141272-69-7Relevant articles and documents
Rapid, highly linear-selective dehydrocoupling of phenylsilane with new group 4 metallocene-based combination catalysts
Woo, Hee-Gweon,Song, Sun-Jung
, p. 457 - 458 (1999)
The dehydrocoupling of phenylsilane with Cp12MCl2/Red-Al (Cp1 = C5H5 or C5Me5; M = Ti, Zr, Hf; Red-Al = Na[H2Al(OCH2CH2OMe)2/sub
Dehydrogenative polymerization of silanes to polysilanes by zirconocene and hafnocene catalysts. A new polymerization mechanism
Woo, Hee-Gweon,Tilley, T. Don
, p. 8043 - 8044 (1989)
We have found that a number of zirconium and hafnium siyl complexes of the type Cp′2M(SiR3)R′ (Cp′ = η5-C5H5, Cp (η5-C5Me5); M = Zr, Hf; R = Me, Ph, SiMe3; R′ = Cl, alkyl, silyl) are catalyst precursors for this dehydrogenative coupling reaction and that polymer molecular weights can vary as a function of reaction conditions and catalyst. Improvement of this method relies heavily on an understanding of the polymerization mechanism, which has remained obscure. This report describes observations that suggest a mechanism for dehydrogenative silane polymerization by zirconocene and hafnocene catalysts.
TRIHYDRIDOSILYL-TERMINATED POLYSILANES AND METHODS OF PREPARATION
-
Page/Page column 5-6, (2012/04/04)
Novel trihydridosilyl-terminated polysilanes and methods for their synthesis, which are applicable to other polysilanes, are provided. The synthetic methods provide for facile preparation of products with minimal handling of pyrophoric intermediates and b
Reactivity of group 4 benzamidinate complexes towards mono- and bis-substituted silanes and 1,5-hexadiene
Volkis, Victoria,Averbuj, Claudia,Eisen, Moris S.
, p. 1940 - 1950 (2007/10/03)
Zirconium and titanium bis(benzamidinate) dimethyl complexes were found to be active catalytic precursors for the oligomerization of mono- and bis-substituted silanes. The activation of such complexes, by an excess of MAO or by an equimolar amount of B(C
Ansa-Metallocenes: Catalysts for the Dehydrocoupling of Hydrosilanes
Shaltout, Raef M.,Corey, Joyce Y.
, p. 4309 - 4320 (2007/10/02)
The dehydrocoupling of PhMeSiH2 to form oligomers and of PhSiH3 to form polysilanes has been performed with the precatalyst combination of 5-C5H5)2MCl2/nBuLi.
A σ-bond metathesis mechanism for dehydropolymerization of silanes to polysilanes by d0 metal catalysts
Woo, Hee-Gweon,Walzer, John F.,Don Tilley
, p. 7047 - 7055 (2007/10/02)
A mechanism for the dehydropolymerization of hydrosilanes to polysilanes, as catalyzed by early-transition-metal metallocene derivatives, is proposed. This mechanism is based on two σ-bond metathesis reactions that pass through four-center transition states: (1) the dehydrometalation of silane, H(SiHR)nH, with a metal hydride to give hydrogen and a silyl derivative, M(SiHR)nH, and (2) coupling of the metal silyl derivative with more hydrosilane, H(SiHR)mH, to produce H(SiHR)n(SiHR)mH and regenerate the active metal hydride catalyst. This proposal is based on a number of observed, stoichiometric σ-bond metathesis reactions involving zirconocene and hafnocene complexes. These reactions, which involve silicon, hydrogen, and a d0 metal center, are rather facile and apparently reflect the tendency of silicon to expand its coordination sphere under these conditions. One reaction of this type is rapid MH/SiH hydrogen exchange, for example between PhSiH3 and CpCp*MHCl (1, M = Zr, or 2, M = Hf), which is observed via deuterium labeling. Hydrogenolysis of CpCp*M[Si(SiMe3)3]Cl (3, M = Zr, 4, M = Hf) provides a convenient route to the monomeric hydride complexes 1 and 2, respectively. The first step in the proposed polymerization mechanism, which is the of M-Si hydrogenolysis, is observed in stoichiometric reactions of 1 or 2 with PhSiH3 to give hydrogen and the phenylsilyl complexes CpCp*M(SiH2Ph)Cl (5, M = Zr, and 6, M = Hf). The thermolytic decomposition of 6 to 2 in Si-Si bond formation, with the production of polysilane oligomers. This second-order reaction exhibits a deuterium isotope effect at 75°C of 2.9 (2) and activation parameters (ΔH? = 19.5 (2) kcal mol-1 and ΔS? = -21 (6) eu) that suggest a four-center transition state. The second-order reaction of 6 with PhSiH3 (to give 2 and (SiHPh)n polysilanes) was also studied kinetically and found to exhibit similar kinetic parameters. This σ-bond metathesis reaction, which corresponds to the step in the proposed mechanism, is believed to pass through a four-center transition state that result from interaction of the CpCp*(Cl)Hf-SiH2Ph and H-SiH2Ph bonds. Evidence for the role of hydride complexes as true catalysts is obtained by comparing gel permeation chromatograms for polysilanes obtained from both 3 and 1 as catalysts. Observed reactions of CpCp*Hf[Si(SiMe3)3]Me (7) with PhSiH3, to give CpCp*Hf(SiH2Ph)Me (8) and then CpCp*Hf(H)Me (9), model proposed processes for the activation of catalyst precursors. The step-growth character of the reaction is illustrated by the slow dehydrocoupling of PhSiH3 by Cp*2HfH2, which allows observation of early polysilane intermediates (di-, tri-, and tetrasilane). The participation of M(SiHPh)nH complexes as intermediates in dehydrocoupling was investigated. Partly on the basis of the observed reaction of CpCp*Hf[(SiHPh)3H]Cl (11) with PhSiH3 to give 6 and H(SiHPh)3H, it is concluded that a preferred dehydrocoupling pathway involves monosilyl intermediates, MSiH2Ph, and chain growth by one monomer unit per catalytic cycle. Implications of the proposed mechanism are discussed.
Condensation of primary silanes in the presence of Cp2MCl2/n-BuLi (M = Ti, Zr, Hf)
Corey, Joyce Y.,Zhu, Xiao-Hong
, p. 1 - 17 (2007/10/02)
The condensation of RSiH3 (R = Ph, nBu, nHex) to silicon oligomers in the presence of the catalyst precursor combination Cp2MCl2/2nBuLi (M = Ti, Zr, Hf) has been monitored by gas chromatography and the intermediate oligomers characterized by GC-MS.The average molecular weights of the isolated products from PhSiH3 depend on the catalyst and increase through the sequence, Hf nBuSiH)4H are produced in equal amounts throughout the reaction period for M = Ti but at different rates for M = Zr and only one diastereomer is observed for M = Hf.The observations are discussed in terms of chain growth through sigma-bond metathesis processes.
