Chemistry Publications Chemistry 8-2003 Theoretical Study of the Bis-Silylation Reaction of Ethylene Catalyzed by Titanium Dichloride Yuri Alexeev Iowa State University Mark S. Gordon Iowa State University, [email protected] Follow this and additional works at: http://lib.dr.iastate.edu/chem_pubs Part of the Chemistry Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ chem_pubs/419. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Chemistry at Iowa State University Digital Repository. It has been accepted for inclusion in Chemistry Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Theoretical Study of the Bis-Silylation Reaction of Ethylene Catalyzed by Titanium Dichloride Abstract Titanium dichloride was investigated as a potential catalyst for the bis-silylation reaction of ethylene with hexachlorodisilane. Ab initio electronic structure calculations at the restricted Hartree−Fock (RHF), density functional (DFT), second-order perturbation (MP2), and couple cluster (CCSD) levels of theory were used to find optimized structures, saddle points, and minimum-energy paths that connect them. The er action was found to have a net zero barrier at the DFT, MP2, and CCSD levels of theory. Dynamic correlation is found to be important for this reaction. Disciplines Chemistry Comments Reprinted (adapted) with permission from Organometallics 22 (2003): 4111, doi:10.1021/om0303350. Copyright 2014 American Chemical Society. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/chem_pubs/419 Organometallics 2003, 22, 4111-4117 4111 Theoretical Study of the Bis-Silylation Reaction of Ethylene Catalyzed by Titanium Dichloride Yuri Alexeev and Mark S. Gordon* Department of Chemistry, Iowa State University, Ames, Iowa 50011 Received May 7, 2003 Titanium dichloride was investigated as a potential catalyst for the bis-silylation reaction of ethylene with hexachlorodisilane. Ab initio electronic structure calculations at the restricted Hartree-Fock (RHF), density functional (DFT), second-order perturbation (MP2), and couple cluster (CCSD) levels of theory were used to find optimized structures, saddle points, and minimum-energy paths that connect them. The reaction was found to have a net zero barrier at the DFT, MP2, and CCSD levels of theory. Dynamic correlation is found to be important for this reaction. Introduction the first successful double silylation of 1,3-butadienes using Ni phosphine complexes as catalysts.5 Later The bis-silylation reaction1 is an important process Okinoshima,6 Watanabe,7-9 and others discovered that for producing bis(silyl) compounds and new C-Si bonds, Rh, Ni, Pt, and Pd phosphine complexes can be used to which can serve as monomers for silicon-containing add substituted disilanes across various unsaturated polymers and silicon carbides. Many of these organo- acetylene and ethylene derivatives. It was found that silicon materials have desirable chemical and physical complexes such as M(PPh ) and MCl (PPh ) , where M properties, such as thermal stability and the ability to 3 4 2 3 2 is Pt or Pd, are the most efficient catalysts. Recently store and transfer optical and electrical information.2,3 Bottoni et al.10 used density functional theory (DFT) However, there is a lack of quantum-chemical calcula- with the B3LYP functional11 to study the bis-silylation tions for the study of the effect of catalysis on the bis- reaction of acetylene with disilane, H Si-SiH ,inthe silylation reaction. Such calculations can potentially 3 3 presence of Pd(PH ) . Pd(PH ) was used to emulate Pd- lead to the development of new catalysts. In the bis- 3 2 3 2 (PPh ) , PdCl (PEt ) , and other catalysts often used in silylation reaction an Si-Si bond adds across a C-C 3 2 2 3 2 experimental studies. The net reaction barrier was double or triple bond, in the process breaking a CC π predicted to be 18 kcal/mol. bond and forming two new C-Si bonds. One may write A theoretical study of Pt(PH ) -catalyzed bis-silylation a schematic for the bis-silylation reaction with an alkene 3 2 and hydrosilylation (using the Chalk-Harrod and modi- as fied Chalk-Harrod mechanisms) of alkenes was re- cently performed by Sakaki et al.12,13 These authors used second-order perturbation theory (MP2),14 fourth- order perturbation theory (MP4SDQ),15 and doubles coupled cluster theory (CCD)16 to study the reactions. Experimental and theoretical studies of this reaction The net reaction barrier is predicted to be 19 kcal/mol in the absence of a catalyst suggest that the reaction in the bis-silylation reaction and 5 kcal/mol in the has a high activation barrier. For example, the predicted Chalk-Harrod mechanism of the hydrosilylation reac- barrier height for the addition of disilane to ethylene tion. Thus, the two theoretical