobutanes in the presence of excess phosphine. Spectral data and reactivity are consistent with a methylene phosphine complex rather than an ylide complex. Bis(77 5 -cyclopentadienyl) titanacyclobutenes are readily synthesized by treatment of sources of "Cp 2TiCH2" with disubstituted alkynes . . A variety of stable titanacyclobutenes were synthesized containing a.ryl, alkyl, and etherial substituents. Titanacyclobutenes, unlike the related titanacyclobutanes, do not reform "Cp2TiCH2" thermally. Titanacyclobutenes insert carbon monoxide, forming an acyl intermediate which rearranges to a titanocene vinyl ketene complex. A trimethylphosphine adduct of one of the ketene complexes was characterized by x-ray diffraction techniques. The carbonylation mechanism involves insertion of carbon monoxide into the more accessible titanium-carbon bond, followed by intra-molecular attack of the vinyl group to the acyl. Insertion oft-butyl isocyanide into a titanacyclobutene yields a cyclic imino-acyl complex, which was also characterized by x-ray diffraction. The vinyl ketene complexes react with many unsaturated substrates (alkynes, ethylene, and aldehydes) to form new organotitanium species. Titanacyclobutenes react with ketones and aldehydes via 1,2-addition to yield titanium oxacyclohexenes. Aldehydes form both titanium-oxygen and titaniumcarbon regioisomers. The organic ligand may be removed from the titanium to give homo-allylic alcohols in good yield. Nitriles also insert into titancyclobutenes to produce titanium imidocyclohexenes. v TABLE OF CONTENTS Page LIST OF TABLES . . vii LIST OF FIGURES AND SCHEMES . . . . . . . . . . . ; . . . . . . ix CHAPTER 1. Synthesis and Reactivity of Bis(77 5 -Cyclopentadienyl) Titanium Methylene Complexes 1 Introduction 2 Results 4 Discussion 9 Conclusions 13 Experimental Section 14 References . . . . . 20 CHAPTER 2. Synthesis of Bis(77 5 -Cyclopentadienyl) Titanacyclobutenes 23 Introduction 24 Results 27 Discussion 33 Conclusions 39 Experimental Section 40 References . . . . . 46 CHAPTER 3. Carbonylation of Bis(77 5 -Cyclopentadienyl) Titanacyclobutenes. Synthesis and Reactivity of Titanocene Vinyl Ketene Complexes 49 Introduction 50 Results 52 Vl Discussion . . 67 Conclusions 78 Experimental Section 79 References . . . . . 100 CHAPTER 4. Insertion of Carbon-Heteroatom Multiple Bonds into Bis(17 5 -Cyclopentadienyl) Titanacyclobutenes 104 Introduction 105 Results 107 Discussion 115 Conclusions 121 Experimental Section 122 References . . . . . 133 APPENDIX I. X-ray Structure Determination of Cp2 TiC4H20 (CsHs) (Si( CH3)3) (P (CH3)3) . . . . . . . . . . . 135 APPENDIX II. X-ray Structure Determination of Cp2TiCaH11N(CsHs)2 . . . . . . . · · · · · 148 vii LIST OF TABLES Page CHAPTER 1. Table 1. Phosphine Exchange Equilibrium Constants 5 Table 2. Selected NMR Data of Methylene Complexes 10 CHAPTER 3. Table 1. Titanocene Vinyl Ketene Trimethylphosphine Complexes . . . . . . . . . . . 53 Table 2. Selected Bond Lengths (A) and Angles (0 ) for 2b 72 Table 3. Selected Bond Lengths (A) and Angles ( 0 ) for 4a 74 CHAPTER 4. Table 1. Ketone Insertions into Titanacyclobutenes .... 108 . . . . 110 Table 2. Rate Constants and Activation Parameters for Acetone Insertion into 2a APPENDIX. I. (X-ray Diffraction Structural Data of 2b) Table 1. Summary of Crystal Data and Intensity Collection Information . . . . . . . . . . . . . 137 Table 2. Atom Coordinates (x10 5 ) and Ueq's (A 2 , x10 4 ) 138 Table 3. Bond Lengths (A) 139 Table 4. Bond Angles (0 ) 141 • Table 5. Gaussian Amplitudes ( x 104 ) 143 Table 6. Hydrogen Atom Coordinates (x10 4 ) and B's (A 2 , x10 4 ) 144 Table 7. Least-Squares Planes 145 Table 8. Torsion Angles (0 ) 147 • viii APPENDIX II. (X-ray Diffraction Structural Data of 4a) Table 1. Summary of Crystal Data and Intensity Collection Information . . . . . . . . . . . . . 150 Table 2. Atom Coordinates (x10 4 ) and B's and U's (A 2 , xl0 4 ) 151 Table 3. Hydrogen Atom Coordinates (x10 4 ) and B's (A 2 , x10 4 ) 153 Table 4. Bond Lengths (A) 155 Table 5. Bond Angles (0 ) • 157 Table 6. Torsion Angles (0 ) 159 Table 7. Least-Squares Planes 160 ix LIST OF FIGURES AND SCHEMES Page CHAPTER 1. Scheme 1. Reactivity of Titanacyclobutanes . . . . . . . . . . 3 CHAPTER 3. Scheme 1. Reactivity of Fischer Carbenes and Alkynes 51 Figure 1. ORTEP Drawing of 2b with Atom Labeling 54 Figure 2. ORTEP Drawing of 2b with Selected Bond Lengths and Angles . . . . . . . . 55 Figure 3. ORTEP Drawing of of 4a 57 Figure 4. ORTEP View of the Metallacycle Plane of 4a 58 Scheme 2. Carbonylation Mechanism of 2d 69 Scheme 3. Isomerization Mechanism of 7b 75 CHAPTER 4. Figure 1. Proposed Carbonyl Complexes of 2a . . . . . . . 117 Figure 2. Proposed Reaction Profile of Aldehyde and Ketone Insertion . . . . . . . . . . . . . 118 1 Chapter 1 Synthesis and Reactivity of Bis(17 5 -Cyclopentadienyl) Titanium Methylene Complexes 2 Introduction Transition-metal methylene or carbene complexes are of great experimental and theoretical interest. Metal-methylene complexes are implicated as intermediates in many important reactions, including olefin metathesis, 1 olefin 2 and alkyne polymerization, 3 cyclopropanation of olefins, 4 and methylenation of carbonyl compounds. 5 Surface-bound methylene species have been postulated to be intermediates in Fischer-Tropsch chemistry. 6 As models for these and other reactions, many bridging metal-methlene compounds have been synthesized and studied. 7 Many carbene complexes containing heteroatom substituents {"Fischer" carbenes) have been synthesized; their chemistry is quite different from methylene complexes. 8 In contrast, the chemistry of terminal methylene and alkylidene complexes is less developed. Terminal methylene complexes appear to be more reactive than their bridging analogues, and a lack of general synthetic methods has made systematic studies difficult. Only a few terminal methylene complexes are well-characterized, the most notable examples being Cp2Ta{CH2)CHa (W{CH2){PMea) 4 Cl)+ {CFaSOs)- 10 • Os{CH2)Cl{NO){P¢a)2 11 • 9 ' and Cp2Ta{CH2)H. 12 Reaction of titanium halides and alkyl aluminum compounds yields an active catalyst for ethylene polymerization. 13 Reinvestigation of this system by Tebbe, utilizing titanocene dichloride and trimethylaluminum, lead to the isolation of a soluble dimethylaluminum chloride-titanocene methylene complex (Tebbe's reagent, 1). 14 The Tebbe reagent demonstrated activity as a metathesis catalyst with terminal olefins and readily methylenated carbonyl compounds. 15 A titanocene methylene species is implicated as the active species. From this same system, Grubbs and coworkers successfuly isolated titanacyclobutane species by reaction of 1 with olefins in the presence of Lewis bases. 16 3 Titanacyclobutanes transfer methylene groups to carbonyl functionality, 5 ring-open polymerize strained olefins, 2 and form bridging methylene dimers 18 (Scheme 1). The existence of titanocene-methylene or a titanocene methylene-olefin complex is implicated by the reactivity and kinetics of titanacyclobutanes. 17 However, the nature of the methylene complex is not known. Scheme 1. Reactivity of Titanacyclobutanes Cp2 n(>( M = Ti, Zr, Rh, Pt This chapter addresses the formation, isolation, characterization and reactivity of titanocene-methylene phosphine complexes. These compounds provide another entry into titanocene-methylene chemistry and information about transition metalcarbon multiple bonding. 4 Results Preparation of Titanocene Methylene Phosphine Complexes Treatment of a solution 16d• 20 of ,8,,8-dimethyltitanacyclobutane, 2a, or ,8, ,8-methylpropyltitanacyclobutane, 2b, with excess trialkylphosphine (trimethyl, dimethylphenyl, or triethylphosphine) at room temperature yields the corresponding titanocene methylene phosphine complex, 3a-c, in equilibrium with the metallacycle (Equation 1). CH3 Cp 2 Ti/'V 0R' + + 2a: R'= CH 3 2b: R' = CH 2CH 2CH 3 (1) 3a: PR3 = PMe3 3b: P~ = PMe 2 Ph 3c: P~ ... PE1:3 If the olefin is removed from the reaction mixture by evacuation, the equilibrium can be shifted entirely to product. The phosphine methylene complexes are isolated as yellow-brown powders, extremely air- and moisture-sensitive. The complexes are quite soluble in aromatic solvents, moderately soluble in diethyl ether, and insoluble in pentane. The stability of the different phosphine complexes reflects the size of the phosphine.:n The stability order is PMe 3 > PMe 2 4> >> PEt3. The measured equilibria (Equation 2) for the different complexes is shown in Table 1. The trimethylphosphine complex is stable as a solid in the dry box at -40 ° C for months and in solution at room temperature for hours. The other phosphine complexes, 3b and 3c, are much less stable than 3a in solution. 5 + + (2) P1 = PMe3 , P2 = PMe 2 Ph P1 = PMe2 Ph, P2 = PE!a Table 1. Phosphine Exchange Equilibrium Constants Complex Equilibrium Ratio Equilibrium Constant (Keq) 3a~3b 3.5 ± 0.2: 1 0.13 ± 0.02 3b~3c 5.6 ± 0.3: 1 0.03 ± 0.01 The equilibrium constant for the initial reaction of phosphine with metallacyclobutane has also been determined ( Equation 3). Cp2 Ti~ + PMe 3 -Keq = 45 ± 10 2a /}CH2 CpzTi~ ' (3) + PMe3 ===< 3a The phosphine complexes 3a-c exhibit a characteristic low-field NMR resonance for the CH 2 group at 6 12.0. The CH 2 and the 17 5 -cyclopentadienyl ligands exhibit 31 P coupling of 6.8 Hz and 2.0 Hz, respectively. The methylene carbon atom 6 has a characteristic 13 C shift of 6 285 and a Jc-P of 30.3 Hz. The Jc-H coupling constant of the methylene carbon in 3a is 127 ± 1 Hz. The small Jc-H coupling constant of 3a prompted the synthesis of the H-D labeled methylene-phosphine complex 3d (Equation 4). The secondary 2 H isotope effect on the metallacycle cleavage produces a 2 : 1 mixture of 3a to 3d. 19 The NMR of 3d exhibits an upfield isotopic shift of 5.04 Hz for the methylene proton. No JH-D coupling was observed even with resolution enhancement. Infrared spectral analysis of 3d revealed a single new peak at 2160 cm- 1 . Cp 2 Ti A ' Cl , AIMe 2 + H D~ DMAP (4) 3d Reactivity of Titanocene Methylene Phosphine Complexes The reaction of several unsaturated substrates with the phosphine-methylene complexes was performed. The phosphine-methylene complexes react cleanly with olefins to regenerate titanacyclobutanes and with disubstituted acetylenes to form titanacyclobutenes (Equation 5). 7 ~Ph (5) 3a Treatment of a C1Ds solution of 3a (Equation 6) with CO yields upon warming from -80 ° C to room temperature a mixture of products. Two of the products are Cp2Ti(C0)2 (o 4.58) and Cp 2Ti(CO)(PMe 3) (o 4.62 d, Jc-P = 2 Hz). 22 A product identified as Cp2Ti(CH2CO)(PMe3) is observed and appears to be the major initial product. 23 The ketene complex decomposes in solution at room temperature; however, no NMR signals attributable to ketene or the ketene dimer are observed. Carbonylation of complex 3b gives similar results. co -80°C to RT (6) 3a Treatment of a C1Ds solution of 3a with C02 results is a rapid reaction at -80°C. The reaction is completed in a few minutes and produces a copious amount of yellow insoluble material, unidentifiable by NMR. The solutions of phosphine-methylene complexes upon standing at room tern- 8 perature yield mostly paramagnetic materials with some methylene dimer 4 (Equation 7). The thermolysis of 3b has been studied by K. Ott. 24 Thermolysis of the phosphine methylene complexes does not yield the same distribution of hydrocarbons as the titanacyclobutanes, 2, or the dimer, 4. While the dimer, 4, yields primarily methane, the phosphine complex 3b yields mostly ethane and little methane. (7) 4 3a Attempts to prepare adducts of Cp 2 TiCH 2 from other Lewis bases such as pyridine, trimethylphosphite, and trifiurophosphine have been unsuccessful. Reaction of the phosphine-methylene complex 3a with acetylene results in the formation of polyacetylene (Equation 8). No intermediate metallacyclobutenes were observed. n 3a HCCH ~n (8) 9 Discussion Titanacyclobutanes are in equilibrium with either a methylene-olefin complex or free Cp 2TiCH2; either may be trapped by a trialkylphosphine to yield a titanocene methylene phosphine complex 3a-c. Physical and chemical characterization of the phosphine-methylene complexes suggests the presence of a true methylene phosphine complex rather than an ylide complex (Equation 9). (9) 3a The stability of the complexes reflects the size and basicity of the phosphine as expected for a simple dative interaction. The phosphine ligands are quite labile and exchange rapidly in solution at room temperature. The NMR chemical shifts for the methylene ligand are noteworthy. The strong downfi.eld shift in both the 1 H NMR and the 13 C NMR spectra are characteristic of an early transition metal methylene complex. The carbon-hydrogen coupling constant of the methylene group (127 Hz) is extremely small for a formally sp 2 carbon atom. This small coupling may be attributed to an electronic effect caused by bonding to a very electropositive titanium. 25 Schrock has also observed a similar low coupling constant for CpTa(CH 3 )CH 2 (Jc-H = 132 Hz). 9 Pertinent NMR data of various methylene complexes are tabulated in Table 2. The carbon phosphorous coupling constant of the methylene group m 3a 10 Table 2. NMR Data of Selected Methylene Complexes CH2 Cp2 Tif' ' 1H 13 C Jc-H (Hz) JP-H (Hz) Jc-P (Hz) 12.12 285.9 127 6.8 31.7 0.78 47 -1.5 149 6.5 90.5 9.88 46 228 132 --0.22 -4.0 122 11. 7121 270 11.036 248 121 8.49 16 188 140 8. 72 18 235 126 12.06 28 306.9 111 2.50 9 83.5 137 PMe 3 (CH3)3P=CH2 CH2 Cp 2Ta( CH3 CH2 1Bu Cp2Zr) ' ' PPh 3 CH2 Cp2Zrf 4.8 14.6 7.3 26.6 PPh 3 Cp2Ti(",A1Me2 Cl Cp2 T i cTiCp2 c,,r, ' 4.1 PMe 3 CH3 Cp2TiO< CH3 11 (Jc-P = 31.7 Hz) is much less than the CH2PMe 3 ylide (Jc-P = 90.5 Hz). 26 The magnitude of the coupling constants, together with the chemical reactivity, support our assignment of 3a-c as phosphine methylene complexes rather than ylide complexes. Schwartz has reported 36 •27 a bis(17 5-cyclopentadienyl) zirconium methylenephosphine complex, 5, and a series of of bis(17 5 -cyclopentadienyl)zirconium phosphine-alkylidene complexes, 6. A substituted titanocene alkylidene-phosphine complex, 7, has also been isolated. 28 The existence of a substituted "Tebbe" derivative has been inferred from the reactivity of alkenyl aluminum compounds and titanocene dichloride. 20 •37 The physical characteristics and reactivity of these alkylidene complexes are consistent with the phosphine-methylene complexes 3a-c. 1 Bu CH 2 Cp 2 Zrf" ' PPh3 5 #CH Cp 2 Zr~ ' 6 PPh 3 c~~p Cp 2 Ti # H ' PMe3 7 The deuterium-labeled methylene complex, 3d, displayed a C-D stretch at 2160 cm - 1 • The calculated C-H frequency from this C-D stretch is 2944 cm - 1 . This frequency is consistent with normal C-H vibrations. If the C-H bonds were interacting with the metal center, the reduced C-H bond-order would be reflected in the stretching frequency. 38 The trimethylphosphine-methylene complex, 3a, reacts with carbon monoxide to yield a titanocene-ketene trimethylphosphine complex (Equation 4). The ti- tanocene ketene complexes are well studied, and the dimethylphenyl phosphine 12 complex is known. 23 The carbonylation most likely procedes through an unobserved Cp 2Ti(CH 2){CO) complex or a C,C bound ketene intermediate. The fate of the ketene and other organic fragments when the ketene complex decomposes to Cp 2Ti(C0)2 and Cp2Ti(CO)(PMe3) is not known. Straus has observed similar instability of the titanium ketene-phosphine complex. 23 Similar CO insertions into terminal methylene units to yield ketene complexes have also been observed in Mn, 29 Mo, 30 and W 31 systems. The reaction of carbon dioxide with the phosphine-methylene complex, 3a, is much more rapid than the carbonylation reaction. The formation of insoluble yellow precipitate is characteristic of titanocene-oxo polymer from methylenation reactions. The product of single methylene transfer to C0 2 would be ketene, CH 2 CO, which likely polymerizes in the presence of the titanocene-oxo product. The thermolysis data determined by Ott suggest that while the methylene complex usually reacts analogously to titanacyclobutanes, the phosphine ligand may influence the reactivity. The coordination of a phosphine increases electron density at the metal relative to either a titanacyclobutane or a methylene-olefin complex. The thermolysis data suggest that carbon-carbon coupling is a major decomposition path for 3b. 13 Conclusions A series of titanocene methylene-phosphine complexes has been isolated. The bonding is best described as a methylene-phosphine complex rather than an ylide complex. The complexes are quite reactive toward unsaturated substrates such as alkenes, alkynes, CO, and C02. The only distinction between the reactivty of methylene-phosphine complexes and titanacyclobutanes is the thermal decomposition. Phosphine-methylene complexes yield mostly C2 products, whereas the titanacyclobutanes or the methylene dimer yield mostly methane. This change in reactivity is attributed to the ability of the phosphine to enhance carbon-carbon coupling by electron donation to the metal. 14 Experimental Section General Considerations. All manipulations of air- and/or water-sensitive compounds were performed using standard high-vacuum or Schlenk techniques. Argon was purified by passage through columns of BASF R3-11 catalyst (Chemalog) and 4 A molecular sieves (Linde). Compounds were transferred and stored in a nitrogen-filled Vacuum Atmospheres glovebox, equipped with an M0-40-1 purification train, DK-3E Dri-Kool conditioner, and Dri-Cold freezer. Flash chromatography was performed by the procedure of Still et al., 33 using silica Woelm 32-63 (32-63 µm). Thin layer chromatography was performed on EM Reagents 0.25 mm silica gel 60-F plates and visualized with either iodine vapor or phosphomolybdic acid / ethanol spray. All reaction temperatures were measured externally. Materials. Toluene, diethylether, and tetrahydrofuran were stirred over CaH2, then transferred to purple sodium-benzophenone ketyl. Pentane and hexane were stirred over concentrated H 2S0 4 , washed with H 20, dried over CaH2, then transferred to purple sodium-benzophenone ketyl with tetraglyme. Dichloromethane was stirred over P 20 5 or CaH 2 and degassed by evacuation of freeze-pump-thaw cycles. Dried degassed solvents were vacuum-transferred into dry glass vessels equipped with Teflon valve closures and stored under argon. Benzened6, toluene-da, and tetrahydrofuran-d 8 (Cambridge Isotopes) were dried and vacuum-transferred from purple sodium-benzophenone ketyl. Dichloromethane-d 2 (Cambridge Isotopes and Norell, Inc.) was dried over CaH 2 or Na-Pb alloy and degassed by several freeze-pump-thaw cycles. Chloroform-d (Aldrich) was dried over 4 A molecular sieves. Tebbe reagent and bis(17 5 -cyclopentadienyl) titanacyclobutanes were prepared by the reported procedures. 34 Carbon monoxide (CP) and carbon dioxide (BoneDry) were obtained from Matheson Gas Co. Alkyl phosphines were purchased from 15 Strem Chemical Co. and degassed prior to use. Instrumentation. NMR spectra were recorded on a Varian EM-390 (90 MHz, 1H), JEOL FX-90Q (89.60 MHz, 1H; 22.53 MHZ, 13 C; 36.27 MHz 31 P), Varian XL-200 (200.3 MHz, 1H; 50.1 MHz, 13 C), JEOL GX-400 (399.65 MHz, 1H; 100.4 MHz, 13 C), or Bruker WM-500 (500.13 MHz, 1H). Chemical shifts are reported o , referenced to residual solvent signals (1 H: CsDs, o 7.15; C1Ds, o 2.09; THF-d 8 , o 3.58 or 1.73; CD 2 Ch, o 5.35; CDCL3, o 7.24; 13 C: CsDs, o 128.0; C 7 D 8 , o 20.9; THF-d 8 , o 61.4; CDCL3, o 77.0). Phosphorous-31 NMR data are referenced externally to 85% H 3P0 4 (positive o, low field). Data are reported in as follows: chemical shift, multiplicity (s=singlet, d=doublet, t=triplet, q=quartet, m=multiplet, br=broad), coupling constant (Hz), integration, and assignment. Difference NOE experiments were performed according to published procedures. 35 Gas chromatography analyses were performed on a Shimatzu GC-Mini-2 equipped with an SE-30 capillary column, flame-ionization detector, and a Hewlett-Packard 3390A integrator. Infrared spectra were recorded on a Beckman 4210, Shimatzu IR-435, or Perkin-Elmer 1310 spectrophotometer. m data are reported in reciprocal centimeters (cm- 1 ) and intensity (s=strong, m=medium, w=weak, sh=shoulder). Combustion analyses (C,H,N) were performed by the California Institute of Technology Analytical Services. Preparation of Cp2TiCH2 · PMe 3 , 3a. Trimethylphosphine (130µ.L, 1.27 mmol) was added to a stirred suspension of ,B, ,B-dimethyltitanacyclobutane (210 mg, 0.846 mmol) in 5 ml of diethylether at -20°C. The mixture was allowed to warm to room temperature under a partial vacuum. Within 10 minutes, the color changed from red to yellow-orange, and a yellow solid had begun to precipitate. After an additional 15 minutes, the volatiles 16 were removed to yield a yellow-brown powder, which was dried at -20 °C. The solid (180 mg, 64%) was stored in the drybox at -40 °C. The material was suitable for most uses without further purification. However, the complex may be recrystalized in poor yield from either diethylether or toluene/pentane cooling to -50 °C: 1 H NMR (90 MHz, C1Ds, -20°C) 6 12.12 (d, JP-H =6.8 Hz, 2H), 5.30 (d, JP-H =2.0 Hz, lOH), 0.72 (d, Jc-P =6.3 Hz, 9H). 13 C{1H} NMR (22.5 MHz, C 7 D 8 , -20°C) 6 285.9 (d, Jc-P =30.3 Hz), 100.6 (s), 20.6 (d, Jc-P =18.6 Hz). The Jc-H of the resonance at 6 285.9 was determined to be 127.2 ± 1.9 Hz by polarization transfer techniques. 32 31 P{1 H} NMR (36.3 MHz, C 7 D 8 , -20°C) 6 11.9 (s). IR (nujol, KBr, cm- 1 ) 1420 (m), 1300 (w), 1280 (m), 1125 (m), 1025 (m), 1010 (m), 950 (s), 935 (m.sh), 805 (m), 790 (s), 775 (m.sh), 740 (m), 665 (w). Anal. Calcd. for C 14 H 21 PTi: C, 62.69; H, 7.89. Found: C, 61.66; H, 7.03. Preparation of Cp2 TiCH2 · PMe2</>, 3b. Dimethylphosphine (64 µL, 0.46 mmol) was added via syringe to a well-stirred solution of .B, .B-dimethyltitanacyclobutane, 2, (104 mg, 0.42 mmol) in diethylether at -10°C. The solution was warmed to room temperature in 15 minutes with periodic opening of the flask to vacuum to remove the isobutylene. A color change from red to orange with the formation of a yellow flocculent precipitate was observed. The solvent was removed in vacuo to yield a yellow powder, which was washed with cold ( -50°C) pentane (2 x 2 ml) and dried in vacuo to yield 107 mg (0.32 mmol, 77%) of 3b: 1H NMR (90 MHz, C 7 D 8 , -20°C) 6 12.36 (d, JP-H =6.59, 2H), 7.07 (m, 5H), 5.39 (d, JP-H =2.2 Hz, lOH), 1.10 (d, JP-H =6.23 Hz, 6H). 13 C{ 1 H} NMR (22.5 MHz, C 7 D 8 , -20°C) 6 288.39 (d, Jc-P =31.13 Hz), 141.41, 131.49, 131.09, 127.51, 125.48, 101.18, 20.77 (d, Jc-P =20.14 Hz). 31 P{1H} NMR (36.3 MHz, C1Ds, -20°C) 6 25.77. IR (nujol, KBr, cm- 1 ) 1310 (m), 1278 (w), 1170 (w), 17 1157 (w), 1095 (w), 1070 (w), 1020 (m), 1012 (m), 970 (w), 940 (m), 902 (m), 840 (w), 793 (s), 739 (s), 695 (m). Preparation of Cp2 TiCH2 · PEta, Sc. Triethylphosphine (260 µL, 1.78 m.mol) was added via syringe to a well-stirred suspension of ,8,,8-dimethyltitanacyclobutane, 2, (111 mg, 0.45 m.mol) in 10 ml of pentane at -10°C. The solution was allowed to warm to room temperature with periodic opening to a vacuum to remove the isobutylene. The color changed from red to orange, and after 15 minutes, the solvent was removed in vacuo. The resulting yellow-brown powder was washed with-50°C pentane (2 x 1 ml) and dried in vacuo to yield 68 mg (0.22 m.mol, 49%) of the desired product contaminated with a small amount of starting material and the dimer, (Cp 2 TiCH 2 )2. 1H NMR (90 MHz, C1D 8 , -20°C) fJ 12.13 (d, JP-H =5.13 Hz, 2H), 5.33 (s, lOH), 1.2-0.4 (m, 15H) 13 C{1H} NMR (22.5 MHz, C D , -20°C) fJ 286.44 (d, Jc-P =27.5 Hz), 100.21 (s), 7 8 20.44 (d, Jc-P =12.82), 8.05 (s). 