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Article type: Research Article
Authors: Shaltout, Raef M. | Corey, Joyce Y.
Affiliations: Department of Chemistry, University of Missouri- St. Louis, MO 63121
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.
DOI: 10.1080/13583149512331338315
Journal: Main Group Chemistry, vol. 1, no. 1, pp. 115-126, 1995
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