Carbon Monoxide Reduction by Sixteen Electron d-Zero Tantalum Complexes. Acrylonitrile Cyclodimerization by Tris(triphenylphosphine) Tetramethylene Ni(II) Citation Berg, Beckie E. (1979) Carbon Monoxide Reduction by Sixteen Electron d-Zero Tantalum Complexes. Acrylonitrile Cyclodimerization by Tris(triphenylphosphine) Tetramethylene Ni(II). Master's thesis, California Institute of Technology. doi:10.7907/qqt5-e721. https://resolver.caltech.edu/CaltechTHESIS:04072010-082613027 Abstract [Part I] The sixteen electon, d-zero complexes Ta(COT)Me_3 and (η^5-C_5Me_5)Ta(C_3H_5)Me_3 were prepared and treated with carbon monoxide. The prep of Ta(COT) Me_3 gave irreproducibly small yields and upon treatment with CO paramagnetic material was observed. The prep of (η^5-C_5Me_5)Ta(C_3H_5)Me_3 resulted in yellow crystals in a red oil and these could not be separated. (η ^5C_5Me_5)Ta(C_3H_4Me)Me_3 was then made. This complex decomposes to the trimethylene methane species (η^5-C_5Me_5)Ta(C_3H_3Me)Me_2, and upon treatment with CO gave an unknown white solid product. [Part II] Tris(triphenylphoshine) tetramethylene Ni(II) was made and treated with acrylonitrile. 1, 2 dicyanocyclobutane was produced in a cis:trans mixture of 45:55 and was isolated by preparative GC. The product was rarely observed and the reaction of nickel metallocycle with acrylonitrile was not catalyzed by acid, base, or Ni(O). Item Type: Thesis (Master's thesis) 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): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 29 June 1979 Additional Information: Two separate Masters theses were submitted. Each is separately numbered: 1. "Carbon Monoxide Reduction by Sixteen Electron d-Zero Tantalum Complexes", pp. i-ii, 1-15. 2. "Acrylonitrile Cyclodimerization by Tris(triphenylphosphine) Tetramethylene Ni(II)", pp. i-ii, 1-17. Record Number: CaltechTHESIS:04072010-082613027 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:04072010-082613027 DOI: 10.7907/qqt5-e721 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 5697 Collection: CaltechTHESIS Deposited By: Tony Diaz Deposited On: 19 Apr 2010 18:24 Last Modified: 21 Nov 2024 20:13 Thesis Files Preview PDF (Combined theses) - Final Version See Usage Policy. 888kB PDF (Carbon Monoxide Reduction by Sixteen Electron d-Zero Tantalum Complexes) - Final Version See Usage Policy. 961kB PDF (Acrylonitrile Cyclodimerization by Tris(triphenylphosphine) Tetramethylene Ni(II)) - Final Version See Usage Policy. 961kB Repository Staff Only: item control page

CARBON MONOXIDE REDUCTION BY SIXTEEN ELECTRON d-ZERO TANTALUM COMPLEXES Thesis by Beckie E. Berg In Partial Fulfillment of the Requirements for the Degree of Master of Science CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 1979 (submitted June 29, 1979) ABSTRACT The sixteen electon, d-zero complexes Ta(COT)Me, and (f’-C,Me,)Ta(C,H,)Me, were prepared and treated with carbon monoxide. The prep of Ta(COT) Me, gave irreproducibly small yields and upon treatment with CO paramagnetic material was observed. The prep of (y'-C; Me,)Ta(C.H,)Me, resulted in yellow crystals in a red oil and these could not be seperated. (q -C,Me,)Ta(C,H,Me)Me, was then ade. This complex de- composes to the trirethylene methane species (\’-Cj"\e,)Ta- (C,H,Mie)ije, 2nd upon treatment with CO gave an unknown white solid product . -ii- TABLE OF CONTENTS Abstract Introduction. , General Methods ,., Experimental Results and Discussion ,,..., Addendum ,,,......-. References ........... ee | Ce ee | eeeaaa eaaaas Ce oy INTRODUCTION Reduction of CO by Ho to alcohols and alkanes is a thermodynamical ly favored process. However, with heterogeneous catalysts, high reaction temperatures and pressures are required. Several homogeneous catalysts have been found to carry on this same process under less severe operating conditions. The 0s (C0) 1, and Ir,(CO)1, clusters have been found to (1) produce methane at 140°C and ~2 atm. Ir, (CO) in molten NaCl+2A1C1 4 12 in the presence of 3:1 H,:CO gives methane, ethane and trace amounts of 3 propane and isobutane at 180°C and 1.5 atm pressure (2) Under mild reaction conditions dicarbonyl] (acetylacetonato) rhodium or Rh, (CO)15 (3), produces ethylene glycol when treated with synthesis gas It has been observed that the 16 electron, d-zero Zr species (n°-CaMeg) ZH, reduces CO to give (4) (n°-C,Me )Zr (OMe) (H) 5 and (n°-C,Me,) 9(H) Z(OCH=CHO)Zr(H) (n >-C.Meg) Reductive elimination to give MeOH and 1,2 dihydroxyethylene does not occur, probably because of the high Zr-0 bond energy. It is believed that reduction of CO is due to 2 factors: (1) electron deficiency of the metal center causing CO to add and (2) the fact that a d-zero species does not require CO to act as a Il acid, thereby allowing facile CO insertion(s) into M-carbon and M-H bonds. By moving one column over in the Periodic Table, one might expect the metal-oxygen bond strength of tantalum not to be as strong as the Zr-O bond, and reductive elimination may be possible if CO adds ina similar fashion. The synthesis of the following two 16 electron, d-zero Ta complexes was therefore attempted: Ta(COT) Me,(COT = cyclooctatetraene) and 3 (n°-C.Meg)Ta (CH, )Me. Since the analogous 16 electron Zr species (1) (1° CMe ZrMe,, adds 2 moles of CO to give 5)2 2 5. (n CMe.) 4 ZPOC(CHy)=C(CH,)0 (Eq. 1) Me a 0 ° > (n° fo $8 7K (rn -C,.Me,) ZrMe, +C0 2 (n Cates) oO =e OL It was hoped that CO would add in much the same way to Ta(COT)Me, and “=t (n°-C.Meg)Ta(CaHz)Me, to give (COT) (Me) Ta(0(CH,)C=C(CH)0) and 5 35° "3 3 (n°-CgMeg) (CsHp) (Me )Ta(O(CH)C=C(CH,)0), respectively. If the Ta(COT)Me 3 and/or (n°-C.Me,)Ta(C3Hz Me, give encouraging results, the corresponding Ta hydride complexes would then be made, treated with CO, and examined as to whether or not catalytic CO reduc- tion with Ho can be achieved. GENERAL METHODS All reactions and other manipulations were performed under Argon purified before use by passage over MnO on vermiculite and activated 4A molecular sieves. Ho was purified in the same manner. High vacuum line and glove box techniques were used. Toluene, diethyl ether and pet ether were dried over LIATH, » degassed and stored over "titanocene", the preparation of which has been previously reported (5). THF was freshly distilled from the sodium-benzophenone ketyl. Carbon monoxide (MCB) was used directly from the cylinder. Reaction products were analyzed by NMR on an EM-390 spectrometer. The NMR solvent, benzene-d,, * was vacuum transferred from "titanocene". Infrared spectra were measured on aBeckman I.R. 12 spectrophotometer. EXPERIMENTAL The following route was used in the preparation of Ta(COT)Me,(6,7) 1.8 eq. ZnMeo K,COT TaMe,Cl, > Ta(COT)Me., -78°C, Tol Tacl ny > 5 fe) EtyO y 25°C Preparation of TaMe C1, 5.869 anhydrous ZnCl, in 30 mis of ether at -78°C was treated with 58.8 mis 1.6M MeLi (10% excess of 2 equivalents Zn) and the mixture warmed to zero degrees. This was stirred for 0.5 to 1.5 hrs, and the ether solution vacuum transferred to a sublimator containing 8.69 sublimed TaCle. This was warmed to room temperature and allowed to stir overnight. The solvent was pumped off and the remaining solid sublimed at 25°C using a probe cooled to -10°C. Yield: 4.58g (62.5%). TaMe C1, is light yellow, very pyrrophoric and decomposes slowly at 25°C. It is soluble in pentane, THF, diethylether, and aromatic hydrocarbons. Usually a mixture of di- and trimethyl] Ta chloride is produced. 100% TaMe C1, can be obtained by treating the mixture (before or after sublimation) with excess ZnMe. . This alkiating agent does not give TaMe,C1. NMR : TaMe.C] S 1.5 6 3° 2 TaMe,C1 S 1.7 6 2 Preparation of Ta(COT) (Me.) Cyclooctatetraene with hydroquinone added, was distilled at ] atmosphere under No at 137°C. The yellow liquid was freeze-pump- thawed and stored at zero degrees. A 0.47M K,COT solution in THF using excess potassium was made. To 5.0g TaMe Cl, was added 125 mls toluene. An equimolar amount 3 of the 0.47 M solution was added dropwise over 0.5 hrs at -78°C and the reaction: was allowed to stir an additional 1.5 hrs at this temperature. The reaction mixture turned dark blue. It was then filtered at -78°C to remove the KC]. The volume was reduced to 5 mls and filtered again. Blue crystals remained on the fritt. (An alternate method is adding pet ether after the volume reduction and then filter- ing). Ta(COT)Me., can be recrystallized from toluene/pet ether. Yield: 1g (17.9%) The solid was sublimed at 70°C using a -10°C cold finger and 0.33 g was recovered. Ti co NMR : COT protons S 5.82 6 area nt <e) Me protons S ./ 6 area Reaction of Ta(COT)Me., with CO 0.100g Ta(COT)Me., was dissolved in 10 mls of toluene. A known amount of CO was introduced at -78°C and allowed to react for 3 hrs. The blue solution turned brown. The unreacted gas was collected and measured using a toepler pump. The solution was warmed to 25°C and again a known amount of CO was introduced, allowed to react for several hours, collected and measured. The toluene was pumped off and the solid was dried. An NMR and IR was taken of the solid. Preparation of (n°-C.Me,)Ta (Cat, Me. Synthetic Scheme: TaMe,Cl, 104 (f-CpMeg)MsC THE (gi-CgMeg) TaMe,c1 7 MeBr, Tol. 25°C pentane | Mex Lo 7 x8 cl Fie 2~-MgBr or “er _s Ar~/ Li Ay . ea Tol.or THF/Tol. Vv (n) -C,Me,)TaMe.(C Hs) Preparation of (n°-CeMeg )TaMe C1 2.3 g TaMe,Cl, was added to a solution of 2.0 g (n°-CgMeg )MgC1 + THF (1.1 eg n?-CgMeg/Ta) in 100 mls of toluene over 10-15 minutes at 25°. The reaction was allowed to stir an additional 45 minutes. The MgCl, was filtered off and the toluene reduced until the yellow crystals began to fall out of solution. Pet ether was then added at -78°C and the solution filtered. Yield: 2g (65%) (n°-CaMe, )TaMe C1 can be sublimed at 50°C without decomposition. NMR: (n°-CaMeg MgC] «THF § 2.16 Me Protons S 9 6 area 9 (n°-CgMeg) protons 5 1.7 6 area 15 Preparation of (n°-C,MedTa(CaH,)Me, To 0.25 g (6.3x107" moles) (n°-CaMe, )TaMe C1 in 25 mls toluene cooled to -78°C was added 6.3x107" moles allyl MgBr in ether. After stirring 45 minutes at -20°C the MgBr., was filtered off. Most of the toluene was then removed and pet ether was added. Additional MgBro was the only compound that precipitated out of solution and this too was filtered off. The solution was then pumped dry, leaving behind yellow crystals in a red oil. The two are not separable, even with the use of cold ether or pet ether. NMR of crude reaction: w (n°-CaMeg) protons 1.6 area 15 Me protons S 7 area 9 allyl protons d 3.] area 4 allyl protons quintet 6.7 area | . 5 . Reaction of Crude (n -C,Me, )Ta(C3H, )Me. with CO Carbon monoxide was added to a toluene solution of the crude . . 5 ) reaction mixture of (n -CeMeg\Ta (CH, Me at -78-C. After 1 hour the solution was warmed to 25°C. After another hour, the toluene was removed and an NMR taken of the yellow solid which remained. RESULTS AND DISCUSSTON Synthesis of Ta(COT)Me, gives irreproducibly small yields, primarily due to the ease of which this complex is converted to Ta(COT),Me (6) | Different solvents were used in attempts to avoid 2 this problem. Both a 1:1 THF/toluene and a pentane solvent were used, both which resulted in the immediate formation of the Ta(COT) Me. The K COT + THF salt was then isolated (8) and used as a solid reactant. When this is added to TaMe Cl, in a THF or toluene solution at -78°C, there is no reaction. Upon warming, it immediately goes brown. If the K,COT-THF is isolated first and then dissolved in enough THF to 2 make a 0.47 M solution, and added to TaMe.C1,/toluene solution, only the Ta(COT) Me complex is made. I have no explanation for this. The blue crystals of the crude Ta(COT)Me., behaved strangely. Sometimes they would sublime, and other times they would not, some- times with an evolution of gas (probably CH, as it did not condense at liquid nitrogen temperatures). It appears to be the case that the more you work with the Ta(COT)Me,, the more it decomposes. For example, after recovering 3 g in the filtration step, only 1 g remained after 2 recrystalliza- tions. Of this, only .020 g sublimed even though quantitative NMR showed that the 1 g was 84% Ta(COT)Me3. Ta(COT)Me, does react with CO. The toepler pump experiment showed that at -78°C, Ta(COT)Me. took up 1.8 CO/Ta. At room temperature, 3 the solution took up an additional .73 moles CO. Both of these gave weak signals in their NMR spectra, suggestive of paramagnetism. The I.R. of the sample warmed to 25°C showed no carbonyl stretch indicating that the simple CO insertion product did not exist at this temperature. The only conclusions that can be drawn from this experiment is that CO is taken up by Ta(COT)Me, to give at least 1 product that is paramag- 3 netic. The main problem was that not enough purified Ta(COT)Me. could be obtained to do any more than one or two CO experiments. After a number of synthetic routes to Ta(COT)Me., had been exhausted, and because it is so difficult to purify, this molecule was abandoned and . 