31 P{1H} NMR (36.3 MHz, C 7 D 8 , -20°C) fJ 38.97 IR (nujol, KBr, cm- 1 ) 1305 (w), 1150 (w), 1035 (w), 1020 (m), 983 (w), 890 (w), 805 (m.sh), 790 (s), 755{m). Phosphine Exchange Equilibrium Measurements. The samples were prepared in the drybox and capped with a septum. The reactant was dissolved in 400 µL of C5D5, and a known amount of the appropriate phosphine added via syringe. The equilibrium concentration was determined by both 1 H and 31 P NMR spectroscopy. The samples were allowed to equilibrate for 15 minutes in the NMR probe before measurement. The 31 P{1 H} NMR data were obtained with inverse gated decoupling to eliminate NOE effects. 18 Reaction of Cp2TiCH2 · PMes, 3a, with CO. A NMR tube was charged with 8 mg (0.030 mmol) of 3a in the dry box, attached to a tefion needle valve adapter and evacuated on the vacuum line. Approximately 400 µ.L of C 7 D 8 were condensed into the NMR tube. The NMR tube was cooled to 77 K; 80 torr (0.033 mmol) of CO introduced and the tube sealed. The solvent was thawed at -80°C and the reaction monitored in the NMR probe. As the probe temperature was raised to room temperature, several new signals appeared. These signals corresponded to Cp2Ti(C0)2 (8 4.56), Cp2Ti(CO)PMe 3 (8 4.62 (d, JP-H =2.4 Hz)), and Cp2Ti(CH2CO)PMe3 (8 5.15 (d, JP-H =2.4 Hz, lOH), 5.54 (s , lH), 3.87 (s, lH), the JP-H coupling to the 17 5 -cyclopentadienyl resonance at 8 5.15 was observed only below -20°C. Based on integration of the resonances versus the solvent only 50% of the starting phosphine complex resulted in identifiable products. The balance of the material formed a very broad NMR signal from 5 to 6 ppm. Reaction of Cp2TiCH2 · PMe2¢, 3b, with CO. An NMR tube was loaded with 9 mg (0.027 mmol) of 3b in the drybox, attached to a tefion needle valve adapter, and evacuated on the vacuum line. Approximately 400 µL of C 6 D 6 were condensed into the tube, the tube cooled to 77 K, 300 torr of CO introduced, and the tube sealed. The solvent was thawed at room temperature and the color changed from yellow-brown to red-orange. The sample darkened over several hours at room temperature. NMR analyses revealed the formation of Cp2Ti(C0)2 (8 4.56), Cp2Ti(CO)(PMe 2¢) (8 4.65 (d, J=2Hz)) and Cp2Ti(CH2CO) · PMe2¢ (8 5.26 (s), 4.01 (s); the other vinyl signal was obscured). From integration of the Cp resonances the yield of ketene complex was less than 20%. 19 Reaction of Cp2TiCH2 · PMea , 3a, with C02. An NMR tube was charged in the drybox with 9 mg (0.034 mmol) of 3a; the tube was attached to a teflon needle valve adapter and evacuated on a vacuum line. Approximately 400 µL of C1D 8 were condensed into the tube followed by 35 torr (0.037 mmol) of C0 2 (dried by sublimation at -78°C) and the tube sealed. As the solvent thawed at -80°C, the yellow solution turned turbid. The NMR spectrum was recorded at -80° C and revealed several Cp resonances, all much smaller than the solvent or trimethylphosphine resonances. The sample was warmed to -40°C and several more resonances appeared, although no resonances attributable to ketene dimer were observed. When the sample was removed from the NMR probe at-40°C, all of the organometallic material had precipitated as flocculent yellow solid, and the solution was pale orange. Reaction of Cp2TiCH2 · PMe2</>, 3b, with C02. An NMR tube was charged in the drybox with 14 mg (0.042 mmol) of 3b, the tube attached to a teflon needle valve adapter and evacuated on the vacuum line. Approximately 400 µL of C 7 D 8 followed by 100 torr of C0 2 were condensed into the tube and the tube sealed. As the solvent thawed at -50°C, the solution changed color to red-brown and a large amount of yellow precipitate formed. NMR analysis at room temperature revealed several small Cp resonances and a very broad signal - centered at 8 6.0. No resonances attributable to ketene dimer were observed. 20 References 1. (a.) Grubbs, R.H. Comprehensive Organometallic Chemistry, G. Wilkinson, Ed., Permagon Press: Oxford, 1982, Vol. 9, Chapter 54, pp. 499-552; (b) Grubbs, R.H. Prog. Inorg. Chem. 19'18, £-1, 1-50. 2. (a) Gilliom, L.R.; Grubbs, R.H. J. Am. Chem. Soc. 1986, 108, 733-42. (b) lvin, K.J.; Rooney, J.J.; Stewart, C.D.; Green, M.L.H.; Mehta!, R. J.C.S. Chem. Comm. 19'18, 604-6. 3. (a) Katz, T.J.; Lee, S.J. J. Am. Chem. Soc. 1980, 102, 422-4. {b) Dyke, A.F.; Knox, S.A.R.; Naish, P.J.; Taylor, G.E. J.C.S. Chem. Comm. 1980, 803-5. 4. (a) Brookhart, M.; Tucker, J.R.; Husk, G.R. J. Am. Chem. Soc. 1983, 105, 258-64. {b) Brandt, S.; Helquist, P.J. J. Am. Chem. Soc. 19'19, 101, 6473-5. 5. (a) Pine, S.H.; Zahler, R.; Evans, D.A.; Grubbs, R.H. J. Am. Chem. Soc. 1980, 102, 3270-2. {b) Clawson, L.E.; Buchwald, S.L.; Grubbs, R.H. Tet. Lett. 1984, 25, 5. 733-6 (c) Brown-Wensley, K.A.; Buchwald, S.L.; Cannizzo, L.F.; Clawson, L.E.; Ho, S.H.; Meinhart, J.D.; Stille, J.R.; Straus, D.A.; Grubbs, R.H. Pure. Appl. Chem. 1983, 55, 1733-44. {d) Cannizzo, L.F.; Grubbs, R.H. J. Org. Chem. 1985, 50, 2316-23. 6. (a) Brady, R.C.; Pettit, R. J. Am. Chem. Soc. 1980, 102, 6181-2. {b) Brady, R.C.; Pettit, R. J. Am. Chem. Soc. 1981, 109, 1287-9. 7. Herrmann, W.A. Adv. Organomet. Chem. 1982, £0, 159-263. 8. Dotz, K.H. Transition Metal Carbene Complexes, Verlag-Chemie: Deerfield Beach, Fl., 1983. 9. Schrock, R.R.; Sharp P.R. J. Am. Chem. Soc. 19'18, 100, 2389-99. 10. Holmes, S.J.; Schrock R.R. J. Am. Chem. Soc. 1981, 109, 4599-4600. 11. Hill, A.F.; Roper, W.R.; Waters, J.M.; Wright, A.H. J. Am. Chem. Soc. 1983, 21 105' 5939-40. 12. van Asselt, A.; Burger, B.J.; Gibson, J.E.; Bercaw, J.E. J. Am. Chem. Soc. 1986, 108' 5347-9. 13. (a) Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Angew. Chem. 1955, 67, 541-7. (b) Boor, Jr., J., Ziegler-Natta Polymerization, Academic Press: New York, 1979. 14. (a) Tebbe, F.N.; Parshall, G.W.; Reddy, G.S. J. Am. Chem. Soc. 1978, 100, 3611-3. (b) Klaubunde, U.; Tebbe, F.N.; Parshall, G.W.; Harlow, R.L. J. Mol. Cat. 1980, 8, 37-51. 15. Tebbe, F.N.; Parshall, G.W.; Ovenall, D.W. J. Am. Chem. Soc. 1979, 101, 5074-5. (b) Tebbe, F.N.; Harlow, R.L. J. Am. Chem. Soc. 1980, 102, 614951. (c) McKinney, R.J.; Tulip, T.H.; Thorn, D.L.; Coolbaugh, T.S.; Tebbe, F.N. J. Am. Chem. Soc. 1981, 109, 5584-6. 16. (a) Howard, T.R.; Lee, J.B.; Grubbs, R.H. J. Am. Chem. Soc. 1980, 102, 6876-8. (b) Lee, J.B.; Gajda, G.J.; Schaefer, W.P.; Howard, T.R.; Ikariya, T.; Straus, D.A.; Grubbs, R.H. J. Am. Chem. Soc. 1981, 109, 7358-61. (c) Straus, D.A.; Grubbs, R.H. J. Mol. Cat. 1985, £8, 9-25. (d) Straus, D.A.; Grubbs, R.H. Organometallics 1982, 1, 1658-61. 17. Anslyn, E.V.; Grubbs, R.H., Submitted for Publication. 18. Ott, K.C.; Grubbs, R.H. J. Am. Chem. Soc. 1981, 109, 5922-3. 19. (a) Upton, T.H.; Rappe, A.K. J. Am. Chem. Soc. 1986, 107, 1206. (b) Franci, M.M.; Pietro, W.J.; Hart, J.F.; Hehre, W.J. Organometallics 1983, 9, 281. and 815. 20. Stille, J.R.; Ph.D. Thesis, California Institute of Technology, 1986. 21. Tolman, C.A. Chem. Rev. 1977, 77, 313-48. 22. Kool, L.B.; Rausch, M.D.; Alt, H.G.; Herberhold, M.; Wolf, B.; Thewalt, U. 22 J. Organomet. Chem. 1985, £91, 159-69. 23. Straus, D.A., Ph.D. Thesis, California Institute of Technology, 1982. 24. Ott, K.C., Ph.D. Thesis, California Institute of Technology, 1982. 25. The Jc-H of Group IV metallocene methyl halide and dialkyl complexes have been correlated with electron density at the metal, Grubbs, R,H.; Straus, D.A.; Meinhart, J.D.; Finch, W.C.; Anslyn, E.V., unpublished results. 26. Schmidbaur, H.; Buchner, W.; Scheutzow, D. Chem. Ber. 1973, 106, 1251-5. 27. (a) Clift, S.M.; Schwartz,J. J. Am. Chem. Soc. 1984, 106, 8300. (b) Hartner, F.W.; Schwartz, J. J. Am. Chem. Soc. 1983, 105, 640. 28. Gilliom, L.R.; Grubbs, R.H. Organometallics 1986, 5, 721-4. 29. (a) Herrmann, W.A.; Plank, J. Angew. Chem. Int. Ed. Eng. 1978, 11, 525. (b) Herrmann, W.A.; Plank, J.; Ziegler, M.L.; Weidenhammer, K. J. Am. Chem. Soc. 1979, 101, 3133. 30. Messerle, L.; Curtis, M.D. J. Am. Chem. Soc. 1980, 10£, 7789. 31. Dorrer, B.; Fischer, E.O. Chem. Ber. 1974, 101, 2683. 32. Turner, C.J. Prog. NMR. Spec. 1984, 16, 311-70. 33. Still, W.C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, .19, 2923. 34. Ott, K.C.; deBoer, J.M.; Grubbs, R.H. Organometallics 1984, 9, 223-30. 35. Sanders, J.K.; Mersh, J.D. Prog. NMR. Spec. 1982, 15, 353-400. 36. Schwartz, J.; Gell, K.I. J. Organomet. Chem. 1980, 18-l, Cl-2. 37. Yoshida, T. Chem. Lett. 1982, 429-32. 38. Park, J.W.; MacKenzie, P.B.; Schaefer, W.P.; Grubbs, R.H. J. Am. Chem. Soc. 1986, 108, 6402-4. 23 Chapter 2 Synthesis of Bis(17 5 -Cyclopentadienyl) Titanacyclobutenes 24 Introduction Olefin metathesis, the process whereby the carbon-carbon double bonds of two olefins are exchanged, has been the subject of intense mechanistic investigation in many laboratories. 1 The accepted mechanism, originally proposed by Herisson and Chauvin, 2 is the interconversion of metal-alkylidenes and metallacyclobutanes (Equation 1). R1 LnM__/ + R2 / \ R3 R3 R1 -- L,M) . . R3 LnM__/ (1) R, R2 + I I R1 Although metallacyclobutanes and transition-metal alkylidenes are required intermediates for olefin metathesis, only recently have derivatives from catalytically active systems been isolated and structurally characterized. 3 •4 Metallacyclobutanealkylidene interconversion has also been studied theoretically. 8 A major advance in this area occurred when Tebbe isolated the dimethylaluminumchloride adduct of a bis(cyclopentadienyl) titanium carbene, 5 now known as "Tebbe reagent," 1. In the presence of Lewis bases, Tebbe reagent is a catalyst for the degenerate metathesis of terminal olefins. Tebbe reagent also reacts with disubstituted acetylenes to form titanocenecyclobutenes in good yield. 1 Following the discovery of titanacyclobutanes, Howard and Grubbs isolated the elusive titanacyclobutanes, 2, and demonstrated the existence of the crucial metallacyclobutanecarbene-olefin interconversion (Equation 2). 6 25 Cp2 Ti()-( (2) + 2 Tebbe and coworkers observed that titanacyclobutenes were not (with the exception of the bis(trimethylsilyl) derivative, 3c) catalysts for olefin metathesis. 1 Based on x-ray crystal structure analysis of three titanacyclobutenes, 3ac, they concluded that 3c was a catalyst due to a distortion toward a carbeneacetylene complex induced by the bis(trimethylsilyl) substituents. All three titanacyclobutenes which Tebbe characterized have a planar metallacycle ring and well-defined carbon-carbon single and double bonds. The bonding in metallacyclobutenes has been studied theoretically. 7 h Cp2 li y-- Si(CH 3 )s Ph 3a 3b 3c Metallacyclobutenes are a relatively rare class of compounds and are known for Ir9 , Rh 10 , Pt 11 , Fe 12 , Zr 13 , and Co 14 • The two most comm.on methods for metallacyclobutene synthesis are 1) addition of alkynes to metal alkylidenes, and 26 2) addition of unsaturated ligands to metal-alkyne complexes. General synthetic routes to metallacyclobutenes are not available. Due to the contrasting reactivity of titanacyclobutenes 3a and 3c, and the metathesis activity of 1 and 2, we desired to synthesize other titanacyclobutene derivatives and explore their chemistry. 27 Results Treatment of 1, with a stoichiometric amount of an internal acetylene in the presence of tetrahydrofuran yields the corresponding titanacyclobutene 3 in high yield (Equation 3). R Cp 2 Ti A ' Cl R' AIMe2 / Cp TIY-R' 2 THF {3) R 3a : R= R'=Ph 3b : R=Ph, R'=Tms 3c : R = R' = Tms Titanacyclobutenes are dark-red or purple crystalline solids with moderateto-high thermal stability. The diphenyl, 3a, phenyltrimethylsilyl, 3b, and bis(trimethylsilyl), 3c, titanacyclobutenes have been previously isolated and each structurally characterized by Tebbe et al .. 1 Utilizing the titanium metallacyclobutene methodology developed by Howard and Grubbs, 6 the formation of titanacyclobutenes has been extended to more reactive acetylenes. The titanacyclobutenes derived from 2-butyne, 3d, 3-hexyne, 3e, 1-phenyl-1-propyne, 3f, may be isolated in high yield (Equation 4) . Titanocenecyclobutene 3f was isolated as a 10:1 mixture of isomers, the major isomer having the phenyl group a to the metal. The regiochemistry was assigned by acidolysis and analysis of the organic product, NOE experiments, or comparison of NMR chemical shifts. The regiochemistry of addition of several unsymmetrical alkynes was explored. Addition of 4-methyl-2-pentyne (isopropyl methyl acetylene) to a solution of /3, /3- 28 Cp 2 Ti A ' Cl , R R' AIMe 2 Cp2 TiY---R' DMAP (4) R 3d : R = R' = CH3 3e : R = R' = CH 2CH3 3 f : R = Ph, R' = CH 3 dimethyltitanacyclobutane at room temperature yields two metallacyclobutenes in a 63:37 ratio. The major isomer has the isopropyl group f3 to the titanium. Reaction of 4,4-dimethyl-2-pentyne (t-butyl methyl acetylene) under the same conditions gave a >20:1 ratio of products, the major isomer having the t-butyl group at the /3-position (Equation 5) . Cp 2 Ti~ R CH 3 Cp2 Tiy---R + Cp2 Tiy---CH3 CH3 R R =CH(CH 3h 63 37 R = C(CH3)3 >95 <5 (5) Propargyl and homopropargyl ethers react cleanly with either 1 or 2 to yield the corresponding titanacyclobutene. Treatment of a solution of 2 with 1-methoxy2-butyne produced an equal mixture of two metallacyclobutenes. Reaction of the same alkyne with 1 was very slow in the absence of added pyridine, and many more by-products were observed. Similarly, treatment of 2 with 1-methoxy-3-pentyne yields two metallacyclobutenes in a 55:45 ratio, the major isomer bearing the larger 29 Cp2 Ti~ R CH3 Cp2 T i y - R + Cp 2 Tiy-CH 3 (6) CH 3 R R = CH 20CH3 50 50 R = CH 2CH 20CH 3 55 45 alkyl group at the /3-position (Equation 6). The tetrahydropyranyl ether of 2-butynol reacts cleanly with 2 to produce two isomeric metallacylobutenes in a 58:42 ratio. Use of 1 also yields the same metallacycles, although the reaction is not as clean (Equation 7). Cp2 Ti~ Cp 2 T i y - R 0 CH,/ D 0 + Cp 2 Tiy-CH 3 CH 3 R 58 42 (7) Treatment of 2 with 1-phenyl-3-methoxy propyne rapidly yields two metallacyclobutenes in a 6:1 ratio. The major isomer has the phenyl group at the a-position to the metal. However, these titanacyclobutenes are unstable and decompose in a solution within hours (Equation 8). Both 2-butynylacetate and methyl 2-butynoate react with 1 or 2 to yield methylene transfer products and only small amounts of metallacyclobutenes. The titanacyclobutenes react readily with HCl to yield the corresponding olefin 30 ~© 'ocH, Cp2Ti~ 86 14 with retention of stereochemistry of the double bond. Treatment of a diethylether suspension of 3a with 2 equivalents of anhydrous HCl produces the hydrocarbon, cis-1,2-diphenylpropene, in 58% yield (Equation 9). The geometry was confirmed by difference NOE experiments. HCI Cp2 Tiy---Ph (9) Ph 3a Treatment of titanacyclobutene 3a with two equivalents of bromine results in the formation of the corresponding 1,3 dibromide (Equation 10). In contrast to the chemistry of titanacyclobutanes, treatment of titanacyclobutenes {-40°C to room temperature) with iodine does not result in the clean formation of a new organotitanium complex or cyclopropenes. 15 The reaction is rapid, and several products are observed. The major identifiable organotitanium product is Cp2 Til2. 31 Cp Tiy---Ph 2 Ph CH 2 Br BryPh (10) Ph 3a The thermal chemistry of titanacyclobutenes was also examined. Titanacycles 3a, b, and f (all bearing at phenyl group alpha to the metal) are stable for days at 80°C in solution. The bis(trimethylsilyl) titanacyclobutene, 3c, decomposes on warming to 80 °C, liberating bis(trimethylsilyl) acetylene. Titanacyclobutenes bearing an alkyl group at the a-position, 3d and e, are not stable at 80° C and decompose within 12 hours to paramagnetic products. The thermolysis of 3d was performed in the presence of 2 equivalents of diphenylacetylene to trap any free methylidene or titanocene. After 24 hours at 80°C, the starting metallacycle had decomposed, and no titanacyclopentadiene was detected by NMR. The major organic product was diphenylethane. Terminal acetylenes react readily with the ,8, .B-dimethyltitanacyclobutane to yield monosubstituted titanacyclobutenes. The monosubstituted titanacy- clobutenes are unstable and decompose within several hours at room temperature. Treatment of 2 with phenyl, t-butyl, trimethylsilyl, or methyl acetylene results in the rapid formation of the corresponding metallacyclobutene (Equation 11). The formation of the monosubstituted titanacyclobutenes is not complete and some of the starting titanacyclobutane remains over when excess alkyne is used. The excess alkyne appears to form polyacetylene, possibly by protonation of the 32 R - H + (11) R=Ph R=CH 3 R = C(CH 3 b R=Si(CH 3 b metallacycles and the formation of titanocene acetylides. The regiochemistry of alkyne addition was not determined. Addition of olefin (t-butyl ethylene) to stabilize or trap carbene intermediates did not alter the reaction. 33 Discussion Titanacyclobutenes, 3, are formed rapidly upon treatment of either Tebbe reagent, 1, or titanacyclobutanes, 2, with disubstituted alkynes. The formation of titanacyclobutenes is irreversible under normal conditions. The exception is the bis(trimethylsilyl) titanacyclobutene, 3c, which shows a distortion in the solid state toward carbene-acetylene complex. 7 The basis for this distortion may be steric, as the trimethylsilyl groups are forced to be cis on the metallacycle ring. 23 Alternatively, Tebbe et al. and have attributed this distortion to an electronic effect induced by the absence of a phenyl ring. 7 However, formation of stable titanacyclobutenes from alkyl-substituted alkynes suggests that steric effects may play a large role. The presence of a phenyl group does direct the regiochemistry of the alkyne addition. Tebbe et al. have attributed this regiochemical control to a polarization of the orbitals of the metallacyclobutene fragment by the phenyl ring. In the crystal structures of titanacyclobutenes 3a and 3b, the a-phenyl ring is perpendicular to the metallacyclobutene plane, and the orbitals can effectively overlap with the titanium-carbon bond. Titanacyclobutenes do not react in a Wittig sense with carbonyl compounds as do titanacyclobutanes {the bis(trimethylsilyl) titanacyclobutene is the exception). The irreversible nature of titanacyclobutene formation from titanocene-methylene and an internal acetylene as compared to titanacyclobutanes is primarily due to the difference in bond strength between the first and second carbon-carbon 71'-bond. The incremental bond strength of the first carbon-carbon 71'-bond is 67 kcal mo1- 1 and the second carbon-carbon 71'-bond is 46 kcal mo1- 1 • 16 Thus, the titanacyclobutene is stabilized by -21 kcal mo1- 1 relative to a titanacyclobutane. This comparison is a rough approximation assuming similar electronic and steric environments. Be- 34 cause titanacyclobutanes are very sensitive to steric interactions, the actual energy difference may be different. 6 However, this calculated stabilization is consistent with the observed reactivity. Thermolysis of titanacyclobutenes does not result in formation of titanocene methylene except for the bis(trimethylsilyl) derivative. The presence of a phenyl group at the a-position enhances the thermal stability of the metallacycle. The a-CH 2 group of the metallacycle does not appear to participate in the thermal chemistry even though it is allylic. H ,8-hydrogens are present, as in metallacycles 3d and e, the compounds decompose at elevated temperatures. The products of the decomposition are presumably paramagnetic, low valent titanocene species due to the lack of NMR signals. Attempts to trap the titanocene or titanocene hydrides as titanacyclopentadienes were unsuccessful. 17 The hydrogenation reactivity of the thermolysis products is consistent with titanocene or titanium hydrides. 18 The mechanism of the decomposition probably occurs via a bond homolysis or exo-cyclic ,8-hydrogen elimination. Exo-cyclic ,8-elimination (Equation 12) would initially yield an allene titanocene hydride, which would be expected to decompose or react rapidly with another titanium center. Titanium-carbon bond homolysis could yield similar products. The marked thermal stability of 3a suggests that bond homolysis is not a dominant path because the phenyl substitutent is oriented to stablize the resulting radical. Exo-cyclic ,8-eliminations have been proposed in other systems 19 · Simple disubstituted alkynes display the anticipated steric bias, placing the largest group at the ,8-position of the metallacycle. Both isopropyl methyl and tbutyl methyl acetylene preferentially place the larger alkyl group at the ,8-position. Propargyl and homo-propargyl ethers did not display any large regiochemical bias. The coordination of an oxygen atom to the titanium-methylene might direct 35 ? (12) the alkyne regiochemistry (Equation 13). However, no exceptional selectivity was observed. The small amount of selectivity that was obtained is attributed to steric effects. Possible reasons for the lack of selectivity are 1) the alkyne is a much better donor than the ether and consequently, the ether does not direct the addition; 2) the geometry is not favorable for ether coordination; 3) prior coordination of ligands does not occur. Cp, T<X CH,--===~/ OCH3 (13) The titanium-methylene intermediate has formally 16-electron configuration. Addition of a 2-electron donor, either the alkyne or ether, achieves an 18-electron configuration. However, the coordination of both an alkyne and an ether would result in a 20-electron complex. The titanacyclobutene has a 16-electron configuration and could potentially coordinate another ligand. The titanium-methylene 36 species is a very high-energy species and has never been observed in its free state. Because of the exothermicity and irreversible nature of the reaction, the formation of titanacyclobutenes may have a very early transition state resulting in low selectivity. Similar results were found when the same reactions were performed starting from 1. If there is a strong interaction between the ether and the dimethylaluminum chloride fragment, some regioselectivity might be attained (Equation 14). The reactions with 1 were quite slow in the absence of pyridine or DMAP, several by-products were observed, and no regio-selectivity was noted. It is known from Tebbe's work that tetrahydrofuran is a sufficiently strong Lewis base to activate 1 by complexing the dimethylaluminum chloride. It appears that progargyl and tetrahydropyranyl ethers are not as reactive as THF toward 1. Cp 2 Ti A!Me 2 CI OCH3 A ' Cl ,, A1Me 2 CH 3-==;;;;;s:r----" Cp T. /'.:····AIMe 2 CI .\ '.\ 2 1 ' • \ CH 3 -.c:=----" OCH 3 - ~OCH 3 (l 4 ) Cp,li I CH3 The instability of the phenyl methoxymethyl titanacyclobutene was unexpected. One possible reason for its instability is the methoxy group f3 to the titanium-carbon bond. A /3-elimination (Equation 15) could form an intermediate containing both a titanium-<>xygen bond and a methylene cyclopropane derivative. The elimination could also be bimolecular involving two titanium centers. The formation of a titanium-<>xygen bond could provide a sufficient driving force for such an 37 elimination, and intermediates containing a methylene cyclopropane moiety would not be expected to be long-lived. ,B-elimination of halides has been observed in other titanocene systems. 22 Ti)A OCH3 Cp2 ? {15) Ph The reaction of terminal alkynes with titanocene methylene to form monosubstituted titanacyclobutenes was straightforward; however, the instability of the products was not expected. One possible explanation of the reactivity is to invoke a metallacyclobutene - vinyl carbene electrocyclic opening (Equation 16). This mechanism is proposed to occur in reactions of Group VI carbene complexes with alkynes 20 and some acetylene polymerizations. 