Steric Effects of Alkylmagnesium Chlorides in the Grignard Reaction with Silanes

Abstract

Rate constants for the reactions of methylvinyldichlorosilane and tetraethoxysilane with alkylmagnesium chlorides RMgCl (R = Et, n-Bu, i-Bu, i-Pr, s-Bu, t-Bu) in diethyl ether were determined. Excellent correlations of rate data with steric constants E S (Si) by Cartledge and v by Charton were found for the reaction of methylvinyldichlorosilane. Linear correlations with break points were obtained for the tetraethoxysilane reaction. It was assumed that this could be referred to a change in the reaction mechanism.

Quantitative substituent effects in the Grignard reaction with silanes

“…So far only one reaction series can be brought for comparison, viz. the reaction between alkylmagnesium chlorides and methylvinyldichlorosilane [10] with d = 1.04 ± 0.03 (R = 0.998).…”

“…(2) have been defined in organic reactions. At present it is understood that the steric parameters derived from reactions of organic carbonyl compounds are not suitable for description of steric effects in reactions taking place at Si atoms [10,11,16,25]. For alkyl substituents appropriate scales of parameters, e.g.…”

“…We have launched an investigation into quantitative aspects of the reactivity in the Grignard reaction with silanes [6][7][8][9][10]. The main attention is focused on the structure-reactivity relationships for the reaction.…”

“…However, quantitative aspects of the reaction have been little investigated. A small number of kinetic studies of the Grignard reaction with silanes have been published [2][3][4][5][6][7][8][9][10] and no attempts to ascertain the structure-reactivity relationships for the reaction were made until our recent work [10].…”

“…In our recent work [10] the reaction between methylvinyldichlorosilane and a series of alkylmagnesium chlorides proved to be a good test of applicability for steric constants E s (Si) of alkyl substituents [11], further allowing calculation of missing constants.…”