Quantitative substituent effects in the Grignard reaction with silanes

Kinetics of reactions of ethyl- and phenylmagnesium chlorides with chlorosilanes, RMeSiCl2, were investigated in diethyl ether under pseudo-first order conditions with a great excess of the Grignard reagent. Rate constants for alkyl substituted silanes correlate well with Es(Si) steric parameters. A good linear correlation of rate data for substituted phenyl derivates with σ0 inductive constants together with correlations of the literature data rule out the resonance effect of substituents at least in nucleophilic displacement reactions at the silicon center. An attempt to calculate the steric constants for polar substituents was made. It appeared that the inductive constants σ∗ derived from the carbon chemistry are not applicable to the silicon chemistry. New scales of parameters for description of polar and steric effects in the organosilicon chemistry need to be created.