21 However, this 2 + 2 electrocyclic ring opening has never been observed in titanocene systems. Alternatively, the alkyne could inititate the decomposition/polymerization via protonation of the metallacycle. It is also possible that the monosubstituted metallacyclobutenes are less stable because they are less sterically encumbered. The oxidative cleavage of the titanacyclobutenes with either HCl or bromine results in the formation of either the hydrocarbon or dibromide. The cleavage proceeds with retention of the double-bond stereochemistry as determined by NMR analysis. This is consistent with direct protonation of the titanium-carbon bonds. In contrast to titanacyclobutanes, neither titanocene alkenyl iodides or cyclo- 38 Cp Tiy-H 2 x (16) Ph propenes were observed upon treatment with iodine, yet several organotitanium products were observed. No cyclopropene was detected by NMR, and it is unlikely that it would be stable in the presence of iodine. Although the two different titanium-carbon bonds of the titanacyclobutanes might cleave at different rates, no differentiation was observed upon reaction with one equivalent of iodine at low temperature. The iodine may attack the double bond of the metallacyclobutene rmg. 39 Conclusions Several new bis(77 5 -cyclopentadienyl)titanacyclobutenes have been isolated. The regiochemistry of alkyne addition is related to both steric and electronic factors. The larger substituent on the alkyne prefers to occupy the ,8-position of the metallacycle, and aromatic substituents prefer to bond to the a-position when present. Placement of ether functionality on the alkyne did not inhibit formation of titanacyclobutenes; however, control of the metallacyle regiochemistry was not observed. Titanacyclobutenes containing aliphatic substituents on the metallacycle were thermally unstable, decomposing via ,8--elimination to titanium hydrides. Similar titanacycles possessing aromatic groups were very thermally stable. 40 Experimental Section See Chapter 1 for General Experimental Considerations and Instrumentation. Materials. Tebbe reagent, 1, titanacyclobutanes, 2, and titanacyclobutenes, 3a, b, and c, were synthesized by published procedures. 6 Diphenyl acetylene and bis(trimethylsilyl) acetylene were obtained from Aldrich Chemical Co. Other alkynes were obtained from Farchan Laboratories. Alkyne derivatives were synthesized by standard procedures. 24 Preparation of Dimethyltitanocenecyclobutene, 3d. To a well-stirred solution of Tebbe reagent (5.00 g (90%), 15.8 mmol) in 20 ml of CH 2 Ch cooled to -20°C was added 2-butyne (2.0 ml, 25.5 mmol) followed by 4-dimethylaminopyridine (DMAP) (2.15 g., 17.6 mmol). The mixture was stirred at -20°C for 15 minutes, and then warmed to 0°C for 15 minutes. The solution was added dropwise via cannula to 200 ml of stirred pentane at 0°C. The dimethylaluminumchloride - DMAP adduct was removed by schlenk filtration and the filtrate concentrated in vacuo at room temperature to yield a red solid. The material was dissolved in the minimum volumes of ether (30 ml) at room temperature, filtered and crystallized at -50°C. The mother liquor was removed via cannula, the crystals washed with cold pentane and dried in vacuo to yield 2.4 g (9.74 mmol, 62%) of the product. Although the metallacycle appeared to be quite stable at room temperature, it was stored in a -40°C freezer: 1 H NMR (90 MHz, C 6 Ds) 8 5.49 (s, lOH); 3.21 (q of d, J=0.7, 2.1 Hz, 2H); 2.13 (t of d, J=0.7, 2.1 Hz, 3H); 1.51 (d of d, J=0.7, 0.7 Hz, 3H) 1 H NMR (90 MHz, THF-d 8 ) 8 5.71 (s, lOH); 3.01 (hrs, 2H); 2.12 (hrs, 3H); 1.34 (br s, 3H). 13 C{1 H} NMR (22.5 MHz, C 6 D 6 ) 8 213.3, 110.2 (Cp), 88.1, 79.8 (CH 2 ), 21.7 (CH 3 ), 14.2 (CH 3 ). IR (KBr, cm- 1 ) 3100 (w), 3075 (w), 2940 (m), 2900 (m), 1440 (m), 1362 (m), 1050 (s), 802 (s). Anal. 41 Calcd. for C 1 sH 18 Ti: C, 73.18; H, 7.37. Found: C, 72.99; H, 7.18. Preparation of Diethyltitanocenecyclobutene, 3e. To a well-stirred solution of Tebbe reagent, 1, (3.00 g (. . . . 93%), 9.8 mmol) in 15 ml of CH 2 Cl 2 at -20°C was added 3-hexyne (1.1 ml, 10.0 mmol) followed by DMAP (1.29 g, 10.5 mmol). The mixture was stirred at -20°C for 10 minutes, warmed to room temperature over the course· of 20 minutes, and then cooled to -20°C. The mixture was added dropwise to 150 ml of stirred pentane at -20°C. The precipitate was removed by schlenk filtration and the filtrate concentrated in vacuo to yield a sticky red solid. The solid was extracted with 20 ml of pentane, the extract filtered and cooled to -50°C to deposit the product as dark red crystals. The product was isolated by removal of the mother liquor at -50°C and dried in vacuo to yield 1.22 g (4.45 mmol, 45%): 1 H NMR (90 MHz, C 6 D 6 ) fJ 5.53 (s, lOH); 3.30 (t, J=l.9 Hz, 2H); 2.53 (q oft, J=7.5, 1.9 Hz, 2H); 2.00 (q, J=7.5, 2H); 1.04 (t, J=7.5, 3H); 0.92 (t, 7.5, 3H). Difference NOE experiments at 500 MHz: irradiation of fJ 3.30 enhances fJ 2.00 , 0.92; irradiation of fJ 2.53 enhances fJ 2.00, 1.04; irradiation of fJ 2.53 enhances fJ 2.00, 1.04, but not fJ 3.30. 13 C{1 H} NMR (22.5 MHz, C 6 D 6 ) fJ 220.88, 109.93 (Cp), 92.00, 77.57, 29.35, 22.46, 16.03, 12.58. IR (KBr, cm- 1 ) 3100 (w), 2900 (w), 2850 (w), 1440 (m), 1360 (m), 1008 (s). Anal. Calcd. for C 11H 22 Ti: C, 74.45; H, 8.08. Found: C, 73.86; H, 7.88. Preparation of 2-phenyl-3-methyl titanocenecyclobutene, 3f. To a well-stirred solution of Tebbe reagent, 1 (3.00 g (.....,93%), 9.8 mmol) in 15 ml CH 2 Ch at -20°C was added 1-phenylpropyne (1.2 ml, 9.8 mmol) followed by DMAP (1.29 g., 10.5 mmol). The mixture was stirred at -20°C for 15 minutes, warmed to 0°C for 15 minutes, then added dropwise via cannula to 150 ml of stirred pentane at -20°C. The precipitate was removed by schlenk filtration and the filtrate 42 concentrated in vacuo to yield a soft, dark solid. The solid was extracted with 60 ml of hexane, the extract filtered and cooled to -S0°C to yield 1.62 g (S.2S kmmol, S5%) of the product as a dark red powder. Alternatively, the filtrate may be extracted with diethylether (8 ml), the extract filtered, layered with an equal volume of pentane and cooled to -S0°C to yield 1.8S g (6.00 mmol, 63%) of the product as a soft, dark-red solid. 1 H NMR (90 MHz, C6D6) 8 7.15 (m, SH), S.S8 (s, lOH), 3.28 (s, 2H), 1.60 (s, 3H). Occasionally, a small amount of the other regioisomer was observed: 1 H NMR (90 MHz, C 6D 6 7.1S (m, SH), S.S6 (s, lOH), 3.39 (q, J=2.0 Hz, 2H), 2.22 (t, J=2.0 Hz, 3H). Major isomer: 13 C{1H} NMR (SO MHz, C D ) 8) 8 210.18, 147.63, 128.27 12S.7S, 124.44, 111.33, 6 6 94.3S, 79.9S, 16.80. IR (KBr, cm- 1 ) 3050 (w), 2920 (m), 2870 (s), 1594 (s), 1472 (m), 1010 (s), 798 (s). Reaction of ,8, ,8-dimethyltitanacyclobutane with 4-methyl-2-pentyne. To a solution of ,8, ,8-dimethyltitanacyclobutane (26 mg, 0.105 mmol) dissolved in 400 µL of C 6 D 6 in an NMR tube was added 4-methyl-2-pentyne (12 µL, 0.105 mmol) via syringe. The solution was allowed to warm to room temperature and the NMR spectrum recorded. Two isomeric titanacyclobutenes were formed in a 63:37 ratio. Major product: 1 H NMR (400 MHz, C 6 D 6 ) 8 S.491 (s, lOH), 3.095 (br q, J=l.95 Hz, 2H), 2.741 (septet, J=6.8 Hz, lH), 2.101 (t, J=l.9S Hz, 3H), 0.887 (d, J=6.8 Hz, 6H). Minor product: 1 H NMR (400 MHz, C 6 D 6 ) 8 5.554 (s, lOH), 3.306 (s, 3H), 2.932 (septet, J=6.8 Hz, lH), 1.517 (s, 3H), 1.04S (d, J=6.8 Hz, 6H). Reaction of ,8,,8-dimethyltitanacyclobutane with 4,4-dimethyl-2-pentyne. To a solution of ,8, ,8-dimethyltitanacyclobutane (26 mg, 0.105 mmol) dissolved in 400 µL of CaD 6 in an NMR tube was added 4,4-dimethyl-2-pentyne (14 µL, O.lOS 43 mmol) via syringe. The solution was allowed to warm to room temperature and the NMR spectrum recorded. Only one titanacyclobutene was formed. 1 H NMR (400 MHz, C6D 6) 6 5.S44 (s, lOH), 3.088 (q, J=l.95 Hz, 2H), 2.158 (t, J=l.9S, 3H), 1.087 (s, 9H). Reaction of ,8,,8-dimethyltitanacyclobutane with 1-methoxy-2-butyne. To a solution of ,8,,8-dimethyltitanacyclobutane (20 mg, 0.081 mmol) dissolved in 400 µL of C6D6 in an NMR tube was added 1-methoxy-2-butyne (10 µL, 0.087 mmol) via syringe. The solution was warmed to room temperature and the NMR spectrum recorded. Two isomeric titanacylobutenes were formed in nearly equal amounts. 2-Methyl isomer 1 H NMR (90 MHz, C6D6) 6 S.67 (s, lOH), 4.24 (br s, 2H), 3.38 (br s, 2H), 3.18 (s, 3H), 1.47 (s, 3H); 3-methyl isomer 1 H NMR (90 MHz, C6D6) 6 5.49 (s, !OH), 3.89 (s, 2H), 3.10 (s, 3H), 3.05 (br s, 2H), 2.19 (br s, 3H). Reaction of ,8, ,8-dimethyltitanacyclobutane with 1-methoxy-3-pentyne. To a solution of ,8,,8-dimethyltitanacyclobutane (42 mg, 0.169 mmol) dissolved in 400 µL of C6D 6 in an NMR tube was added 1-methoxy-3-pentyne via syringe. The solution was warmed to room temperature and the NMR spectrum recorded. Two isomeric titanacyclobutenes were found in nearly equal amounts; however, complete assignment of the spectrum was not possible due to overlapping peaks. Partial NMR data: 1 H NMR (90 MHz, C6D 6) 6 S.S5 (s, SH, Cp), S.53 (s, SH, Cp), 3.29 (m), 3.19, 3.13 (s, 3H, OCH 3 ), 2.81 (m), 2.26 (m), 2.14 (t, 3H, CH 3 ), 1.48 (s, 3H, CH3) Reaction of ,8,,8-dimethyltitanacyclobutane with tetrahydropyranyl 2butynyl ether. To a solution of ,8, ,8-dimethyltitanacyclobutane (32 mg, 0.123 mmol) dissolved 44 in 400 µL of C6 D 6 in an NMR tube was added tetrahydropyranyl ether of 2-butynol (22 µL, 0.128 mmol) via syringe. The solution was warmed to room temperature and the NMR spectrum recorded. Two metallacyclobutenes were formed in a 58:42 ratio; however, the spectrum was not assigned due to overlapping resonances. Partial NMR data: 1 H NMR (90 MHz, C 6 D 6 ) 8 5.70, 5.68, (major Cp), 5.52, 5.50 (minor Cp), 4.25 (m), 4.20 (m), 3.73 (m), 3.29 (m), 3.05 (hrs), 2.25 (t), 1.47 (s), 1.29 (hr m), 0.73 (s) . Acidolysis of metallacyclobutene 2a. To a stirred suspension of diphenyl metallacyclobutene (205 mg, 0.554 mmol) in 5 ml of ether cooled to 0°C was added anhydrous HCl gas (30 ml, 1.4 mmol) via syringe. Immediate precipitation of Cp 2 TiC1 2 was observed and the mixture was warmed to room temperature. The mixture was filtered through a frit and the filtrate concentrated at reduced pressure to yield 112 mg of an oil. The material was flashed through a 1-inch plug of silica gel with petroleum ether to yield 62.5 mg (58%) of cis-1,2-diphenyl propene as a white crystalline solid. 1 H NMR (400 MHz, CDCL3) 8 7.25 (m, 3H), 7.19 (m, 2H), 7.07 (m, 3H), 6.94 (m, 2H), 6.47 (br s, lH), 2.20 (d, J=l.5 Hz, 3H). Different NOE experiments: irradiation of 8 6.47 enhances 8 2.20, 6.94; irradiation of 8 2.20 enhances 8 6.47. Bromination of metallacycle 2a. To a stirred suspension of diphenyltitanacyclobutene, 3a (200 mg, 0.540 mmol) in 2 ml of diethyl ether cooled to 0°C was added bromine (56 µL, 1.09 mmol) via syringe. The mixture warmed to room temperature, filtered through a 1-inch plug with silica gel with pet ether, and the filtrate concentrated at reduced pressure to yield 121 mg of a clear oil. 1 H NMR (90 MHz, CDCL 3) 8 7.41-7.07 (m, !OH), 4.60 (s, 2H). Some of the monobromides were also observed, 8 5.95 and 2.40, due to HBr 45 contamination of the Br2. The material turned black after several days at room temperature even when protected from light. 46 References 1. (a) Grubbs, R.H. Comprehensive Organometallic Chemistry, G. Wilkinson, Ed., Permagon Press: Oxford, 1982, Vol. 9, Chapter 54, pp. 499-552. (b) Grubbs R.H. Prog. Inorg. Chem. 1978, 24, 1-50.. 2. Herisson, J.L.; Chauvin, Y. Makromol. Chem. 1970, 141, 161. 3. Schaverien, C.J.; Dewan, J.C.; Schrock, R.R. J. Am. Chem. Soc. 1986, 108, 2771-3. 4. Wallace, K.C.; Dewan, J.C.; Schrock, R.R. J. Am. Chem. Soc. 1986, 5, 2162-4. 5. (a) Tebbe, F.N.; Parshall, G.W.; Reddy, G.S. J. Am. Chem. Soc. 1978, 100, 3611-3. (b) Klaubunde, U.; Tebbe, F.N.; Parshall, G.W.; Harlow, R.J. J. Mol. Cat. 1980, 8, 37-50. 6. (a) Howard, T.R.; Lee, J.B.; Grubbs, R.H. J. Am. Chem. Soc. 1980, 102, 6876-8. (b) Lee, J.B.; Gajda, G.J.; Schaefer, W.P.; Howard, T.R.; Ikariya, T.; Straus, D.A.; Grubbs, R.H. J. Am. Chem. Soc. 1981, 109, 7358-61. (c) Straus, D.A.; Grubbs, R.H. J. Mol. Cat. 1985, 28, 9-25. (d) Straus, D.A.; Grubbs, R.H. Organometallics 1982, 1, 1658-61. 7. (a) Tebbe, F.N; Parshall, G.W.; Ovenall, D.W. J. Am. Chem. Soc. 1979, 101, 5074-5. (b) Tebbe, F.N.; Harlow, R.L. J. Am. Chem. Soc. 1980, 102, 614951. (c) McKinney, R.J.; Tulip, T.H.; Thorn, T.H.; Coolbaugh, T.S.; Tebbe, F.N. J. Am. Chem. Soc. 1981, 109, 5584-6. 8. (a) Upton, T.H.; Rappe, A.K. J. Am. Chem. Soc. 1985, 107, 1206. (b) Eisenstein, O.; Hoffmann, R.; Rossi, A.R. J. Am. Chem. Soc. 1981, 109, 5582-4. 9. Calabrese, J.C.; Roe, D.C.; Thorn, D.L.; Tulip, T.H. Organometallics 1984, 9' 1223-30. 47 10. Bianchini, C.; Mealli, C.; Meli, A.; Sabat, M. Organometallics 1985, ,t, 4212;. Bianchini, C.; Mealli, C.; Meli, A.; Sabat, M.; Silvestre, J .; Hoffmann, R. Organometallics 1986, 5, 1733-41. 11. Forcolin, S.; Pellizer, G.; Graziani, M.; Lenarda, M.; Ganzerla, R. J. Organomet. Chem. 1980, 19,t, 203-9. 12. Mathew, M.; Palenik, G.J.; Carty, A.J.; Paik, H.N. J.C.S. Chem. Comm. 1974, 25-6. 13. deBoer, H.J.R.; Akkermann, O.S.; Bickelhaupt, F.; Erker, G.; Czisch, P.; Mynott, R.; Wallis, J.M.; Kruger, C. Angew. Chem. Int. Ed. Eng. 25, 2986' 639-40. 14. Wakatuski, Y.; Miya, S.; Ikuta, S.; Yamazaki, H. J.C.S. Chem. Comm. 1985, 35-7. 15. Ho, S.C.H.; Straus, D.A.; Grubbs, R.H. J. Am. Chem. Soc. 1984, 106, 1533-4. 16. Lowery, T.H. and Richardson, K.S., Mechanism and Theory in Organic Chemistry, Harper & Row: New York, 1981. 17. Wailes, P.C.; Coutts, R.S.P.; Weigold, H., Organometallic Chemistry of Titanium, Zirconium, and Hafnium, Academic Press: New York, 1974. 18. Pez, G.P.; Armor, J.N. Adv. Organomet. Chem. 1981, 19, 1-50. 19. (a) McDermott, J.X.; White, J.F.; Whitesides, G.M. J. Am. Chem. Soc. 1976, 98, 6521-8. (b} Schwartz, J.; Hart, D.W.; McGiffert, B. J. Am. Chem. Soc. 1974, 96, 5613-4. (c) Bottrill, M.; Green, M. J. Am. Chem. Soc. 1977, 99, 5795-6. 20. (a) Dotz, K.H. Pure. Appl. Chem. 1983, 55, 1689-1706. (b) Wulff, W.D.; Tang, P-C. J. Am. Chem. Soc. 1984, 106, 434-6. (c) Semmelhack, M.F.; Tamura, R.; Schnatter, W.; Springer, J. J. Am. Chem. Soc. 1984, 106, 48 5363-4. 21. Katz, T.J.; Sivavec, T.M. J. Am. Chem. Soc. 1985, 107, 737-8. 22. Straus, D.A., Ph.D. Thesis, California Institute of Technology, 1982. 23. (a) Sakuri, H.; Tobita, H.; Nakadaira, Y. Chem. Lett. 1982, 1251-4. (b) Ermer, O.; Lifson, S. Tetrahedron 1974, 90, 2425-9. 24. Brandsma, L., Preparative Acetylenic Chemistry, Elsevier: Amsterdam, 1971. 49 Chapter 3 Carbonylation of Bis(ry 5 -Cyclopentadienyl) Titanacyclobutenes. Synthesis and Reactivity of Titanocene Vinyl Ketene Complexes 50 Introduction Mediation of complex organic transformations by organometallic catalysts and reagents is an important area of organic chemistry. Incorporation of small organic molecules by organometallic catalysts into larger more complex structures has prompted a great deal of study. 1 Potential regio- and stereoselectivity by the appropriate metal-ligand combinations has also attracted the interest of both organic and inorganic chemists. In particular, "Fischer" carbene complexes of Cr and Fe react with a variety of alkynes and carbon monoxide to form hydroquinones, 2 napthols, 2 napthoquinones, 3 or pyrones 4 and with imines to yield ,B-lactams 5 (Scheme 1). The mechanism of these complex tranformations have yet to be determined, and further understanding will provide better insight into the scope and limitations of this reaction. Several proposed mechanisms suggest the formation of a metallacyclobutene complex derived from the carbene and the alkyne, followed by carbon monoxide insertion and rearrangement. 2 •4 However, no metallacyclobutenes or acyl complexes have been isolated and characterized from these systems. One report of trapping experiments suggests vinyl ketenes are intermediates, 6 and a vinyl ketene has been isolated and structurally characterized as a Cr arene complex. 7 In light of the complexity and potential utility of these annulation reactions, and our long-standing interest in titanocene-methylene chemistry, carbonylation of the titanacyclobutene system has been investigated. 26 51 Scheme 1. Reactivity of Fischer Carbenes and Alkynes OH OCH 3 Ph Ph CH3 (C0) 5 Cr ~ CH3 OCH3 Et Et Ph~OMe Et--==~- Et 0 OEt + (C0) 4 Fe=< co Ph Ph Ph 0 EtO ~ Ph OMe OMe (C0) 5 Cr=< CH3 H + Ph >=N;- CH3 hv Ph H,cKH 0 CH3 52 Results Synthesis of Titanocene Vinyl Ketene Complexes Treatment of a toluene solution of titanacyclobutene, 1, with carbon monoxide in the presence of 1 equivalent of trimethylphosphine (Equation 1) produces 9 the titanium vinyl ketene complex, 2. Cp TiY-R' co 2 R R 1a R = R'= Ph 1b R=Ph, R'=TMS 1c R=R'=TMS 1d R= R'=CH 3 1e R = R' = CH 2 CH3 (1) R' The carbonylation proceeds with a variety of titanacyclobutenes to yield the corresponding ketene complex in good yield, Table 1. The bis(trimethylsilyl) titanacyclobutene, lf, does not react to yield an analogous product even under forcing conditions (80 °C, 3 days). 10 The use of 13 C-enriched CO (90% 13 C), followed by 13 C NMR analysis shows exclusive incorporation of the 13 C label at the metalbound ketene carbon. In the absence of a Lewis base, the carbonylation prodeeds to produce a sparingly soluble, oligomeric ketene adduct, 3, which may be dissolved by the addition of a ligand such as trimethylphosphine, pyridine, or THF. 9 h The carbonylation and rearrangement is not reversible on prolonged heating. Exhaustive carbonylation at room temperature leads to the formation of paramagnetic products and a small amount of free vinyl ketene. Crystals of 2b suitable for an x-ray diffraction analysis were obtained and the refined structure is shown in Figures 1 and 2. 11 Details of the data collection and 53 Table 1. Titanocene - Vinyl Ketene Trimethylphosphine Complexes Compound R R' Yield (%) 2a <I> <I> 82 2b <I> TMS 92 2c <I> CH3 80 2d CH3 CH3 77 2e CH2CHa CH2CH3 70 refinement are in Appendix 1. Ketene complexes 2c, 2d, and 2e exist in two isomeric forms. Based on NMR nuclear Overhauser experiments, the isomerization occurs about the carbon-carbon double bond of the ketene (Equation 2). PMe3 ' 0 Cp2Ti)-< R' R (2) R R' R = CH 3 , CH 2CH 3 , Ph R' = CH 3 , CH 2CH3 Addition of trimethylphosphine to a suspension of the oligomeric ketene complex (vide supra) initially yields one isomer of the complex (1H NMR), but over several hours at room temperature an equilibrium between isomers is established. Monitoring the isomerization by NMR yields a forward rate constant, k 1 = 6.8± 1.0 x 103 min- 1 and a reverse rate constant, k_ 1 = 4.1±0.6x10 3 min- 1 54 Figure 1. ORTEP Drawing of 2b with Atom Labeling. 55 CP!2l C(9) 2.!192(2) Figure 2. ORTEP Drawing of 2b with Selected Bond Lengths and Angles. 56 at 303 K. Titanacyclobutenes also readily insert molecules, which are isoelectronic with CO, such as isocyanides (Equation 3). Treatment of a solution of titanacyclobutene 2a with one equivalent of t-butylisocyanide yields the iminoacyl complex , 4, quan- titatively by NMR. 26 The iminoacyl complexes are orange, crystalline compounds and exhibit ffi stretches at ,..., 1700 cm- 1 . The compounds are thermally stable and do not rearrange to an aza-ketene (Equation 4). N I 1Bu Cp TiY--R' Cp li>:i R R 2 2 ~R' (3) 4a R= R'= Ph 4b R = Ph, R' = TMS 4c R = Ph, R' = CH3 4d R= R'=CH 3 N I 1Bu C~li>:i ~Ph x (4) Ph Ph Crystals of 4a suitable for x-ray diffraction analysis were obtained from toluene solution and the refined structure is shown in Figure 3. Details of the data collection and structure refinement are in Appendix 2. 57 Figure 3. ORTEP Drawing of 4a. 58 Figure 4. ORTEP View of the Metallacycle Plane of 4a. 59 Mechanism of Titanacyclobutane Carbonylation During the carbonylation of ld, a transient green color was observed. By use of low-temperature 1 H a.nd 13 C NMR, 13 CO labeling a.nd IR, the intermediate was identified as the tita.nocene acyl complex 5. Only tita.nacyclobutene ld gives an observable acyl intermediate, although a transient green or brown color is observed during the carbonylation of le a.nd le. 5 The intermediate is unstable in solution above -30 °C but is moderately stable in the solid state at room temperature. The IR shows an intense absorption at 1615 cm- 1 , indicative of a.n acyl with little 17 2 -character. 14 •15 In order to establish which side of the metallacycle the CO inserts, the acyl intermediate was synthesized with 13 CO a.nd the 13 C - 13 C coupling constants determined from the 13 C{ 1 H} NMR. The 13 C NMR signal for the acyl carbon is o 294. The 13 C- 13 C coupling constant from the acyl carbon to the methylene carbon was 11.9 ± 0.9 Hz, but neither of the 13 C couplings to the ole:finic carbons was larger than 5.5 ± 0.9 Hz. The 11.9 Hz coupling is small for a one-bond 13 C- 13 C coupling, 16 but it is consistent with other tita.nocene acyls. 17 To test for the possibility of a reversible carbonylation of the metallacycle, a toluene solution of the acyl 5 was prepared with 13 CO (90% 13 C) a.nd immediately cooled to -78 °C. The 13 CO atmosphere was replaced with natural abundance 12 CO 60 at 100 psi and the solution warmed to -30 °C to effect the rearrangement. NMR analysis of the ketene complex revealed complete loss of the 13 C label. The high pressure of CO is necessary to obtain 1 equivalent of CO in solution, due to the low solubility of CO in toluene. 18 The loss of the 13 C label was observed regardless of solvent (toluene, diethylether, THF), or the addition of trimethylphosphine. Attempts to identify the acyl species by decomposition of the intermediate 5 with either trifluoracetic acid or HCl were unsuccessful due to the apparent rapid decarbonylation of the acyl in the absence of excess carbon monoxide. 27 However, if a solution of the acyl in diethyl ether under 100 psi of CO is treated with excess anhydrous HCl at -78 °C, the corresponding titanocene acyl chloride 6 may be obtained (Equation 5). The 1 H NMR confirms the predicted structure of the acyl chloride derived from titanium-vinyl bond cleavage by one equivalent of HCl. If the reaction mixture is warmed to -20 °C in the presence of excess HCl, the products are titanocene dichloride and 3-methyl-3-pentenal. The aldehyde was very difficult to isolate, so it was transformed to the 2,4-dinitrophenylhydrazone (DNP) derivative. NMR analysis of the DNP derivative showed that the /3 - / double bond had migrated into conjugation with the hydrazone. CH 3 CH 3 H3C~CHO 0 Cp2 Ti~ HCI -78 c ..--:; CH 3 CH3 CH3 HCI -20C (5) + Cp 2TiCl 2 5 In order to determine if the acyl complex 5 is on the reaction path to ketene 61 product, a solution of 5, was treated with t-butylisocyanide. The t-butyl isocyanide traps any free metallacyclobutene formed from decarbonylation of 5. Both the metallacyclobutene ld and the vinyl ketene complexes 2d and 3d react with t-butyl isocyanide to give observable products. 19 Treatment of the ketene complex with t-butylisocyanide gives a mixture of products; however, the ratio of the products is reproducible. Treatment of metallacyclobutene ld with one equivalent of t- butylisocyanide yields quantatively the iminoacyl complex 4d ( vide supra). To determine the relative rates of the insertion of t-butylisocyanide versus CO into the metallacyclobutene, a solution with equimolar concentrations of t-butylisocyanide and CO was reacted with the metallacycle. Within the detection limits of the NMR, only the formation of 4d was observed. This result demonstrates that if any ld were formed during the rearrangement of 5 to 2d, it would be rapidly trapped by the t-butylisocyanide. The iminoacyl complex 4d does not react with CO under the experimental conditions. Treatment of 5 in the absence of CO at -78 °C with four equivalents of t-butylisocyanide, followed by warming to room temperature, results in a 15:1 ratio of vinyl ketene products to 4d (Equation 6). /Bu 0 Cp2Ti~ N Cp2 Ti~ 4 eq 1BuNC ~CH3 ~CH3 CH3 (e) CH3 5 15 Attempts to determine accurately the kinetic parameters of the carbonylation were thwarted by several factors. The observed rate of rearrangement of 5 is de- 62 pendent on the concentration of PMe3 and the partial pressure of CO. An increased concentration of PMe 3 slows the rearrangement, and an increase of CO presence accelerates the rate of reaction. However, neither trimethylphosphine nor excess CO is necessary for conversion of the metallacycle to ketene complex. In efforts to demonstrate the cyclobutenone complex as a viable intermediate, a sample of 1,3-diphenylcyclobut-2-ene-1-one was prepared 21 and treated with titanocene dicarbonyl and titanocene carbonyl triethylphosphine complex 22 (Equation 7). However, in neither case was a titanocene ketene product observed. 