5 the synthesis of (n -C.Me, )Ta(CH, )Me, pursued. (n°-CaMe Ta(C.H )Me, proved to be no more stable than the 5) 35 Ta(COT)Me3, In the first step, the synthesis of (n°-C,Meg )TaMe C1 , the TaMe C1, must be added over a period of time. (1°-CeMe, )MgC1 «THF reacts very quickly and any excess TaMe,C1., present seems to result in the exchange reaction: TaMe,C1, + (n°-CxMeg)TaMe,Clz(n?-C,Meg )TaMe C1, This is suggested by NMR. The parent cyclopentadienyl complex (n°-CgH, )TaMe C1 has been pre- pared by Schrock using T1(CeHe) in which the exchange reaction did not occur to any appreciable extent, if at all (9) (n°-CeMe,)TaMe 401 is easily made. The allyl species, however, is not. All attempts resulted in a red oil in which sometimes yellow, prismatic crystals were seen. An NMR -10- of the crude reaction mixture, however , was surprisingly clean and did confirm the existence of the (n°-CeNeg)Ta(CaH, Me. The NMR showed the expected singlet for the permethylcyclopentadieny] protons and the splitting pattern of an allyl group whose protons are undergoing rapid syn-anti interconversion. The most surprising result, however, is that, at 34°C on the NMR time scale, all 3 of the methyl groups are equivalent. One structure which fits the data is the following: Me <> Me Me | fe. ; Me yw Me ——Ta* “SS Me , eee ~— In this trigonal bypyramidal structure, the 3 methyl groups lie in the equatorial plane while the 2 axial ligands are rotating at a rate such that each Me is in the same environment. Alternatively, the pseudo five-coordinate species may be undergoing rapid site exchange, as in the tetragonal pyramidal (n°-C.Hg )Ta(ChCMe) (CHyPh) C1. reported by Schrock (10) | Me—Ta——Me _ Me—Ta— Me all e Me VY The crude reaction mixture of (n°-CeMeg)Ta(C Hz Me. was treated with carbon monoxide. Upon introduction of CO at -78°C to a toluene solution of the complex, the mixture went from orange to yellow. When warmed to 25°C the color did not change. The NMR showed broad peaks characteristic of paramagnetic material. The only conclusion to be made here is that something becomes paramagnetic. -12- ADDENDUM Dr. Calvin Curtis took over the project from here, All allyl reagents resulted in an oi], so methyl] allyl was tried. 2 methyl allyl was chosen because the allyl group of the metal-allyl species formed cannot rearrange to give a different product. The following reaction resulted in the desired compound: -80°C gC! + ALMeCl FO (y-CpMe,)Ta(C.H,Me)Meg 1 ~ (n- C,Me,)TaMe 1 undergoes a reaction with Ho. Whether using excess Ho or a deficiency of Ho» the products were always the same: 1 + Hy ———5CHy + >= + m— «Ll Since under Hy deficient conditions both methyl and allyl] groups are lost, it appears the allyl ligand is not especially labile. When 1 is dissolved in THF, pet ether, toluene or benzene-d, and allowed to remain at room temperature for 24 hrs, CH, is evolved and the yellow complex, Tantalum trimethylene methane (TMM) (2) is formed -13- A labeling study done with ] shows that the methane is evolved from the methy! groups on the Ta: C5Me, ta Pa 24hrs OD 4 (p’-C-Mex)Ta(CDq)o(TMM) 7 \7 CDs Tol 25°C 3 AB 5 32 a CDg There is no evidence as yet where the H is coming from. When 2 is treated with H the result is the same as with I]. 2? 2 has also been treated with 1 equivalent of HCI: q HCL, ipig-CgMex)TaMesCl + ‘= + /a2 Treatment of 2 with CO gives an unknown white solid product. Syn-anti interconversion occurs in the allyl group of both | and 2, Variable temperature NMR was performed on 2 and the singlet and doublet of doublets, separated by 3.5 ppm, were frozen out only at -80°C, indicating that there is a very low barrier to syn-anti interconversion. -14- REFERENCES 1. 10. M. G. Thomas, B. F. Beier, E. L. Muetterties, J. Am. Chem. Soc., 98, 1296 (1976). G. C. Demitras, E. L. Muetterties, J. Am. Chem. Soc., 99, 2796 (1977). R. L. Pruett and W. E. Walker, (Union Carbide Corp.), German Offen. 2 262 318 (1973); U.S. Appl. 210 538 (1971). Juan M. Manriquez, Donald R. McAlister, Robert D. Sanner, and John E. Bercaw, J. Am. Chem. Soc. 100, 2716 (1978). R. H. Marvich and H. H. Brintzinger, J. Am. Chem. Soc. 93, 2046 (1971). R. R. Schrock, L. J. Guggenberger, and A. D. English, J. Am. Chem. Soc., 98, 903 (1976). R. R. Schrock and G. W. Parshall, Chemical Reviews 76, 243 (1976). Von H. P. Fritz and H. Keller, Z. Naturforsch, 166, 231-234 (1961). R. R. Schrock and P. R. Sharp, J. Am. Chem. Soc., 100, 2389 (1978). C. D. Wood, S. J. McLain, and R. R. Schrock, J. Am. Chem. Soc., 101, 3210 (1979). -15- ACRYLONITRILE CYCLODIMERIZATION BY TRIS(TRIPHENYLPHOSPHINE ) TETRAMETHYLENE Ni(IT) Thesis by Beckie E. Berg In Partial Fulfillment of the Requirements for the Degree of Master of Science California Institute of Technology Pasadena, California 1979 (submitted June 29, 1979) ABSTRACT Tris(triphenylphoshine) tetramethylene Ni(II) was made and treated with acrylonitrile 1, 2 dicyanocyclobutane was pro- duced in 3 cis:trans mixture of 45:55 and was isolated by prep- arative GC. The product was rarely observed and the reaction of of nickel metallocycle with acrylonitrile was not catalyzed by acid, base, or Ni(0). -ji- TABLE OF CONTENTS Page AbStract co.cc ccc cent eng acces Lh Introduction ........ cc ccc cere eee teers anes 2 General Methods ....,..555 55339999 9999339999 4 Experimental,.....,...-. a rr) Results and Discussion ..........0ceeeaee ees 12 Table TL vi... c eee eee cece ee eeeeeeees JD ReferenceS ...,.. ccc ccc cence ean e nee e ees 17 -1- Transition metal metallocycles have been demonstrated to be inter- mediates in a variety of metal catalyzed reactions. Metallocyclopentanes have been suggested as intermediates in some metal catalyzed [2+2] cycloadditions and cyclo-reversions of olefins. The metallocyclopentanes aD (3) A” so) 6) of Ti, Pt’, Rhv, T Zy~ and Ni~° are now known and vary greatly in stability. The 1,4~tetramethylene bis(cyclopentadienyl) titanium (IV) complex prepared by the Whitesides group is thermally labile and can be isolated only at low temperatures. It is characterized only through its reactions as it is too unstable for elemental analysis C1) The (n?-CoHe) oP rhodacyclopentane is difficult to isolate, as opposed to the Rh(II) cyclohexane and RH(II) cycloheptane. Its existence is inferred by Br, and HC] decomposition (3) The bis(phosphine) Pt(II) (2) cyclopentanes, on the other hand, are quite stable and easily isolated Bis(triphenyl phosphine) Nickelacyclopentane is easily isolated, but is somewhat thermally labile at long periods at 2500? All are relatively more stable than their acyclic counter- parts due to the inaccessibility of the 8-H in the metallocycle. 46) A 513) 542) (3} The tetramethylene complexes of Ni » Pt” and RA? can be prepared by the corresponding metal dihalides treated with dilithiobutane 9 or a,6 diGrignard reagents. The Ta’ and 7*) metal locyclopentanes can be made from the reduced metallocenes and ethylene. {6,7,8,13) (7) Substituted tetramethylene metallocycles of N Ti 5 and 9) zr can be prepared by reacting the unsubstituted metallocycle with a primary olefin. uM + R-CH=CH, —> Ly a SR, + CH=CH, Tris(triphenylphosphine) nickelacyclopentane (8) | and bis (7) (cyclopentadieny1l) titanium cyclopentane react with 1,7 octadiene to give the following: L mM oo > + _ LM i me ~~ noe Jt uM TO) trans cis M = Ni n=3 n'=2 100% 0% Ti n-2-m! 75% 25% (A Zr species, CppZr(Po.), also reacts with 1,7 octadiene to give the cis and trans hydrindane complex in a 1:1 mixture). (9) The oxidation of the bis (triphenylphosphine) nickelacyclopentane 6613) There- results in the reductive elimination product, cyclobutan fore, oxygen quenching of any bis substituted Ni metallocyclopentane should yield the substituted cyclobutane molecule (8) Indeed the bis (phosphine)Nihydrindane isolated gave bicyclo [4.2.0] cyclooctane. Because the Ni metallocycle gives 100% of the trans isomer, tris (triphenylphosphine) nickelacyclopentane has potential utility in natural products synthesis. It is therefore of interest to look at the reactivity of this nickel complex towards different olefins and determine the yield and stereospecificity of the oxygen quenched products. Olefins chosen should represent a wide range of Alfrey-Price e values to see if there is any correspondence between the yield and stereospecificity of the products and the electronic properties of the olefins. This paper explores the reaction of tris(triphenylphosphine) nickelacyclopentane with acrylonitrile. GENERAL METHODS All reactions and other manipulations, with exception of the ZPNICT, prep, were performed under argon purified before use by a BASF deoxygenation catalyst and activated 4A molecular sieves. High vacuum line and glove box techniques were used. Diethyl] ether and toluene were dried over sodium-benzophenone ketyl under an argon at- mosphere and were freshly distilled before use. The absolute ethanol used was degassed prior to use. Acrylonitrile was reagent grade and was distilled from Cah, and stored under argon. Reaction products were analyzed by gas chromatography on a Varian Series 1400 instrument equipped with a flame ionization detec- tor. Proton NMR spectra were made on an EM-390 spectrometer. The cyclodimerization product, dicyanocyclobutane, was purified by gas chromatography on a Varian Model 920 spectrometer and identified using NMR by comparison with an authentic sample. Yields of this product were determined by peak area comparisons with the internal standard dibromobutane. EXPERIMENTAL Preparation of bis(triphenylphosphine) nickel(II) dichloride A hot solution of 75g (.28 moles) triphenylphosphine in 500 mis glacial acetic acid was added with stirring to a solution of 24g (.11 moles) nickel(II) chloride hexahydrate, 20 mls of water and 250 mls glacial acetic acid. The solution was allowed to stir at >80°C for at least .5 hrs. The solution was filtered at 80°C to minimize product contamination with unreacted triphenylphosphine. The dark blue-green crystals were washed two times with ethanol to partially remove the acetic acid and unreacted nickel(II) chloride. The solid was dried and 51g (bP) NiCT, was recovered. The product can be recrystallized from butanol. The yield was 77%. Preparation of Bis(triphenylphosphine) tetramethylenenickel (II) (6) To 6 .05g (9.4 mmol) ($3P) NiCT, that had been finely ground to a dark green powder was added 75 mis ether. After cooling the suspension to -78°C, 43 mls of a 0.37M 1,4-dilithiobutane ether solution was Slowly added by syringe. (The amount of ether should total 20 mls/g Ni and Li(CH,) gLi/Ni = 1.7). After addition, the reaction mixture was stirred for ten minutes at -78°C, after which the cold bath was removed and the stirring maintained. The dark violet crystals of the Ni(II) starting material began to dissolve in the ether, forming a dark brown solution and gold crystals began precipitating out. After ten minutes, the starting material was completely gone. As soon as the yellow solid ceased forming, which was an additional five minutes, the solution was filtered. The yellow solid was washed with ether, followed by an ethanol wash to remove LiCl. The solid was vacuum dried and 4.4g was recovered. (Store at -40°c) Yield: 74% % Ni:7.8% hhgP: 93% *C4 : 90% P/N7i = 2.1 Preparation and Standardization of 1,4-Dilithiobutane In a 1000 ml 3-necked round bottom flask fitted with an argon line, 250 ml dropping funnel, and mechanical stirrer, was placed 8g (1.14 moles) flattened Li ribbon and 250 mls ether. This was cooled to -10°C and this temperature was maintained over the entire course of the reaction. To the Li was added, dropwise over 2 hrs, a solution of 25 mis (.228 moles) 1,4-dichlorobutane in 150 mls of ether. During the addition, the solution became milky white as the LiCl precipitated out. Following the addition of the dichlorobutane, the mixture was allowed to stir overnight. The liquid was then separated from the LiCl by filtration and stored under argon at -30°C. The concentration of the 1,4 dilithiobutane solution was determined as follows (6). 1.95x107? moles durene (recrystallized from ethanol) was placed in a vial which was then stoppered and purged with argon. A 10.0 ml aliquot of the 1,4 dilithiobutane solution was added, followed by 2 mls of trimethylchlorosilane. The solution became hot and turned cloudy as the LiCl precipitated out. The ether solution was analyzed by gas chromatography and the peak areas of durene and MeSi(CH,) ,SiMe, were compared, assuming equal response factors. G.C. conditions: SE-30 . 6! 1/4" diameter T= 110°C Flowrate = 90cc/min The retention times for C1(CH,)4CT, Me,Si (CH) ,SiMe, and durene are 1.4 min, 3.4 min, and 3.7 min, respectively. Yield: 72% based on 1,4-dichlorobutane Preparation of Tris(triphenylphosphine) tetramethylene nickel (11) ‘8 Bis(triphenylphosphine) tetramethylenenickel(1I) (8g; 12 mmoles) was dissolved in 300 mls toluene at O°C and filtered to remove LiCl. Temperatures above 0°c must be avoided for prolonged periods to prevent decomposition to the ($5P) Ni (CHo=CH, ) complex. To the dark gold solution was added 6.5g (25 mmol) triphenylphosphine.. The solution turned red immediately and the reaction was stirred at 0°c for 2 hours. Approximately 200 mls toluene was removed and the solution was stored overnight at -40°C. The orange crystals which precipitated on cooling were filtered and washed with cold toluene, followed by pentane. 