Solvation effects in partially solvated Grignard reagents

Grignard reagents were prepared from alkyl chlorides (n-BuCl, i-PrCl, s-BuCl and t-BuCl) in toluene in the presence of one or less equivalents of various organic bases (ethers, triethylamine). Ultrasound was used to promote the process. Diethyl ether proved to be the most effective donor affording Grignard reagents with a very small content of the base. Some of the reagents art: disproportionate to magnesium chloride and the dialkylmagnesium. Stronger solvation of the species is favourable for the dismutation process. Increasing bulkiness of the alkyl group in the Grignard reagent hinders the complexing with the donor and shifts the equilibrium to the formation of unsymmetrical species. The extent and the rate of the reaction are also governed by the solvating power of donors. The importance of specific solvation in the Grignard chemistry and the decisive role of the steric requirements of the reagents over their intrinsic acid-base properties were demonstrated. (C) 1999 Elsevier Science S.A. All rights reserved.