0 ;==( Ph + or x (7) Ph Ph Ph Reactivity of Titanocene Vinyl Ketene Complexes Titanocene vinyl ketene complexes react with several unsaturated organic substrates. Ketene complex 2a reacts rapidly with acetylene (Equation 8) to yield the corresponding green titanaoxacyclopentene 7a in high yield. The reaction works equally well with the ketene oligomer 3a. The reaction is faster in coordinating solvents that solubilize the ketene oligomer. The resulting titanaoxacyclopentenes are thermally stable. Ketene complex 2d or the oligomer 3d also inserts acetylene to yield a titanaoxacyclopentene; however, the initial oxacyclopentene isomerizes to an equilibrium mixture of two oxacyclopentenes, 7b and 7c (Equation 9) . Both isomers have 63 HCCH Ph Ph (8) Ph Ph 7a 2a or 3a very similar NMR spectra and color. Based on the NMR spectra, the isomerization occurs about the exo-cyclic double bond. The titanaoxacyclopentenes did not react with methyl iodide. 0 HCCH Cp2 Ti/ 7b (9) 7c 2a Terminal alkynes also insert into the vinylketene complexes. Propyne and phenyl acetylene react with 3a to yield substituted titanaoxacyclopentenes 8 and 9, respectively. Analysis of the products shows only one regioisomer. NMR analysis and NOE experiments indicate that the substituent is located at the a-position of the metallacyclic ring (Equation 10). Internal alkynes do not react with the ketene complexes. Ketene complex 3d also reacts with propyne to form an analogous titanaoxacyclopentene !Ob. As was found with the acetylene insertion, the kinetic isomer, 64 Ph PMe 3 I o Ph R Cp 2 Ti/ (10) Ph R 8: R=CH 3 9: R=C6H5 Ph 2a CH3 PMe 3 J 0 Cp 2 Ti/ 0 CH3 CH3 Cpz Ti/ + --.:;::; CH3 2d CH 3 0 CH3 Cp 2 Ti/ (11) --.:;::; CH3 10a 10b !Ob, equilibrated to a mixture of isomers, !Ob and lOc (Equation 11). In contrast to alkynes, nitriles did not insert into 3a. NMR spectra did confirm that the nitrile was coordinated to the ketene complex, yet no reaction was observed. Ketene complex 2a will insert ethylene under moderately vigorous conditions (80 °C, 12 hrs) to yield a purple titanaoxacyclopentane (Equation 12). Substituted alkenes are unreactive toward insertion. The vinyl ketene complex 3a did not appear to be nucleophilic. The complex did not react with methyl iodide at room temperature. Treatment of the vinyl ketene complexes at room temperature with aldehydes results in the immediate formation of a new purple complex. The 1 H NMR shows inequivalent 17 5 -cyclopentadienyl resonances and absence of the terminal vinyl CH2 65 Ph Ph (12) Ph Ph 2a resonances. The complex is unstable and decomposes over several hours to paramagnetic products. Quenching of the reaction mixture followed by normal organic work-up and flash chromatography yields the lactones lla and llb (Equation 13) in 44% and 25% yield, respectively. Attempts to increase the yield by adding reagents such as diphenylacetylene to trap the titanium by-products were unsuccessful. DPh PM ea 0 CHaCHO J 0 Cp2Ti/ Hao+ I HaC Ph Ph Ph 11a 2a or 3a (13) PM ea J 0 CH a 0 Cp2Ti/ p-CHaC6 H4CHO Hao+ CH a CH a CH a 2d or 3d HaC 11 b Examination of the initial aldehyde reaction by 13 C NMR with 13 C-enriched ketene complex (derived from 13 CO), revealed a new resonance at 6 276.2. The IR spectrum of the reaction solution also revealed a band at 1595 cm- 1 , which shifted 66 to 1560 cm- 1 when the starting ketene complex was labeled with 13 CO. Ketones (acetone, acetophenone) did not react. The vinyl ketene complexes also react rapidly with alkyl aluminum reagents. Addition of one equivalent of dimethylaluminum chloride to a suspension of the ketene oligomer in C6D6 at room temperature results in the immediate formation of a new ketene complex. The NMR spectra suggest that the new complex is a 1:1 adduct, in which the aluminum is complexed to the ketene oxygen (Equation 14). An analogous, but less stable, complex is also formed from trimethylaluminum. The complexation does not activate the ketene complexes toward olefin insertion. (14) R R R 67 Discussion Titanacyclobutenes carbonylate to yield vinyl ketene complexes, 2, in high yield. This reactivity is in contrast to titanacyclobutanes, which carbony late to yield titanocene ene-diolate complexes (Equation 15). 28 The formation of ene-diolate complexes presumably arises from rapid interception of the initially formed acyl species by a second equivalent CO. Cyclobutanones can be isolated in low yield from the carbonylation under conditions of limited CO. Carbonylation of titanacyclobutenes shows no evidence for the formation of either cyclobutenes or enediolates. co (15) The difference in reactivity could arise from two factors. The coordination and insertion of the second CO molecule may be hindered by the substituent on the metallacyclobutene ring. All titanacyclobutenes in this study have a substituent at the a-position. A second possibility may be that the intramolecular migration of the vinyl group to the acyl is faster than alkyl group migration. No data on the relative rates of alkyl vs. vinyl migration are available. Substituent effects on the migration of benzyl groups in CpMo(C0) 3 (benzyl) indicate that electron donation accelerates the migratory insertion. 29 Although the isolation and characterization of the acyl complex 5 is inter- 68 esting, it does not provide sufficient evidence to distinguish among other possible mechanisms leading to vinyl ketene formation. Three reasonable mechanisms for the carbonylation and formation of ketene complexes are shown in Scheme 2. The metallacyclobutenes have two different titanium-carbon bonds and carbonylation of either bond could lead to the observed product (Scheme 2). It must be determined if 1) the isolated acyl complex 5 leads directly to ketene product (Scheme 2, path a), or 2) it is the kinetic product of carbonylation into the more sterically accessible titanium-carbon bond which, in a subsequent step, decarbonylates, and the reaction occurs via carbonylation of the titanium-vinyl bond (Scheme 2, path b). The methyl group at the a-position of the metallacycle could hinder the insertion of CO into the Ti-vinyl bond and result in the kinetic formation of 5. The loss of the 13 C label proves that the acyl intermediate, 5, carbonylates reversibly. However, it does not distinguish between paths a or b. An alternative mechanism involves the ring opening of the titanocenecyclobutene to a titanocene vinyl alkylidene complex (Scheme 2, path c). 24 Carbonylation of the alkylidene could yield the ketene complex. 2 •30 This mechanism is unlikely for several reasons: the observation and isolation of the acyl intermediate, 3, the results of the isocyanide trapping experiments, and the lack of alkylidene transfer reactions of the titanocenecyclobutenes with ketones. In contrast to the reactivity of titanocenecyclobutanes, which is dominated by titanocene-methylene chemistry, 20 the titanocenecyclobutenes exhibit reactivity similar to that observed for titanocene alkyl complexes. 19 The intermediate acyl complex has a relatively high ffi stretch at 1615 cm- 1 . Transition metal acyl complexes containing an 17 2 -acyl usually display IR stretches at ca. 1500 cm- 1 •31 The high ffi stretch suggests that 5 has considerable 71 1acyl character. The 13 C NMR shift of o 285 is consistent with both 17 1 - and 17 2 - 69 Scheme 2. Mechanism of Carbonylation of 2d 0 2 Cp T i l = l CH 3 Cp2 Tiy---CH3 CH3 ~ b co CH 3 1d CH a 2d or 3d transition-metal acyl complexes. 32 Acidolysis of 5 yielded the expected aldehyde. It was necessary to perform the acidolysis under a high pressure of CO to prevent decarbonylation. Although the aldehyde double bond had shifted into conjugation with the carbonyl, only CO insertion into the sp 3 titanium-earbon bond can result in the observed product. The differentiation of the cleavage of the cyclic acyl species, 5, is interesting. The titanium-earbon bond is cleaved by HCl at -78°C, but the remaining titanium acyl bond does not react rapidly until approximately -20°C. These observations firmly establish that CO inserts into the Ti-C(sp 3 ) bond in the initial carbonylation step. The competitive trapping of 5 with t-butylisocyanide demonstrates that it is not necessary for the acyl complex to decarbonylate during the reaction. If any of 70 the metallacycle were formed, it would be trapped as 4. In order for the two acyl species to equilibrate, the CO must migrate to the other side of the metallacycle. Although a bi-molecular mechanism cannot be ruled out, migration of the CO to the opposite side of the metallacycle without trapping by the t-butyl isocyanide is unlikely. Therefore, the reaction proceeds via carbonylation of the sp 2 bond of the metallacycle. Given the experimental data, path a of Scheme 2 is the most likely mechanism. The intramolecular attack of a coordinated, cyclic acyl to form a ketone complex in a Zr system has been postulated. 15 Carbonylation of hafnocene metallacyclobutanes yields a dimer containing both cyclobutanone and ene-diolate complexes. 33 Cyclobuteneones have been isolated from the reaction of Fischer carbene complexes with alkynes. 25 The lack of 17 2-acyl character in 5 and the formation of a Ti-0 bond in the ketene provide a driving force for the reaction. To confirm that a cyclobuteneone complex is a viable intermediate, diphenyl cyclobuteneone was treated with Ti 11 precursors, Cp2Ti(C0)2 and Cp2Ti(CO)(PEt3). No ketene products were observed in either case. A ketene complex was not formed due to the difficulty of displacing the ligands already on the titanium and the propensity of low-valent titanium derivatives to reduce ketones. 23 The isomerization of the ketene complexes was unexpected. Previously isolated Group IV ketene complexes did not display any evidence for isomerization or liberation of ketene. The rate of isomerization and the equilibrium ratio is not influenced by excess trimethylphosphine. The mechanism for isomerization may involve a 7r-bound ketene intermediate. 12 •13 The ketene complexes 2a and 2b have bulkier substituents on the ketene skeleton that apparently prevent the isomerization. The intermediacy of a 7r-bound ketene complex could explain the formation of a small amount of free vinyl ketene during prolonged carbonylation 71 PMe3 PMe 3 i 0 -- Cp2Ti/ PMe3 i 0 Cp 2Ti- -- CH 3 i 0 Cp TI1-< (16) 2 CHa CH a CH a CHa CH a 2d The crystal structure of 2b displays some interesting features. The 11 2 - coordination of the ketene group places the six atoms Ti, 0, C(l), C(3), and C(5) in a plane (maximum deviation from Ti-0-C(l) plane 0.13 A). The vinyl ketene moiety adopts an s-cis conformation to reduce the steric interaction between the trimethylsilyl group and the cyclopentadienyl ligands. The terminal double bond and the phenyl rings were expected to be coplanar to maximize electronic overlap. However, the substituents are twisted relative to the ketene plane by 38.5(8) 0 and 42. 7(7) 0 , respectively. The absence of a planar vinyl ketene has been observed for an arene-coordinated Cr vinyl ketene complex and is attributed to the steric repulsions prevailing over the electronic effects. 7· The trimethylphosphine ligand is slightly (0.42 A) out of the plane defined by the Ti, 0, and C(l). The ketene complex, 2b, retains the relative connectivity of the carbon skeleton found in the starting titanacyclobutene, 2a. Sb The only other structurally characterized titanocene ketene complex is a bridged diphenyl ketene dimer. 9 c A closely related ketene complex of permethylzirconocene has been structurally characterized as the pyridine adduct. 9 a All three crystal structures exhibit similar fJ:rbonding of the ketene fragment. Pertinent bond lengths and angles are in Table 2. 72 Table 2. Selected Bond Lengths (A) and Angles ( 0 ) of 2b. Ti-0 Ti - C(l) Ti- Cp(l)* 2.064(3) 2.098(5) 2.091 Ti- Cp(2)* 2.081 Ti-P 2.592(2) C(l) - 0 1.298(6) C(l) - C(2) 1.349(6) C(2) - C(3) 1.500(7) C(3) - C(4) 1.321(8) C(l) -Ti- 0 36.4(2) Ti- C(l) - 0 70.4(2) C(l) - 0 -Ti 0-Ti-P 73.2(2) Ti - C(l) - C(2) 158.9(4) 0 - C(l) - C(2) 130.0(4) Cp(l) - Ti - Cp(2)* 131.2 71.6(1) • Cp(l) and Cp(2) are the 17 5 -cyclopentadienyl ring centroids. The crystal structure of iminoacyl complex 4a has some strong similarities with the structures of the titanacyclobutenes 3a-c. Due to decomposition of the crystal in the x-ray beam, the errors in the atomic positions are moderate; however, the structure contains some interesting features . Pertinent bond lengths and angles are in Table 3. The metallacycle ring is fiat, containing well-defined carboncarbon double and single bonds. The a-phenyl ring is oriented perpendicular to the metallacycle plane. The Ti-N distance is 2.23(2)A, and the Ti-(Cl)-N and C(2)-C(l)-N angles are 83(2) 0 and 147(3) 0 , respectively. The Ti-C(l) distance of 2.02(3)A is substantially less than the Ti-C(4) distance 2.34(3)A. The Ti-C(4) distance is exceptionally long for a Ti-C bond and thus may reflect distortion prior 73 to migration of the vinyl ligand. In contrast, the titanacyclobutene metallacycle structures contain nearly equal sp 2 and sp 3 Ti-C bond lengths. The iminoacyl group is correctly positioned relative to the titanocene fragment to interact with the empty LUMO on the metal. The iminoacyl complex is formally a 16 electron complex and could accommodate imido-coordination. The coordination could also contribute to lengthening of the Ti-C(4) bond. The Ti-N distance is 2.23(3)A, a reasonable distance for interaction. The intense stretch at 1772 cm- 1 is more consistent with ,, 1-bonding of the iminoacyl group. Zirconocene 1] 2 -iminoacyl complexes exhibit infrared stretches ca. 1520-1580 cm- 1 •34 Structurally characterized 1] 1-iminoacyl complexes of Pt have infrared stretches ca. 1620 cm- 1 . 35 Organic secondary imines have a band at 1650 cm- 1 •36 The vinyl ketene complexes 3a - e insert terminal alkynes to form titanaoxacyclopentenes, 8-10. The yield of insertion products is high; however, some poly-alkyne is formed. The insertion works well for the ketene oligomers, even in non-coordinating solvents. The alkyne may act as a Lewis base and solubilize the oligomer. Terminal alkynes insert regiospecifically, the substituent placed at the aposition. The a-position may appear to be the more sterically crowded regioisomer, but analysis of the .B-isomer reveals a severe 1,3 allylic interaction with the exomethylene substituent (Equation 17). 37 The titanacycle ring is quite fiat, due to the three adjacent sp 2 carbons, and the a-substituent is held in the plane of the metallacycle, minimizing steric interactions with the 1] 5 -cyclopentadienyl rings. Similar additions across transition metal ketene and ketone complexes have been observed previously for titanium and zirconium. 9 a, 3 s Similar oxacyclopentenes have been synthesized by addition of ketones and aldehydes to alkyne and alkene complexes. 39 The isomerization of titanaoxacyclopentenes 7b and 7c is surprising. The mechanism of isomerization could proceed through a zwitterionic enolate resonance, 74 Table 3. Selected Bond Lengths (A) and Angles ( 0 ) for 4a. Ti- C(l) C(l) - N C(l) - C(2) C(2) - C(3) C(3) - C(4) Ti - R(l)* Ti - R(2)* 2.02(3) 2.34(3) 2.23{2) 1.19(4) 1.57(4) 1.49(4) 1.36(4) 2.11 2.08 C(l) - Ti - C(4) Ti - C(l) - C(2) C(l) - C(2) - C(3) C(2) - C(3) - C(4) C(3) - C(4) - Ti Ti- C(l) - N N - C(l) - C(2) C(S) - N - C(l) R(l) - Ti - R(2)* 71(1) 128(2) 103(2) 119(2) 116(2) 83(2) 147(3) 134(2) 134.4 Ti - C(4) Ti-N • R(l) and R(2) are the 77 5 -cyclopentadienyl ring centroids. followed by bond rotation of the intermediate (Scheme 3). Alternatively, alkyne insertion may be reversible to form a ketene-alkyne complex, which isomerizes by a mechanism similar to the ketene-phosphine complex, 2a. As was found with the ketene-phosphine complexes; the diphenyl isomer, 2a, does not isomerize, whereas the dimethyl complex, 2d, isomerizes to a more stable complex. The lack of reactivity of 7b with methyl iodide suggests that the titanaoxacyclopentenes are not strong nucleophiles, and zwitterionic intermediates are not involved. The only alkene that inserts into the vinyl ketene complexes 2a or 3a is 75 CH 3 CH 3 0 Cp2 Ti/ CH3 PMe3 ~ ~ 10a CH 3 Cp2 Ti/ ' 0 (17) CH3 CH 3 ~ Cp 2Ti CH3 / CH3 0 2d or 3d CH3 ~ Scheme 3. Isomerization Mechanism of 7b cp)H0 ? / CH3 0 CH3 \ CH3 CH3 Cp2Ti/ " 0 Cp2 Ti/ ~ 7b CH3 ? ' o+ Cp 2Ti ~ CH3 / /~ ~ CHr ethylene. Substituted alkenes do not react due to steric interactions with the ry 5 cyclopentadienyl rings. Based on the reactivity of alkynes, the insertion of aldehydes into ketene complexes 3a and 3d was anticipated; however, the products were unexpected. We had expected aldehydes should insert to yield a titanocene diolate complex; however, spectral data of the intial product are inconsistent with a titanocene diolate complex. Spectral data suggest the formation of a titanocene acyl alkoxide complex. 76 Formation of an acyl alkoxide requires reaction of the ketene complex from the dieneolate manifold and a 1,2-addition across the aldehyde (Equation 18). The 13 C NMR resonance at 6 276.2 and the isotopic shift of the infrared stretch at 1595 cm- 1 are characteristic of Group IV acyl complex. 31 Ph 0 CH 3CHO Ph Cp 2 Ti \ (18) 0 Ph CH3 3a Ph The acyl alkoxide reductively eliminates to yield the lactone 11, but the overall yield is low (25-44%). Possible explanations for the low yield are decompostion initated by the titanocene fragment or decarbonylation of the acyl alkoxide to a titanoxacyclopentane. No other products were observed in the reaction mixture; however, the signals were severely broadened by paramagnetic decomposition. Rapid hydrolysis of the acyl alkoxide intermediate may produce higher yields of lactone. Ketones do not react with the ketene complexes, reflecting the steric constraints of the titanocene system. Lewis acids are cocatalysts of many organometallic reactions. Organo- aluminum reagents readily react with zirconocene ketene oligomers to form novel compounds. 40 Titanocene vinyl ketene oligomers, Sa and Sd, form stable 1:1 adducts with either trimethylaluminum or dimethylaluminum chloride. The complex is probably monomeric, but a molecular weight determination has not been performed. A simple Lewis acid-Lewis base interaction of the titanium and alu- 77 minum species is consistent with the NMR data. The aluminum complexation did not enhance the reactivity of the ketene complex toward olefin insertion. 78 Conclusions We have demonstrated that carbonylations of titanocenecyclobutene complexes yield titanocene vinyl ketene complexes. The mechanism appears to involve several steps and one of the intermediates has been isolated. This reaction may provide insight into the mechanism of Fischer carbene annulation reactions of carbon monoxide and alkynes as well as the carbonylation of metal alkyl complexes. In particular, the observed products could be derived from the opening of the metallacyclobutene to a vinyl alkylidene, though this is not a viable mechanism in our system. Our findings shed some doubt on the use of a metallacyclobutene opening to a vinyl alkylidene in mechanisms of related reactions 24 and suggest that such reactions may also occur by direct insertion into the metal-carbon single bonds of intermediates. The structure of a titanocene vinyl ketene complex has been determined by x-ray diffraction and is the first structurally characterized example of a monomeric titanium ketene complex. Isocyanides insert into titanacyclobutenes to yield iminoacyl complexes, analogous to the acyl intermediate, 5. The structure of the iminoacyl compound shows an 17 2 -coordination of the imino group, and a very long titanium-carbon bond across from the iminoacyl ligand. The structure may provide an indication of the bonding in the titanium acyl intermediate as it proceeds toward the transition-state to product. The vinyl ketene complexes also react with unsaturated molecules such as alkynes and aldehydes. Addition of alkynes occurs across the titanium-carbon bond to yield titanaoxacyclopentenes. With aldehydes, the ketene complexes act as dieneolates and form a titanium acyl alkoxide intermediate, which reductively eliminates to form a lactone. 79 Experimental Section General Considerations. All manipulations were performed with the use of standard Schlenk techniques under argon or in a Vacuum Atmospheres Co. glove box under nitrogen. Argon was purified by passage through columns of BASF R3-ll (Chemalog) and Linde 4 A molecular sieves. Carbonylations were performed in Lab-Glass pressure bottles (60 or 100 mL) fitted with two inlet valves and a pressure gauge. Toluene, benzene, THF, and diethyl ether were vacuum-transferred from sodium benzophenone ketyl and stored in teflon-valve sealed vessels under argon. Pentane and hexane were stirred over concentrated H2S04, dried, vacuumtransferred from sodium benzophenone ketyl and stored in teflon-valve sealed vessels under argon. Methylene chloride was vacuum-transferred from P20s or CaH2 and stored under argon. Benzene-d6, toluene-ds, and THF-ds were vacuum-transferred from sodium benzophenone ketyl. Carbon monoxide (CP) was obtained from Matheson. 13 C-enriched carbon monoxide (90% 13 C) was obtained from Monsanto- Mound Laboratories. Trimethylphosphine was obtained from Strem Chemicals. Acetylenes were obtained from Aldrich, Farchan Laboratory, or Wiley Organics and dried or distilled before use. Instrumentation. Infrared spectra were recorded on either a Beckman 4240, Shimatzu IR-435, or Perkin-Elmer 1310 spectrophotometer. 1 H NMR were recorded on a Varian EM-390, JEOL FX-90Q, Varian XL-200, JEOL GX-400, or Bruker WM-500 and referenced to residual solvent (C 6 D 6 , 8 7.15; C1Ds, 8 2.09; THF-d 8 , 8 3.58 or 1.73; CDCL 3 , 8 7.24). 31 P{1H} NMR were recorded on a JEOL FX-90Q and referenced to external 85% H3 P0 4 (positive 8, lower field). 13 C{1 H} NMR were recorded on a JEOL FX-90Q, Varian XL-200, or JEOL GX-400. Difference NOE spectra were recorded on a JEOL GX-400 or a Bruker WM-500 at the Southern California Regional NMR Facility located at the California Institute of 80 Technology. Reaction kinetics were performed on the JEOL FX-90Q using an automated routine. Elemental analyses were performed by Dornis and Kolbe, Mulheim, West Germany, and the analytical facility of the California Institute of Technology. 77 2 -(C,0)-2,3-Diphenyl Vinyl Ketene Titanocene Trimethylphosphine, 2a. A solution of 2,3-diphenyl titanacyclobutene (150 mg, 0.405 mmol) and trimethylphosphine( 45 µL, 0.444 mmol) in 2 mL of toluene was transferred into a Lab-Glass pressure bottle fitted with a stirbar and pressure gauge. The transfer cannula and schlenk flask were rinsed twice with 0.5 mL portions of toluene. The pressure bottle was partially evacuated, and CO (20 psi) was introduced with stirring. After 10 min the color had changed from dark-red to yellow and the CO was vented . The solution was transferred into a schlenk flask and the pressure bottle rinsed twice with 0.5 mL portions of toluene. The volatiles were removed in vacuo to yield a yellow solid, which was washed twice with 2 mL portions of pentane and dried in vacuo to yield the product as a yellow powder (158 mg, 0.333 mmol, 82%). 1H NMR (200 MHz, C6 D 6 ) 6 8.20 (d, J = 8.0 Hz, 2H), 7.84 (d, J = 7.0 Hz, 2H), 7.35 (t, J = 7.6 Hz , 2H), 7.2-7.0 (m, 4H), 5.89 (d, J = 2.7 Hz, lH), 5.72 (d, J = 2.7 Hz, lH), 5.10 (s, lOH), 0.73 (d, J = 6.3 Hz, 9H); 31 P{1H} NMR (36.3 MHz, THF-d 8 , -20°C) 6 5.72 (s); 13 C{1H} NMR (22.5 MHz, THF-d 8 , -20 °C) 8 193.6 (d, Jc-P = 11.0 Hz), 152.7, 145.4, 143.4, 128.6, 128.2, 127.6, 127.2, 126.6, 121.1, 112.4, 104.8, 102.3 (.d, Jc-P = 3.7 Hz), 14.2 (d, Jc-P = 14.6 Hz); IR (nujol, cm- 1) KBr 1590 (m), 1565 (m), 1540 (s), 1487 ( s), 1425 (m), 1305 (m), 1282 (m), 1265 (m), 1155 (m), 1072 (m), 1045 (m), 1028 (m), 1018 (m), 952 (s), 918 (w), 895 (w), 805 (s) . The band at 1540 cm- 1 shifts to 1512 cm- 1 upon the use of 13 CO. Anal. Calcd. for C29H31 OPTi: C, 73.42; H, 6.59. Found: C, 73.21; H, 6.68. 