studies agree that, even to form 1,2-disilylethane is predicted to be approxi- in the presence of a catalyst, the energy barrier is still mately 50 kcal/mol, using second-order perturbation nontrivial. theory.4 Indeed, this high barrier seems to be insensitive (5) Okinoshima, H.; Yamamoto, K.; Kumada, M. J. Am. Chem. Soc. to the level of theory employed. This suggests, as is well- 1972, 94, 9263. known to experimentalists, that a catalyst is required (6) Okinoshima, H.; Yamamoto, K.; Kumada, M. J. Organomet. to make this reaction practical, certainly in any indus- Chem. 1975, 86, C27. (7) Watanabe, H.; Kobayashi, M.; Saito, M.; Nagai, Y. J. Organomet. trial sense. Chem. 1981, 149, 216. A number of bis-silylation catalysts have been em- (8) Watanabe, H.; Saito, M.; Sutou, N.; Kishimoto, K.; Inose, J.; Nagai, Y. J. Organomet. Chem. 1982, 225, 343. ployed since 1972, when Okinoshima et al. carried out (9) Watanabe, H.; Kitahara, T.; Motegi, T.; Nagai, Y. J. Organomet. Chem. 1977, 215, 139. * Corresponding author. (10) Bottoni, A.; Higueruelo, A. P.; Miscione, G. P. J. Am. Chem. (1) Jones, R. G.; Ando, W.; Chojnowski, J. Silicon-Containing Soc. 2002, 124, 5506. Polymers: The Science and Technology of Their Synthesis and Ap- (11) Koch, W.; Holthausen, M. C. A Chemist’s Guide to Density plications; Kluwer Academic: Dordrecht, The Netherlands, 2000. Functional Theory; Wiley: Weinheim, Germany, 2000. (2) (a) Lee, H. H. Fundamentals of Microelectronic Processing; (12) Sakaki, S.; Ogawa, M.; Musashi, Y. J. Organomet. Chem. 1997, McGraw-Hill: New York, 1990. (b) Mort, J.; Jansen, F. Plasma 535, 25. Deposited Thin Films; CRC Press: Boca Raton, FL, 1986. (c) Sueta, (13) Sakaki, S.; Mizoe, N.; Sugimoto, M.; Musashi, Y. Coord. Chem. T.; Okoshi, T. Ultrafast and Ultra-Parallel Optoelectronics; Wiley: Rev. 1999, 190-192, 933. Tokyo, 1995. (d) Prasad, P. N.; Ulrich, D. R. Nonlinear Optical and (14) Moler, C.; Plesset, M. S. Phys. Rev. 1934, 46, 618. Electroactive Polymers; Plenum Press: New York, 1988. (15) Cramer, C. J. Essentials of Computational Chemistry; Wiley: (3) (a) Bradley, D. C. Chem. Rev. 1989, 89, 1317. (b) Hench, L. L.; New York, 2000. West, J. K. Chem. Rev. 1990, 90, 33. (16) Crawford, T. D.; Schaefer, H. F., III. Rev. Comput. Chem. 1996, (4) Raaii, F.; Gordon, M. S. J. Phys. Chem. A 1998, 102, 4666. 14, 33. 10.1021/om0303350 CCC: $25.00 © 2003 American Chemical Society Publication on Web 08/30/2003 4112 Organometallics, Vol. 22, No. 20, 2003 Alexeev and Gordon It is well-known that complexes of early transition the catalytic activity is similar in the Ziegler-Natta and metals, such as Ti and Zr, exhibit catalytic properties. hydrosilylation reactionssthe initial formation of a very In the Ziegler-Natta polymerization reaction, the com- stable intermediate. monly used catalysts are MCl4-AlR3 and MR2, where The purpose of the present work is to present ab initio MisTiorZr.17 The first step in the currently accepted calculations on possible mechanisms for the catalyzed mechanism is formation of a metal-alkyl-olefin com- bis-silylation reaction. On the basis of the discussion in + plex. The addition of Cl2TiCH3 to C2H4 was studied the previous paragraph, TiCl2 is used as a model recently by Bernardi et al.18 with DFT using the B3LYP catalyst for the bis-silylation reaction of ethylene with functional. The reaction is predicted to require no net hexachlorodisilane. This choice of reactants allows us barrier. A π-complex intermediate that is found to be to study this reaction at reliable levels of theory without lower in energy than the reactants by 38 kcal/mol compromising accuracy, and, as noted above, TiCl2 is apparently drives this catalyzed reaction by providing expected to reliably mimic TiCp2. Since TiCp2 is thought an initially large exothermicity. to be the active industrial catalyst for producing organ- Titanocene- (TiCp2, where Cp ) cyclopentadienyl) and osilicon polymers on the basis of the results of Harrod 20 19 zirconocene-based catalysts (ZrCp2) were recently re- et al. and the recent report by Terao et al., it is ported to be efficient catalysts for double silylation by reasonable to consider TiCl2 as a viable model for the 19 Terao et al. and Harrod et al. In particular, double efficient catalyst TiCp2. silylation of isoprene with chlorotriethylsilane proceeds with 91% yield at 0 °C in the presence of Cp2TiCl2 and Computational Methods BuMgCl in THF solution. The double silylation of p-chlorostyrene by Me PhSiCl in the presence of BuMgCl All calculations performed for this paper were carried out 2 using the GAMESS program,22 and figures were generated and Cp TiCl in THF solution under the same conditions 2 2 using the MacMolPlt program.23 The basis set used in the gives a 72% yield.