5g was recovered. The compound can be recrystallized at -40° from toluene that has been saturated with triphenylphosphine at -60°C. (Store at 40°C). Yield: 43% Reaction of Tris(triphenylphosphine) Tetramethylenenickel(II) with Acrylonitrile Both recrystallized and unrecrystallized metallocycle has been used. To .100g metallocycle, and sometimes .5 equivalents triphenyl- phosphine, is added 1 ml of toluene followed by 1.5 mls acrylonitrile. Reactions were also done in which CH CHCN/Ni ratio varied from 12.5 to 187 and in concentrations ranging from 0.75M to 9.12M CHOCHCN. The solution was warmed to -15°C and filtered. The reaction was allowed to continue stirring for 5 hrs at -10°C. The solution was cooled to -78°C and the vial partially evacuated and opened to air or injected with oxygen. The reaction was warmed slowly to 25°C and the Ni solid was allowed to settle out. The liquid was analyzed by gas chromatography using an 18' 1/8" SE-30 with the following program: j=110°C, t=350 sec, T,=180°C Rate = 10°/min. The retention time for dicyanocyclobutane is 588 sec for the trans + isomer and 801 for the cis. The results are summarized in Table I. Reaction of Tris(triphenylphosphine) Tetramethylenenickel with Acrylonitrile in the Presence of Acid or Base To .100g nickelmetallocycle was added 1 ml toluene followed by 1.5 mls acrylonitrile at -78°C. Enough acetic acid or sodium acetate was added to make a 107M solution. The solution was warmed to -15°C, filtered and allowed to stir for 5:-hrs at this temperature. The re- action was quenched with oxygen and analyzed as above. The results are summarized in Table I. Reaction of Tris(triphenylphosphine) Tetramethylenenickel with Acrylonitrile in the Presence of Ni(0) To .100g of metallocycle and .010g (4,P),Ni(CH,=CH,) or .010g (3P) ,Ni was added 7] ml toluene and 1.5 mls acrylonitrile at -78°C. The solution was slowly warmed to -15°C, filtered and allowed to stir at this temperature for 5 hrs. The reaction was quenched with oxygen and analyzed as above. Reaction of Bis(triphenylphosphine) Nickel(0) Ethylene with Acrylo- nitrile To .100g (3P) Ni (CH.,=CH, ) was added 1 equivalent triphenylphosphine. 1 ml toluene and 1.5 ml acrylonitrile was added at -78°C, warmed to -15°C, filtered and allowed to stir at this temperature for 5 hrs. The reaction was quenched with oxygen and analyzed as above. The results are summarized in Table I. Reaction of Triphenylphosphine with Acrylonitrile To .012g, .018g, .030g and .048g triphenylphosphine was added .6 mls toluene followed by .8 mis acrylonitrile at -78°C. The solutions were slowly warmed to -15°C and stirred for 5 hrs. Two .030g triphenyl- phosphine samples were prepared in which one stirred at 25°C for 5 hrs and the other one stirred at 60°C. Oxygen was introduced into all samples at -78°C and they were allowed to warm to 25°C. Products were analyzed by gas chromatography. The results are summarized in Table I. Analysis of Nickel Complexes I. Nickel The % Ni was determined as follows: A known amount of Ni complex was decomposed with oxygen and weighed. The sample was sent to the analytical lab for % Ni and that value was extrapolated back to the undecomposed material. -10- TI. % C4 metallocycle To a known amount of Ni complex of approximately .050g in a stoppered vial equipped with a stirring bar was added .500 ml internal standard (methane or propane). The vial was cooled to -30 and .4 mis concentrated aqueous HC] was added while the solid was vigorously stirred in order to avoid localized heat buildup, which accelerates C-C bond cleavage (10) | After acidolysis was completed, a gas sample was analyzed by gas chromatography on a duropak column. The metallo- cyclopentanes decomposed to give butane, |1-butene, cis and trans 2- butene and ethylene, and the peak areas of the C4 and C2 hydrocarbons were compared with the corrected peak areas of the internal standard (butane/Me=3.65; butane/propane=4/3). Note: Decomposition by concentrated H5S0q gave consistently lower values and only ethylene and butane were observed. III. %P A known amount of Ni complex of approximately .5q was decomposed with 1 ml HoSOq. mts H,0. The 4P=0 was extracted approximately 10 times with toluene 1 ml of 30% H,0, was then added, followed by a few and the toluene layer was collected. After stripping off the solvent, the oP = 0 was dried, weighed, and a T.L.C. and melting point taken as a purity check. -l1- RESULTS AND DISCUSSION The cyclodimerization of acrylonitrile followed by oxygen de- composition to produce dicyanocyclobutane was observed only in a few cases. The first was a batch of tris(triphenylphosphine) nickelacyclo- pentane that was left out at 20°C for 5 days. This nickel complex with .5 equivalents OP added gave a yield of 600% dicyanocyclobutane based on nickel, and was reproducible. (This batch did not work before although .5 equivalents oP was not added.) This was an interesting result because excess oP decreases the amount of reductive elimination product (11) indicating that the P had nothing to do with promoting the reaction. Another batch of tris metallocycle that had been set out at 20°C for 5 days did not work with or without the excess OP added, strongly suggesting that the .5 eq. oP did not matter in the previous batch, but that the critical factor was what occurred to the complex during the 5 days. The only other case which gave product was a batch of tris metallocycle which analyzed, for 15% C4 hydrocarbons after acidolysis (theoretical is 100%), and 2.2% Ni (theoretical is 6.5%), and gave a yield of approximately 350% dicyanocyclobutane. Another batch of tris metallocycle which did not yield the desired product analyzed to 65% C4 metallocycles. I have no explanation at this time why so few batches of tris metallocycle worked. Purity does not seem to be the critical factor, however. -12- Dicyanocyclobutane was also observed in yield of <1% when using (5P) Ni (CH =CH,) and 1 equivalent of oP. The mechanism for the 2 dimerization of ethylene has been proposed as follows; (917) PaPNi <= (6,P),Ni — (aP).Ni | x | » O, O, oO, | via ( 4,P),Nir Oa CH-CH, + (6,P),Ni-|| Ethylene adds to (3P) Ni (CH=CH, ) to go through a proposed tetrahedral (6) intermediate which undergoes ring closure upon adding another oP. This pentacoordinate complex then loses a ligand to give the square planar bis metallocycle which undergoes reductive elimination to give cyclobutane. As pointed out earlier substituted olefins should behave in a similar manner and this has been successfully demonstrated in the isolation and decomposition of the nickelhydrindane complex (8) The results of the control experiments with bP and acrylonitrile indicate that cyclodimerizations were not performed by bP. and that the nickel complex was required. The closure to metallocycle is not catalyzed by acid, base or the Ni(0) complexes (oaP)Ni (CH,=CH,) or (>P) Ni (0), the latter being a decomposition product in the pre- sence of excess gP and heat. The formation of bis(acrylonitrile) bis(triphenylphosphine)Ni(0) seems to be occurring. The reaction always forms the irridescent -13- (12) yellow crystals characteristic of this compound (Oxygen decom- position followed by G.C. analysis confirms the fact that this solid is an acrylonitrile complex). The monophosphine bis(acrylonitrile) complex are orange crystals (having been identified as such by elemental analysis and G.C. after oxygen decomposition) that are often seen precipitating out of the reaction mixture of the tris metallocycle with acrylonitrile. This, too, supports that the bis(acrylonitrile) ) (12) species (at least the square planar species is being formed. Why so very few times closure to metallocycle occurs is unknown. -14- aged yxou uo 3,u09 -oT- WL°9 = [A=] OS S[W Qt L SEM OUN[OA [BIOL “IN/ A= DAQLL SE A> Siw g’ *2 NS ND sf 1 - n n P bagel teg’ - " " " bag" /9*We"€ - " " " beg EWS" T - \ e n bagol {M9 - 0 IpGi- Say ZL bezst ‘N6=[ 5 (61°) tn’, SS/Sb “OSE I,GL- sy ZL yy SLU (67) tay - 0 IoGL- SAY ZL fo¢ bag" /, =S{w 8° (51°) Ine, - 0 J9Gt- SAY FY YO OWH We OL/ "SL 8° - 0 IpGl- say ZL esl 8 (517) INST, - 0 I9Gl- SAU S Sos lu 8" (61°) ane, $9/S0 %009 IoSk- SAY G a beg"/ a= Sug" (51°) Neg - 0 36L- say | gE SLtl 8", (6L°) Nea, - 0 I9Sl- say d$(b2,_OLxS" L800") - 0 19617 SAU d©0(ba,_o1xs"6‘60¢0" ) - 0 9,09 SAY d©$(ba._O1XS"6$60€0°) - 0 3992 Sau d°0(9,_01xS" 66060" ) - 0 I99l- SAU d& (be. _CLxL"S!6810") - 0 IoGL- SAY § d®o(ba,_oLxe"€16210") (soto ZLo"ssiw 8°) - 0 I5Gk- sau noHo°Ha - 0 IpGl- sau 81 fog be z 0¢/os wL> IoGl- say I fog ba | - 0 IoGl- SAy BL fog bas (51°) Lb-in@9 sueIa/S19 PISTA GB] SULT STUETTUSY “pura UOLIRLTLU] T d1avi First preparation of L. L3 of the first prep left out at 20°C for 5 days prior to reaction. Second prep of L., Third prep of L This analyzed to 65% C4 metallocycle 3° L. of third prep left out at 20°C for 5 days prior to reaction Fourth batch prepared in part by Akira Miyashita. L. analyzed to 2.2% Ni and 15% C4 metallocycle. (Theoretical is~6.7% and 100%, respectively) First prep with varying concentrations of ON. -16- REFERENCES ]. 10. Vt. 12. 13. G. M. Whitesides and J. McDermott, J. Am. Chem, Soc. 96, 947 (1974). 3. McDermott, M. Wilson, and G. M. Whitesides, ibid, 98, 6529 (1976). G. M. Whitesides, J. White and J. McDermott, J. Am. Chem. Soc., 95, 4451 (1973); ibid, 98, 6521 (1976). R. Diversi, G. Ingrosso, A. Lucherini, Chem. Comm., 52 (1977). S. J. McLain, C. D. Wood and R. R. Schrock, J. Am. Chem. Soc., 99, 3519 (1977). Juan M. Manriquez, Donald R. McAlister, Robert D. Sanner, and John E. Bercaw, J. Am. Chem. Soc., 100, 2716 (1978). R. H, Grubbs, A. Miyashita, M.-I. Liu, P. L. Burk, J. Am. Chem. Soc., 99, 3863 (1977). R. H. Grubbs and Akira Miyashita, Chem. Comm., 864 (1977). R. H. Grubbs and Akira Miyashita, J. Organometallic Chem. 161 (1978) 371-380. Kerrie 1, Well and Jeffrey Schwartz, Chem. Comm., 244 (1979). Akira's and my observations R, H. Grubbs, Akira Miyashita, Mei-In Liu, Patrick L. Burk, J. Am. Chem. Soc., 99, 3863 (1977), G. N. Schrauzer, J. Am. Chem. Soc., 82, 1008 (1960). R. H. Grubbs and A. Miyashita, J. Am. Chem. Soc., 100, 1300 (1978). -17- CARBON MONOXIDE REDUCTION BY SIXTEEN ELECTRON d-ZERO TANTALUM COMPLEXES Thesis by Beckie E. Berg In Partial Fulfillment of the Requirements for the Degree of Master of Science CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 1979 (submitted June 29, 1979) ABSTRACT The sixteen electon, d-zero complexes T8(COT)Me 3 and (t{-C 5 Me 5 )Ta(C 3H5 )Me 3 were prepared and tre8ted with carbon monoxide. The prep of T8(COT) Me 3 gave irreproducibly small yields ::ind upon treatn:.ent with CO p8r::1magnetic nrnteri;:il w::is observed. The prep of (��:-C 5 Me 5 )Ta(C 3H5 )M e 3 resulted in yellow cryst?ls in 8 red oil clnd these could not be sep?:mted. (•·t-Csi'1\e 5 )T:::i(C 3H4 Me)Me 3 was then !r':::ide. This complex de­ composes to the triLrnthylene Methane species (r{-C 5t"1e 5 )Ta­ (C 3Hl'\e)ft'\e :, 8nd upon treatment with CO gave an unknown white solid product . -ii- T .ABLE OF CONTENTS P8ge Abstract..................... , .... . ........ . ii Introduction ............................ , ... 2 Gener8l Methods .. , ... , .................... , 4 Experimental ............................. , . 4 Results and Discussion ............... , , ..... 9 A... ddendum , . , . . . . . . . . .. . . . . . . . , .. . . . . . . � . . . .. . , 13 References . . .. . . .. . ... . . . .................. 