A Silicon‐29 NMR Study of Adduct Formation in Organosilanes

Abstract

The reactions of a series of methyl‐and phenylsilanes containing one or more electronegative groups such as chloro, triflate (OTf), trifluoroacetate, and trifluoroethoxy with the base HMPA were investigated with ²⁹Si NMR and conductivity titrations in both methylene chloride and acetonitrile solvents. Formation of both five‐coordinate adduct and four‐coordinate electrolyte (such as Me₃Si(HMPA)⁺OTf⁻) was observed for some of the strongly electron attracting groups, whereas only adduct formation was observed for the chloro group. Electrolyte formation is also favored by an increase in the base to acid mole ratio and the more polar acetonitrile. The effect of the Si–H bond on the Lewis acidity of organosilanes in intermolecular adduct formation was documented and is believed to be a result of bond strengthening steric effect.

Keywords:

• Organosilanes
• Adduct formation
• 29‐Si NMR

Acknowledgments

We are indebted to the donors of the Petroleum Research Fund, administered by the American Chemical Society, to Dow Corning Corporation, and to the Arnold and Mabel Beckman Foundation (Beckman Scholars Program) for support of this research. We also thank the Franklin and Marshall College Hackman program and the Elizabethtown College Faculty Grants Committee for summer stipends.