81 77 2 -(C,0)-2-Phenyl-3-Trimethylsilyl Vinyl Ketene Titanocene Trimethylphosphine, 2b. A solution of 2-phenyl-3-trimethylsilyl titanocenecyclobutene (500 mg, 1.36 mmol) and trimethylphosphine (150 µL, 1.48 mmol) in 8 mL of THF was transferred into a Lab-Glass pressure bottle fitted with a stirbar and pressure gauge. The transfer cannula and schlenk flask were rinsed twice with 1 mL portions of THF. The pressure bottle was charged with 60 psi of CO. The solution was stirred at room temperature for 3 hr during which time the color changed from purple to yellow. The CO was vented and the solution transferred to a schlenk flask. The volatiles were removed in vacuo to yield a yellow solid, which was washed twice with 2 mL of pentane and dried in vacuo to yield the product (590 mg, 1.25 mmol, 92%). The material can be recrystallized from diethyl ether at -50 °C (10 mg/mL). 1 H NMR (90 MHz, C6D6) fJ 7.80 (m, 2H), 7.37 (m, 3H), 6.33 (d, lH, J = 3.7 Hz), 5.82 (d, lH, J = 3.7 Hz), 5.16 (s, lOH), 0.69 (d, 9H, J = 6.6 Hz), 0.33 (s, 9H); 1 H NMR (90 MHz, THF-ds) fJ 7.33 (m, 2H), 7.04 (m, 2H), 6.81 (m, lH), 6.04 (d, lH, J = 3.9 Hz), 5.51 (d, lH, J = 3.9 Hz), 5.42 (s, lOH), 1.38 (d, 9H, J = 7.1 Hz), 0.01 (s, 9H); 31 P{ 1 H} NMR (36.3 MHz, THF-d 8 , -20 °C) fJ 5.25, 31 P{1H} NMR (36.3 MHz, C 7 D 8 , -20 °C) fJ 3.06; 13 C{1H} NMR (22.5 MHz, THF-d 8 , -20 °C) fJ 190.3 (d, Jc-P = 12.2 Hz), 155.7, 145.1, 128.0, 127.6, 12 2.4, 121.4, 104.8, 14.0 (d, Jc-P = 14.6 Hz), 1.3; ffi (nujol, cm- 1 ) KBr 1585 (w), 1520 (m), 1300 (m), 1280 (m), 1258 (m), 1235 (m), 1062 (w), 103 0 (w), 1015 (m), 975 (m), 960 (m), 910 (w), 870 (m), 855 (m), 838 (m), 825 (m), 805 (s). The absorption at 1520 cm- 1 shifts to 1492 cm- 1 upon the use of 13 CO. Anal. Calcd. for C 26 H35 0PSiTi: C, 66.37; H, 7.50. Found: C, 66.03; H, 7.29. 82 17 2 -(C,0)-2-Phenyl-3-Methyl Vinyl Ketene Titanocene Trimethylphosphine, 2c. A solution of 2-phenyl-3-methyl titanocenecyclobutene (200 mg, 0.649 mmol) and trimethylphosphine (70 µL, 0.69 mmol) in 2 mL of toluene was transferred into a Lab-Glass pressure bottle fitted with a stirbar and pressure gauge. The transfer cannula and schlenk flask were rinsed twice with 0.5 mL portions of toluene. The pressure bottle was charged with 15 psi CO. The solution was stirred for 10 min during which time the color changed from dark-red to yellow. The CO was vented, the solution transferred to a schlenk flask, and the volatiles removed in vacuo. The yellow solid was washed twice with 2 mL portions of pentane and dried in vacuo to yield the product (215 mg, 0.521 mmol, 80%). Analysis by 1 H NMR revealed two isomers in a 3:1 ratio. 1 H NMR (90 MHz, C6 D 6 ) 6 major isomer 7.84 (m, 2H), 7.39 (m, 3H), 5.32 (m, lH), 5.20 (m, lH), 5.17 (s, lOH), 2.39 (m, 3H), 0.65 (hr d, 9H); minor isomer 5.10 (s, lOH), 2.42 (br s, 3H), 0.65 (br d, 9H), vinyl resonances obscured. 13 C{1 H} NMR (22.5 MHz, C1D 8 , -20°C) 6 major isomer 188.6 (d, Jc-P = 11.0 Hz), 146.8, 144.9, 138.3, 136.3, 129.3, 122.9, 106.2, 105.1 (d, Jc-P = 3.7 Hz), 103.9, 24.9 (s), 13.3 (d, Jc-P = 14.6 Hz); minor isomer 102.8; 31 P{1H} NMR (36.3 MHz, C 7 D 8-d8, -20 °C) 6 major isomer 3.84, minor isomer 4.78; IR (nujol, cm- 1 ) KBr 1608 (w), 1575 (m), 1560 (m), 1525 (s), 1300 (w), 1278 (m), 1260 (w), 1062 (w), 1010 (s), 945 (s), 895 (m), 850 (m), 838 (m), 800 (s). The absorption at 1525 cm- 1 shifts to 1498 cm- 1 upon the use of 13 CO. Anal. Calcd. for C2 4 H2 9 0PTi: C, 69.91; H, 7.09. Found: C, 69.58; H, 7.00. 83 17 2 -(C,0)-2,3-Dimethyl Vinyl Ketene Titanocene Trimethylphosphine, ld. A solution of 2,3-dimethyl titanocenecyclobutene (200 mg, 0.812 mmol) and trimethylphosphine (100 µL, 0.986 mmol) in 2 mL of toluene were transferred into a Lab-Glass pressure bottle fitted with a stirbar and pressure gauge. The schlenk flask and cannula were rinsed twice with 0.5 mL portions of toluene. The pressure bottle was charged with 15 psi of CO. The solution was stirred for 10 min during which time the color changed from red to yellow. The CO was vented and the solution transferred to a schlenk flask and the volatiles removed in vacuo. The yellow solid was washed twice with 2 mL of portions of pentane and dried in vacuo to yield the product (220 mg, 0.628 mmol, 77%). Analysis by 1 H NMR revealed two isomers in approximately 2:1 ratio. 1 H NMR (90 MHz, C 6 D 6 ) o major isomer 5.15 (s, lOH), 4.95 (m, 2H), 2.61 (s, 3H), 2.45 (br s, 3H), 0.72 (d, 9H, J = 6.5 Hz); minor isomer 5.05 (s, lOH), 4.78 (m, 2H), 2.61 (s, 3H), 2.31 (s, 3H), 0.72 (d, 9H, J = 6.5 Hz); 1 H NMR (500.13 MHz, C 7 D 8 ) o major isomer 5.126 (s, lOH), 4.885 (d, lH, J = 2.1 Hz), 4.815 (br s, lH), 2.411 (s, 3H), 2.355 (hrs, 3H), 0.798 (br s, 9H) (irradiation of the signal at o 2.355 results in the collapse of the signal at o 4.815 to a doublet, J = 2.1 Hz); minor isomer 5.041 (s, lOH), 4.738 (d, lH, J = 1.7 Hz), 4.575 (br s, 1 H), 2.455 (hrs, 3H), 2.208 (s, 3H), 0. 798 (br s, 9H) (irradiation of the signal at o 2.455 results in the collapse of the signal at o 4.575 to a doublet, J = 1. 7 Hz); 1 H NMR (500.13 MHz, C 6 D 6 ) o major isomer 5.154 (s, lOH), 5.074 (d, lH, J = 2.5 Hz), 4.987 (br s, lH), 2.603 (s, 3H), 2.450 (hrs, 3H), 0.71 (br s, 9H); minor isomer 5.058 (s, lOH), 4.937 (d, lH, J = 2.4 Hz), 4.772 (br s, lH), 2.613 (br s, 3H), 2.31 3 (s, 3H), 0.71 (br s, 9H); 1 H NMR (500.13 MHz, THF-d 8 ) o major isomer 5.382 (s, 10H), 4.290 (d, lH, J = 2.7 Hz), 4.245 (br s, lH), 2.124 (s , 3H), 1.862 (s, 3H), 0.90 (v br, 9H) (irradiation of the signal at o 2.124 results in the collapse 84 of the signal at 6 4.245 to a doublet, J = 2.7 Hz); minor isomer 6 5.316 (s, lOH, 4.116 (d, lH, J = 2.7 Hz), 3.968 (hr s, lH), 2.012 (s, 3H), 1.912 (s, 3H), 0.90 (v hr, 9H) (irradiation of the signal at 6 2.012 results in the collapse of the signal at 6 3.968 to a doublet, J = 2.7 Hz). 13 C labeled ketene complex: 1 H NMR (500.13 MHz, C 7 D 8 ) 6 major isomer 5.126 (s, lOH), 4.885 (d, lH, J = 2.1 Hz), 4.815 (hrs, lH), 2.411 (d, 3H, Jc-H = 4.4 Hz), 2.355 (s, 3H ), 0.798 (hrs, 9H); minor isomer 6 5.041 (s, lOH), 4.738 (d, lH, J = 1.7 Hz), 4.575 (hrs, lH), 2.455 (s, 3H), 2.208 (d, 3H, Jc-H = 5.9 Hz ), 0.798 (hrs, 9H); 1H NMR (500.13 MHz, THF-d 8) 6 major isomer 5.381 (s, lOH), 4.293 (d, lH, J = 2.4 Hz), 4.247 (hrs, lH), 2.124 (s, 3H), 1.862 (d, 3H, Jc-H = 4.3 Hz), 0.90 (v hr, 9H); minor isomer 5.315 (s, lOH), 4.118 (d, lH, J = 2.3 Hz), 3.968 (hr s, lH), 2.013 (s, 3H), 1.912 (d, 3H, Jc-H = 5.89 Hz), 0.90 (v hr, 9H); 31 P{ 1 H} NMR (36.3 MHz, C 7 D 8 , -20 °C) 6 minor isomer 4.55, major isomer 3.53; 13 C{1H} NMR (22.5 MHz, C 7 D 8 , -20 °C) 6 major isomer 185.47 (d, Jc-P = 11.0 Hz), 146.84, 103.83, 98.63, 98.36 (d, Jc-P = 3.6 Hz), 22.95, 19.53, 13.14 (d, Jc-P = 14.6 Hz); minor isomer 185.25 (d, Jc-P = 9.8 Hz), 146.14, 102.91, 97.82 (d, Jc-P = 9.8 Hz), 96.89, 24.84, 18.66, 13.14 (d, Jc-P = 14.6 Hz); IR (nujol, cm- 1 ) KBr 1598 (m), 1558 (s), 1546 (s), 1421(m),1317 (m), 1300 (m), 1278 (m), 1205 (m), 1120 (w), 1020 (m), 1010 (m), 948 (s), 830 (m), 795 (s). The use of 13 CO results in a shift of the absorption at 1546 cm- 1 to 1523 cm- 1 . Anal. Calcd. for C 19 H 2 10PTi: C, 65.15; H, 7.77. Found: C, 65.20; H, 7.55 .. Assignment of geometry by difference NOE experiments: Major isomer (Cp 6 5.382), irradiation of the signal at 6 1.862 results in enhancement of the signal at 6 4.290. Irradiation of the signal at 6 2.124 results in enhancement of the signals at 6 4.245 and 5.382. The Jc-H of 6 1.862 with 13 CO is 4.3 Hz. Minor isomer (Cp 6 5.316), irradiation of the signal at 6 1.912 results in enhancement of the signal at 4.116. Irradiation of the signal at 2.012 results in enhancement of the signal at 6 3.968. The Jc-H of 6 85 1.912 with 13 CO is 5.8 Hz. '7 2 -(C,O)-Diethyl Vinyl Ketene Titanocene Trimethylphosphine, le. A solution of 2,3-diethyl titanocenecyclobutene (150 mg, 0.547 mmol) and trimethylphosphine (60 µL, 0.590 mmol) in 1 mL of toluene was transferred into a Lab-Glass pressure bottle fitted with a stirbar and pressure gauge. The cannula and schlenk flask were rinsed twice with 0.5 mL portions of toluene. The pressure bottle was charged with 20 psi of CO. The solution was stirred at room temperature for 10 min during which time the color changed from red to yellow. The excess CO was vented and the solution transferred to a schlenk flask and the volatiles removed in vacuo. The yellow solid was washed twice with 1 mL portions of pentane and dried in vacuo to yield the product (145 mg, 0.383 mmol, 70%). Analysis by 1 H NMR revealed two isomers in approximately a 3:1 ratio. 1 H NMR (500.13, MHz, C 6 D 6 ) o major isomer 5.175 (s, lOH), 5.158 (d, J = 1.93 Hz, lH), 4.952 (br s, lH), 2.988 (q, J = 7.29 Hz, 2H), 2.731 (q, J = 7.45 Hz, 2H), 1.516 (t, J = 7.45 Hz, 3H), 1.396 (t, J = 7.29 Hz, 3H), 0.711 (d, JP-H = 6.89 Hz, 9H); minor isomer 5.102 (s, lOH), 4.914 (d, J = 2.27 Hz, lH), 4.876 (br s, lH), 3.010 (q, J = 7.27 Hz, 2H), 2.787 (q, J = 7.29 Hz, 2H), 1.662 (t, J = 7.27 Hz, 3H), 1.2 84 (t, J = 7.29 Hz, 3H), 0.711 (d, JP-H = 6.89 Hz, 9H); 1 H NMR (90 MHz, THF-d 8 ) o major isomer 5.39 (s, lOH), 4.49 (d, J = 2.2 Hz, lH), 4.31 (br s, lH), 2.44 (br q, J = 7.6 Hz, 2H), 2.35 (q, J = 7.3 Hz, 2H), 1.34 (d, JP-H = 6.8 Hz, 9H), 1.21 (t, J = 7.6 Hz, 3H), 0.88 (t, J = 7.3 Hz, 3H); 13 CO labeled product: 1 H NMR (90 MHz, C6 D 6 ) o major isomer 5.17 (s, lOH), 5.13 (sh, lH), 4.93 (br s, lH), 2.97 (d of q, J = 7.3 Hz, 4.4 Hz, 2H), 2.72 (q, J = 7.3 Hz, 2H), 1.51 (t, J = 7.3 Hz, 3H), 1.39 (t, J = 7.3 Hz, 3H), 0.71 (d, J = 6.6Hz, 9H); 13 C{1H} NMR (22.5, MHz, THF-d 8, -20 °C) o 185.9 (d, Jc-P = 11.0 Hz), 152.2, 109.9, 104.6, 94.3, 27.2 (partially obscured by solvent), 15.8, 14.6, 13.7 86 (d, Jc-P = 14.6 Hz). 31 P{1H} NMR (36.3 MHz, THF-d 8 , -20 °C) o major isomer 5.55, minor isomer 6.06; IR (KBr, cm- 1 ) 3110 (w), 3085 (w), 3070 (w), 2965 (m), 29 20 (m), 2860 (m), 1590 (w), 1570 (m), 1538 (s), 1443 (m), 1420 (w), 1370 (w), 1355 (w), 1305 (w), 1286 (m), 1280 (m), 1264 (m), 1245 (w), 11 95 (m), 1130 (m), 1058 (w), 1015 (m), 948 (s), 845 (w), 808 (s). The use of 13 CO results in a shift of the absorption at 1538 cm- 1 to 1508 cm- 1 • Anal. Cakd. for C 21 H31 OPTi: C, 66.67; H, 8.26. Found: C, 66.92; H, 8.01. General Procedure for the Synthesis of Titanocene Vinyl Ketene Oligomer, 3a-d. A solution of the titanacyclobutene 1 in toluene was transferred into a pressure bottle fitted with a stirbar and pressure gauge. Carbon monoxide (-20 psi) was introduced with stirring. After approximately 15 minutes the solution was orange with a yellow precipitate. The CO was vented, the mixture transferred into a schlenk tube, and the volatiles removed in vacuo. The solid was sometimes purple due to an unidentified by-product, which may be removed by washing with pentane. The material was usually washed with pentane and dried in vacuo to yield the product, 3, as a yellow powder. 3,4-Dimethyl Titanacyclopent-3-ene-1-one, 5. A solution of the dimethyltitanacyclobutene (112 mg, 0.455 mmol) and trimethylphosphine (50 µL, 0.493 mmol) in 1 mL of toluene was transferred in a Lab-Glass pressure bottle fitted with a stirbar and pressure gauge. The schlenk fl.ask and cannula were rinsed twice with 1 mL portions of toluene. The pressure bottle was briefly evacuated, cooled to -50° C, and 10 psi of CO added. The solution was warmed slowly from -50 °C with stirring. When the temperature had reached approximately -20°C to -10°C a color change from red-+ brown-+ green 87 was observed. The solution was immediately cooled to -78°C, excess CO vented, and placed under argon atmosphere. The solution was rapidly transferred by cannula into a precooled schlenk flask with no apparent change of color. The solution was layered with 4 mL of pentane and allowed to stand at -78°C for several hours. A green precipitate was deposited on the walls of the flask. The mother liquor was removed via cannula; the green solid was washed twice with 2 mL portions of -78°C pentane and dried in vacuo to yield 72 mg of green powder. The product was stored at -40 °C in the drybox. NMR data are reported from sealed tube reactions and formation of the intermediate in situ. 1 H NMR (90 MHz, THF-d 8 , -25°C) 6 6.20 (s, lOH), 2.42 (br s, 2H), 1.32 (s, 3H), 0.80 (br s, 3H). When 13 CO is used, the signal at 6 2.42 becomes a broad doublet Jc-H = 4.6 Hz; 1H NMR (90 MHz, C 7 D 8 , -30°C) 6 5.81 (s, lOH), 2.67 (br s, 2H), 1.46 (s, 3H), 0.70 (s, 3H); 13 C{ 1 H} NMR (22.5 MHz, THF-d 8 , -25°C) 6 294.0, 186.4, 121.6, 115.5, 61.3, 17.5, 16.5; 13 C{1H} NMR (22.5 MHz, C 7 D 8 , -30°C) 6 293.6, 185.6, 121.6, 114.8, 61.3, 17.7 , 16.7; labeled with 13 CO: 13 C{1H} NMR (22.5 MHz, THF-d 8, -25°C) 6 294.0 (s), 185.2 (s), 121.6 (d, Jc-c = 7± 1.8 Hz), 115.3 (s), 61.3 (d, Jc-c = 13 ± 1.8 Hz), 17.5 (d, Jc-c = 6 ± 1.8 Hz), 16.5 (s); 13 C{1H} NMR (22.5 MHz, C 7D 8, -30°C) 6 · 293.4 (s), 185.3 (s), 121. 2 (d, jcc = 5.5 ± 0.9 Hz), 114.5 (s), 61.0 (d, Jc-c = 11.9 ± 0.9 Hz), 17.5 (d, Jc-c = 5.5 ± 0.9 Hz), 16.3 (s). The resonance at 6 185 may be obscured by the ketene complex; the use of pyridine instead of trimethyl phosphine shifts the resonance of the ketene product to lower field. IR (KBr, cm.:.. 1 ) 3090 (m), 2960 (m), 2890 (m), 2845 (s), 2820 (s), 2745 (m), 1615 (s), 1435 (m), 1365 (m), 1280 (w), 1168 (w), 1148 (w), 1128 (w), 1070 (m), 1050 (m), 1013 (s), 972 (w), 950 (m), 820 (s), 805 (s). 88 3-Methyl-trans-3-pentenoyl Titanocene Chloride, 6. A solution of dimethyl titanocenecyclobutene Id {210 mg, 0.853 mmol) in 10 mL of diethyl ether was transferred into a 100 mL Lab-Glass pressure bottle fitted with a pressure gauge and stirbar. The solution was cooled to -78°C and 100 psi of CO added. The solution was warmed with stirring until the color began to change to a brown-green, then immediately cooled to -78°C to obtain a green solution with some green precipitate. To this mixture was added 25 psi of anhydrous HCl gas (Matheson) to bring the total pressure to 125 psi. Over 15 min at -78°C with stirring, all of the green color disappeared and a yellow-orange precipitate was formed. The pressure was vented and the reaction vessel evacuated at -78°C for several hours. To speed the removal of solvent, the diethylether mixture was splashed onto the warmer sides of the vessel where the solvent immediately evaporated. After the solvent had been removed, the solid was dried overnight in vacuo to yield 175 mg of a red-orange powder. NMR analysis (CDCL 3 ) indicated the material was approximately 66% Cp 2 TiC1 2 and 34% acyl chloride, 5 {0.192 mmol, 22%). 1 H NMR {400 MHz, CDCL 3 ) o 5.77 {s, lOH), 5.57 {d of q, J = 6.8, 1.2 Hz, lH), 3.95 {br s, 2H), 1.81 {d, J = 1.2, 3H), 1.69 {d oft, J = 6.8, 1.2 Hz, 3H); IR {KBr, cm- 1) 1610. The acyl chloride may be cleaved to the aldehyde and Cp 2 TiC1 2 by treatment with HCl at >-20°C. The aldehyde was characterized by 1 H NMR {90 MHz, C 6 D 6 ) 8 9.48 {t, J = 2.3 Hz, lH), 5.03 {br q, lH), 2.17 {br t, J = 2.3 Hz, 2H), CH 3 groups obscured by residual diethyl ether. The aldehyde was immediately converted to the 2,4-DNP derivative, mp. 135°. Trapping Experiments of 3 by t-Butyl lsocyanide. Compound 3 {16 mg, 0.058 mmol) was weighed into an NMR tube in the drybox; the tube was capped with a septum, removed from the box and cooled 89 to -78°C . Toluene-d 8 (400 µL) was added by syringe through the septum at a rate such that the solvent cooled as it flowed down the side of the tube. The tbutyl isocyanide (22 µL, 0.23 mmol) was then added by syringe to the sample. The tube was shaken to dissolve the solid and the sample warmed quickly to room temperature. An immediate color change from green to red was observed and the 1 H NMR recorded at room temperature. The major products had resonances at 8 6.05 and 5.47. The 1 H NMR 17 5 -cyclopentadienyl resonance of the imino acyl insertion product 5, was well separated at fJ 5.20. The resonances at fJ 6.05 and 5.47 were confirmed to be derived from reaction of the ketene complex oligomer 2d with tbutyl isocyanide by independent reactions. Integration of the 17 5 -cyclopentadienyl resonances yielded a ratio of ketene products to metallacyclobutene products of 15 to 1. Kinetics Study of the Isomeri.zation of 2d. Two NMR tubes were charged with 14 mg (0.051 mmol) of the phosphine-free ketene oligomer of 3d. To each tube was added 400 µL ofbenzene-d6, and then each was capped with a septum. The tubes were removed from the drybox and frozen in an ice bath. To one tube was added 6 µL (0.059 mmol) trimethylphosphine via syringe. To the second tube 18 µL (0.177 mmol) of trimethylphosphine was added. Both samples were thawed simultaneously at room temperature, and the progress of the isomerization followed by 1 H NMR integration of the CH 3 resonances. The initial NMR spectrum showed a >30:1 ratio of isomers. Over 18 hrs the reaction was monitored periodically until an equilibrium ratio of 0.60 ± 0.1 (8 5.15 isomer to 8 5.05 isomer) was reached. The forward and reverse rate constants were calculated in the usual manner. 90 Reaction to Determine 13 C0/1 2 CO Exchange. A solution of the dimethyl titanacyclobutene (100 mg, 0.406 mmol) in 4 mL diethyl ether was transferred into a Lab- Glass pressure bottle fitted with a stirbar and pressure gauge. The cannula was rinsed twice with 0.5 mL portions of toluene. The pressure bottle was partially evacuated, cooled to -78°C, and 15 psi of 13 CO (90% 13 C) were introduced. The reaction mixture was allowed to warm slowly to about -10°C to 0°C at which time a clear green solution had formed. The reaction was immediately cooled to -78°C and CO vented. The pressure bottle was refilled with 100 psi of 12 CO (natural abundance) and allowed to warm to -30°C with stirring. The rearrangement as noted by the loss of green color was complete in approximately 15 min. The ketene complex was isolated as previously described to yield 70 mg (0.255 mmol, 63%) of product. Analysis by 1 H NMR (C 6 D 6 ) showed the signal at 6 2.61 to be a singlet, indicative of no incorporation of 13 CO in the product. 2-t-Butylimino-4,5-Diphenyltitanocenecyclopentene, 4a. A stirred solution of 2,3 diphenyltitanocenecyclobutene, 2a, (310 mg, 0.837 mmol) in 2 ml of toluene was treated with t-butylisocyanide (160 µL, 1.64 mmol) at room temperature. The color of the solution immediately changed from purple to orange and the volatiles removed in vacuo. The solid was dissolved in the minimum amount of toluene at 50°C (- 3 ml) and slowly cooled to -50°C. The crystals were collected, washed with 3 x 0.5 ml of cold pentane and dried in vacuo to yield 216 mg (0.496 mmol, 59%) of 4a: 1 H NMR (400 MHz, C 6 D 6 ) 6 7.28-6.94 (m, lOH), 5.276 (s, lOH), 4.127 (s, 2H), 0.927 (s, 9H). The crystals had occluded 1 molecule of toluene per 2 molecules of 4a. 13 C{1 H} NMR (100 MHz, C5D 6 ) 6 220.08, 194.68, 156.11, 142.04, 141.42, 129.86, 129.26, 128.49, 128.11, 127.25, 91 125.64, 125.14, 122.84, 106.28, 60.19, 52.80, 29.81. ffi (KBr, cm- 1 ) 1772 (s). Anal. Calcd for C 30 H 31 NTi · 0.5 toluene: C, 80.55; H, 7.06; N, 2.80. Found: C, 80.61; H, 7.03, N, 2.79. 2-t-Butylimino-4-Trimethylsilyl-5-Phenyl-Titanacyclopentene, 4b. A stirred solution of 2-phenyl-3-trimethylsilyl titanacyclobutene, lb (260 mg, 0. 709 mmol) in 2 ml of toluene was treated with t-butylisocyanide (110 µ,L, 1.09 mmol) at room temperature. The color immediately changed from red to orange. The solution was stirred for approximately 5 minutes and the volatiles removed in vacuo. The orange solid was dissolved in 1 ml of toluene at 50°C and slowly cooled to -50°C. The crystals were collected at -50°C, washed with cold pentane (3 x 0.5ml), and dried in vacuo to yield 165 mg (0.367, 52%) of 4b: 1 H NMR (400 MHz, C6D6) o 7.13 (m, 4H), 6.91 (m, lH), 5.09 (s, lOH), 3.89 (s, 2H), 0.801 (s, 9H), 0.00 (s, 9H). 13 C{ 1 H} NMR {100 MHz, C 6D 6) o 227.02, 213.75, 157.47, 144.81, 125.86, 123.37, 112.63, 106.08, 60.22, 54.37, 29.83, 2.18. IR (KBr, cm- 1 ) 1758 (s). Anal. Calcd for C 2 1H3 sNSiTi: C, 72.14; H, 7.85; N, 3.12. Found: C, 71.81; H, 7.71, N, 3.14. 2-t-Butylimino-4-Methyl-5-Phenyltitanacyclopentene, 4c. A stirred solution of 3-methyl-2phenyl titanacyclobutene, 2c (250 mg, 0.811 mmol) in 2 ml of toluene was treated with t-butylisocyanide (160 µ,L, 1.62 mmol) at room temperature. The color immediately changed from red to orange. The mixture was stirred at room temperature for 5 minutes; then the volatiles were removed in vacuo. The orange solid was dissolved in the minimum amount of toluene (3.5 ml) at 50°C, then slowly cooled to -50°C. The crystals were collected at -50°C, washed 3 x 0.5 ml with cold pentane and dried in vacuo to yield 179 mg (0.457 mmol, 56%) of 4c: 1 H NMR (400 MHz, C 6D 6) o7.36 (m, 2H), 7.27 (m, 2H), 92 7.08 (m, lH), 5.25 (s, lOH), 3.55 (s, 2H), 1.87 (s, 3H), 0.925 (s, 9H). 13 C{1H} NMR (100 MHz, CaDa) 6 222.89, 187.25, 156.73, 136.19, 126.52, 122.83, 112.73, 106.13, 59.98, 52.71, 29.83, 18.65. ffi (KBr, cm- 1 ) 1775 (s). Anal. Calcd for C 25 H 29 NTi: C, 76.72; H, 7.47; N, 3.58. Found: C, 76.42; H, 7.36, N, 3.62. 2-t-Butylimino-4,5-Dimethyltitanocenecyclobutene, 4d. A stirred solution of 2,3- dimethyltitanocenecyclobutene (166 mg, 0.67 mmol) in 1 mL of THF was treated with t-butylisocyanide (68 µL, 0.74 mmol) at room temperature. An immediate color change from red to orange was observed. The mixture was stirred at room temperature for 15 minutes, then the volatiles removed in vacuo. The solid was extracted with 4 mL of hexane, the solution filtered and cooled to -50°C. The orange crystals were isolated, washed twice with 0.5 mL portions of cold pentane, and dried in vacuo to yield the 112 mg of the product (0.34, 51%). 1 H NMR (90 MHz, C 6 D 6 ) 6 5.24 (s, lOH), 3.55 (br s, 2H), 2.14 (br s, 3H), 1.98 (br, s, 3H), 0.93 (s, 9H); 13 C{ 1 H} NMR (22.5 MHz, C 6 D 6 ) 6 224.81, 181.75, 134.70, 105.36, 59.68, 52.93, 29.88, 26.55, 16.02; IR (Nujol, KBr, cm- 1 ) 1770. Anal. Calcd for C 20 H 21NTi: C, 72.94; H, 8.26; N, 4.25. Found: C, 72.88; H, 8.06, N, 4.23. Reaction of 3a with Acetylene. A Fischer-Porter bottle fitted with a stirbar was charged with diphenyltitanocene vinyl ketene oligomer, 3a (330 mg, 0.837 mmol) dissolved in 3 ml of toluene. Approximately 10 psi of acetylene gas were introduced from a cylinder with stirring. Immediately the color began to change from yellow to green. After 3 minutes, the ketene complex had dissolved and green crystals began to precipitate. After an additional 5 minutes the excess acetylene was vented, and the volatiles were removed in vacuo to yield 310 mg of a light-green powder (0.730 mmol, 87%): 93 1 H NMR (400 MHz, C 6 D6 ) o 7.88 (d of d, J=8.4, 1.2 Hz, 2H), 7.75 (d of d, J=7.7, 1.2 Hz, 2H), 7.21 (d, J=8.3 Hz, 2H), 7.13 (d, J+7.7 Hz, 2H), 7.01 (m, lH), 6.96 (m, lH), 6.96 (d, J=9.0 Hz, lH), 6.46 (d, J=9.0 Hz, lH), 5.90 (d, J=9.0 Hz, lH), 5.52 (d, J=2.0 Hz, lH), 5.79 (s, lOH). Difference NOE experiments: irradiation of o 6.96 enhances o 7.21, 6.46, 5.79; irradiation of o 6.46 enhances o 6.96; irradiation of b 5.79 enhances b 7.88, 7.75, 6.96. 13 C{1H} NMR (22.5 MHz, C 6 D 6 ) b 202.33 (CH), 162.67, 148.59, 142.52, 140.73, 139.48 (CH), 128.76, 128.54, 127.24, 127.51, 124.48, 117.33 (CH 2), 116.08 (Cp), 111.85. IR (KBr, cm- 1 ) 3090 (w), 3030 (w), 1605 (m), 1580 (m), 1540 (s), 1510 (s), 1495 (s). Anal. Calcd. for C2sH2 4 0Ti: C, 79.24; H, 5.70. Found: C, 76.94; H, 5.59. Reaction of 3a with Ethylene. A Fischer-Porter bottle fitted with a pressure gauge and stirbar was charged with diphenyltitanocene vinyl ketene oligomer, 3a (304 mg, 0.821 mmol), 6 ml of toluene and 20 psi of ethylene. The reaction mixture was placed in a 70°C oil bath for 12 hours during which the color changed from yellow to purple and much of the oligomer dissolved. The mixture was cooled to room temperature, the excess ethylene vented, and the mixture transferred to a schlenk flask. The volatiles were removed in vacuo and the residue extracted with diethylether. The extract was filtered and the solvent removed in vacuo to yield 250 mg (0.628 mmol, 76%) of the product: 1 H NMR (90 MHz, C 6 D 6 ) b 7.74 (m, 4H), 7.30-6.90 (m, 6H), 5.87 (d, J=2.0 Hz, lH), 5.78 (s, lOH), 5.37 (d, J=2.0 Hz, lH), 3.71 (t, J=7.3 Hz, 2H), 1.85 (t, J=7.3 Hz, 2H). 