15 -1- INTRODUCTION Reduction of CO by H2 to alcohols and alkanes is a thermodynamically favored process. However, with heterogeneous catalysts, high reaction temperatures and pressures are required. Several homogeneous catalysts have been found to carry on this 51me process under less severe operating The Os3(CO)12 and Ir4(CO)13 clusters have been found to produce methane at l40 °C and ~2 atm. (l) Ir4(CO)12 in molten NaCl·2AlCl3 in the presence of 3:1 H2:CO gives methane, ethane and trace amounts of propane and isobutane at l80 °C and l. 5 atm pressure (2). Under mild conditions. reaction conditions dicarbonyl (acetylacetonato) rhodium or Rh4(CO)12 produces ethylene glycol when treated with synthesis gas (3) It has been observed that the 16 electron, d-zero Zr species (n 5 -c 5 Me 5 )2ZrH2 reduces CO to give (4) (n 5 -C Me )Zr(OMe)(H) and 5 5 Reductive elimination to give MeOH and l,2 dihydroxyethylene does not occur, probably because of the high Zr-O bond energy. It is believed that reduction of CO is due to 2 factors: (l) electron deficiency of the metal center causing CO to add and (2) the fact that a d-zero species does not require CO to act as a IT acid, thereby allowing facile CO insertion(s) into M-carbon and M-H bonds. -2- By moving one column over in the Periodic Table, one might expect the metal-oxygen bond strength of tantalum not to be as strong as the Zr-O bond, and reductive elimination may be possible if CO adds in a similar fashion. The synthesis of the following two 16 electron, d-zero Ta complexes was therefore attempted: Ta(COT) Me3(COT = cyclooctatetraene) and (n -C 5 Me5 )Ta(C3H5 )Me . Since the analogous 16 electron Zr species 3 5 (n -c 5Me 5 )2ZrMe2 adds 2 moles of CO to give (l) 5 r--···· - , (n -C5Me 5 )2 ZrOC(CH3)=C(CH)O (Eq. l) It was hoped that CO would add in much the same way to Ta(COT)Me3 and (n 5 -C 5 Me5)Ta(C3H 5 )Me3 to give (COT)(Me)Ta(O(CH3)C=C(CH3)O) and (n 5 -C5Me 5)(C3H 5 )(Me)Ta(O(CH3)C=C(CH3)O), respectively. If the Ta(COT)Me3 and/or (n 5 -c 5Me 5)Ta(C3H 5)Me3 give encouraging results, the corresponding Ta hydride complexes would then be made, treated with CO, and examined as to whether or not catalytic CO reduc­ tion with H2 can be achieved. -3- GENERAL METHODS All reactions and other manipulations were performed under Argon purified before use by passage over MnO on vermiculite and activated 4A molecular sieves. H2 was purified in the same manner. High vacuum line and glove box techniques were used. Toluene, diethyl ether and pet ether were dried over LiAlH4, degassed and stored over 11 titanocene 11 , the preparation of which has been previously reported (5) THF was freshly distilled from the sodium-benzophenone ketyl. Carbon monoxide (MCB) was used directly from the cylinder. Reaction products were analyzed by NMR on an EM-390 spectrometer. The NMR solvent, benzene-d6, was vacuum transferred from 11 titanocene 11 • Infrared spectra were measured on a Beckman I. R. 12 spectrophotometer. EXPERIMENTAL The following route was used in the preparation of Ta(COT)Me3(6,7) -78 ° C ) Tol Ta(COT)Me 3 Preparation of TaMe3c12 5.86g anhydrous ZnC12 in 30 mls of ether at -78° C was treated with 58.8 mls 1 .6M Meli (10% excess of 2 equivalents Zn) and the mixture warmed to zero degrees. This was stirred for 0.5 to 1.5 hrs, and the -4- ether solution vacuum transferred to a sublimator containing 8.6g sublimed TaCl5. This was warmed to room temperature and allowed to stir overnight. The solvent was pumped off and the remaining solid sublimed at 25° c using a probe cooled to -10° c. Yield: 4.58g (62.5%). TaMe3c12 is light yellow, very pyrrophoric and decomposes slowly at 25 °C. It is soluble in pentane, THF, diethylether, and aromatic hydrocarbons. Usually a mixture of di- and trimethyl Ta chloride is produced. 100% TaMe3c12 can be obtained by treating the mixture (before or after sublimation) with excess ZnMe2. agent does not give TaMe4Cl. NMR: TaMe/12 TaMe2c12 s s This alk./ilating l. 5 cS l. 7 cS Preparation of Ta(C0T}(Me3) Cyclooctatetraene with hydroquinone added, was distilled at 1 atmosphere under N2 at 137° c. The yellow liquid was freeze-pump­ thawed and stored at zero degrees. A 0.47M K2C0T solution in THF using excess potassium was made. To 5.0g TaMe3c12 was added 125 mls toluene. An equimolar amount of the 0.47 M solution was added dropwise over 0.5 hrs at -78 °C and the reaction was allowed to stir an additional l .5 hrs at this temperature. The reaction mixture turned dark blue. It was then -5- filtered at -78° C to remove the KCl. and filtered again. The volume was reduced to 5 mls Blue crystals remained on the fritt. (An alternate method is adding pet ether after the volume reduction and then filter­ ing). Ta(COT)Me3 can be recrystallized from toluene/pet ether. Yield: lg (17.9%) The solid was sublimed at 70 °C using a -lo 0 c cold finger and 0.33 g was recovered. NMR: s s COT protons Me protons 5.82 o .7 o area = 8 area = 9 Reaction of Ta(COT)Me3 with CO O.lOOg Ta(COT)Me3 was dissolved in 10 mls of toluene. A known amount of CO was introduced at -78 ° C and allowed to react for 3 hrs. The blue solution turned brown. using a toepler pump. The unreacted gas was collected and measured The solution was warmed to 25° c and again a known amount of CO was introduced, allowed to react for several hours, collected and measured. was dried. The toluene was pumped off and the solid An NMR and IR was taken of the solid. -6- Synthetic Scheme· �MgBr,or �Li Tol.or THFITol. 2.3 g TaMe3ci 2 was added to a solution of 2.0 g (n 5 -c5Me 5)MgCl•THF (l.l eq n 5 -c 5 Me5/Ta) in 100 mls of toluene over 10-1 5 minutes at 2 5 ° . The reaction was allowed to stir an additional 4 5 minutes. The MgCl2 was filtered off and the toluene reduced until the yellow crystals began to fall out of solution. Pet ether was then added at -78 ° C and the solution filtered. Yield: 2 g (6 5 %) (n 5 -C 5 Me 5 )TaMe3Cl can be sublimed at 5 o0c wi_thout decomposition. NMR: (n 5 -C 5Me 5 )MgCl•THF Me Protons (n 5 -C 5 Me 5 ) protons -7- s 2, l 0 s .9 0 area 9 s 1.7 0 area 15 To 0.2 5 g (6.3xl □- 4 moles) (n 5 -C 5Me 5 )TaMe3Cl in 2 5 mls toluene cooled to -7s 0 c was added 6.3xl □- 4 moles allyl MgBr in ether. After stirring 45 minutes at -2 □0 c the MgBr2 was filtered off. Most of the toluene was then removed and pet ether was added. Additional MgBr2 was the only compound that precipitated out of solution and this too was filtered off. The solution was then pumped dry, leaving behind yellow crystals in a red oil. The two are not separable, even with the use of cold ether or pet ether. NMR of crude reaction: (n 5 -C 5 Me 5 ) protons s l.6 area 1 5 Me protons s .7 area 9 allyl protons d 3. 1 area 4 quintet 6.7 area l allyl protons Carbon monoxide was added to a toluene solution of the crude reaction mixture of (n 5 -C 5Me�a(C3H 5 )Me3 at -78 ° C. the solution was warmed to 2 5 ° C. After 1 hour After another hour, the toluene was removed and an NMR taken of the yellow solid which remained. -8- RESULTS AND DISCUSSION Synthesis of Ta(COT)Me3 gives irreproducibly small yields, primarily due to the ease of which this complex is converted to Ta(COT)2Me (5)_ Different solvents were used in attempts to avoid this problem. Both a l :l THF/toluene and a pentane solvent were used, both which resulted in the immediate formation of the Ta(COT)2Me. The K2COT•THF salt was then isolated (3) and used as a solid reactant. When this is added to TaMe3c12 in a THF or toluene solution at -78°C, there is no reaction. Upon warming, it immediately goes brown. If the K2COT•THF is isolated first and then dissolved in enough THF to make a 0.47 M solution, and added to TaMe3c12;toluene solution, only the Ta(COT) Me complex is made. I have no explanation for this. 2 The blue crystals of the crude Ta(COT)Me3 behaved strangely. Sometimes they would sublime, and other times they would not, some­ times with an evolution of gas (probably CH4 as it did not condense at liquid nitrogen temperatures). It appears to be the case that the more you work with the Ta(COT)Me3, the more it decomposes. For example, after recovering 3 g in the filtration step, only 1 g remained after 2 recrystalliza­ tions. Of this, only .020 g sublimed even though quantitative NMR showed that the l g was 84% Ta(COT)Me3. Ta(COT)Me3 does react with CO. The toepler pump experiment showed that at -78°C, Ta(COT)Me3 took up 1.8 CO/Ta. At room temperature, -9- the solution took up an additional ,73 moles CO. Both of these gave weak signals in their NMR spectra, suggestive of paramagnetism. The I.R. of the sample warmed to 2s 0 c showed no carbonyl stretch indicating that the simple CO insertion product did not exist at this temperature. The only conclusions that can be drawn from this experiment is that CO is taken up by Ta(COT)Me3 to give at least l product that is paramag­ netic. The main problem was that not enough purified Ta(COT)Me3 could be obtained to do any more than one or two CO experiments. After a number of synthetic routes to Ta(COT)Me3 had been exhausted, and because it is so difficult to purify, this molecule was abandoned and the synthesis of (n 5 -C 5 Me 5)Ta(C3H 5 )Me3 pursued. (n 5 -C 5 Me 5 )Ta(C3H 5 )Me3 proved to be no more stable than the T�(COT}Me 3. In the first step, the synthesis of (n 5 -c 5 Me 5)TaMe3Cl, the TaMe3c12 must be added over a period of time. (n 5 -c 5 Me 5 )MgCl·THF reacts very quickly and any excess TaMe3c12 present seems to result in the exchange reaction; TaMe3c12 + (n 5 -C 5Me 5 )TaMe3Cl.t(n 5 -C 5 Me 5)TaMe2c12 This is suggested by NMR. The parent cyclopentadienyl complex (n 5 -c 5H 5 )TaMe3Cl has been pre­ pared by_Schrock using Tl(C 5 H 5 ) in which the exchange reaction did not occur to any appreciable extent, if at all (9) easily made. The allyl species, however, is not. All �ttempts resulted in a red oil in which someti.mes yellow, prismatic crystals were seen. -10- An NMR of the crude reaction mixture 1 however 1 was surprisingly clean and did confirm the existence of the Cn 5 -C 5Me 5)Ta(C3H5 )Me3. The NMR showed the expected singlet for the permethylcyclopentadienyl protons and the splitting pattern of an allyl group whose protons are undergoing rapid syn-anti interconversion. The most surprising result, however, is that, at 34 ° C on the NMR time scale, all 3 of the methyl groups are One structure which fits the data is the following: equivalent. In this trigonal bypyramidal structure, the 3 methyl groups lie in the equatorial plane while the 2 axial ligands are rotating at a rate such that each Me is in the same environment. Alternatively, the pseudo five-coordinate species may be undergoing rapid site exchange, as in the tetragonal pyramidal (n 5 -C 5H5)Ta(Ch2CMe3)(CH2Ph)Cl2 reported by Schrock (10) r{-C 5Me5 I Me-Ta-Me ��e -11- The crude reaction mixture of (n 5 -c 5Me 5 )Ta(C3H 5 )Me3 was treated with carbon monoxide. Upon introduction of CO at -78°C to a toluene solution of the complex, the mixture went from orange to yellow. When warmed to 2 5°c the color did not change. The NMR showed broad peaks characteristic of paramagnetic material. The only conclusion to be made here is that something becomes paramagnetic. -12- ADDENDUM Dr. Calvin Curtis took over the project from here. All allyl reagents resulted in an oil, so methyl allyl was trfed. 2 methyl allyl was chosen because the allyl group of the metal-allyl species formed cannot rearrange to give a different product. The following reaction resulted in the desired compound: l ! undergoes a reaction with H2. Whether using excess H2 or a deficiency of H2, the products were always the same: 1 + >- + 1 Since under H2 deficient conditions both methyl and allyl groups are lost, it appears the allyl ligand is not especially labile. When l is dissolved in THF, pet ether, toluene or benzene-d6 and allowed to remain at room temperature for 24 hrs, CH4 is evolved and the yellow complex, Tantalum trimethylene methane (TMM) (g) is formed C Me 5 5 y l Me Ta., ....'-Me -13- A labeling study done with l shows that the methane is evolved from the methyl groups on the Ta: 24hrs Tol 25 ° C There is no evidence as yet where the His coming from. When 2 is treated with H2, the result is the same as with 1· 2 has also been treated with l equivalent of HCl: )== Treatment of 2 with CO gives an unknown white solid product. - l and .2 Syn-anti interconversion occurs in the allyl group of both .,... Variable temperature NMR was performed on� and the singlet and doublet of doublets, separated by 3.5 ppm, were frozen out only at -so 0 c, indicating that there is a very low barrier to syn-anti interconversion. -14- REFERENCES l. M. G. Thomas, B. F. Beier, E. L. Muetterties, J. Am. Chem. Soc., 98_, 1296 (1976). 2. G. C. Demitras, E. L. Muetterties, J. Am. Chem. Soc., 99, 2796 (1977). 3. R. L. Pruett and W. E. Walker, (Union Carbide Corp.), German Offen. 2 262 318 (1973); U.S. Appl. 210 538 (1971). 4. Juan M. Manriquez, Donald R. McAlister, Robert D. Sanner, and John E. Bercaw, J. Am. Chem. Soc. 100, 2716 (1978). 5. R. H. Marvich and H. H. Brintzinger, J. Am. Chem. Soc. 2l_, 2046 (1971). 6. R. R. Schrock, L. J. Guggenberger, and A. D. English, J. Am. Chem. Soc., 98, 903 (1976). 7. R. R. Schrock and G. W. Parshall, Chemical Reviews J..i, 243 (1976). 8. Von H. P. Fritz and H. Keller, Z. Naturforsch, 166, 231-234 (1961). 9. R. R. Schrock and P. R. Sharp, J. Am. Chem. Soc., 100, 2389 (1978). 10. C. D. Wood, S. J. McLain, and R. R. Schrock, J. Am. Chem. Soc., 101, 3210 (1979). -15- ACRYLONITRILE CYCLODIMERIZATION BY TRIS(TRIPHENYLPHOSPHINE)TETRAMETHYLENE Ni(II) Thesis by Beckie E. Berg In Partial Fulfillment of the Requirements for the Degree of Master of Science California Institute of Technology Pasadena, California 1979 (submitted June 29, 1979) PBSTR.ACT Tris(triphenylphoshine) tetr::imethylene Ni(II) W8S made and treated with ::icrylonitrile. 1, 2 dicy8nocyclobut:':ine w::is pro- duced in ::i cis:trans mixture of 45:55 and w::is isol::ited by prep­ arative GC. The product wc1s r::irely observed and the reaction of of nickel metallocycle with acrylonitrile was not catalyzed by acid, base, or Ni(O). -ii- T .ABLE OF CONTENTS P::ige Abstract .... ..... .... . ........... . . ........ ii Introduction r • , .. . � .. .. .. .. .. . . . . , • , . .. , , • • • , , , • • , , 2 Gener�l Methods , ... , .. , , , , , , , , , , , , , , , , , , , , , 4 Experimenttll .. ............... ., ............... , .. . . . 5 Results :::ind Discussion .... .... . . .... . ... . ... 12 Table I ......... , , . , , ............ . ........ . 15 References ................. , .. . . ..... . . . . . . 