Catalytic Dehydropolymerization of PhSiH₃ to Polyphenylsilane with Substituted Group IV Metallocenes

Abstract

Phenylsilane can be converted catalytically to polyphenylsilane using substituted achiral group IV metallocene dichloride precatalysts (Cp R ) 2 MCl 2 (M = Ti, Zr; Cp R = C 5 H 4 C(Me) 2 CH(Me) 2 ) and Cp(Cp R )MCl 2 (M = Ti, Zr; Cp = C 5 H 5 ) in combination with 2 equiv of n -BuLi. The performance of each precatalyst is described in terms of polymer molecular weight, polydispersity, and polymer microstructure. The polysilanes from each catalyst system were obtained as a mixture of oligocyclic and linear materials with M w values ranging from 1100 to 4000. Characterization of the crude polymers by 1 H and 29 Si{ 1 H} DEPT 135° NMR spectroscopy indicated a mostly atactic microstructure with a small syndiotactic bias. A Bernoullian statistical analysis of a typical 29 Si{ 1 H} polymer spectrum indicated a syndioselective probability (1-Pm) of 0.55 during propagation of the pseudochiral chain. The degree of polymerization was found to be dependent on the metal and the degree of Cp-ring substitution of the metallocene precatalyst.