13 C{1H} NMR (22.5 MHz, C 6 D 6 ) b 163.65, 149.13, 142.03, 141.27, 130.33, 128.60, 128.43, 127.54, 125.67, 123.94, 116.52 (CH2), 115.27 (Cp), 113.96, 108.17, 54.54 (CH 2), 54.06 (CH 2). IR {KBr, cm- 1 ) 3090 (w), 3040 (w), 2920 {s), 1560 {s), 1495 {m). Anal. Calcd. for C 28 H 26 0Ti: C, 78.87; H, 6.15. 94 Found: C, 78.05; H, 6.20. Reaction of 3a with Propyne. An NMR tube was charged with 3a (36 mg, 0.091 mmol) in the drybox, attached to a tefl.on valve and degassed on the vacuum line. The solvent, C6D6, was condensed into the tube followed by propyne (0.128 mmol) and the tube sealed. The solvent was thawed at room temperature and over 30 minutes the starting material dissolved to yield a green solution: 1 H NMR (400 MHz, C 6D 6) S 7.87 (d, J=7.8 Hz, 2H), 7.76 (d, J=7.6 Hz, 2H), 7.21 (t, J=7.8 Hz, 2H), 7.13 (t, J=7.6 Hz, 2H), 7.00 (m, 2H), 6.95 (m, 2H), 6.30 (q, J=l.5 Hz, lH), 5.935 (d, J=2.2 Hz, lH), 5.831 (s, lOH), 5.543 (d, J=l.95 Hz, lH), 1.613 (d, J=l.7 Hz, 3H). Difference NOE experiments: irradiation of S 1.61 enhances S 6.30; irradiation of S 6.30 enhances S 1.61; irradiation of S 5.83 enhances S 7.87, 7.76, 6.30, 1.61. 13 C{1 H} NMR (100 MHz, C6D 6) S 212.04, 160.60, 148.48, 142.36, 140.71, 136.36 (CH), 128.62, 128.52, 128.41, 128.12, 127.88, 127.84, 127.50, 127.22, 124.24, 117.41 (CH2), 116.15 (Cp), 114.07, 106.48, 29.05. Reaction of 3d with Acetylene. To a suspension of vinyl ketene oligomer 3d (13 mg, 0.047 mmol) in 400 µL of C6D6 in an NMR tube was added 4 µL (1 equivalent) of THF. Some of the ketene complex dissolved. To this mixture was added acetylene (5 ml, 0.11 mmol) via syringe. During the following 10 minutes the solution turned green, and after 20 minutes the reaction was > 90% complete by NMR. The NMR indicated only one isomer. 1 H NMR (200 MHz, C 6D 6) S 6.97 (d, J=8.8 Hz, lH), 6.68 (d, J=8.8 Hz, lH), 5.84 (s, lOH), 5.11 (br d, J=2.9 Hz, lH), 5.02 (d of q, J=2.9, 1.5 Hz, lH), 1.95 (br s, 3H), 1.86 (s, 3H). During the next several hours the initial isomer isomerized to produce approximately a 1:1 ratio of products. New isomer 1 H NMR (200 MHz, 95 C6D 6) 6 7.08 (d, J=8.8 Hz, lH), 6.52 (d, J=8.8 Hz, lH), 5.77 (s, lOH), 5.07 (br d, J=2.2 Hz, lH), 4.97 (br s, lH), 2.13 (br s, 3H), 2.02 (s, 3H). The isomer at 6 5.78 will eventually become the major isomer at equilibrium (57:43). The reaction and isomerization do not require THF and can be accelerated by warming to 80°C, although copious amounts of polyacetylene are also produced. 13 C{ 1H} NMR (22.5 MHz, C6D 6) 6 mixture of isomers 201.30 (CH), 197 .24 (CH), 161.80, 159.42, 146.37, 145.72, 137.81 (CH), 137.21 (CH), 115.59 (Cp are isochronous), 112.40, 109.91, 109.74, 105.57, 25.67 (CH3), 23.39 (CH3), 16.73 (CH3), 14.18 (CH3). Reaction of 3d with Propyne. An NMR tube was charged in the drybox with vinyl ketene complex 3d (35 mg, 0.128 mmol), attached to a tefion adapter and 400 µL of C6D6 transferred into the tube. Propyne (0.13 mmol) was condensed into the tube and the tube sealed. The mixture was thawed at room temperature and the ketene complex reacted over several days to yield two isomeric titanaoxacyclopentenes in a 56:44 ratio: major isomer 1H NMR (400 MHz, C 6D 6) 6 6.28 (s, lH), 5.79 (s, lOH), 5.06 (d, J=l.2 Hz, lH), 4.95 (br s, lH), 2.14 (br s, 3H), 2.04 (s, 3H), 1.74 (br s, 3H). Minor isomer 1H NMR (400 MHz, C 6D 6) 6 6.51 (s, lH), 5.86 (s, lOH), 5.13 (d, J=2.4 Hz, lH), 5.04 (hrs, lH), 1.98 (s, 3H), 1.88 (s, 3H), 1.76 (br s, 3H). 13 C{1H} NMR (22.5 MHz, C 6D 6) 6 (mixture of isomers) 211.27, 206.93, 159.80, 157.20, 146.42, 145.77, 135.15, 134.23, 115.59 (Cp are isochronous), 112.18, 109.42, 108.55, 108.12, 107.68, 105.68, 104.00, 28.50, 28.43, 25.77, 23.50, 16.67, 14.13. Synthesis of Lactone lla. To a stirred solution of diphenylketene complex, 3a (150 mg, 0.376 mmol), in 1 ml of THF was added acetaldehyde (25 µL, 0.72 mmol) at room temperature. The reaction mixture immediately changed color from brown to purple. The reaction 96 was stirred at room temperature for 18 hours. The reaction was quenched with 1 ml of 15% aqueous NaOH and 2 ml of diethylether.The aqueous layer was extracted with 4 x 2 ml of diethylether, the organic extracts combined, dried over MgS0 4 , and concentrated at reduced pressure to yield 94 mg of an amber oil. The product could be flash-chromatographed (diethylether : petroleum ether, 1:1) to yield 44 mg ( 0.167 mmol, 44 %) of lactone lla as a crystalline solid. 1 H NMR (400 MHz, CDCL 3 ) o 7.215-7.012 (m, lOH), 4.793 (d of d of q, J=ll.72, 3.66, 6.35 Hz, lH), 2.888 (d of d, J=17.57, 11.72 Hz, lH), 2.771 (d of d, J=17.57, 3.66 Hz, lH), 1.529 (d, J=6.35 Hz, 3H). 13 C{ 1 H} NMR (22.5 MHz, CDCL 3 ) o 165.63, 151.44, 138.49, 134.86, 130.74, 128.63, 128.36, 128.09, 127.76, 127.33, 73.10, 37.72, 20.60. IR {KBr, CC14 , cm- 1 ) 1700 {s). Synthesis of Lactone llb. To a stirred solution of dimethyl ketene complex, 3d (150 mg, 0.54 7 mmol), in 2 ml of THF was added p-tolualdehyde (71 µL, 0.602 mmol) via syringe at room temperature. The color immediately changed from yellow-brown to purple and after several minutes a purple solid began to precipitate. Toluene, 2 ml, was added to redissolve to solid. The mixture was stirred for 1 hour at room temperature, then quenched with 15% aqueous NaOH. The pH was adjusted to near neutral with aqueous HCl and the mixture stirred for 12 hours. The mixture was extracted with 2 x 10 ml of diethylether, the organic extracts combined, dried over MgS0 4 , and concentrated at reduced pressure. The material was flash-chromatographed on silica gel (petroleum ether : diethylether, 60:40) to yield 30 mg (0.139 mmol, 25%) of lactone llb an oil that crystallized on standing: 1 H NMR (400 MHz, CDCL 3 ) o 7.280 (d, J=8.0 Hz, 2H), 7.170 (d, J=8.0 Hz, 2H), 5.290 (d of d, J=3.9, 12.45 Hz, lH), 2.688 {bf t, J=16.6 Hz, lH), 2.405 (d of d, J=3.9, 17.09 Hz, lH), 2.350 (s, 97 lOH), 1.970 (s, 3H), 1.939 (d, J=0.8 Hz, 3H). 13 C{1H} NMR (22.5 MHz, CDCL 3 ) 0 166.22, 148.40, 138.12, 136.00, 129.17, 125.92, 122.51, 77.60, 38.21, 21.04, 20.12, 12.48. IR (KBr, CC14 , cm- 1 ) 1720 (s). Reaction of 3a with Acetaldehyde. Treatment of a suspension of diphenyl vinyl ketene complex 3a (14 mg, 0.03S mmol) in 400 µL of C 6 D 6 with acetaldehyde (4 µL, 0.06 mmol) immediately yields a new purple product: 1 H NMR (90 MHz, C 6 D 6 ) 8 7.63 (m, 4H), 7.15-6.77 (m, 6H), 5.85 (s, SH), 5.76 (s, SH), 4.66 (m, lH), 2.51 (m, 2H), 1.11 (d, J=6.6 Hz, 3H). The compound decomposed over several hours to species that had very broad NMR signals. Infrared analysis of the purple intermediate displayed an absorption at 1595 cm- 1 , which shifted to 1560 cm- 1 when 13 C labeled ketene complex was used. 13 C NMR analysis of the purple intermediate from the 13 C labeled complex displayed an intense singlet at 8 276.16. Reaction of 3a with Pivaldehyde. Treatment of a suspension of 3a (28 mg, 0.070 mmol) in 400 µL of C 6 D 6 with pivaldehyde (8 µL, 0.118 mmol) immediately produced a new species: 1 H NMR (200 MHz, C 6 D 6 ) 8 7.80 (m, 4H), 7.20-6.90 (m, 6H), 6.07 (s, SH), 5.81 (s, SH), 4.44 (d, J=7.3 Hz, lH), 2.54 (d, J=14.2 Hz, lH), 2.35 (d of d, J=13.6, 7.6 Hz, lH), 0.92 (s, 9H). The material decomposed to brown paramagnetic species during the next 12 hours. Reaction of 3a with t-Butylacetylene. Treatment of a suspension of diphenyl ketene oligomer 3a (32 mg, 0.080 mmol) in 400 µL of C5D5 with t-butylacetylene (11 µL, 0.20 mmol) reacted over several hours to yield a red solution. Warming the reaction mixture to 80 °C accelerated 98 the reaction. The product was identified as the titanaoxacyclopentene insertion product: 1 H NMR (400 MHz, C6D6) 6 7.60 (d, J=7.6 Hz, 2H), 7.55 (d, J=7.6 Hz, 2H), 7.39 (s, lH), 7.22 (t, J=7.8 Hz, 2H), 7.11 (t, J=7.6 Hz, 2H), 7.02 (m, 2H), 5.806 (s, lOH), 1.33 (s, 9H). Difference NOE experiments: irradiation of 6 5.81 enhanced 6 7.39. Reaction of 3a with Phenylacetylene. A suspension of ketene complex 3a (36 mg, 0.09 mmol) in 400 µL of C 6D 6 was treated with phenylacetylene (11 µL, 0.116 mmol) at room temperature. After 1 hour the ketene complex had dissolved to yield a red solution: 1 H NMR (400 MHz, C 6D 6) 6 7.61-7.51 (m, 6H), 7.21-6.90 (m, 9H), 5.815 (s, lOH), 5.33 (d, J=l.95 Hz, lH), 5.31 (d, J=l.95, lH). A minor product was also observed at 6 5.97 (s, Cp). Reaction of 3a with Dimethylaluminum Chloride. A suspension of complex, 3a, (25 mg, 0.063 mmol) in C6D6 was treated with a solution of dimethylaluminum chloride (2M in C 6D 6, 32 µL, 0.064 mmol) at room temperature. An immediate reaction occurred to yield an orange solution: 1 H NMR (400 MHz, C6D6) 6 7.42 (d, J=7.6 Hz, 4H), 7.23 (t, J=7.6 Hz, 2H), 7.14-6.98 (m, 4H), 5.49 (s, lOH), 5.34 (d, J=l.9 Hz, lH), 5.14 (d, J=l.9 Hz, lH), -0.451 (s, 6H). 13 C{1H} NMR (100 MHz, C 6D 6) 6 184.8, 149.1, 143.0, 141.3, 137.1, 136.6, 128.7, 127.9, 127.8, 127.7, 127.5, 126.8, 125.6, 117.3, 115.1, 111.5 (Cp), -6.48 (br s). The complex was stabie for hours at room temperature. The complex did not react with propene. Reaction of 3a with Trimethylaluminum. A suspension of complex 3a (25 mg, 0.063 mmol) in C6D6 was treated with trimethylaluminum (2M in C 6D 6, 32 µL, 0.064 mmol) at room temperature. An im- 99 mediate reaction occurred to yield a red-brown solution: 1 H NMR (400 MHz, C 6 D 6 ) o 7.67 (d, J=7.1 Hz, 2H), 7.41 (d, J=7.1 Hz, 2H), 7.28 (d, J=7.6 Hz, 2H), 7.10-6.96 (m, 4H), 5.49 (s, lOH), vinyl CH 2 not observed, -0.899 (s, 9H). 13 C{1 H} NMR (100 MHz, C6 D 6 ) o 188.6, 148.9, 142.5, 139.8, 128.7, 127.9, 127.6, 127.4, 127.2, 126.9, 125.3, 124.3, 114.7, 113.6, 112.5 (Cp), 111.5, -8.99 (br s). The trimethylaluminum complex was less stable than the dimethylaluminumcomplex and did not react with propene. Reaction of 3d with Dimethylaluminum Chloride. A suspension of complex 3d (26 mg, 0.095 mmol) in 400 µL of C 6 D 6 was treated with dimethylaluminum chloride (2M in C 6 D5, 47 µL, 0.094 mmmol) at room temperature. The ketene complex immediately dissolved to yield an orange solution: 1 H NMR (90 MHz, C 6 D 6 ) o 5.56 (s, lOH), 4.91 (hr s, 2H), 2.03 (s, 3H), 1.63 (s, 3H), -0.25 (s, 6H). Reaction of 3d with Trimethylaluminum. A suspension of complex 3d (26 mg, 0.095 mmol) in 400 µL of C5D5 was treated with dimethylaluminum chloride (2M in C 6 D5, 47 µL, 0.094 mmmol) at room temperature. The ketene complex immediately dissolved to yield an orange solution: 1 H NMR (90 MHz, C 6 D 6 ) o 5.75 (s, lOH), 4.87 (br s, 2H), 2.19 (s, 3H), 1.27 (s, 3H), -0.68 (s, 9H). 100 References 1. Collman, J.P.; Hegedus, L.S. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1980. 2. Dotz, K. H. Pure. Appl. Chem. 1983, 55, 1689-1706. 3. Wulff, W. D.; Tang, P-C. J. Am. Chem. Soc. 1984, 106, 434-6. 4. Semmelhack, M. F.; Tamura, R.; Schnatter, W.; Springer, J. J. Am. Chem. Soc . 1984, 106, 5363-4. 5. Hegedus, L. S.; McGuire, M. A.; Schultze, L. M.; Yijun, C.; Anderson, 0. P. J. Am. Chem. Soc. 1984, 106, 2680-87. 6. Yamashita, A.; Scahill, T. A. Tet. Lett. 1982, f9, 3765-69. 7. (a) Dotz, K. H. Angew. Chem. Int. Ed. Eng. 1979, 18, 954-5. (b) Schubert, N.; Dotz, K. H. Cryst. Struct. Commun. 1979, 18, 989-994. 8. (a) Tebbe, F. N.; Harlow, R. L. J. Am. Chem. Soc. 1980, 102, 6149-51. (b) McKinney, R. J.; Tulip, T. H.; Thorn, D. L.; Coolbaugh, T. S.; Tebbe, F. N. J. Am. Chem. Soc. 1981, 109, 5584-6. (c) The synthesis of titanacyclobutenes le-le was accomplished via titanocyclobutanes: Howard, T. R.; Lee, J. B.; Grubbs, R. H. J. Am. Chem. Soc. 1980, 102, 6876-8. 9. For other titanium ketene complexes see: (a) Straus, D. A.; Grubbs, R. H. J. Am. Chem. Soc. 1982, 104, 5499-5500. (b) Moore, E. J.; Straus, D. A.; Armantrout, J.; Santarsiero, B. D.; Grubbs, R. H.; Bercaw, J. E. J. Am. Chem. Soc. 1983, 105, 2068-70. (c) Fachinetti, G.; Biran, C.; Floriani, C.; Chiesi-Villa, A.; Guastini, G. J. Am. Chem. Soc. 1978, 100, 1921-2. 10. The crystal structure of the bis(trimethylsilyl) titanacyclobutene (see 4b) shows a distortion toward a ca.rbene-acetylene complex and free bis(trimethylsilyl) acetylene is observed during ca.rbonylation. 11. For other transition-metal vinyl ketene complexes see: (a) Yamashita, A.; 101 Scahill, T. A. Tet. Lett. 1982, es, 3765-68. (b) Newton, M. G.; Panteleo, N. S.; King, R. B.; Chu, C-K. J.C.S. Chem. Comm. 1979, 10-12. (c) Binger, P.; Cetinkaya, B.; Kruger, C. J. Organomet. Chem. 1978, 159, 63-72. (d) Mitsudo, T.; Sasaki, T.; Watanabe, Y.; Takegami, Y.; Nishigaki, S.; Nakatsu, K. J.C.S. Chem. Comm. 1978, 252-3. (e) Klines, J.; Weiss, E. Angew. Chem. Int. Ed. Eng. 1982, f1, 205. (f) Templeton, J. L.; Herrick, R. S.; Rusilo, C. A.; McKenna, C. E.; McDonald, J. W.; Newton, W. E. Inorg. Chem. 1985, e-', 1383-8. (g) Hill, A. E.; Hoffmann, H. M. R. J.C.S. Chem. Comm. 1972, 574-5. (h) Gambarotta. S.; Pasquali, M.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1981, eo, 1173-8. 12. Thermal decomposition or exhaustive carbonylation of the vinyl ketene complexes affords some free vinyl ketene. 13. Wolzanski, P. T.; Bercaw, J.E. Accts. Chem. Res. 1980, 19, 121-7. 14. Fachinetti, G.; Fochi, G.; Floriani, C. J.C.S. Dalton Trans. 1977, 1946-50. 15. Erker, G. Accts. Chem. Res. 1984, 17, 103-9. 16. Marshall, J. L. Carbon-Carbon and Carbon-Proton NMR Couplings; Verlag Chemie International: Berlin, 1983. 17. The 1 J11c-11c for Cp2Ti 13 COCH 3 (Cl) is 19 Hz. Meinhart, J. D.; Grubbs, R. H. Unpublished results. 18. Linke, W.F. Solubilities of Inorganic and Metal-Organic Compounds, Vol. 1; American Chemical Society: Washington D.C., 1958, 4th ed. 19. This thesis, Chapter 4. 20. Brown-Wensley, K. A.; Buchwald, S. L.; Cannizzo, L.; Clawson, L.; Ho, S.; Meinhart, D.; Stille, J. R.; Straus, D.; Grubbs, R. H. Pu.re. Appl. Chem. 1983, 55' 1733-44. 21. Falmagne, J-B.; Escudero, J.; Taleb-Sahrasui, S.; Ghosez, L. Angew. Chem. 102 Int. Ed. Eng. 1981, eo, 879-80. 22. Edwards, B. H.; Rogers, R. D.; Sikora, D. J.; Atwood, J. L.; Rausch, M. D. J. J. Am. Chem. Soc. 1983, 105, 416-26. 23. (a) Floriani, C.; Fachinetti, G. J. J.C.S. Chem. Comm. 1972, 790. (b) McMurry, J.E.; Miller, D. D. J. Am. Chem. Soc. 1983, 105, 1660-1. 24. (a) Katz, T. J.; Lee, S. J. J. Am. Chem. Soc. 1980, 102, 422-4. (b) Katz, T. J.; Ho, T. H.; Shih, N-Y.; Ying, Y-C.; Stuart, V. I. W. J. Am. Chem. Soc. 1984, 106, 2659-68. (c) Katz, T. J.; Sivavec, T. M. J. Am. Chem. Soc. 1985, 107, 737-8. 25. Cyclobutenones have been isolated from reactions of Fischer carbenes and acetylenes: (a) Dotz, K. H.; Dietz, R. J. Organomet. Chem. 1978, 157, C55-57. (b) Wulff, W. D.; Chan, K. S. Abstracts of the 189th ACS National Meeting, Miami Beach, Florida, 1985, American Chemical Society: Washington D.C., 1985. 26. A partial report of this work has appeared: Meinhart, J.D.; Santarsiero, B.D.; Grubbs, R.H. J. Am. Chem. Soc. 1986, 108, 3318-23. 27. Fachinetti, G.; Fochi, G.; Floriani, C. J.C.S. Dalton Trans. 1977, 1946-50. 28. Straus, D.A., Ph.D. Thesis, California Institute of Technology, 1982. 29. Cotton, J.D.; Crisp, G.T.; Daly, V.A. Inorg. Chim. Acta., 1981, 47, 165-9. 30. (a) Herrmann, W.A.; Plank, J. Angew. Chem. Int. Ed. Eng. 1978, 17, 525. (b) Messerle, L.; Curtis, M.D. J. Am. Chem. Soc. 1980, 102, 7787. 31. Erker, G. Accts. Chem. Res. 1984, 17, 103-9. 32. Mann, B.E.; Taylor, B.E. 13 C NMR Data for Organometallic Compounds, Acedemic Press: New York, 1981. 33. (a) Erker, G.; Czisch, P.; Schlund, R.; Angermund, K.; Kruger, C. Angew. Chem. Int. Ed. Eng. 1986, 25, 364-5. 103 34. (a) Lappert, M.F.; Luong-Thi, N.T.; Milne, C.R.C. J. Organomet. Chem. 1979, 174, C35-7. (b) Froemberg, W.; Erker, G. J. Organomet. Chem. 1985, £80, 355-63. (c) Wolczanski, P.T.; Bercaw, J.E. J. Am. Chem. Soc. 1979, 101, 6450-2. 35. (a) Adams, R.D.; Chodosh, D.F. Inorg. Chem. 1978, 17, 41-8. (b) Treichel, P.M.; Hess, R.W. J. Am. Chem. Soc. 1970, 92, 4731-3. (c) Wagner, K.P.; Treichel, P.M.; Calabrese, J.C. J. Organomet. Chem. 1974, 71, 299-308. 36. Handbook of Chemistry and Physics, Weast, R.C., Ed., CRC Press: Boca Ra- ton, Florida, 1980. 37. Johnson, F. Chem. Rev. 1968, 68, 375-413. 38. (a) Waymouth, R.M.; Grubbs, R.H. Unpublished results. (b) Roddick, D.M., Ph.D. Thesis, California Institute of Technology, 1984. 39. (a) Shur, V.B.; Burlakov, V.V.; Yanovsky, A.I.; Petrovsky, P.V.; Struchkov, Yu.T.; Vol'pin, M.E. J. Organomet. Chem. 1985, £97, 51-9. (b) Yasuda, H.; Tatasumi, K.; Nakamura, A. Accts. Chem. Res. 1985, 18, 120-6. 40. (a) Waymouth, R.M.; Clauser, K.R.; Grubbs, R.H. J. Am. Chem. Soc. 1986, 108, 6385-7. (b) Waymouth, R.M.; Santarsiero, B.D.; Grubbs, R.H. J. Am. Chem. Soc. 1984, 106, 4050-1. 104 Chapter 4 Insertion of Carbon-Heteroatom Multiple Bonds into Bis(77 5 -Cyclopentadienyl) Titanacyclobutenes 105 Introduction Insertion of unsaturated organic molecules into transition-metal carbon bonds has received much attention during the past thirty years. Insertion of carbon-carbon multiple bonds into transition-metal alkyl complexes has been the focus of many laboratories due to the economic importance of poly-olefins. 1 Carbon-heteroatom multiple bonds (i.e. ketone, ester, nitrile, and imine) also insert into transitionmetal alkyl complexes. 2 Application of transition-metal alkyl complexes rather than main group complexes for nucleophilic addition to carbon-heteroatom bonds has the potential to alter the reactivity and selectivity by the appropriate combination of ancillary ligands. Organic chemistry contains many examples of metal alkyl addition to carbonheteroatom multiple bonds. The Grignard reaction is a classic example of this type of reaction. Alkyl and aryl compounds derived from Li, Na, Al, and Cd are commonly used in organic synthesis. 3 The reactivity of these complexes is generally 1,2 addition to carbonyl groups, with varying selectivity. Few transition-metal organometallic reagents have been developed for addition to carbon-heteroatom functionality. Dialkyl cuprate complexes (R 2 CuLi) add to a, P-unsaturated ketones in a 1,4 sense to yield a ')'-alkylated ketone. 4 In contrast, an alkyl lithium reagent adds in a 1,2 sense to the same ketone to yield an alcohol. This modified selectivity of a main group complex via a transition metal may provide new methods for regio- and stereo-controlled reactions. Likewise, (iPrO)aTiCl, when treated with a Grignard reagent, forms an alkyl titanium derivative, which is selective for aldehydes in the presence of ketones and nitriles. 5 Thus, the need for protection-deprotection of sensitive functionality may be reduced. This same titanium reagent also reacts in a highly diastereoselective manner with ketones and a.ldehydes. Transition metal alkyl complexes from the left 106 half of the transition block are highly reactive toward carbonyl compounds due to the oxophilicity of the metal. Several reactions are known where a transition metal complex serves as a catalyst, transferring or coupling alkyl groups from a donor complex to the unsaturated substrate. 6 Recently, 1,2-addition of carbonyl compounds to metallacyclobutane complexes has been postulated by product analysis. 7 Cp2 M~ + M =Zr, Hf Due to the lack of methylene transfer chemistry of titanacyclobutenes, the reactivity of titanacyclobutenes with carbon-heteroatom bonds was investigated. Titanacyclobutenes offer a unique template for the study of insertion into titaniumcarbon bonds. 107 Results Treatment of a solution of diphenyl titanocenecyclobutene, la, with acetone at room temperature for 2 days yields titanoceneoxacyclohexene, 2a, in quantitative yield (Equation 1). The reaction is greatly accelerated by warming the sample to 80°C for approximately 10-15 minutes. The methyl phenyl titanacyclobutene, lb, works equally as well. The titanaoxacyclohexenes, 2, are isolated as yellow solids. R' Cp Tiy--R 2 Ph 1 a : R =Ph 1b : R = CH3 P~·R" Cp Ti>=<' 2 Ph (1) R 2 The reaction is general for a variety of organic ketones (Table 1). Methylene transfer reaction to the ketone is not observed. Enolization of the ketone by the titanacyclobutene is not a significant side reaction. However, titanacyclobutenes with ,8-hydrogens do not insert ketones to an appreciable extent. The metallacycle begins to react, and the insertion product decomposes rapidly at room temperature. 16 The kinetics of the insertion reaction of acetone into la was monitored by NMR (Equation 2). The rate expression was first order in metallacycle and ketone, second order overall. At 50°C a second-order rate constant was calculated, k 323 = 5.94(3) x 10- 4 M- 1 sec- 1 • The activation parameters were determined by Eyring analysis of the rate constants over a 40°C temperature range (Table 2). The NMR of the reaction solution at room temperature shows sharp signals 108 Table 1. Ketone Insertion into Titanacyclobutenes. Ketone Titanacycle Product 0 A la Ph 0 A Ph la 0" Ph Q Ph Cp 2 Ti Ph 0 6 6 la la C~Ti~ ~ 2c Ph c~n;-r Ph 2d Ph 0/ 0 2b Ph Ph 0 2a CP2 Ti CP2 Ti la Ph 2e Ph Ph Q"v 0 Ph~ cpzli la Ph 0 Co ol)O la c~nd3 Ph la 2g Ph c~u;=t(;? Ph 2f Ph Ph 2h 109 Table 1. (cont.) Titanacycle Ketone &CH, Product Q 0 la Ph H,CDy 2i Cp2Ti'O_ Ph 0 la 2j Ph j:yo Ph la 2k Ph "·~~ Ph CH3 la I 21 0 CP2 Ti Ph 0 ~OEt la Ph Q"lr'OEt . Cp2 Ti 2m 0 0 Ph 0 A lb Ph Q CP2 Ti Ph 0 ~Ph lb 2n " CH 3 Q Cp2 Ti Ph 'Ph CH 3 2o 110 (2) Ph 1a Table 2. Ph 2a Rate Constants and Activation Parameters for Acetone Insertion into 2a. Temperature (K) k (M- 1 sec- 1 x 104 ) 293 3.51(7) 301 5.9(1) 313 16.8(2) 323 29.5(4) D.G~ 01 = 22.0(5) kcal mo1- 1 D.Ht = 13.1(4) kcal mo1- 1 D.S~ 01 . -29(1) eu for the metallacycle but a broad signal for the acetone. Upon cooling, the acetone signal broadens and disappears at ca. -40°C at 90 MHz. Upon further cooling to -80°C, the acetone signal begins to sharpen but does not split into a resolved doublet. Aldehydes also insert cleanly into titanacyclobutenes (Equation 3) . Treatment of a solution of la with p-tolualdehyde at room temperature cleanly results on disappearance of the starting material. Examination of the reaction mixture by 111 NMR reveals the formation of two products in a 2:1 ratio. The major product is the expected isomer 3a containing a titanium-oxygen bond. However, the second product appears to be a regioisomer, 3b, in which the aldehyde ha.s inserted in the opposite sense, forming a titanium-carbon bond. The dialkyl titanocene species, 3b, is much less stable than 3a. The titanaoxacyclohexenes are moderately air-stable and may be chromatographed on silica. The dialkyl isomers, 3b, are air-sensitive and decompose upon warming to 80°C. Insertion of acetaldehyde also yields two isomeric insertion products 4a and 4b in a nearly 1:1 ratio. R R Cp2 Tiy-Ph Ph RCHO Cp2TI~ Ph J--o + Ph Cp2 T i w Ph (3) Ph 1a 3a : R "'C6 H4 CH3 4a: R=CH 3 Sa : R=C6 H5 3b : R = C6 H4 CH 3 4b: R=CH 3 Sb : R=C6 H5 The insertion of benzaldehyde into la has also been studied by K. BrownWensley. 