The nature of the interaction between hexamethyl-phosphortriamide and trimethylhalosilanes; cations containing tetracovalent silicon as possible intermediates in nucleophile-induced substitution of silicon halides

Abstract

Stable ionic 1 1 adducts, thought to be of the type [(Me 2N) 3POSiMe 3] +X − have been isolated from the interaction of HMPT with the halides Me 3SiX (X  Br or I). Conductometric studies show that the equilibrium for formation of these adducts in CH 2Cl 2 lies well over to the products for X  Br or I, but for X  Cl the equilibrium lies close to the reactants. The known kinetic characteristics of reaction involving HMPT-catalysed racemisations or substitutions of silicon halides can be interpreted in terms of the formation of such phosphonium intermediates.