Rhodium(II) Perfluorobutyrate Catalyzed Silane Alcoholysis. A Highly Selective Route to Silyl Ethers

Rhodium(II) perfluorobutyrate, Rh₂(pfb)₄, is an effective catalyst for the alcoholysis of trialkylsilanes at room temperature. Primary alcohols react with triethylsilane approximately 5 times faster than do secondary alcohols, and tertiary alcohols are virtually inert Enhanced selectivity is achieved with tert-butyldimethylsilane. Hydrosilylation of olefinic alcohols is relatively unimportant even with terminal alkenes, but Rh₂(pfb)₄ does promote hydrogenation of 3-phenyl-2-propen-l-ol. Selected diols have been silylated with complete regioselectivity in Rh₂(pfb)₄-catalyzed reactions with either triethylsilane or tert-butyldimethylsilane. Methanolysis of (S)-(-)-1-naphthylphenylmethylsilane occurs with nearly complete inversion of configuration at silicon, and spectral analysis of the catalytic reaction suggests a mechanism for silane alcoholysis in which the rhodium(II) catalyst coordinates with the silicon hydride to activate silicon for backside nucleophilic attack by the alcohol.