8 Again, two products 5a and 5b were observed in a 2:1 ratio. The isomers were physically separated and hydrolyzed with HCl. The organic products were identified and are consistent with proposed regiochemistry. Several other carbon-heteroatom multiple bonds add to titanacycles la. Tetramethy lguanidine inserts to yield a titanocene amidocyclohexene 6 (Equation 4). The 90 MHz 1 H NMR exhibits a broad singlet for the N(CH 3 )2 groups at room temperature. The signal passes through coalescence at +15°C, and becomes two singlets (.i::lv = 47.8 Hz) at -80°C. The 11 5 -cyclopentadienyl resonance also is a singlet until -47°C when it passes through coalescence and becomes two singlets 112 HO~Me2 "NMe2 Cp2Ti I Ph 1a (4) Ph 6 (~v = 73.5 Hz) at -80 °C. Nitriles also react with titanocyclobutenes (Equation 5); however, the reactions are not as clean as ketone insertions, and the products are not as stable. Treatment of a solution of la in 400 µL of C 6 D 6 with one equivalent of benzonitrile yielded, over 24 hours, a titanocene iminocyclohexene complex, '1. The product was stable for days in solution but eventually decomposed. The insertion reaction works for a variety of nitriles: p-tolyl, a-methyl propyl, a-phenyl propyl, and methacrylonitrile. Acetonitrile yielded several products that decomposed rapidly at room temperature. Insertion of nitriles into titanacycle lb was also facile. Hydrolysis of the insertion products yields the corresponding ketones (Equation 6). R-CN Cp 2 Tiy--Ph Ph (5) 1a A variety of substrates do not react with the titanacyclobutenes: esters, car- 113 (6) N_ Cp2 Ti I Ph ~ CH 2 >=< Ph 0 Ph Ph bonates, C02, CS2, and imines. The titanaoxacyclohexenes 2a can be removed from the metal fragment by hydrolysis with HCl to yield a homcrallylic alcohol in high yield (Equation 7). HCI Ph OH Ph~ ~ 1. I Ph Ph ~ ,CH 3 "CH3 (7) H We had hoped to insert CO into the remaining titanium-carbon bond of 2a to eventually yield a lactone (Equation 8). However, all attempts to react 2a with CO either thermally or photochemically failed. Lewis acids are known to accelerate migratory insertions of CO into metalcarbon bonds. 9 Treatment of 2a with one equivalent of dimethylaluminumchloride results in immediate formation of a new complex. The new complex was darkred and the NMR spectrum was very complex. Treatment of this complex with CO yielded starting material 2a. The deep-red color of the reaction mixture and 114 p-r~H, Cp 2 Ti>=< Ph co x (8) Ph Ph 2a analysis of the NMR spectrum suggest that the Ti-0 bond transmetallates to the dimethylaluminum chloride, forming a titanocene alkenyl chloride and aluminum alkoxide (Equation 9). Trimethyl tin chloride did not react with 2a. p-{~~H, Cp 2 Ti>=< Ph Ph AIMe 2 Ci Me2AI \ Cl Cp2T( 0 ;--{.,CH3 CH 3 >=<- Ph '( Ph (9) 115 Discussion Titanocenecyclobutenes readily insert ketones to yield titanoceneoxacyclohexenes. The reaction is quite general for many ketones, and a few examples deserve mention. The insertion shows very little facial selection for cyclohexenone derivatives. Insertion of 2-methylcyclohexanone yields two diastereomeric products in nearly equal ratios. Insertion of l-carvone gives two diastereomeric products in a 62:38 ratio. The lack of diasteroselection reflects both a lack of adverse steric interactions at the transition state and the relatively high reaction temperature. Attempting to increase the diastereoselection by reducing the temperature is impractical because of the slow reaction rate at room temperature. Titanacyclobutenes will add very sterically crowded ketones, such as dcamphor, although the reaction is much slower. The NMR data and difference NOE experiments suggest that the metallacycle adds to the endo-face of the camphor molecule (Equation 10). 20 Cp,Tiy--Ph (10) + Ph 1a Ph Ph Phenylcyclopropyl ketone inserts without any rearrangement to produce a single product in high yield. If the insertion mechanism involved a one-electron reduction or oxidation of the ketone, the cyclopropyl carbinyl radical could open. 11 116 Although rearrangement is not observed, this experiment does not conclusively rule out a radical mechanism. Ethyl leuvinate reacts exclusively at the methyl ketone to yield the expected oxacyclohexene, 2m. Simple esters such as methyl benzoate do not react with the titanacyclobutenes. This selectivity for ketones over esters may arise from two factors. Esters are slightly weaker bases than ketones (1-2 pKa units). 10 The carbonyl carbon of an ester is less electrophilic compared to a ketone, due to resonance from the other oxygen atom. 18 Both factors, the less ha.sic carbonyl oxygen and the less electrophilic carbon, contribute to the selectivity. Steric factors are not significant. Unlike ketones, which display an exchanged broadened NMR signal for the ketone during reaction, the NMR signals of the ester remain sharp. The NMR spectra during the reaction suggest that the ketone is associated with the metallacycle prior to reaction. Titanacyclobutenes are formally 16-electron complexes and have a vacant orbital into which the carbonyl may coordinate. Variable temperature NMR experiments confirm a dynamic process with a very low activation barrier, possibly ketone coordination, occurs. Kinetic data and activiation parameters (Table 2) are consistent with a second-order reaction. A rapid pre-equilibrium does not change the observed rate analysis. 12 The regiochemistry of aldehyde insertion also provides information about the mechanism. Formation of a titanium-carbon bond compared to a more thermodynamically stable titanium-oxygen bond is very unusual. The estimated energy difference of a Ti-C and a Ti-0 bond is ...... 50 kcal mo1- 1 • 19 The formation of a Ti-C bond has been observed in the head-to-tail coupling of diphenyl ketene units in a titanium diphenyl ketene complex. 23 A possible explanation for the product distribution is kinetic control of the insertion proceeding via a 1r-bound aldehyde complex. An organic carbonyl group can 117 coordinate either in a 11"-sense or O'-sense to the metallacycle. A Cp 2 V(acetone)+ complex in which the acetone molecule is 17 1-coordinated through the sp 2 lone pair of the oxygen atom has been structually characterized. 21 The variable temperature NMR results may be explained, by a reversible coordination of the carbonyl group in either geometry. However, a 11"-Complex is the necessary transition state for the insertion due to orbital overlap constraints. 13 If 17 1-coordination of the oxygen atom lead directly to product, then only 3 should be formed because the carbon would never interact with the titanium. A 11"-complex could give two isomeric complexes, one with the oxygen atom toward the metallacycle and one with the oxygen away from the metallacycle. Due to steric interactions, ketones react only with the alkyl substituents directed away from the 17 5 -cyclopentadienyl rings, resulting in the observed regiospecifi.city. Since aldehydes have only one alkyl group, they can twist slightly to accommodate reaction in either direction (Figure 1). Larger substituents on the aldehyde favor the Ti-0 product as predicted. The metal center is d 0 , and a rotation barrier resulting from back-bonding to the 11"* orbital should not exist. Figure 1. Proposed Carbonyl Complexes of 2a 118 The products are also consistent with an early transition state. Based on the Hammond postulate, an early transition state should be "reactant-like" and not reflect the relative stability of the products. 24 A substituent-effect study of the kinetics may provide information about the polarization of the transition state. A proposed reaction coordinate is shown in Figure 2. CH 3 0>-H \ Cp,Tly--Ph Ph Cp,Tly--Ph Ph E CHs O.TI~ Ph REACTION Ph COORDINATE Figure 2. Proposed Energy Profile for Aldehyde and Ketone Insertion Insertion of nitriles is analogous to insertion of ketones. However, the products appear to be less stable. The remaining methylene group at the '"'(-position may be quite acidic due to resonance delocalization (Equation 11), and deprotonation could lead to decomposition. Nitrile insertions into zirconocene hydride and alkyl complexes yield stable complexes. 14 If the nitrile insertion product is immediately hydrolyzed, the expected ketone is isolated in low yield. The most unusual substrate that inserts into titanacyclobutenes is tetramethylguanidine. The insertion product, 6, has two fiuxional processes by NMR. 15 The higher-energy process coalesces at +15°C at 90 MHz, yielding a ~Gt = 14.2 ± 119 Ph IN=\ Cp,TiHH Ph (11) Ph 0.3 kcal mo1- 1 • This process is attributable to hindered rotation of the N(CH 3 )2 groups. The lower-energy process coalesces at -47°C, yielding a ta.Gt = 10.9 ± 0.3 kcal mo1- 1 • This process is attributable to the inversion of the NH group bonded to the titanium. The nitrogen lone pair presumably interacts with the vacant LUMO on the metal (Equation 12). 22 This interaction would lead to inequivalent 11 5 -cyclopentadienyl rings, if the rate were slowed below the NMR time scale. <1 p~ L>\<=?'' fhNMo ~ •• (12) NMo, The lack of carbonylation of 2a is consistent with other titanium and zirconium alkyl alkoxide complexes. The lack of carbonylation is usually explained by invoking donation of the oxygen lone-pair into the LUMO on the titanium. Dative interaction from the oxygen fills the orbital, which would be used for coordination 120 of the CO. This 1!'-donation from the oxygen of titanium alkoxides has been structurally verified. 17 Attempts to complex the oxygen to another Lewis acid failed. Dimethylaluminum chloride appeared to transmetallate the Ti-0 bond, although the resulting complex did not react with CO. 121 Conclusions Titanacyclobutenes readily insert ketones, aldehydes, and nitriles to form new organometallic complexes. These reactions proceed in good yield with titanacyclobutenes that have a phenyl group at the a-position. Titanacyclobutenes that have alkyl substituents at the a-position form unstable products. The reaction is general for many ketones and highly selective for ketones and aldehydes over esters. Aldehydes yield two products, the predicted Ti-0 bound isomer but also the Ti-C bound isomer. The product distribution is consistent with a 7r-bound carbonyl group at the rate-determining transition state. A detailed kinetics study of the insertion, including substituent effects, would be useful in understanding the mechanism. Insertion of nitriles forms an analogous product; however, they are less stable than the ketone products. The titanaoxacyclohexenes, 2, may be hydrolyzed to the corresponding homoallylic alcohols in high yield. Unfortunately, the titanaoxacyclohexenes would not insert CO under any of the conditions used. Extensions of this work utilizing functionalized titanacyclobutenes and different Lewis acids may find use in organic synthesis. 122 Experimental Section See Chapter 1 for Gereral Considerations and Instrumentation. Materials. Titanacyclobutenes were synthesized as previously described. Ke- tones, aldehydes, and nitrites were purchased from Aldrich Chemical Co. and used as received. Tetramethylguanidine was obtained from Kodak and dried over 4 A molecular sieves. Insertion of Ketones into Titanacyclobutenes la and lb. All reactions were performed by the same general procedure. A stirred solution or suspension of the titanacyclobutene (typically O.S Min toluene) was treated with the ketone. The mixture was stirred for 24- 48 hours at room temperature, at which time the solution was clear orange. As an alternate method, the reaction mixture was heated to 80°C for 10-lS minutes and cooled to room temperature. The orange solution was filtered and the volatiles removed, the solid washed with pentane or ether, and dried in vacuo to yield the product. 3,3-Dimethy1-5,6 Dipheny1-2-oxo-titanocenecyclohex-5-ene 2a. Yield: 93%. 1 H NMR (90 MHz, C 6 D 6 ) c 7.08-6.64 (m, lOH), S.77 (s, lOH), 2.67 (s, 2H), 1.21 (s, 6H). 13 C{ 1 H} NMR (22.S MHz, C 6 D 6 ) c 190.32, 1S4.32, 147.23, 134.30, 129.82, 127.SS, 124.68, 122.87, 113.64 (Cp), 88.16, S8.79, 28.64. IR (KBr, cm- 1 ) 3010 (w), 2960 (m), 2920 (m), 16SO (w), llSS (s), 99S (s), 800, (s). Anal. Calcd. for C2aH2aOTi: C, 78.SO; H, 6.S9. Found: C, 78.SO; H, 6.72. 3-Methyl-3,5,6-Triphenyl-2-oxa-titanocenecylotex-5-ene, 2b. Yield: 87%. 1 H NMR (400 MHz, C 6 D 6 ) c 7.267-6.789 (m, lSH), S.9S4 (s, SH), S.S91 (s, SH), 3.089 (d, J=lS.4 Hz, lH), 2.962 (d, J=lS.4 Hz, lH), 1.S78 (s, 3H). Difference NOE experiments: irradiation of 8 S.9S4 enhances 8 7.220, 6.789, S.S91, 123 3.089; irradiation of 8 5.591 enhances 8 6. 789, 5.954. 13 C{1 H} NMR (22.5 MHz, CsD 6 ) 8 190.7 154.2, 150.6, 147.3, 133.9, 129.8, 128.3, 127.7, 126.4, 124.9, 123.1, 114.9 (Cp), 113.2 (Cp), 90.8, 58.3, 29.3. IR (KBr, cm- 1 ) 302S (m), 2975 (m), 1600 (w), 1090 (s), 1068 (s), 1000 (s), 804 (s). Anal. Calcd. for C 33 H 30 0Ti: C, 80.81; H, 6.16. Found: C, 79.70; H, 6.06. Reaction of Cyclohexanone with la, 2c. Yield: 90%. 1 H NMR (400 MHz, CsDs) 8 7.029 (m, 6H), 6.883 (t oft, J=7.0, 2.0 Hz, lH), 6.767 (m, 3H), S.77S (s, !OH), 2.646 (s, 2H), 1.710 (m, 2H), 1.472 (m, SH), 1.349 (m, 2H), 1.239 (m, lH). Difference NOE experiments: irradiation of 8 5. 77S enhances 8 6. 767, 2.646, 1. 710; irradiation of 8 2.646 enhances 8 5. 775, 1.349. 13 C{1H} NMR (50 MHz, C 6 D 6 ) 8 189.4, 1S4.7, 147.6, 133.6, 129.9, 128.3, 124.6, 122.8, 113.5 (Cp), 89.9, 57.1, 37.8 (x 2), 26.6, 23.6 (x 2). ffi (KBr, cm- 1 ) 3030 (m), 2925 (s), 1068 (s), 99S (s), 800 (s). Anal. Calcd. for C 31 H 32 0Ti: C, 79.48; H, 6.88. Found: C, 78.62; H, 6.69. Reaction of Cyclohex-2-ene-l-one with la, 2d. Yield: S7%. 1H NMR (400 MHz, C 6 D 6 ) 8 7.062-7.046 (m, 6H), 6.868 (m, lH), 6.804 (m, 3H), 6.044 (d, J=lO.O Hz, lH), 5.841 (s, SH), 5.742 (s, 5H), 5.74 (d, overlapping Cp, lH), 2.838 (d, J=15.4 Hz, lH), 2.750 (d, J=15.4 Hz, lH), 1.932-1.755 (m, 3H), 1.641-1.518 (m, 3H). Difference NOE experiments: irradiation of 8 5.841 enhances 8 6.84, 2.838; irradiation of 6 5.742 enhances 6 6.044, 2.750. 13 C{1H} NMR (SO MHz, C 6 D 6 ) 6 190.7 154.2, 147.2, 133.3, 133.6, 129.9, 128.7, 128.3, 127.8, 124.8, 122.9, 113.9 (Cp), 113.7 (Cp), 87.4, S7.8, 36.6, 2S.9, 2S.4, 20.3. IR (KBr, cm- 1 ) 301S (w), 2920 (m), 1068 (s), 993 (s), 80S (s). Anal. Calcd. for C 29 H 28 0Ti: C, 79.08; H, 6.41. Found: C, 77.09; H, 6.67. 124 3-Cyclopropyl-3,5,6 Triphenyl-2-oxa-titanocenecyclohex-5-ene, 2e. Yield: 77%. 1 H NMR {400 MHz, C6D6) 6 7.23-6.76 {m, lSH), S.842 (s, SH), S.673 (s, SH), 3.381 (d, J=lS.4 Hz, lH), 3.283 (d, J=lS.4 Hz, lH), 1.472 (m, lH), 0.430 (m, 2H), 0.29S (m, lH), 0.198 (m, lH). Difference NOE experiments: irradiation of 6 S.842 enhances 6 7.06 6.77, 3.28; irradiation of S.673 enhances 6 6.77, 1.47, 0.43, 0.198. 13 C{1H} NMR (22.S MHz, C 6D 6 ) 6 189.3, 1S4.4, 147.6, 146.7, 133.7, 130.1, 127.S, 127.7, 126.4, 124.9, 123.0, llS.1 (Cp), 112.8 (Cp), 91.7, S7.1, 22.8, 2.19, 1.47. ffi (KBr, cm- 1 ) 3010 (m), 2930 (w), 1030 (s), 810 (s) Anal. Calcd. for C 3 sH 32 0Ti: C, 81.39; H, 6.24. Found: C, 76.34; H, 6.13. Reaction of a-tetralone with la, 2f. Yield: 96%. 1H NMR {400 MHz, C 6 D 6 ) 8 7.940 (d, J=7.6 Hz, lH), 7.237 (m, lH), 7.108 (m, lH), 7.044 (m, SH), 6.860 (m, 2H), 6.796 (m, lH), S.998 (s, SH), S.673 (s, SH), 3.lSO (d, J=16.1 Hz, lH), 2.920 (d, J=16.1 Hz, lH), 2.643 (m, lH), 2.S88 (m, lH), 2.320 (m, lH), 1.923 (m, lH), 1.81S (m, 2H). Difference NOE experiments: irradiation of 8 S.998 enhances 8 7.940, 6.860, S.673, 3.lSO; irradiation of 8 S.673 enhances 6 6.860, S.998, 2.920, 1.923. Reaction of ,8-tetralone with la, 2g. Yield: 77%. 1 H NMR (400 MHz, C 6 D 6 ) 6 7.236-6.911(m,14H), S.961 (s, lH), S.S61 (s, SH), 3.270 (d, J=16.3 Hz, lH), 2.942 (m, lH), 2.920 (d, J=lS.6 Hz, lH), 2.880 (d, J=16.6 Hz, lH), 2.722 (d, J=lS.6 Hz, lH), 1.82S (m, lH), 1.780 (m, lH). Difference NOE experiments: irradiation of 8 S.961 enhances 8 6.91, S.561, 2.920; irradiation 6 S.561 enhances 8 6.91, 5.961, 3.270. 3-Methyl-5,6-Diphenyl-3-Vinyl 2-oxa-titanocenecylohex-5-ene 2h. Yield: 62%. 1 H NMR (400 MHz, C 6 D 6 ) 8 7.03-6.76 (m, lOH), 5.97 (d of d, 12S J=lO.S, 17.1 Hz, lH), S.938 {s, SH), S.612 {s, SH), S.100 {d of d, J=17.1, 2.2 Hz, lH), 4.970 {d of d, J=lO.S, 2.2 Hz, lH), 2.910 {d, J=lS.4 Hz, lH), 2.S8 {d, J=lS.4 Hz, lH), 1.34 s 3 . Difference NOE experiments: irradiation of 6 S.940 and S.970 enhances 6 6. 76, S.61, 2.91; irradiation of 6 S.61 enhances 6 6. 76, S.94; irradiation of 6 1.34 enhances 7.02, S.97, S.61, S.10, 2.S8. 13 C{1H} NMR {22.S MHz, C 6 D 6 ) 6 190. 7' 154.3, 14 7.0, 146.1, 133.4, 129.9, 127 .6, 124.8, 123.0, 114.S, 113.4, 110.3, 89. 7' S7.0, 26.2. IR (KBr, cm- 1 ) 300S {m), 2910 {s), 101S (s), 987 (s), 800 (s). Anal. Calcd. for C29H2sOTi: C, 79.08; H, 6.41. Found: C, 77.09; H, 6.67. Reaction of Ethyl Leuvinate with la. Synthesis of 2m. 1 H NMR {400 MHz, C 6 D 6 ) 6 7.02-6.69 (m, 6H), 6.88 (t oft, J=7.0, 2.0 Hz, lH), 6.75 {m, 3H), 5.901 {s, SH), S.S96 (s, SH), 4.010 (m, 2H), 2.720 (d, J=lS.4 Hz, lH), 2.460 (d, J=lS.4 Hz, lH), 2.31S (m, 2H), 2.138 (m, lH), 2.01 (m, lH), 1.77 (m, lH), 1.134 (s, 3H), 1.020 (t, J=7.1 Hz, 3H). Difference NOE experiments: irradiation of b S.901 enhances 6 6.7S and 2.72; irradiation of 6 S.S96 enhances 6 6.7S. 13 C{1H} NMR (22.S MHz, C 6 D 6 ) 6 190.S2, 173.Sl, 1S4.27, 147.18, 133.8S, 129.84 (CH), 127.62 (CH), 124.7S (CH), 122.96 (CH), 114.19 (Cp), 113.S9 (Cp), 89.38 (quat), 60.07 (CH2), 57.S2 {CH2), 37.S3 (CH2), 30.11 (CH2), 24.64 (CH3), 14.34 (CH3). Reaction of l-Carvone with la. Synthesis of 2j. Major isomer: 1 H NMR (400 MHz, C 6 D 6 ) 6 7.31-6.7S (m, lOH), 6.076 (s, SH), S.441 {s, SH), S.32 (br s, lH), S.05 (t, J=l.O Hz, lH), 4.91 (t, J=l.O Hz, lH), 3.16 (d of d, J=15.8, 1.7 Hz, lH), 2.70 (m, lH), 2.69 {d, J=lS.8 Hz, lH), 2.SO (m, 2H), 1.9S (m, lH), 1.83 (br s, 3H), 1.79 {s, 3H). Difference NOE experiments: irradiation of b 6.074 enhances 6 6.880, S.441, 3.16; irradiation of 6 S.441 enhances 6 6.076. 13 C{1 H} NMR {22.S MHz, C 6 D 6 ) 6 190.95, 1S4.22, 149.Sl, 147.4S, 140.13, 134.34, 126 130.11, 129.9S, 127.67, 12S.94, 12S.40, 124.08, 123.18, 123.07, 113.37 (Cp), 114.Sl (Cp), 109. 71, 93.33, S3.68, 40.89, 39.27, 31.89, 20.S2, 19.22. Minor isomer: 1 H NMR (400 MHz, C 6 D6) 8 7.31-6.7S (m, lOH), 6.032 (s, 5H), 5.66S (s, SH), 5.44 (br d, J=12 Hz, lH), S.01 (t, J=l.0 Hz, lH), 4.89 (t, J=l.0 Hz, lH), 3.3S (d, J=15.6 Hz, lH), 2.41 (d, J=15.6 Hz, lH), 2.70 (m, lH), 2.50 (m, 2H), 1.95 (m, lH), 1.88 (br s, 3H), 1.78 (s, 3H). Difference NOE experiments: irradiation of 8 6.032 enhances 8 6. 7S, S.66S, 3.35; irradiation of 8 5.665 enhances 8 6. 75, 6.032. 13 C{1H} NMR (22.S MHz, C 6 D 6 ) 8 190.14, 1S4.44, 149.78, 147.12, 137.86, 134.23, 130.11, 129.9S, 127.67, 125.94, 125.40, 124.08, 123.18, 123.07, 114.51 (Cp), 113.48 (Cp), 109.64, 91.00, 56.06, 41.81, 38. 72, 32.33, 20.95, 19.54. (Some signals of the isomers overlap.) Reaction of N orcamphor with la. Synthesis of 2k. 1 H NMR (400 MHz, C 6D 6) 8 7.05-6.99 (m, 6H), 6.86 (t oft, J=7.1, 2.0 Hz, lH), 6.78 (m, 3H), S.825 (s, SH), 5.692 (s, SH), 2.84 (d, J=15.4 Hz, lH), 2.73 (d, J=15.4 Hz, lH), 2.18-2.15 (m, 2H), 1.81 (m, lH), 1.73 (m, lH), 1.53 (m, lH), 1.35-1.15 (m, 4H), 0.93 (m, lH). Difference NOE experiments: irradiation of 8 5.825 enhances 8 6. 78, S.692, 2.84; irradiation of 8 5.692 enhances 8 6. 78, 5.825, 2. 73, 1.35. 13 C{1 H} NMR (22.5 MHz, C6D 6) 8 190.30, 154.92, 147.34, 134.12, 129.90, 127.62, 127.51, 124.70, 122.8S, 113.59 (Cp), 113.48 (Cp), 97.4S, S7.52, 48.26, 45.44, 38.24, 37.42, 29.29, 22.85. Reaction of d-Camphor with la. Synthesis of 21. 1 H NMR (400 MHz, C 6D 6) 8 7.14-6.99 (m, 6H), 6.86-6.78 (m, 4H), 5.961 (s, lOH), 5.641 (s, lOH), 2.940 (d, J=15.4 Hz, lH), 2.360 (d, J=lS.4 Hz, lH), 2.195 (d oft, J=12.9, 1.S, lH), 1.72 (t, J=4.6 Hz, lH), 1.68 (d, J=13.2 Hz, lH), 1.56 (m, 2H), 1.32 (m, 2H), 1.017 (s, 3H), 0.932 (s, 3H), 0.852 (s, 3H). Difference NOE 127 experiments: irradiation of fJ 5.961 enhances fJ 5.641, 2.96, 1. 72, 0.932; irradiation of fJ 5.641 enhances fJ 5.961, 2.360, 2.195, 1.017. 13 C{1H} NMR (22.5 MHz, C6D 6) {J 190.57' 154.82, 14 7. 77' 134.39, 129.95, 128.49, 127.67' 127 .57' 124. 75, 122.96, 113.64 (Cp), 113.37 (Cp), 100.80, 54.65, 54.43, 49.40, 45.88, 31.57, 27.51, 21.55, 21.39, 12.12. Reaction of 2-Methyl Cyclohexanone with la. Synthesis of 2i. First isomer: 1 H NMR (400 MHz, C 6D 6) fJ 7.06-6.75 (m, lOH), 6.000 (s, 5H), 5.644 (s, 5H), 2.80 (d; J=15.6 Hz, lH), 2.56 (d, J=15.6 Hz, lH), 2.01 (m, lH), 1.56-1.10 (m, SH), 0.995 (d, J=6.6 Hz, 3H). Second isomer: 1 H NMR (400 MHz, C6D 6) fJ 7.06-6.75 (m, lOH), 5.943 (s, 5H), 5.601 (s, 5H), 2.96 (d, J=15.6 Hz, lH), 2.53 (d, J=15.6 Hz, lH), 2.01 (m, lH), 1.56-1.04 (m, SH), 0.950 (d, J=7.1 Hz, 3H). Difference NOE experiments: irradiation of fJ 6.000 enhances fJ 6. 75, 2.80; irradiation of fJ 5.943 enhances fJ 6. 75, 2.96; irradiation of fJ 5.664 enhances fJ 6. 75, 2.56, 2.01, 1.53; irradiation of fJ 5.601 enhances fJ 6. 75, 2.53, 2.01. 13 C{1 H} NMR (22.5 MHz, C 6D 6) fJ 189.60, 189.27, 154.82, 154.55, 147.94, 147.61, 134.45, 134.28, 129.95, 127.62, 124.75, 122.91, 114.19, 114.02, 113.32, 113.05, 93.4, 92.52, 55.68, 50.15, 41. 76, 41.43, 35.25, 31. 79, 24.53, 24.42, 24.09, 23.94, 16.46. 3,3-Bis ( dimethylamino )-5,6-Diphenyl-2-aza-titanocene cyclohex-5-ene,6. Yield: 92%. 1 H NMR (90 MHz, C 7 D 8 ) fJ 7.30-6.24 (m, lOH), 5.72 (s, lOH), 2.56 (br s, 6H), 2.45 (s, 3H). 13 C{1H} NMR (22.5 MHz, C 7 D 8 ) fJ 178.70, 161.09, 158.76, 150.15, 129.29, 127.88, 127.34, 127.07, 124.09, 121.71, 110.28 (Cp), 39.20 (br), 30.96. IR (KBr, cm- 1 ) 3060 (w), 3020 (w), 2920 (m), 2870 (m), 1570 (s), 1485 (s), 1455 (s), 1425 (s), 1360 (s), 1122 (s), 1022 (s), 805 (s). Anal. Calcd for C 30 H 35 N 3 Ti: C, 74.21; H, 7.27; N, 8.65. Found: C, 74.05; H, 7.18, N, 8.52. 128 3,3,5-Trimethyl-6-Phenyl-2-oxa-titanocenecyclohex-5-ene, 2n. Yield: 74%. 1 H NMR (90 MHz, C 6 D5) S 7.38-6.87 (m, SH), S.74 (s, lOH), 2.26 (s, 2H), 1.64 (s, 3H), 1.13 (s, 6H). 13 C{1 H} NMR (22.S MHz, C 6 D 6 ) S 186.8, lSS.O, 123.0, 113.6, 88.0, S7.4, 28.S, 24.2. IR (KBr, cm- 1 ) 3020 (w), 2980 (m), 2910 (m), 1000 (s), 80S (s). Anal. Calcd. for C2aH250Ti: C, 7S.41; H, 7.lS. Found: C, 7S.16; H, 7.03. 3,5-Dimethyl-3,6-Diphenyl-2-oxa-titanocenecyclohex-5-ene, 2o. Yield: 8S%. 1 H NMR (90 MHz, C 6 D5) S 7.33-6.9S (m, lOH), S.88 (s, SH), S.62 (s, SH), 2.83 (d of d , J=lS.3, 1.0 Hz, lH), 2.42 (d, J=lS.3 Hz, lH), 1.70 (d, J=l.0 Hz, 3H), 1.42 (s, 3H). 13 C{1 H} NMR (22.S MHz, C 6 D 6 ) S 187.0S, 1S4.87, lS0.81, 128.27, 126.S4, 126.37, 124.91, 123.40, 114.67 (Cp), 113.10 (Cp), 90.78, S6.82, 28.64, 24.42. m (KBr, cm- 1 ) 3060 (w), 2990 (m), 2890 (m), 1100 (s), 1070 (s), 808 (s), Anal. Calcd. for C 28 H 28 0Ti: C, 78.SO; H, 6S9. Found: C, 77.S7; H, 6.61. Acidolysis of 2a. A stirred suspension of 2a (llS mg, 0.268 mmol) in 2 ml of diethyl ether at 0 °C was treated with anhydrous HCl gas (lS ml, 0.67 mmol). The mixture immediately turned red and a red precipitate formed. The reaction was warmed to room temperature over lS minutes, diluted with 10 ml more diethylether, filtered through a 1-inch plug of silica gel and the filtrate concentrated at reduced pressure to yield an orange residue. The residue was extracted with petroleum ether: ether (3:1), the extract filtered through glass wool, and concentrated at reduced pressure to yield the product 2-methyl-4,S diphenyl-pent-4-ene-2-al (61 mg, 0.242 mmol, 90%) as yellowish crystals. 1 H NMR (400 MHz, CDCL 3 ) S 7.279-7.198 (m, SH) , 7.100-7.0S2 (m, 3H), 6.940-6.921 (m, 2H), 6.S22 (s, lH), 2.768 (s, 2H), 1.497 (br s, lH), 1.lSS (s, 6H) . 13 C{1 H} NMR (22.S MHz, CDCL 3 ) S 141.41, 139.3S, 137.13, 129 130.68, 129.00, 128.63, 127.82, 127.11, 126.3S, 71.S3, S3.71 (CH2), 29. 76 (CHa). Reaction of p-Tolualdehyde with la. To a stirred suspension of titanacyclobutene la (36S mg, 0.986 mm.cl) in 2 ml toluene at room temperature was added p-tolualdehyde (140 ml, 1.18 mm.cl). The mixture was stirred at room temperature for 12 hours, then the volatiles removed in vacuo to yield a red-orange form. The foam was triturated with diethylether, the yellow precipitate filtered from the red solution, and both fractions taken to dryness. The yellow fraction {lSO mg, 0.307 mm.cl) was the insertion product lOa: 1 H NMR {90 MHz, C 6 D 6 ) 6 7.37-6.67 {m, 14H), 6.06 (s, SH), S.S9 {s, SH), S.48 {m, lH), 3.0S {s, lH), 2.97 {d, J=3.2 Hz, lH), 2.18 {s, 3H). 1 H NMR {400 MHz, C6 D 6 ) 6 7.29-6.9S (m, lOH), 6.89 {t oft, J=7.1, 0.8 Hz, 2H), 6.78 {t oft, J=7.l, 0.8 Hz, 2H), 6.119 {s, SH), S.610 {s, SH), S.S3 {d of d, J=l0.1, 2.8 Hz, lH) , 3.07 {d of d, J=16.6, 2.9 Hz, lH), 2.98S {d of d, J=16.6, 10.2 Hz, lH), 2.18 (s, 3H). 