17 -1- INTRODUCTION Transition metal metallocycles have been demonstrated to be inter­ mediates in a variety of metal catalyzed reactions. Metal"Jocyclopentanes have been suggested as intermediates in some metal catalyzed [2+2] cycloadditions and cyclo-reversions of olefins. The metallocyclopentanes of T1.\1), Pt<.21>, Rh(3), Ta(4), Zr,5) and N1.(6) are now known and vary greatly in stability. The 1,4-tetramethylene bis(cyclopentadienyl) titanium (IV) complex prepared by the Whitesides group is thermally labile and can be It is characterized only through The its reactions as it is too unstable for elemental analysis (l) isolated only at low temperatures. (n 5 -c5H )¢ P rhodacyclopentane is difficult to isolate, as opposed to 5 3 the Rh (II) cyclohexane and RH ( II) cycloheptane. Its existence is The bis(phosphine) Pt(II) inferred by Br2 and HCl decomposition (3) cyc l opentanes, on the other hand, are quite stable and easily isolated (2) . Bis (triphenylphosphine) Nickelacyclopentane is easily isolated, but is \.o) somewhat thermally labile at long periods at 2s 0c. All are relatively more stable than their acyclic counter­ parts due to the inaccessibility of the S-H in the metallocycle. 6) ll 13) (2) 'J The tetramethylene complexes of Nf, Ti ' , Pt and R� J can be prepared by the corresponding metal dihalides treated with dilithiobutane or a,o diGrignard reagents. The TJ4) and Z�'5) metallocyclopentanes can be made from the reduced metallocenes and ethylene. Substituted tetramethylene metallocycles of N,(5 , 7 , s, l3l, Tf ), and 7 Zr can be prepared by reacting the unsubstituted metallocyc le with a (9} -2- primary olefin. Tris(triphenylphosphine) nickelacyclopentane (B), and bis (cyclopentadienyl) titanium cyclopentane (7) react with l, 7 octadiene to give the following: � LM n '\-- j + /...........,,,.-,:;:.� - LM[(J M = Ni trans n =3 n' =2 100% Ti n n-2-m' / + 75% L0 (r) cis 0% 25% (A Zr species, Cp2Zr(P¢3)2 also reacts with 1,7 octadiene to give the cis and trans hydrindane complex in a l :l mixture). ( 9) The oxidation of the bis ( triphenylphosphine) nickelacyclopentane results in the reductive elimination product, cyclobutanJ6 • 13� There­ fore, oxygen quenching of any bis substituted Ni metallocyclopentane should yield the substituted cyclobutane molecule (B) Indeed the bis (phosphine)Nihydrindane isolated gave bicyclo [4.2.0] cyclooctane. Because the Ni metallocycle gives 100% of the trans isomer, tris -3- (triphenylphosphine) nickelacyclopentane has potential utility in natural products synthesis. It is therefore of interest to look at the reactivity of this nickel complex towards different olefins and determine the yield and stereospecificity of the oxygen quenched products. Olefins chosen should represent a wide range of Alfrey-Price e values to see if there is any correspondence between the yield and stereospecificity of the products and the electronic properties of the olefins. This paper explores the reaction of tris(triphenylphosphine) nickelacyclopentane with acrylonitrile. GENERAL METHODS All reactions and other manipulations, with exception of the �3PNiCl2 prep, were performed under argon purified before use by a High BASF deoxygenation catalyst and activated 4A molecular sieves. vacuum line and glove box techniques were used. Diethyl ether and toluene were dried over sodium-benzophenone ketyl under an argon at­ mosphere and were freshly distilled before use. used was degassed prior to use. The absolute ethanol Acrylonitrile was reagent grade and was distilled from CaH2 and stored under argon. Reaction products were analyzed by gas chromatography on a Varian Series 1400 instrument equipped with a flame ionization detec­ tor. Proton NMR spectra were made on an EM-390 spectrometer. -4- The cyclodimer\zation product, dicyanocyclobutane, was purified by gas chromatography on a Varian Model 920 spectro meter using NMR by comparison with an authentic sample. and identified Yields of this product were determined by peak area comparisons with the internal standard dibromobutane. EXPERIMENTAL Preparation of bis(triphenylphosphine) nickel(II) dichloride A hot solution of 75g (.28 moles) triphenylphosphine in 500 rnls glacial acetic acid was added with stirring to a solution of 24g (.11 moles) nickel(II) chloride hexahydrate, 20 mls of water and 250 mls glacial acetic acid. The solution was allowed to stir at >S0 ° c for at least .5 hrs. The solution was filtered at so 0 c to minimize product contamination with unreacted triphenylphosphine. The dark blue-green crystals were washed two times with ethanol to partially remove the acetic acid and unreacted nickel(II) chloride. The solid was dried and 51g (¢ 3P)2NiC12 was recovered. The product can be recrystallized from butanol. The yield was 77%. Preparation of Bis(triphenylphosphine) tetramethylenenickel(II) (6) To 6.05g (9.4mmol) (¢ 3P)2NiC12 that had been finely ground to a dark green powder was added 75 mls ether. -5- After cooling the suspension to -78 ° c, 43 mls of a 0.37M 1,4-dilithiobutane ether solution was slowly added by syringe. (The amount of ether should total 20 mls/g Ni and Li(CH2)4Li/Ni = 1.7). After addition, the reaction mixture was stirred for ten minutes at -78 ° c, after which the cold bath was removed and the stirring maintained. The dark violet crystals of the Ni(II) starting material began to dissolve in the ether, forming a dark brown solution and gold crystals began precipitating out. After ten minutes, the starting material was completely gone. As soon as the yellow solid ceased forming, which was an additional five minutes, the solution was filtered. The yellow solid was washed with ether, followed by an ethanol wash to remove LiCl. dried and 4.4g was recovered. The solid was vacuum (Store at -4o 0 c) %C4;90% Yield: 74% P/Ni = 2.1 Preparation and Standardization of l,4-Dilithiobutane In a 1000 ml 3-necked round bottom flask fitted with an argon line, 250 ml dropping funnel, and mechanical stirrer, was placed 8g (1.14 moles) flattened Li ribbon and 250 mls ether. This was cooled to -lo 0 c and this temperature was maintained over the entire course of the reaction. To the Li was added, dropwise over 2 hrs, a solution of 25 mls (.228 moles) l ,4-dichlorobutane in 150 mls of ether. -6- During the addition, the solution became milky white as the LiCl precipitated out. Following the addition of the dichlorobutane, the mixture was allowed to stir overnight. The liquid was then separated from the LiCl by filtration and stored under argon at -3o 0 c. The concentration of the 1,4 dilithiobutane solution was determined as follows ( 5). l.95xl0-3 moles durene recrystallized from ethanol) ( was placed in a vial which was then stoppered and purged with argon. A 10.0 ml aliquot of the 1,4 dilithiobutane solution was added, followed by 2 mls of trimethylchlorosilane. The solution became hot and turned cloudy as the LiCl precipitated out. The ether solution was analyzed by gas chromatography and the peak areas of durene and Me3Si(CH2)4SiMe3 were compared, assuming equal response factors. G.C. conditions: SE-30 T 6' = ll0 C ° l/4 11 diameter Flowrate = 90cc/min The retention times for Cl ( CH2)4Cl, Me3Si (CH2)4SiMe3, and durene are 1.4 min, 3.4 min, and 3,7 min, respectively. Yield: 72% based on 1,4-dichlorobutane Preparation of Tris ( triphenylphosphine) tetramethylene nickel (II) (6) Bis ( triphenylphosphine) tetramethylenenickel ( II) ( 8g; 12 mmoles) was dissolved in 300 mls toluene at o 0 c and filtered to remove LiCl. Temperatures above o 0 c must be avoided for prolonged periods to prevent -7- To the dark gold solution was added 6.5g (25 mmol) triphenylphosphine. The solution turned red immediately and the reaction was stirred at o 0 c for 2 hours. Approximately 200 mls toluene was removed and the solution was stored overnight at -40° c. The orange crystals which precipitated on cooling 5g were filtered and washed with cold toluene, followed by pentane. was recovered. The compound can be recrystallized at -40° from toluene that has been saturated with triphenylphosphine at -6o 0 c. (Store at -40°C). Yield: 43% Reaction of Tris(triphenylphosphine) Tetramethylenenickel(II) with Acrylonitrile Both recrystallized and unrecrystallized metallocycle has been used. To .l00g metallocycle, and sometimes .5 equivalents triphenyl­ phosphine, is added 1 ml of toluene followed by 1.5 mls acrylonitrile. Reactions were also done in which CH2CHCN/Ni ratio varied from 12.5 to 187 and in concentrations ranging from 0.75M to 9.12M CH2CHCN. The solution was warmed to -1s 0 c and filtered. The reaction was allowed to continue stirring for 5 hrs at -10° c. The solution was cooled to -78° c and the vial partially evacuated and opened to air or injected with oxygen. The reaction was warmed slowly to 25 °C and the Ni -8- solid was allowed to settle out. The liquid was analyzed by gas chromatography using an 18 1 l/8 11 SE-30 with the following program: Rate = 10° /min. T1=110 °C, t�350 sec, T2=180 °C The retention time for dicyanocyclobutane is 588 sec for the trans isomer and 801 for the cis, The results are summarized in Table I. Reaction of Tris(triphenylphosphine) Tetramethylenenickel with Acrylonitrile in the Presence of Acid or Base To .lOOg nickelmetallocycle was added l ml toluene followed by 1.5 mls acrylonitrile at -78 ° c. Enough acetic acid or sodium acetate was added to make a l0-5M solution. The solution was warmed to -1s 0 c. filtered and allowed to stir for 5 hrs at this temperature. action was quenched with oxygen and analyzed as above. The re­ The results are summarized in Table I. Reaction of Tris(triphenylphosphine) Tetramethylenenickel with Acrylonitrile in the Presence of Ni(O) To . lOOg of metallocycle and .OlOg (r£/)2Ni (CH2=CH2) or .OlOg (¢/) 4Ni was added l ml toluene and 1.5 mls acrylonitrile at -78°C. The solution was slowly warmed to -15 °C, filtered and allowed to stir at this temperature for 5 hrs. The reaction was quenched with oxygen and analyzed as above. -9- Reaction of Bis(triphenylphosphine) Nickel(O) Ethylene with Acrylonitrile To .lOOg (�3P)2Ni(CH2=CH2) was added l equivalent triphenylphosphine. 1 ml toluene and 1.5 ml acrylonitrile was added at -78° c, warmed to -15 ° c, filtered and allowed to stir at this temperature for 5 hrs. The reaction was quenched with oxygen and analyzed as above. The results are summarized in Table I. Reaction of Triphenylphosphine with Acrylonitrile To .012g, .Ol8g, .030g and .048g triphenylphosphine was added .6 mls toluene followed by .8 mls acrylonitrile at -78° c. The solutions were slowly warmed to -l5 ° c and stirred for 5 hrs. Two .030g triphenyl­ phosphine samples were prepared in which one stirred at 25 ° c for 5 hrs and the other one stirred at 60 ° c. Oxygen was introduced into all samples at -78° c and they were allowed to warm to 25 ° c. Products were analyzed by gas chromatography. The results are summarized in Table I. Analysis of Nickel Complexes I. Nickel The% Ni was determined as follows: A known amount of Ni complex was decomposed with oxygen and weighed. The sample was sent to the analytical lab for% Ni and that value was extrapolated back to the undecornposed material. -10- II. % C 4 metallocycle To a known amount of Ni complex of approximately .050g in a stoppered vial equipped with a stirring bar was added.500 ml internal standard (methane or propane), The vial was cooled to -30 and .4 mls concentrated aqueous HCl was added while the solid was vigorously stirred in order to avoid localized heat buildup, which accelerates C-C bond cleavage (lO). After acidolysis was completed, a gas sample was analyzed by gas chromatography on a duropak column. The metallo­ cyclopentanes decomposed to give butane, 1-butene, cis and trans 2butene and ethylene, and the peak areas of the C 4 and C 2 hydrocarbons were compared with the corrected peak areas of the internal standard (butane/Me= 3.65; butane/propane =4/3). Note: Decomposition by concentrated H2 so 4 gave consistently lower values and only ethylene and butane were observed. III. % P A known amount of Ni complex of approximately .5g was decomposed with l ml H2 so 4. l ml of 30% H2 o 2 was then added, followed by a few m1s H20. The ¢3P=O was extracted approximately 10 times with toluene and the toluene layer was collected. After stripping off the solvent, the ¢3P = 0 was dried, weighed, and a T.L.C. and melting point taken as a purity check. -11- RESULTS AND DISCUSSION The cyclodimerization of acrylonitrile followed by oxygen de­ composition to produce dicyanocyclobutane was observed only in a few cases. The first was a batch of tris(triphenylphosphine) nickelacyclo­ pentane that was left out at 20° c for 5 days. This nickel complex with .5 equivalents ¢3P added gave a yield of 600% dicyanocyclobutane based on nickel, and was reproducible. (This batch did not work before although .5 equivalents ¢3P was not added.) This was an interesting result because excess ¢3P decreases the amount of reductive elimination product (ll) indicating that the ¢3P had nothing to do with promoting the