Catalytic Dehydrocoupling of Hydrosilanes with Trimethylsilyl Substituted Hafnocene and Ansa-Hafnocene Complexes

Abstract

The dehydrocoupling of hydrosilanes to polysilane products is promoted by the combination of a Group 4 metallocene dichloride with nBuLi. The effect of a trimethylsilyl Cp-substituent on the rate and product distribution for the dehydrocoupling of PhRSiH₂(R = H, Me) has been examined for hafnium precursors. A slower rate of reaction is observed with (C₅H₄SiMe₃)₂HfC1₂-(1)/2nBuLi compared to (C₅H₅)₂HfC1₂/2nBuLi but the average molecular weight of the polysilane produced is of similar magnitude. Both rac(2)- and meso(3)-[Me₂C(C₅H₃SiMe₃)₂] HfCl₂ precatalysts convert PhSiH₃ to polysilane products at a faster rate than does [Me₂C(C₅H₄)₂]HfCl₂, but only oligomeric products are formed at room temperature. When dehydrocoupling reactions of PhSiH₃ promoted by 2 and 3 are conducted above room temperature, loss of the Cp-based ligand is observed. The silylcyclopentadienyl hafnium systems are ineffective for the coupling of secondary silanes. The reaction of 1 and 2 with 2 equiv of nBuLi is rapid at room temperature to give Cp₂^′ HfBu₂, but 3 gives primarily Cp₂^′ HfBuCl. It is proposed that the observed reactivity trends in the hafnocene combination catalysts suggest that the intermediate leading to silicon-silicon bond formation may involve Cp₂^′ Hf(Si ≡ )Bu instead of the previously proposed Cp₂^′Hf(Si ≡ )H.