13 C{ 1 H} NMR (22.S MHz, C 6 D 6 ) 6 191.44, 1S3.03, 146.71, 136.Sl, 136.29, 130.06, 129.08, 128.43, 127.62, 12S.72, 124.97, 123.23, 114.3S {Cp), 113.86 (Cp), 88.67, S7.09, 21.11. The diethylether soluble fraction revealed a 2:1 ration of products. The major product was the same as the yellow precipitate; the minor product had 1 H NMR 17 5 -cyclopentadienyl resonances at 6 S.91, S.82. Reaction of Acetaldehyde with la. To a stirred suspension of titanacyclobutene la (320 mg, 0.864 mm.cl) in 3 ml of toluene at room temperature was added acetaldehyde {60 ml, 1.07 mm.cl) via syringe. The reaction vessel was wrapped in Al foil and the mixture stirred for 12 hours. The reaction mixture was taken to dryness and the red-orange solid was extracted with 2 ml toluene at -78°C. Both fractions were dried in vacuo. The extract was red-orange and the residue was dark-red. The red-orange extract 130 material was a 2:1 ratio of the Ti-0 product. Orange isomer: 1 H NMR (90 MHz, C6D6) 6 7.34-6.S7 (m, lOH), S.98 (s, SH), S.60 (s, SH), 4.66-4.29 (m, lH), 2.70 (s, ?H), 2.64 (d, J=2.9 Hz, lH), 1.06 (d, J=S.8 Hz, 3H). 1 H NMR (400 MHz, C 6D 6) 6 7.406-6.728 (m, lOH), S.982 (s, SH), S.S92 (s, SH), 4.498 (m, lH), 2.70 (d of d, J=16.4, 2.8 Hz, lH), 2.60 (d of d, J=16.4, 9.S Hz, lH), 1.06 (d, J=S.9 Hz, 3H). 13 C{1 H} NMR (22.S MHz, C 6D 6) 6 191.11, 1S3.30, 136.18, 130.49, 130.06, 128.33, 127.S7, 124.91, 123.12, 114.19 (Cp), 113.S4 (Cp), 83.2S, SS.9S, 23.77. Red isomer: 1 H NMR (400 MHz, C 6D 6) 6 7.336-6.944 (m, lOH), S.890 (s, SH), S.883 (s, SH), S.641 (q, J=6.3S Hz, lH), 4.470 (d of d, J=lO.O, 4.2 Hz, lH), 1.48 (d, J=9.8 Hz, lH), 1.21S (d, J=6.3S Hz, 3.H) 13 C{1H} NMR (22.S MHz, C 6D 6) 6 181.76, 148.32, 146.09, 144.63, 143.06, 130.44, 130.00, 128.27, 127 .S7, 126.0S, 12S.67, 113.54 (Cp), 111.29 (Cp), 87.97, S9.42, 22.41. Reaction of Benzonitrile with la. A solution of titanacycle la (34 mg, 0.092 mmol) in 400µ1 of C 6D 6 in an NMR tube was treated with benzonitrile (10µ1, 0.098 mmol). After 24 hours the solution was dark orange and NMR analysis revealed a new compound: 1 H NMR (90 MHz, C 6D 6 ) 6 7.S0-6.80 (m, lSH), S.64 (s, lOH), 4.03 (s, 2H). Reaction of p-Tolunitrile with la. A solution of titanacyclobutene la (38 mg, 0.103 mmol) in 400 µ1 of C5D 6 in an NMR tube was treated with p-tolunitrile. After 18 hours the color had changed to dark-orange, and the NMR spectrum revealed the reaction as 90% complete: 1 H NMR (90 MHz, C 6D 6 ) 6 7.S0-6.80 (m, 14H), S.66 (s, lOH), 4.01 (s, 2H), 2.13 (s, 3H). 131 Reaction of a-phenylpropionitrile with la. A solution of la (38 mg, 0.103 mmol) in 400 µ1 of CaDa in an NMR tube was treated with a-phenyl propionitrile (14µ1, O.lOS mmol) at room temperature. The color changed slowly over 24 hours from red to dark-orange. NMR analysis revealed a single product and some remaining starting materials: 1 H NMR (90 MHz, C 6 D 6 ) 8 7.15-6.60 (m, lSH), S.63 (s, SH), S.61 (s, SH), 3.S4 (br s, 2H), 3.08 (q, J=7.0 Hz, lH), 1.32 (d, J=7.0 Hz, 3H). Reaction of a-methyl propionitrile with la. A solution of la (38 mg, 0.103 mmol) in 400 µLof C 6 D6 in an NMR tube was treated with a-methyl propionitrile (10µ1, 0.11 mmol) at room temperature. The color changed slowly over 24 hours from red to dark-orange. NMR analysis revealed a single product and some remaining starting materials: 1 H NMR (90 MHz, C 6 D 6 ) 8 7.lS-6.60 (m, lOH), S.60 (s, lOH), 3.Sl (s, 2H), 1.94 (septet, J=7.1 Hz, lH), 0.93 (d, J=7.1 Hz, 6H). Reaction of Methacrylonitrile with la. A solution of la (26 mg, 0.071 mmol) in 400 µL of C6 D 6 was treated with methacrylonitrile (6 µL, 0.071 mmol) at room temperature. After 12 hours the reaction was -60% complete by NMR analysis: 1 H NMR (90 MHz, C 6 D 6 ) 8 7.166.SO (m, lOH), S.60 (s, SH), S.S8 (s, SH), S.03 (m, 2H), 3.87 (s, 2H), 1.82 (br s, 3H). Hydrolysis of the Insertion Product of la and p-Tolunitrile. To a stirred solution of metallacycle la (200 mg, O.S4 mmol) in 3 ml of THF was added p-tolunitrile (7S µL, 0.627 mmol) at room temperature. The reaction was stirred at room temperature for 24 hours. The volatiles were removed in vacuo 132 and the solid suspended in diethylether and hydrolyzed with 5% aqueous HCl for 30 minutes. The aqueous phase was separated and extracted with diethylether 3 x 5 ml, the organic phases combined, dried over MgS0 4 , and concentrated in vacuo. The product was flash-chromatographed (CHCL 3 ) to yield 41 mg of the product ketone: 1 H NMR (90 MHz, CDCL 3 ) 8 7.80-7.00 (m, 14H), 6.55 (br s, lH), 4.11 (d, J=l.2 Hz, 2H), 2.37 (s, 3H). Reaction of p-Tolunitrile with lb. A solution of metallacycle lb (97 mg, 0.315 mmol) in 500 µL of C 6D6 was treated with p-tolunitrile (36 µL, 0.32 mmol) at room temperature. The reaction was complete within 4 hours to yield a dark-orange solution: 1 H NMR (90 MHz, C6D6) 8 7.50-6.80 (m, 9H), 5.70 (s, lOH), 3.68 (s, 2H), 2.20 (s, 3H), 1.65 (s, 3H). 133 References 1. Keim, W.; Behr, A.; Roper, M. Comprehensive Organometallic Chemistry, Volume 8, Chapter 52, 371-46, Willkinson, G., Ed., Permagon Press: Oxford, 1982. 2. Comprehensive Organic Chemistry, Volume 3, Part 15, 941-1126, Barton, D., et al., Eds., Permagon Press: Oxford, 1982. 3. (a) Transition Metals in Organic Synthesis, Volume II, Chapter 3, Alper, H., Ed., Academic Press: New York, 1978. b. Organic Synthesis by Means of Transition Metal Complexes, Tsuji, J. in Reactivity and Structure Concepts in Organic Chemistry, Volume 1, Hafner, K. et al., Eds., Springer-Verlag: Berlin, 1975. 4. Jukes, A.E. Adv. Organomet. Chem. 1974, 12, 215-322. 5. (a) Reetz, M.T. Top. Curr. Chem. 1982, 106, 1-54. (b) Weidmann, B.; Seebach, D. Angew. Chem. Int. Ed. Eng. 1983, 22, 31-45. 6. (a) Goure, W.F.; Wright, M.E.; Davis, P.D.; Labadie, S.S.; Stille, J.K. J. Am. Chem. Soc. 1984, 106, 6417-22. (b) Heck, R.F. Accts. Chem. Res. 1979, 12, 146-51. (c) Schwartz, J.; Loots, M.J.; Kosugi, H. J. Am. Chem. Soc. 1980, 10!!' 1333-40. 7. Seetz, J.W.F.L.; Van de Heisteeg, B.J.J.; Schat, G.; Akkerman, O.S.; Bickelhaupt, F. J. Mol. Cat. 1985, 28, 71-83. 8. Brown-Wensley, K.A., Ph.D. Thesis, California Institute of Technology, 1981. 9. Richmond, T.G.; Basolo, F.; Shriver, D.F. Inorg. Chem. 1982, 21, 1272-3. 10. The Proton: Applications to Organic Chemistry, Stewart, R., Academic Press: New York, 1985. 11. (a) Tanner, D.D.; Diaz, G.E.; Potter, A. J. Org. Chem. 1985, 50, 2149-54. (b) Rearrangements in the Ground and Excited States, deMayo, P., Ed., Academic 134 Press: New York, 1980, Volume 1. 12. Kinetics and Mechanism, Moore, J.W.; Pearson, R.G., Wiley and Sons: New York, 1981. 13. Baldwin, J.E. J. C.S. Chem. Comm. 1976, 738-41. 14. (a) Froemberg, W.; Erker, G. J. Organomet. Chem. 1985, 280, 343-54. (b) Erker, G.; Froemberg, W.; Atwood, J.L.; Hunter, W.E. Angew. Chem. Int. Ed. Eng. 1984, £9, 68-9. 15. Dynamic Nuclear Magnetic Resonance, Jackman, L.M.; Cotton, F .A., Eds., Academic Press: New York, 1975. 16. This thesis, Chapter 2. 17. (a) Marsella, J.A.; Moloy, K.G.; Caulton, K.G. J. Organomet. Chem. 1980, 201, 389-98. (b) Huffman, J.C.; Moloy, K.G.; Marsella, J.A.; Caulton, K.G. J. Am. Chem. Soc. 1980, 102, 3009-14. 18. Carey, F .A.; Sundberg, R.J. Advanced Organic Chemistry, Part A, Plenum Press: New York, 1984. 19. Lappert, M.F.; Patil, D.S.; Pedley, J.B. J.C.S. Chem. Comm. 1975, 830-1. 20. A preliminary x-ray crystal structure confirms this assignment. 21. Gambarotta, S.; Pasquali, M.; Floriani, C.; Chesi-Villa, A.; Guastini, C. Inorg. Chem. 1981, £0, 1173-8. 22. (a) Lauher, J.W.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 1729-42. (b) Hillhouse, G.L.; Bercaw, J.E. J. Am. Chem. Soc. 1984, 106, 5472-8. (c) Simpson, S.J.; Andersen, R.A. Inorg. Chem. 1981, £0, 3627-9. 23. Fachenetti, G.; Biran, C.; Floriani, C.; Cheisi-Villa, A.; Guastini, C. Inorg. Chem. 1978, 11, 2995-3002. 24. March, J. Advanced Organic Chemistry, Wiley & Sons: New York, 1985. 135 Appendix I. X-ray Structure Determination of Cp2TiC4H20(C5Hs) (Si(CH3)3) (P(CH3)3) A thin crystalline prism (0.023 x 0.033 x 0.198mm) of (77 5 -C 5 Hs)2Ti(C,0-17 2 CH2=C(Me3Si)C(C6Hs)=CO) (PMe3), obtained after slow cooling of an ether solution to -50°Cfor 5 days, was mounted approximately along c in a glass capillary under N 2. A series of oscillation and Weissenberg photographs indicated monoclinic symmetry and the space group P2i/c (OkO absent fork odd, hOl absent for l odd); data were collected on a locally modified Syntex P2 1 diffractometer with graphite monochromator and MoKa radiation (.A = 0.7107 A). The unit cell parameters (Table 1) were obtained by least-squares refinement of the average 20-values from four sets of seventeen reflections: '±20' hkl and '±20' hkl, 20 < 20 < 39°. The three check reflections indicated no decomposition. No absorption correction was performed. The data were averaged over the Laue symmetry and reduced to ~; the form factors were taken from Table 2.2B, International Tables for X-Ray Crystallography (1974); those for Ti, Si, and P were corrected for anomalous dispersion. The details of data collection are summarized in Table 1. The position of the Ti atom was derived from the Patterson map, and the Fourier map phased on the Ti atom revealed the remainder of the structure. Hydrogen atoms H(l) and H(2) were located from the difference map and refined with isotropic U; the remaining H-atoms were introduced into the model with fixed coordinates and isotropic Gaussian amplitudes at idealized positions. Leastsquares refinement of the non-hydrogen atoms with anisotropic Uij 's, minimizing Ew[F~ - (F c/k) 2 ] 2, using all the data (3038 reflections) led to S = 1.66, RF = 0.050, and Rt = 0.084;* final shift/errors < 0.10. A correction for secondary extinction (A.C. Larson, Acta. Cryst., 23 , 664-665 (1967), Eqn. 3) was included, and the final 136 value of the extinction coefficient was 0.22(4)x10- 6 . All calculations were carried out on a VAX 11/780 computer using the CRYRM system of programs. *RF = EIF o - IF cll/EF o' S = yfEw.6. 2 /(n - v), RF = yfEw.6. 2 /EF~, w- 1 = [s + r 2 b + (0.02s) 2 ]k 4 /(Lp) 2 , s =scan counts, r =scan-to-background time ratio, b = total background counts, k = 0.9813(19) (scale factor on F 0 ) , .6. = F~ - (F c/k) 2 , n = 3038, v = 280. 137 Table 1. Summary of Crystal Data and Intensity Collection Information. Formula C2sH3sOPSiTi Formula weight 470.528 Space group P21/c a 9.625(2)A b 16.211(2)A c 16.917(4)A /3 101.28(10) 0 v 2589.5(9)A3 z 4 Deale Crystal size 1.207(4) g/ml 0.023 x 0.033 x 0.198 mm ,\ 0.110733 A µ, 0.403 mm- 1 Scan range 1.0° above Ka:1, 1.0° below Ka:2 Reflections +h, ±k, ±l Collected 6717 reflections Averaged 3038 reflections (2735 I > 0, 1775 I > 3u1) 138 Table 2. Atom Coordinates (x10 5 ) and Ueq's (A 2 , x10 4 ). Ti 0 C(l) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(lO) p C(31) C(32) C(33) Si C(41) C(42) C(43) C(ll) C(12) C(13) C(14) C(15) C(21) C(22) C(23) C(24) C(25) x y z 8771(11) -8753(34) -8238(54) -17514(54) -15991(62) -3481(77) -30079(55) -33087(62) -43925(74) -52114(70) -49157(72) -38185(64) 5140(17) -12764(65) 6118(75) 16238(67) -31867(20) -25827(79) -44557(87) -40140(82) 12870(84) -918(87) -7633(67) 2791(94) 15625(76) 19603(63) 21772(62) 30543(67) 34013(62) 27213(65) 18445(5) 12452(18) 19629(28) 23268(29) 32106(31) 35419(41) 18565(31) 19017(33) 14425(38) 9553(39) 9048(37) 13463(34) 4885(8) 4069(37) -4444(32) 2245(34) 38989(10) 49961(36) 38229(47) 36777(42) 31759(34) 31429(36) 25683(42) 22492(35) 26241(39) 17483(38) 9852(34) 11054(40) 19455(42) 23425(36) 12208(5) 5749(18) 2415(27) -3578(28) -5892(26) -5976(35) -8108(29) -16466(32) -20938(36) -17036(46) -8757(49) -4264(34) 19660(9) 21720(38) 13873(34) 29331(32) -6651(11) -5992(48) -16036(54) 1964(56) 18116(37) 14584(31) 18789(42) 24968(35) 24530(36) 708(32) 4615(35) 12212(38) 12966(36) 5931(38) Ueq 428{2) 455(9) 400(14) 399(15) 428(14) 591(20) 457(14) 579(16) 757(20) 817(26) 822(26) 617(19) 526(4) 861(21) 898(22) 782(19) 681(5) 1219(31) 1686(37) 1415(32) 678(20) 656(19) 721(20) 728(20) 705(20) 627(17) 613(18) 720(20) 713(23) 64 7(19) 139 Table 3. Bond Lengths(A). Ti-0 Ti-C(l) Ti-P Ti-C(ll) Ti-C(12) Ti-C(13) Ti-C(14) Ti-C(15) Ti-C(21) Ti-C(22) Ti-C(23) Ti-C(24) Ti-C(25) 0-C(l) C(l)-C(2) C(2)-C(3) C(2)-C(5) C(3)-C(4) C(3)-Si C(4)-H(l) C(4)-H(2) C(5)-C(6) C(5)-C(10) C(6)-C(7) C(7)-C(8) C(8)-C(9) C(9)-C(10) P-C(31) P-C(32) P-C(33) Si-C(41) Si-C(42) Si-C(43) C(11)-C(12) C(11)-C(15) 2.064(3) 2.098(5) 2.592(2) 2.380(7) 2.369(6) 2.408(7) 2.431(7) 2.417(7) 2.385(6) 2.405(6) 2.413(6) 2.412(6) 2.380(6) 1.298(6) 1.349(7) 1.500(7) 1.506(7) 1.321(8) 1.876(5) 0.92(5) 1.09(3) 1.389(7) 1.384(8) 1.380(8) 1.373(9) 1.376(10) 1.375(9) 1.828(6) 1.814(6) 1.822(6) 1.868(7) 1.808(8) 1.828(8) 1.345(9) 1.392(9) 140 C(12)-C(13) C(13)-C(14) C(14)-C(15) C(21)-C(22) C(21)-C(25) C(22)-C(23) C(23)-C(24) C(24)-C(25) CP(l)-Ti CP(2)-Ti 1.404(9) 1.399(10) 1.391(9) 1.399(8) 1.412(8) 1.406(9) 1.403(9) 1.398(9) 2.091 2.081 141 Table 4. Bond Angles{ 0 ) . C(l)-Ti-0 C(l)-0-Ti 0-C(l)-Ti C(2)-C(l)-Ti C(2)-C(l)-O C(3)-C(2)-C(l) C(5)-C(2)-C(l) C(5)-C(2)-C(3) C(4)-C(3)-C(2) Si-C(3)-C(2) Si-C(3)-C(4) H(l)-C(4)-C(3) H(2)-C(4)-C(3) H(2)-C(4)-H(l) C(5)-C(6)-C(7) C(6)-C(7)-C(8) C(7)-C(8)-C(9) C(8)-C(9)-C(10) C(9)-C(10)-C(5) C(10)-C(5)-C(6) C(ll)-C(12)-C(13) C(12)-C(13)-C(14) C(13)-C(14)-C(15) C(14)-C(15)-C(ll) C(15)-C(ll)-C{12) C(21)-C(22)-C(23) C(22)-C(23)-C{24) C(23)-C(24)-C(25) C(24)-C(25)-C(21) C{25)-C(21)-C(22) C(3)-Si-C(41) C(3)-Si-C( 42) C(3)-Si-C{43) C(41)-Si-C(42) C(42)-Si-C( 43) 36.4(2) 73.2(2) 70.4(2) 158.9(4) 130.0(4) 122.0{4) 120.5(4) 117.4(4) 121.8(5) 117.8(4) 119.3(4) 125(3) 128(2) 106(4) 120.9(5) 119.4(6) 120.0(6) 121.0(6) 119.6(5) 119.1(5) 108.2(6) 106.9(6) 108.2(6) 106.7(6) 110.0(6) 108.4(5) 107.9(5) 107.8(5) 108.5(5) 107.3(5) 108.8(3) 114.9(3) 107.7(3) 105.4(4) 111.2(4) 142 C(43)-Si-C(41) C(31)-P-C(32) C(32)-P-C(33) C(33)-P-C(31) P-Ti-0 CP(l)-Ti-CP(2) 108.6(3) 101.1(3) 101.9(3) 102.7(3) 71.6(1) 131.2 143 Table 5. Ti 0 C(l) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(lO) p C(31) C(32) C(33) Si C(41) C(42) C(43) C(ll) C(12) C(13) C(14) C(15) C(21) C(22) C(23) C(24) C(25) Gaussian amplitudes (xl0 4 ). Uu U22 Uaa U12 U1a U2a 470(8) 426(26) 349(40) 264(39) 419(43) 444(54) 391(41) 532(45) 719(56) 509(56) 458(53) 429(47) 549(12) 625(51) 1443(67) 812(53) 567(14) 1109(67) 1198(76) 1076(70) 1028(62) 1049(65) 658(55) 1214(72) 800(61) 603(48) 513(48) 525(51) 350(45) 441(47) 350(5) 359(20) 409(33) 452(32) 434(31) 624(43) 384(29) 522(34) 614(40) 628(45) 623(43) 589(39) 390(8) 773(45) 397(34) 704(42) 460(10) 453(41) 1141(65) 927(57) 313(31) 435(35) 783(47) 550(39) 649(44) 675(41) 643(41) 781(45) 885(50) 688(43) 445(5) 522(21) 436(30) 462(31) 404(29) 669(41) 570(34) 618(37) 835(47) 1147(63) 1338(67) 806(44) 578(9) 194(54) 786(44) 710(40) 980(14) 2168(83) 2224(97) 2544(101) 721(43) 479(36) 756(47) 441(36) 582(41) 631(37) 688(41) 853(47) 864(47) 825(46) 5(5) -6(18) -36(26) 4(27) 4(32) -14(43) 121(30) -39(33) -23(39) -30(37) -89(37) -28(34) -15(8) -77(39) 4(41) -143(37) 87(9) 119(43) 524(61) 428(53) -175(38) 211(41) 46(40) 10(45) 33(41) 66(37) 161(34) 217(39) -26(38) 17(35) 40(5) -52(18) 58(27) 21(28) 8(27) 17(37) 23(30) -50(32) -106(42) -251(48) 59(49) 48(38) -40(8) 199(42) 46(43) -153(38) 57(11) 494(62) -886(70) 1091(70) 234(42) 135(41) 217(43) 211(43) -76(40) 183(34) 124(36) 127(40) 14(36) 152(38) -10(5) 14(16) -44(25) -3(25) 27(26) 159(33) 44(29) -32(31) -34(35) -76(43) 198(43) 151(33) 49(7) 342(40) -82(31) 240(32) 46(9) -58(48) -421(64) 411(61) -161(32) -57(31) -380(38) 41(30) -101(34) 41(34) -71(33) 86(38) -68(40) 128(36) 144 Table 6. Hydrogen Atom Coordinates (x10 4 ) and B's (A 2 , x10 4 ). H(l) H(2) H(6) H(7) H(8) H(9) H(lO) H(ll) H(12) H(13) H{14) H(15) H(21) H(22) H(23) H(24) H(25) H(311) H(312) H(313) H(321) H(322) H(323) H(331) H(332) H(333) H(411) H(412) H(413) H(421) H(422) H(423) H(431) H(432) H(433) x y -189(57) 4086(32) 672(37) 3230(18) -2706 2282 -4612 1465 -6045 643 -5562 518 -3636 1304 2057 3551 -575 3484 -1851 2405 106 1820 2520 2480 1350 1863 1739 427 3404 649 4021 2222 2777 2970 -1300 634 -1580 -152 -1929 745 394 -926 1564 -511 -76 -432 1635 716 1295 -229 2570 175 -2128 5134 -3336 5365 -1913 5097 -5133 3342 -5005 4324 -3983 3695 -3526 3965 -3958 3097 -4984 3838 z u -712(30) 84(21) -543(16) -3(8) -1951 89 -2731 89 -2047 89 -620 89 200 89 1649 89 978 89 1752 89 2925 89 2822 89 -491 89 220 89 1649 89 1806 89 461 89 2696 152 2153 152 1783 152 1685 152 1270 152 881 152 3312 152 3149 152 2890 152 -27 152 -728 152 -929 152 -1622 152 -1758 152 -2075 152 667 152 318 152 95 152 145 Table 7. Least-Squares Planes. Phenyl Ring Atom C{S) C{6) C(7) C{8) C{9) C{lO) Deviation(A) 0.004 0.006 -0.013 0.009 0.002 -0.008 Ketene Fragment Atom Ti C{S) p Deviation(A) 0.011 0.008 -0.040 0.021 0.131 0.009 0.425 Atom C{2) C(3) C(4) Si Deviation(A) 0.024 -0.070 0.028 0.019 0 C{l) C{2) C{3) Vinyl Fragment 77 5 -Cyclopentadienyl Ring - CP(l) Atom C(ll) C{12) C{13) C{14) C{15) Ti Deviation(A) 0.006 -0.005 0.002 0.002 -0.004 -2.091 146 77 5 -Cyclopentadienyl Ring - CP(2) Atom Deviation( A) C(21) -0.001 C(22) 0.004 C(23) -0.006 C(24) 0.005 C(25) -0.003 Ti -2.081 147 Table 8. Torsion Angles ( 0 ) . Atom C(l)-C(2)-C(3)-C( 4) C(l)-C(2)-C(3)-Si C(l)-C(2)-C(5)-C(10) C(l)-C(2)-C(5)-C(6) O-C(l)-C(2)-C(5) O-C(l)-C(2)-C(3) Ti-C(l)-C(2)-C(3) Ti-C(l)-C(2)-C(5) C(2)-C(3)-C(4)-H(l) C(2)-C(3)-C(4)-H(2) Angle( 0 ) 38.5(8) -129.3(4) 42.7(7) -133.5(5) -7.0(8) 171.7(5) 7.3(13) -171.4(8) -177(4) 10(2) 148 Appendix Il. Crystal Structure Determination of Cp 2TiCaH 11 N(C6H5)2 A single crystal of (11 5 - C5Hs)2Ti(C = N(C4H9)CH2C(C6H5) = C(C6Hs)), obtained from slow cooling of a toluene solution was sealed in a thin-walled glass capillary under N 2. Oscillation and Weissenberg photographs of the crystal showed only one axis of symmetery, which characterizes monoclinic cells. The crystal was then optically centered on an Enraf-Nonius CAD 4 diffractometer equipped with a graphite monochromator and MoKo: radiation. Space group P2ifn, a special setting of # 14, was chosen based on systematic absences (hOl absent for h+l = 2n+l, and O/cO absent for k = 2n+l). A total of 1325 reflections was collected with 10 ::; 8 ::; 15°in the quadrant (±h, +k, +l). The crystal data parameters are in Table 1. Crystal decay was monitored by 3 check reflections, which were collected every 123 reflections. The check reflection intensities decreased at an average rate of 17 .0% over the 10.46 hours of exposure. The reflection intensities were scaled accordingly. The position of the titanium atom was determined from a Patterson map, and the Fourier map phased on the Ti atom revealed the remainder of the structure. All hydrogen atoms were placed at idealized positions with fixed coordi- nates and isotropic Gaussian amplitudes. The titanium atom was refined with an anisotropic Uij, and all other non-hydrogen atoms were refined with isotropic parameters. Least-squares refinement, minimizing :Ew[F~ - (F c/k) 2]2, converged to RF=0.1415 for 1097 reflections (I > 0) and RFI = 0.111 for Fo > 3uF6. The goodness-of-fit was 4.50 for n=l097 reflections and p=l37 parameters. A molecule of solvent, toluene, was found at the center of symmetry. Due to large distortion, the solvent was modeled as benzene, and no refinement was done on the coordinates. 149 Final parameters are listed in Tables 2, 3, and 4. All calculations were performed on a VAX 11/750 computer using the CRYRM system of programs. 150 Table 1. Summary of Crystal Data and Intensity Collection Information. Formula C30H31NTi Formula weight 453.9 g/mol Crystal system Monoclinic Space group P2i/n(# 14) a 18.430(9)A b 14.335(4)A c 10.776(5)A {3 106.41(4) 0 v 2731(2)A3 z 4 Deale 1.119 g/ml .\ 0.110733 A µ 0.403 mm- 1 Scan range 1.0°above Ka.1, 1.0°below Ka.2 Reflections ±h,+k,+l Collected 1325 1097 I> O 151 Table 2. Atom Coordinates (x10 4 ) and B's and U's (A 2 x10 4 ). Atom :z: Ti 1709(3) Cl 2806(14) C2 3246(14) C3 2683(15) C4 1964(14) N 2818(10) cs 3391(16) C6 3034(17) C7 3836(18) CB 3924(19) cu 1261(15) C12 1567(14) C13 1111(15) C14 556(14) C15 672(15) C21 1465(17) C22 911(16) C23 1257(17) C24 2026(16) C25 2147(15) C31 2958(15) C32 2575(16) C33 2832(18) C34 3578(18) C35 3997(15) C36 3716(15) C41 1433(4) C42 798(16) C43 308(14) C44 457(16) C45 1069(17) C46 1582(13) C91 5230 C92 5532 y 842(3) 1238(18) 1755(17) 1816(17) 1504(16) 914(14) 836(21) 819(23) -56(24) 1694(25) 1654(19) 2330(17) 2374(17) 1707(19) 1277(17) -704(18) -517(18) -357(19) -499(18) -728(19) 2319(18) 2938(21) 3440(21) 3250(20) 2601(21) 2111(18) 1477(17) 2027(17) 1981(19) 1330(21) 788(19) 855(19) 514 855 z 2090(5) 2576(30) 1731(28) 432(27) 271(25) 3600(23) 4831(30) 5901(32) 4810(34) 4929(34) 3719(26) 3069(28) 1852(27) 1641(27) 2827(30) 2616(27) 1525(32) 496{29) 1031(29) 2296(30) -529(27) -1364(32) -2296(31) -2284(28) -1512(30) -633(26) -1048(26) -1406(27) -2643(30) -3497(28) -3162(29) -1923(28) 1252 49 B 3.25(9)* 3.3(8) 3.6(8) 2.5(7) 1.5(7) 2.1(5) 4.6(8) 8.8(10) 9.2(11) 9.6(11) 3.3(8) 2.2(7) 2.8(7) 3.2(7) 3.3(8) 4.5(8) 5.0(9) 5.1(9) 4.0(8) 4.5(8) 2.5(7) 5.2(9) 6.6(10) 5.1(9) 4.3(8) 3.4(7) 1.3(6) 2.7(7) 3.4(8) 4.3(8) 4.3(8) 2.8(7) 14.4(15) 15.9(16) 152 5257 C93 375 -1188 15.1(16) • Uu U22 U33 U12 U13 U23 Ti 347(35) 446(38) 547(45) -36(38) 302(33) -17(46) 153 Table 3. Hydrogen Atom Coordinates (x10 4 ) and B's (A 2 x 10 4 ). Atom Hl H2A H2B H6A H6B H6C H7A H7B H7C HSA HBB HBC Hll H12 H13 H14 H15 H21 H22 H23 H24 H25 H32 H33 H34 H35 H36 H42 H43 H44 H45 H46 H91 H92 :r; y 3282 1472 3502 2309 3753 1348 3485 775 2876 1462 2750 419 4311 -131 3913 -121 3536 -606 4286 1682 4212 1586 3651 2202 1505 1412 2018 2757 1163 2881 182 1566 322 822 1378 -740 381 -497 1014 -151 2424 -470 2669 -942 2041 3144 2525 3933 3794 3597 4493 2512 4024 1622 695 2461 -121 2424 120 1213 1237 345 2045 378 5357 873 5881 1357 z 2397 2210 1812 6853 6081 5865 5355 3820 4809 5893 4452 4835 4598 3478 1225 776 2993 3478 1328 -462 621 2938 -1351 -2888 -2957 -1552 -78 -740 -3019 -4353 -3761 -1636 2024 149 B 4.6 4.6 4.6 9.4 9.4 9.4 10.1 10.1 10.1 11.4 11.4 11.4 3.9 3.9 3.9 3.9 3.9 5.2 5.2 5.2 5.2 5.2 5.7 5.7 5.7 5.7 5.7 4.1 4.1 4.1 4.1 4.1 10.0 10.0 154 H93 5374 602 -1937 10.0 lSS Table 4 . Bond Lengths (A). Atom Ti Ti Ti Ti Ti Ti Ti Ti Ti Ti Ti Ti Ti Ti Ti Cl Cl C2 C3 C3 C4 N cs cs cs Cll C12 C13 C14 ClS C21 C22 C23 C24 Atom Distance( A) Cl C4 N cu Cl2 Cl3 Cl4 ClS C21 C22 C23 C24 C2S CP1• CP2• C2 N C3 C4 C31 C41 cs C6 C7 C8 C12 Cl3 C14 ClS Cll C22 C23 C24 C2S 2.02(3) 2.34(3) 2.23(2) 2.44(3) 2.43(3) 2.44(3) 2.39(3) 2.3S(3) 2.36(3) 2.41(3) 2.41(3) 2.39(3) 2.38(3) 2.11 2.08 1.S7(4) 1.19(4) 1.49(4) 1.36(4) 1.47(4) 1.48(4) 1.45(4) 1.48(4) 1.S2(S) 1.S6(S) 1.40(4) 1.34(4) 1.37(4) 1.38(4) 1.34(4) 1.3S(4) 1.4S(4) 1.39(4) 1.36(4) 156 C25 C31 C32 C33 C34 C35 C36 C41 C42 C43 C44 C45 C46 C21 C32 C33 C34 C35 C36 C31 C42 C43 C44 C45 C46 C41 1.39(4) 1.32(4) 1.42(4) 1.40(4) 1.34(4) 1.39(4) 1.46(4) 1.37(4) 1.38(4) 1.39(4) 1.33(4) 1.40(4) 1.38(4) *Centroid of TJ 5 -cyclopentadienyl Rings 1S7 Table 5. Bond Angles ( 0 ) . Atoms Cl -Ti- C4 Ti- Cl -C2 Ti- C4-C3 N- Cl-Ti Rl-Ti-R2 N- Cl- C2 C3- C2-Cl C4- C3- C2 C31- C3-C2 C31- C3- C4 C41-C4-C3 CS-N- Cl C6- CS-N C7- CS-N CS- CS-N C7- CS- C6 CS- CS- C6 CS-CS- C7 ClS - Cn - Cl2 c13 - c12 - en Cl4 - Cl3 - Cl2 ClS - Cl4 - Cl3 C14 - ClS - en C25 - C21 - C22 C23 - C22 - C21 C24 - C23 - C22 C25 - C24 - C23 C24 - C25 - C21 C32- C31- C3 C36- C31-C3 C36 - C31 - C32 C33 - C32 - C31 C34 - C33 - C32 C35 - C34 - C33 Angle{ 0 ) 71(1) 128(2) n6(2) 83{2) 134{3) 147(3) 103(2) n9(2) n3(2) 126(2) n9(2) 134(2) no(2) 107(2) 106(2) no(3) nl(3) 109(3) 106(2) 106(2) n1(2) 104(2) ln(3) 107(3) 108(3) 106(3) 108(3) 109(3) 126(3) n8(2) ns(3) 126(3) n4(3) 122(3) 158 C36 - C35 - C34 C35 - C36 - C31 C42- C41- C4 C46- C41- C4 C46- C41- C42 C43 - C42 - C41 C44 - C43 - C42 C45 - C44 - C43 C46 - C45 - C44 C45 - C46 - C41 120(3) 119(2) 122(2) 117(2) 119(2) 121(3) 118(3) 121(3) 120(3) 118(3) 159 Table 6. Torsion Angles ( 0 ) . Atoms Ti-Cl-N-C5 Ti - Cl - C2 - C3 Cl - C2 - C3 - C4 C2 - C3 - C4 - TI Ti - C4 - C41 - C42 C4 - C3 - C31 - C32 Angle( 0 ) -177(2) -4(3) 3(3) -2(3) 74(3) 36(5) 160 Table 7. Least-Squares Planes. 5 'l -cyclopentadieny1- Rl Atoms Deviation(.A) cu 0.0215 C12 -0.0274 C13 0.0232 C14 -0.0089 C15 -0.0084 Ti -2.1074 5 'l -cyclopentadieny1- R2 Atoms Deviation(A) C21 -0.0219 C22 0.0181 C23 -0.0075 C24 -0.0057 C25 0.0170 Ti -2.0789 Metallacycle Plane Atoms Deviation(A) Ti 0.0112 Cl -0.0240 C2 0.0259 C3 -0.0145 C4 0.0014 N -0.0604 cs -0.0743 C31 0.0837 C41 -0.1807