reaction. Another batch of tris metallocycle that had been set out at 20 ° c for 5 days did not work with or without the excess ¢3P added, strongly suggesting that the .5 eq. ¢3P did not matter in the previous batch, but that the critical factor was what occurred to the complex during the 5 days. The only other case which gave product was a batch of tris metallocycle which analyzed/for 15% C4 hydrocarbons after acidolysis (theoretical is 100%), and 2.2% Ni (theoretical is 6.5%), and gave a yield of approximately 350% dicyanocyclobutane. Another batch of tris metallocycle which did not yield the desired product analyzed to 65% C4 metallocycles. I have no explanation at this time why so few batches of tris metallocycle worked. Purity does not seem to be the critical factor, however. -12- Dicyanocyclobutane was also observed in yield of <1% when using (¢3P)2Ni ( CH2 = cH2) and l equivalent of ¢3P. The mechanism for the dimerization of ethylene has been proposed as follows: (5 . l l) Ethylene adds to (¢3 P)2Ni(CH2= cH2) to go through a proposed tetrahedral intermediate (5 ) which undergoes ring closure upon adding another ¢3P. This pentacoordinate complex then loses a ligand to give the square planar bis metallocycle which undergoes reductive elimination to give cyclobutane. As pointed out earlier substituted olefins should behave in a similar manner and this has been successfully demonstrated in the isol ation and decomposition of the nickelhydrindane complex ( S). The results of the control experiments with ¢3P and acrylonitrile indicate that cyclodimerizations were not performed by ¢3P, and that the nickel complex was required. The closure to metallocycle is not catalyzed by acid, base or the Ni ( O) complexes (¢3P,l2Ni ( CH2=cH2) or (¢3P) Ni ( O), the latter being a decomposition product in the pre­ 4 sence of excess ¢3P and heat. The formation of bis(acrylonitrile) bis ( triphenylphosphine)Ni ( O) seems to be occurring. The reaction always forms the irridescent -13- yellow crystals characteristic of this compound (l2) (Oxygen decom- position followed by G.C. analysis confirms the fact that this solid is an acrylonitrile complex). The monophosphine bis(acrylonitrile) complex are orange crystals (having been identified as such by elemental analysis and G.C. after oxygen decomposition) that are often seen precipitating out of the reaction mixture of the tris metallocycle with acrylonitrile. This, too, supports that the bis(acrylonitrile) species (at least the square planar species) (l2) is being formed. Why so very few times closure to metallocycle occurs is unknown. -14- CornROUOd 1L Ni-11 (.lg) 2 Reactants Initiation Time .Seq P¢3 l eq Ptp3 2 eq P¢3 CrlzCHCN (.8 mls;.012 moles) (.012g;3.8xl0-3eq)¢3P (.Ol8g;5.7xl0-3eq)¢3P ' ' P (.030g;9.5xl0-3 eq1¢ 3 (.030g;9.5xl0-3eq)¢3P (.030g;9.5xl0 -3eq) ¢3P (.048g;1.5x10-2eq)¢3P al Ni 3 bL3Ni cliJi dL Ni 3 (.lg) (.lg) (. lg) (.lg) eL3 Ni fL Ni gL3Ni 3 (.lg) ( . lg) ( . 1 g) 2.8 m1s.=-J"N .8 mls=1CN /.5eq l .8 mls-="CN .8 mls="CN .8 ml sec='CN/10 -5M HAc ori¼. •8 ml S=CN/. 5eq P¢3 .8 mls __=1CN [=�N]=9M; 162eq 6M; l08eq 4.5M; 8leq 3.8M;67.5eq . 63;13.5eq TABLE I Temp. ° Yield 18 hrs 18 hrs 18 hrs -15 C -15 °C -l5°C 5 hrs 5 hrs 5 hrs 5 hrs 5 hrs 5 hrs 5 hrs -15 °C -15° C -15 °C 25 °C 60 °C -15 °C -15 °C 0 0 0 0 0 0 0 5 hrs 5 hrs 5 hrs 12 hrs 5 hrs 12 hrs 12 hrs 12 hrs -15°C -15 °C -15 °C -15 °C -15 °C -15 °C -15°C -15°C 0 600% 0 0 0 0 350% 0 . ,.1 II 0 <1% 0 c:_is/trans 50/50 45/55 45/55 t\ II It ll ,1 It L = ¢3 p " 2. . 8 m,1 s ='"' N 1• s 110eq ==1CNI /'�. Total volum2 was 1.8 mls so C=:1CN J = 6.7 M , , • l. -15- ccn't on next page a. b. c. d. e. f. g. First preparation of L 3 L 3 of the first prep left out at 20 ° c for 5 days prior to reaction. Second prep of L3 Third prep of L3. This analyzed to 65% C4 metallocycle L3 of third prep left out at 20 ° c for 5 days prior to reaction Fourth batch prepared in part by Akira Miyashita. L analyzed to 2.2% Ni and 15% C4 metallocycle. (Theoretical is36.7% and 100%, respectively) • F•1rst prep w1• th varying concent rat ions of _:,JCN . • -16- REFERENCES l. G. M. Whitesides and J. McDermott, J. Am. Chem. Soc. 96, 947 (1974). a. McDermott, M. Wilson, and G, M. Whitesides, ibid, 98, 6529 (1976). 2. G. M. Whitesides, J. 11hite and J. McDermott, J. Am. Chem. Soc., 95, 4451 (1973); ibid, 9ti, 6521 (1976). 3, R. Diversi, G. Ingrosso, A. Lucherini, Chem. Comm., 52 (1977). 4. S. J. McLain, C. D. Wood and R. R. Schrock, J. Am. Chem. Soc., ?9, 3519 (1977). 5. Juan M. Manriquez, Donald R. McAlister, Robert D. Sanner, and John E. Bercaw, J. Am. Chem. Soc., 100, 2716 (1978). 6. R. H. Grubbs, A. Miyashita, M.-I. Liu, P. L. Burk, J. Am. Chem. Soc., 99, 3863 (1977). 7. R. H. Grubbs and Akira Miyashita, Chem, Comm., 864 (1977). 8. R. H. Grubbs and Akira Miyashita, J. Organometallic Chem. 161 (1978) 371-380. 9. Kerrie I. Well and Jeffrey Schwartz, Chem. Comm., 244 (1979). 10. Akira's and my observations 11. R. H, Grubbs, Akira Miyashita, Mei-In Liu, Patrick L. Burk, J. Am. Chem. Soc., 99, 3863 (1977), 12. G, N. Schrauzer, J. Am, Chem. Soc., 82, 1008 (1960), 13. R. H. Grubbs and A. Miyashita, J. Am. Chem. Soc., 100, 1300 (1978). -17-  CARBON MONOXIDE REDUCTION BY SIXTEEN ELECTRON d-ZERO TANTALUM COMPLEXES Thesis by Beckie E. Berg In Partial Fulfillment of the Requirements for the Degree of Master of Science CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 1979 (submitted June 29, 1979) ABSTRACT The sixteen electon, d-zero complexes T8(COT)Me 3 and (t{-C 5 Me 5 )Ta(C 3H5 )Me 3 were prepared and tre8ted with carbon monoxide. The prep of T8(COT) Me 3 gave irreproducibly small yields ::ind upon treatn:.ent with CO p8r::1magnetic nrnteri;:il w::is observed. The prep of (��:-C 5 Me 5 )Ta(C 3H5 )M e 3 resulted in yellow cryst?ls in 8 red oil clnd these could not be sep?:mted. (•·t-Csi'1\e 5 )T:::i(C 3H4 Me)Me 3 was then !r':::ide. This complex de­ composes to the triLrnthylene Methane species (r{-C 5t"1e 5 )Ta­ (C 3Hl'\e)ft'\e :, 8nd upon treatment with CO gave an unknown white solid product . -ii- T .ABLE OF CONTENTS P8ge Abstract..................... , .... . ........ . ii Introduction ............................ , ... 2 Gener8l Methods .. , ... , .................... , 4 Experimental ............................. , . 4 Results and Discussion ............... , , ..... 9 A... ddendum , . , . . . . . . . . .. . . . . . . . , .. . . . . . . � . . . .. . , 13 References . . .. . . .. . ... . . . .................. 15 -1- INTRODUCTION Reduction of CO by H2 to alcohols and alkanes is a thermodynamically favored process. However, with heterogeneous catalysts, high reaction temperatures and pressures are required. Several homogeneous catalysts have been found to carry on this 51me process under less severe operating The Os3(CO)12 and Ir4(CO)13 clusters have been found to produce methane at l40 °C and ~2 atm. (l) Ir4(CO)12 in molten NaCl·2AlCl3 in the presence of 3:1 H2:CO gives methane, ethane and trace amounts of propane and isobutane at l80 °C and l. 5 atm pressure (2). Under mild conditions. reaction conditions dicarbonyl (acetylacetonato) rhodium or Rh4(CO)12 produces ethylene glycol when treated with synthesis gas (3) It has been observed that the 16 electron, d-zero Zr species (n 5 -c 5 Me 5 )2ZrH2 reduces CO to give (4) (n 5 -C Me )Zr(OMe)(H) and 5 5 Reductive elimination to give MeOH and l,2 dihydroxyethylene does not occur, probably because of the high Zr-O bond energy. It is believed that reduction of CO is due to 2 factors: (l) electron deficiency of the metal center causing CO to add and (2) the fact that a d-zero species does not require CO to act as a IT acid, thereby allowing facile CO insertion(s) into M-carbon and M-H bonds. -2- By moving one column over in the Periodic Table, one might expect the metal-oxygen bond strength of tantalum not to be as strong as the Zr-O bond, and reductive elimination may be possible if CO adds in a similar fashion. The synthesis of the following two 16 electron, d-zero Ta complexes was therefore attempted: Ta(COT) Me3(COT = cyclooctatetraene) and (n -C 5 Me5 )Ta(C3H5 )Me . Since the analogous 16 electron Zr species 3 5 (n -c 5Me 5 )2ZrMe2 adds 2 moles of CO to give (l) 5 r--···· - , (n -C5Me 5 )2 ZrOC(CH3)=C(CH)O (Eq. l) It was hoped that CO would add in much the same way to Ta(COT)Me3 and (n 5 -C 5 Me5)Ta(C3H 5 )Me3 to give (COT)(Me)Ta(O(CH3)C=C(CH3)O) and (n 5 -C5Me 5)(C3H 5 )(Me)Ta(O(CH3)C=C(CH3)O), respectively. If the Ta(COT)Me3 and/or (n 5 -c 5Me 5)Ta(C3H 5)Me3 give encouraging results, the corresponding Ta hydride complexes would then be made, treated with CO, and examined as to whether or not catalytic CO reduc­ tion with H2 can be achieved. -3- GENERAL METHODS All reactions and other manipulations were performed under Argon purified before use by passage over MnO on vermiculite and activated 4A molecular sieves. H2 was purified in the same manner. High vacuum line and glove box techniques were used. Toluene, diethyl ether and pet ether were dried over LiAlH4, degassed and stored over 11 titanocene 11 , the preparation of which has been previously reported (5) THF was freshly distilled from the sodium-benzophenone ketyl. Carbon monoxide (MCB) was used directly from the cylinder. Reaction products were analyzed by NMR on an EM-390 spectrometer. The NMR solvent, benzene-d6, was vacuum transferred from 11 titanocene 11 • Infrared spectra were measured on a Beckman I. R. 12 spectrophotometer. EXPERIMENTAL The following route was used in the preparation of Ta(COT)Me3(6,7) -78 ° C ) Tol Ta(COT)Me 3 Preparation of TaMe3c12 5.86g anhydrous ZnC12 in 30 mls of ether at -78° C was treated with 58.8 mls 1 .6M Meli (10% excess of 2 equivalents Zn) and the mixture warmed to zero degrees. This was stirred for 0.5 to 1.5 hrs, and the -4- ether solution vacuum transferred to a sublimator containing 8.6g sublimed TaCl5. This was warmed to room temperature and allowed to stir overnight. The solvent was pumped off and the remaining solid sublimed at 25° c using a probe cooled to -10° c. Yield: 4.58g (62.5%). TaMe3c12 is light yellow, very pyrrophoric and decomposes slowly at 25 °C. It is soluble in pentane, THF, diethylether, and aromatic hydrocarbons. Usually a mixture of di- and trimethyl Ta chloride is produced. 100% TaMe3c12 can be obtained by treating the mixture (before or after sublimation) with excess ZnMe2. agent does not give TaMe4Cl. NMR: TaMe/12 TaMe2c12 s s This alk./ilating l. 5 cS l. 7 cS Preparation of Ta(C0T}(Me3) Cyclooctatetraene with hydroquinone added, was distilled at 1 atmosphere under N2 at 137° c. The yellow liquid was freeze-pump­ thawed and stored at zero degrees. A 0.47M K2C0T solution in THF using excess potassium was made. To 5.0g TaMe3c12 was added 125 mls toluene. An equimolar amount of the 0.47 M solution was added dropwise over 0.5 hrs at -78 °C and the reaction was allowed to stir an additional l .5 hrs at this temperature. The reaction mixture turned dark blue. It was then -5- filtered at -78° C to remove the KCl. and filtered again. The volume was reduced to 5 mls Blue crystals remained on the fritt. (An alternate method is adding pet ether after the volume reduction and then filter­ ing). Ta(COT)Me3 can be recrystallized from toluene/pet ether. Yield: lg (17.9%) The solid was sublimed at 70 °C using a -lo 0 c cold finger and 0.33 g was recovered. NMR: s s COT protons Me protons 5.82 o .7 o area = 8 area = 9 Reaction of Ta(COT)Me3 with CO O.lOOg Ta(COT)Me3 was dissolved in 10 mls of toluene. A known amount of CO was introduced at -78 ° C and allowed to react for 3 hrs. The blue solution turned brown. using a toepler pump. The unreacted gas was collected and measured The solution was warmed to 25° c and again a known amount of CO was introduced, allowed to react for several hours, collected and measured. was dried. The toluene was pumped off and the solid An NMR and IR was taken of the solid. -6- Synthetic Scheme· �MgBr,or �Li Tol.or THFITol. 2.3 g TaMe3ci 2 was added to a solution of 2.0 g (n 5 -c5Me 5)MgCl•THF (l.l eq n 5 -c 5 Me5/Ta) in 100 mls of toluene over 10-1 5 minutes at 2 5 ° . The reaction was allowed to stir an additional 4 5 minutes. The MgCl2 was filtered off and the toluene reduced until the yellow crystals began to fall out of solution. Pet ether was then added at -78 ° C and the solution filtered. Yield: 2 g (6 5 %) (n 5 -C 5 Me 5 )TaMe3Cl can be sublimed at 5 o0c wi_thout decomposition. NMR: (n 5 -C 5Me 5 )MgCl•THF Me Protons (n 5 -C 5 Me 5 ) protons -7- s 2, l 0 s .9 0 area 9 s 1.7 0 area 15 To 0.2 5 g (6.3xl □- 4 moles) (n 5 -C 5Me 5 )TaMe3Cl in 2 5 mls toluene cooled to -7s 0 c was added 6.3xl □- 4 moles allyl MgBr in ether. After stirring 45 minutes at -2 □0 c the MgBr2 was filtered off. Most of the toluene was then removed and pet ether was added. Additional MgBr2 was the only compound that precipitated out of solution and this too was filtered off. The solution was then pumped dry, leaving behind yellow crystals in a red oil. The two are not separable, even with the use of cold ether or pet ether. NMR of crude reaction: (n 5 -C 5 Me 5 ) protons s l.6 area 1 5 Me protons s .7 area 9 allyl protons d 3. 1 area 4 quintet 6.7 area l allyl protons Carbon monoxide was added to a toluene solution of the crude reaction mixture of (n 5 -C 5Me�a(C3H 5 )Me3 at -78 ° C. the solution was warmed to 2 5 ° C. After 1 hour After another hour, the toluene was removed and an NMR taken of the yellow solid which remained. -8- RESULTS AND DISCUSSION Synthesis of Ta(COT)Me3 gives irreproducibly small yields, primarily due to the ease of which this complex is converted to Ta(COT)2Me (5)_ Different solvents were used in attempts to avoid this problem. Both a l :l THF/toluene and a pentane solvent were used, both which resulted in the immediate formation of the Ta(COT)2Me. The K2COT•THF salt was then isolated (3) and used as a solid reactant. When this is added to TaMe3c12 in a THF or toluene solution at -78°C, there is no reaction. Upon warming, it immediately goes brown. If the K2COT•THF is isolated first and then dissolved in enough THF to make a 0.47 M solution, and added to TaMe3c12;toluene solution, only the Ta(COT) Me complex is made. I have no explanation for this. 2 The blue crystals of the crude Ta(COT)Me3 behaved strangely. Sometimes they would sublime, and other times they would not, some­ times with an evolution of gas (probably CH4 as it did not condense at liquid nitrogen temperatures). It appears to be the case that the more you work with the Ta(COT)Me3, the more it decomposes. For example, after recovering 3 g in the filtration step, only 1 g remained after 2 recrystalliza­ tions. Of this, only .020 g sublimed even though quantitative NMR showed that the l g was 84% Ta(COT)Me3. Ta(COT)Me3 does react with CO. The toepler pump experiment showed that at -78°C, Ta(COT)Me3 took up 1.8 CO/Ta. At room temperature, -9- the solution took up an additional ,73 moles CO. Both of these gave weak signals in their NMR spectra, suggestive of paramagnetism. The I.R. of the sample warmed to 2s 0 c showed no carbonyl stretch indicating that the simple CO insertion product did not exist at this temperature. The only conclusions that can be drawn from this experiment is that CO is taken up by Ta(COT)Me3 to give at least l product that is paramag­ netic. The main problem was that not enough purified Ta(COT)Me3 could be obtained to do any more than one or two CO experiments. After a number of synthetic routes to Ta(COT)Me3 had been exhausted, and because it is so difficult to purify, this molecule was abandoned and the synthesis of (n 5 -C 5 Me 5)Ta(C3H 5 )Me3 pursued. (n 5 -C 5 Me 5 )Ta(C3H 5 )Me3 proved to be no more stable than the T�(COT}Me 3. In the first step, the synthesis of (n 5 -c 5 Me 5)TaMe3Cl, the TaMe3c12 must be added over a period of time. (n 5 -c 5 Me 5 )MgCl·THF reacts very quickly and any excess TaMe3c12 present seems to result in the exchange reaction; TaMe3c12 + (n 5 -C 5Me 5 )TaMe3Cl.t(n 5 -C 5 Me 5)TaMe2c12 This is suggested by NMR. The parent cyclopentadienyl complex (n 5 -c 5H 5 )TaMe3Cl has been pre­ pared by_Schrock using Tl(C 5 H 5 ) in which the exchange reaction did not occur to any appreciable extent, if at all (9) easily made. The allyl species, however, is not. All �ttempts resulted in a red oil in which someti.mes yellow, prismatic crystals were seen. -10- An NMR of the crude reaction mixture 1 however 1 was surprisingly clean and did confirm the existence of the Cn 5 -C 5Me 5)Ta(C3H5 )Me3. The NMR showed the expected singlet for the permethylcyclopentadienyl protons and the splitting pattern of an allyl group whose protons are undergoing rapid syn-anti interconversion. The most surprising result, however, is that, at 34 ° C on the NMR time scale, all 3 of the methyl groups are One structure which fits the data is the following: equivalent. In this trigonal bypyramidal structure, the 3 methyl groups lie in the equatorial plane while the 2 axial ligands are rotating at a rate such that each Me is in the same environment. Alternatively, the pseudo five-coordinate species may be undergoing rapid site exchange, as in the tetragonal pyramidal (n 5 -C 5H5)Ta(Ch2CMe3)(CH2Ph)Cl2 reported by Schrock (10) r{-C 5Me5 I Me-Ta-Me ��e -11- The crude reaction mixture of (n 5 -c 5Me 5 )Ta(C3H 5 )Me3 was treated with carbon monoxide. Upon introduction of CO at -78°C to a toluene solution of the complex, the mixture went from orange to yellow. When warmed to 2 5°c the color did not change. The NMR showed broad peaks characteristic of paramagnetic material. The only conclusion to be made here is that something becomes paramagnetic. -12- ADDENDUM Dr. Calvin Curtis took over the project from here. All allyl reagents resulted in an oil, so methyl allyl was trfed. 2 methyl allyl was chosen because the allyl group of the metal-allyl species formed cannot rearrange to give a different product. The following reaction resulted in the desired compound: l ! undergoes a reaction with H2. Whether using excess H2 or a deficiency of H2, the products were always the same: 1 + >- + 1 Since under H2 deficient conditions both methyl and allyl groups are lost, it appears the allyl ligand is not especially labile. When l is dissolved in THF, pet ether, toluene or benzene-d6 and allowed to remain at room temperature for 24 hrs, CH4 is evolved and the yellow complex, Tantalum trimethylene methane (TMM) (g) is formed C Me 5 5 y l Me Ta., ....'-Me -13- A labeling study done with l shows that the methane is evolved from the methyl groups on the Ta: 24hrs Tol 25 ° C There is no evidence as yet where the His coming from. When 2 is treated with H2, the result is the same as with 1· 2 has also been treated with l equivalent of HCl: )== Treatment of 2 with CO gives an unknown white solid product. - l and .2 Syn-anti interconversion occurs in the allyl group of both .,... Variable temperature NMR was performed on� and the singlet and doublet of doublets, separated by 3.5 ppm, were frozen out only at -so 0 c, indicating that there is a very low barrier to syn-anti interconversion. -14- REFERENCES l. M. G. Thomas, B. F. Beier, E. L. Muetterties, J. Am. Chem. Soc., 98_, 1296 (1976). 2. G. C. Demitras, E. L. Muetterties, J. Am. Chem. Soc., 99, 2796 (1977). 3. R. L. Pruett and W. E. Walker, (Union Carbide Corp.), German Offen. 2 262 318 (1973); U.S. Appl. 210 538 (1971). 4. Juan M. Manriquez, Donald R. McAlister, Robert D. Sanner, and John E. Bercaw, J. Am. Chem. Soc. 100, 2716 (1978). 5. R. H. Marvich and H. H. Brintzinger, J. Am. Chem. Soc. 2l_, 2046 (1971). 6. R. R. Schrock, L. J. Guggenberger, and A. D. English, J. Am. Chem. Soc., 98, 903 (1976). 7. R. R. Schrock and G. W. Parshall, Chemical Reviews J..i, 243 (1976). 8. Von H. P. Fritz and H. Keller, Z. Naturforsch, 166, 231-234 (1961). 9. R. R. Schrock and P. R. Sharp, J. Am. Chem. Soc., 100, 2389 (1978). 10. C. D. Wood, S. J. McLain, and R. R. Schrock, J. Am. Chem. Soc., 101, 3210 (1979). -15- ACRYLONITRILE CYCLODIMERIZATION BY TRIS(TRIPHENYLPHOSPHINE)TETRAMETHYLENE Ni(II) Thesis by Beckie E. Berg In Partial Fulfillment of the Requirements for the Degree of Master of Science California Institute of Technology Pasadena, California 1979 (submitted June 29, 1979) PBSTR.ACT Tris(triphenylphoshine) tetr::imethylene Ni(II) W8S made and treated with ::icrylonitrile. 1, 2 dicy8nocyclobut:':ine w::is pro- duced in ::i cis:trans mixture of 45:55 and w::is isol::ited by prep­ arative GC. The product wc1s r::irely observed and the reaction of of nickel metallocycle with acrylonitrile was not catalyzed by acid, base, or Ni(O). -ii- T .ABLE OF CONTENTS P::ige Abstract .... ..... .... . ........... . . ........ ii Introduction r • , .. . � .. .. .. .. .. . . . . , • , . .. , , • • • , , , • • , , 2 Gener�l Methods , ... , .. , , , , , , , , , , , , , , , , , , , , , 4 Experimenttll .. ............... ., ............... , .. . . . 5 Results :::ind Discussion .... .... . . .... . ... . ... 12 Table I ......... , , . , , ............ . ........ . 15 References ................. , .. . . ..... . . . . . . 17 -1- INTRODUCTION Transition metal metallocycles have been demonstrated to be inter­ mediates in a variety of metal catalyzed reactions. Metal"Jocyclopentanes have been suggested as intermediates in some metal catalyzed [2+2] cycloadditions and cyclo-reversions of olefins. The metallocyclopentanes of T1.\1), Pt<.21>, Rh(3), Ta(4), Zr,5) and N1.(6) are now known and vary greatly in stability. The 1,4-tetramethylene bis(cyclopentadienyl) titanium (IV) complex prepared by the Whitesides group is thermally labile and can be It is characterized only through The its reactions as it is too unstable for elemental analysis (l) isolated only at low temperatures. (n 5 -c5H )¢ P rhodacyclopentane is difficult to isolate, as opposed to 5 3 the Rh (II) cyclohexane and RH ( II) cycloheptane. Its existence is The bis(phosphine) Pt(II) inferred by Br2 and HCl decomposition (3) cyc l opentanes, on the other hand, are quite stable and easily isolated (2) . Bis (triphenylphosphine) Nickelacyclopentane is easily isolated, but is \.o) somewhat thermally labile at long periods at 2s 0c. All are relatively more stable than their acyclic counter­ parts due to the inaccessibility of the S-H in the metallocycle. 6) ll 13) (2) 'J The tetramethylene complexes of Nf, Ti ' , Pt and R� J can be prepared by the corresponding metal dihalides treated with dilithiobutane or a,o diGrignard reagents. The TJ4) and Z�'5) metallocyclopentanes can be made from the reduced metallocenes and ethylene. Substituted tetramethylene metallocycles of N,(5 , 7 , s, l3l, Tf ), and 7 Zr can be prepared by reacting the unsubstituted metallocyc le with a (9} -2- primary olefin. Tris(triphenylphosphine) nickelacyclopentane (B), and bis (cyclopentadienyl) titanium cyclopentane (7) react with l, 7 octadiene to give the following: � LM n '\-- j + /...........,,,.-,:;:.� - LM[(J M = Ni trans n =3 n' =2 100% Ti n n-2-m' / + 75% L0 (r) cis 0% 25% (A Zr species, Cp2Zr(P¢3)2 also reacts with 1,7 octadiene to give the cis and trans hydrindane complex in a l :l mixture). ( 9) The oxidation of the bis ( triphenylphosphine) nickelacyclopentane results in the reductive elimination product, cyclobutanJ6 • 13� There­ fore, oxygen quenching of any bis substituted Ni metallocyclopentane should yield the substituted cyclobutane molecule (B) Indeed the bis (phosphine)Nihydrindane isolated gave bicyclo [4.2.0] cyclooctane. Because the Ni metallocycle gives 100% of the trans isomer, tris -3- (triphenylphosphine) nickelacyclopentane has potential utility in natural products synthesis. It is therefore of interest to look at the reactivity of this nickel complex towards different olefins and determine the yield and stereospecificity of the oxygen quenched products. Olefins chosen should represent a wide range of Alfrey-Price e values to see if there is any correspondence between the yield and stereospecificity of the products and the electronic properties of the olefins. This paper explores the reaction of tris(triphenylphosphine) nickelacyclopentane with acrylonitrile. GENERAL METHODS All reactions and other manipulations, with exception of the �3PNiCl2 prep, were performed under argon purified before use by a High BASF deoxygenation catalyst and activated 4A molecular sieves. vacuum line and glove box techniques were used. Diethyl ether and toluene were dried over sodium-benzophenone ketyl under an argon at­ mosphere and were freshly distilled before use. used was degassed prior to use. The absolute ethanol Acrylonitrile was reagent grade and was distilled from CaH2 and stored under argon. Reaction products were analyzed by gas chromatography on a Varian Series 1400 instrument equipped with a flame ionization detec­ tor. Proton NMR spectra were made on an EM-390 spectrometer. -4- The cyclodimer\zation product, dicyanocyclobutane, was purified by gas chromatography on a Varian Model 920 spectro meter using NMR by comparison with an authentic sample. and identified Yields of this product were determined by peak area comparisons with the internal standard dibromobutane. EXPERIMENTAL Preparation of bis(triphenylphosphine) nickel(II) dichloride A hot solution of 75g (.28 moles) triphenylphosphine in 500 rnls glacial acetic acid was added with stirring to a solution of 24g (.11 moles) nickel(II) chloride hexahydrate, 20 mls of water and 250 mls glacial acetic acid. The solution was allowed to stir at >S0 ° c for at least .5 hrs. The solution was filtered at so 0 c to minimize product contamination with unreacted triphenylphosphine. The dark blue-green crystals were washed two times with ethanol to partially remove the acetic acid and unreacted nickel(II) chloride. The solid was dried and 51g (¢ 3P)2NiC12 was recovered. The product can be recrystallized from butanol. The yield was 77%. Preparation of Bis(triphenylphosphine) tetramethylenenickel(II) (6) To 6.05g (9.4mmol) (¢ 3P)2NiC12 that had been finely ground to a dark green powder was added 75 mls ether. -5- After cooling the suspension to -78 ° c, 43 mls of a 0.37M 1,4-dilithiobutane ether solution was slowly added by syringe. (The amount of ether should total 20 mls/g Ni and Li(CH2)4Li/Ni = 1.7). After addition, the reaction mixture was stirred for ten minutes at -78 ° c, after which the cold bath was removed and the stirring maintained. The dark violet crystals of the Ni(II) starting material began to dissolve in the ether, forming a dark brown solution and gold crystals began precipitating out. After ten minutes, the starting material was completely gone. As soon as the yellow solid ceased forming, which was an additional five minutes, the solution was filtered. The yellow solid was washed with ether, followed by an ethanol wash to remove LiCl. dried and 4.4g was recovered. The solid was vacuum (Store at -4o 0 c) %C4;90% Yield: 74% P/Ni = 2.1 Preparation and Standardization of l,4-Dilithiobutane In a 1000 ml 3-necked round bottom flask fitted with an argon line, 250 ml dropping funnel, and mechanical stirrer, was placed 8g (1.14 moles) flattened Li ribbon and 250 mls ether. This was cooled to -lo 0 c and this temperature was maintained over the entire course of the reaction. To the Li was added, dropwise over 2 hrs, a solution of 25 mls (.228 moles) l ,4-dichlorobutane in 150 mls of ether. -6- During the addition, the solution became milky white as the LiCl precipitated out. Following the addition of the dichlorobutane, the mixture was allowed to stir overnight. The liquid was then separated from the LiCl by filtration and stored under argon at -3o 0 c. The concentration of the 1,4 dilithiobutane solution was determined as follows ( 5). l.95xl0-3 moles durene recrystallized from ethanol) ( was placed in a vial which was then stoppered and purged with argon. A 10.0 ml aliquot of the 1,4 dilithiobutane solution was added, followed by 2 mls of trimethylchlorosilane. The solution became hot and turned cloudy as the LiCl precipitated out. The ether solution was analyzed by gas chromatography and the peak areas of durene and Me3Si(CH2)4SiMe3 were compared, assuming equal response factors. G.C. conditions: SE-30 T 6' = ll0 C ° l/4 11 diameter Flowrate = 90cc/min The retention times for Cl ( CH2)4Cl, Me3Si (CH2)4SiMe3, and durene are 1.4 min, 3.4 min, and 3,7 min, respectively. Yield: 72% based on 1,4-dichlorobutane Preparation of Tris ( triphenylphosphine) tetramethylene nickel (II) (6) Bis ( triphenylphosphine) tetramethylenenickel ( II) ( 8g; 12 mmoles) was dissolved in 300 mls toluene at o 0 c and filtered to remove LiCl. Temperatures above o 0 c must be avoided for prolonged periods to prevent -7- To the dark gold solution was added 6.5g (25 mmol) triphenylphosphine. The solution turned red immediately and the reaction was stirred at o 0 c for 2 hours. Approximately 200 mls toluene was removed and the solution was stored overnight at -40° c. The orange crystals which precipitated on cooling 5g were filtered and washed with cold toluene, followed by pentane. was recovered. The compound can be recrystallized at -40° from toluene that has been saturated with triphenylphosphine at -6o 0 c. (Store at -40°C). Yield: 43% Reaction of Tris(triphenylphosphine) Tetramethylenenickel(II) with Acrylonitrile Both recrystallized and unrecrystallized metallocycle has been used. To .l00g metallocycle, and sometimes .5 equivalents triphenyl­ phosphine, is added 1 ml of toluene followed by 1.5 mls acrylonitrile. Reactions were also done in which CH2CHCN/Ni ratio varied from 12.5 to 187 and in concentrations ranging from 0.75M to 9.12M CH2CHCN. The solution was warmed to -1s 0 c and filtered. The reaction was allowed to continue stirring for 5 hrs at -10° c. The solution was cooled to -78° c and the vial partially evacuated and opened to air or injected with oxygen. The reaction was warmed slowly to 25 °C and the Ni -8- solid was allowed to settle out. The liquid was analyzed by gas chromatography using an 18 1 l/8 11 SE-30 with the following program: Rate = 10° /min. T1=110 °C, t�350 sec, T2=180 °C The retention time for dicyanocyclobutane is 588 sec for the trans isomer and 801 for the cis, The results are summarized in Table I. Reaction of Tris(triphenylphosphine) Tetramethylenenickel with Acrylonitrile in the Presence of Acid or Base To .lOOg nickelmetallocycle was added l ml toluene followed by 1.5 mls acrylonitrile at -78 ° c. Enough acetic acid or sodium acetate was added to make a l0-5M solution. The solution was warmed to -1s 0 c. filtered and allowed to stir for 5 hrs at this temperature. action was quenched with oxygen and analyzed as above. The re­ The results are summarized in Table I. Reaction of Tris(triphenylphosphine) Tetramethylenenickel with Acrylonitrile in the Presence of Ni(O) To . lOOg of metallocycle and .OlOg (r£/)2Ni (CH2=CH2) or .OlOg (¢/) 4Ni was added l ml toluene and 1.5 mls acrylonitrile at -78°C. The solution was slowly warmed to -15 °C, filtered and allowed to stir at this temperature for 5 hrs. The reaction was quenched with oxygen and analyzed as above. -9- Reaction of Bis(triphenylphosphine) Nickel(O) Ethylene with Acrylonitrile To .lOOg (�3P)2Ni(CH2=CH2) was added l equivalent triphenylphosphine. 1 ml toluene and 1.5 ml acrylonitrile was added at -78° c, warmed to -15 ° c, filtered and allowed to stir at this temperature for 5 hrs. The reaction was quenched with oxygen and analyzed as above. The results are summarized in Table I. Reaction of Triphenylphosphine with Acrylonitrile To .012g, .Ol8g, .030g and .048g triphenylphosphine was added .6 mls toluene followed by .8 mls acrylonitrile at -78° c. The solutions were slowly warmed to -l5 ° c and stirred for 5 hrs. Two .030g triphenyl­ phosphine samples were prepared in which one stirred at 25 ° c for 5 hrs and the other one stirred at 60 ° c. Oxygen was introduced into all samples at -78° c and they were allowed to warm to 25 ° c. Products were analyzed by gas chromatography. The results are summarized in Table I. Analysis of Nickel Complexes I. Nickel The% Ni was determined as follows: A known amount of Ni complex was decomposed with oxygen and weighed. The sample was sent to the analytical lab for% Ni and that value was extrapolated back to the undecornposed material. -10- II. % C 4 metallocycle To a known amount of Ni complex of approximately .050g in a stoppered vial equipped with a stirring bar was added.500 ml internal standard (methane or propane), The vial was cooled to -30 and .4 mls concentrated aqueous HCl was added while the solid was vigorously stirred in order to avoid localized heat buildup, which accelerates C-C bond cleavage (lO). After acidolysis was completed, a gas sample was analyzed by gas chromatography on a duropak column. The metallo­ cyclopentanes decomposed to give butane, 1-butene, cis and trans 2butene and ethylene, and the peak areas of the C 4 and C 2 hydrocarbons were compared with the corrected peak areas of the internal standard (butane/Me= 3.65; butane/propane =4/3). Note: Decomposition by concentrated H2 so 4 gave consistently lower values and only ethylene and butane were observed. III. % P A known amount of Ni complex of approximately .5g was decomposed with l ml H2 so 4. l ml of 30% H2 o 2 was then added, followed by a few m1s H20. The ¢3P=O was extracted approximately 10 times with toluene and the toluene layer was collected. After stripping off the solvent, the ¢3P = 0 was dried, weighed, and a T.L.C. and melting point taken as a purity check. -11- RESULTS AND DISCUSSION The cyclodimerization of acrylonitrile followed by oxygen de­ composition to produce dicyanocyclobutane was observed only in a few cases. The first was a batch of tris(triphenylphosphine) nickelacyclo­ pentane that was left out at 20° c for 5 days. This nickel complex with .5 equivalents ¢3P added gave a yield of 600% dicyanocyclobutane based on nickel, and was reproducible. (This batch did not work before although .5 equivalents ¢3P was not added.) This was an interesting result because excess ¢3P decreases the amount of reductive elimination product (ll) indicating that the ¢3P had nothing to do with promoting the reaction. Another batch of tris metallocycle that had been set out at 20 ° c for 5 days did not work with or without the excess ¢3P added, strongly suggesting that the .5 eq. ¢3P did not matter in the previous batch, but that the critical factor was what occurred to the complex during the 5 days. The only other case which gave product was a batch of tris metallocycle which analyzed/for 15% C4 hydrocarbons after acidolysis (theoretical is 100%), and 2.2% Ni (theoretical is 6.5%), and gave a yield of approximately 350% dicyanocyclobutane. Another batch of tris metallocycle which did not yield the desired product analyzed to 65% C4 metallocycles. I have no explanation at this time why so few batches of tris metallocycle worked. Purity does not seem to be the critical factor, however. -12- Dicyanocyclobutane was also observed in yield of <1% when using (¢3P)2Ni ( CH2 = cH2) and l equivalent of ¢3P. The mechanism for the dimerization of ethylene has been proposed as follows: (5 . l l) Ethylene adds to (¢3 P)2Ni(CH2= cH2) to go through a proposed tetrahedral intermediate (5 ) which undergoes ring closure upon adding another ¢3P. This pentacoordinate complex then loses a ligand to give the square planar bis metallocycle which undergoes reductive elimination to give cyclobutane. As pointed out earlier substituted olefins should behave in a similar manner and this has been successfully demonstrated in the isol ation and decomposition of the nickelhydrindane complex ( S). The results of the control experiments with ¢3P and acrylonitrile indicate that cyclodimerizations were not performed by ¢3P, and that the nickel complex was required. The closure to metallocycle is not catalyzed by acid, base or the Ni ( O) complexes (¢3P,l2Ni ( CH2=cH2) or (¢3P) Ni ( O), the latter being a decomposition product in the pre­ 4 sence of excess ¢3P and heat. The formation of bis(acrylonitrile) bis ( triphenylphosphine)Ni ( O) seems to be occurring. The reaction always forms the irridescent -13- yellow crystals characteristic of this compound (l2) (Oxygen decom- position followed by G.C. analysis confirms the fact that this solid is an acrylonitrile complex). The monophosphine bis(acrylonitrile) complex are orange crystals (having been identified as such by elemental analysis and G.C. after oxygen decomposition) that are often seen precipitating out of the reaction mixture of the tris metallocycle with acrylonitrile. This, too, supports that the bis(acrylonitrile) species (at least the square planar species) (l2) is being formed. Why so very few times closure to metallocycle occurs is unknown. -14- CornROUOd 1L Ni-11 (.lg) 2 Reactants Initiation Time .Seq P¢3 l eq Ptp3 2 eq P¢3 CrlzCHCN (.8 mls;.012 moles) (.012g;3.8xl0-3eq)¢3P (.Ol8g;5.7xl0-3eq)¢3P ' ' P (.030g;9.5xl0-3 eq1¢ 3 (.030g;9.5xl0-3eq)¢3P (.030g;9.5xl0 -3eq) ¢3P (.048g;1.5x10-2eq)¢3P al Ni 3 bL3Ni cliJi dL Ni 3 (.lg) (.lg) (. lg) (.lg) eL3 Ni fL Ni gL3Ni 3 (.lg) ( . lg) ( . 1 g) 2.8 m1s.=-J"N .8 mls=1CN /.5eq l .8 mls-="CN .8 mls="CN .8 ml sec='CN/10 -5M HAc ori¼. •8 ml S=CN/. 5eq P¢3 .8 mls __=1CN [=�N]=9M; 162eq 6M; l08eq 4.5M; 8leq 3.8M;67.5eq . 63;13.5eq TABLE I Temp. ° Yield 18 hrs 18 hrs 18 hrs -15 C -15 °C -l5°C 5 hrs 5 hrs 5 hrs 5 hrs 5 hrs 5 hrs 5 hrs -15 °C -15° C -15 °C 25 °C 60 °C -15 °C -15 °C 0 0 0 0 0 0 0 5 hrs 5 hrs 5 hrs 12 hrs 5 hrs 12 hrs 12 hrs 12 hrs -15°C -15 °C -15 °C -15 °C -15 °C -15 °C -15°C -15°C 0 600% 0 0 0 0 350% 0 . ,.1 II 0 <1% 0 c:_is/trans 50/50 45/55 45/55 t\ II It ll ,1 It L = ¢3 p " 2. . 8 m,1 s ='"' N 1• s 110eq ==1CNI /'�. Total volum2 was 1.8 mls so C=:1CN J = 6.7 M , , • l. -15- ccn't on next page a. b. c. d. e. f. g. First preparation of L 3 L 3 of the first prep left out at 20 ° c for 5 days prior to reaction. Second prep of L3 Third prep of L3. This analyzed to 65% C4 metallocycle L3 of third prep left out at 20 ° c for 5 days prior to reaction Fourth batch prepared in part by Akira Miyashita. L analyzed to 2.2% Ni and 15% C4 metallocycle. (Theoretical is36.7% and 100%, respectively) • F•1rst prep w1• th varying concent rat ions of _:,JCN . • -16- REFERENCES l. G. M. Whitesides and J. McDermott, J. Am. Chem. Soc. 96, 947 (1974). a. McDermott, M. Wilson, and G, M. Whitesides, ibid, 98, 6529 (1976). 2. G. M. Whitesides, J. 11hite and J. McDermott, J. Am. Chem. Soc., 95, 4451 (1973); ibid, 9ti, 6521 (1976). 3, R. Diversi, G. Ingrosso, A. Lucherini, Chem. Comm., 52 (1977). 4. S. J. McLain, C. D. Wood and R. R. Schrock, J. Am. Chem. Soc., ?9, 3519 (1977). 5. Juan M. Manriquez, Donald R. McAlister, Robert D. Sanner, and John E. Bercaw, J. Am. Chem. Soc., 100, 2716 (1978). 6. R. H. Grubbs, A. Miyashita, M.-I. Liu, P. L. Burk, J. Am. Chem. Soc., 99, 3863 (1977). 7. R. H. Grubbs and Akira Miyashita, Chem, Comm., 864 (1977). 8. R. H. Grubbs and Akira Miyashita, J. Organometallic Chem. 161 (1978) 371-380. 9. Kerrie I. Well and Jeffrey Schwartz, Chem. Comm., 244 (1979). 10. Akira's and my observations 11. R. H, Grubbs, Akira Miyashita, Mei-In Liu, Patrick L. Burk, J. Am. Chem. Soc., 99, 3863 (1977), 12. G, N. Schrauzer, J. Am, Chem. Soc., 82, 1008 (1960), 13. R. H. Grubbs and A. Miyashita, J. Am. Chem. Soc., 100, 1300 (1978). -17-