Magnesium(I) Halide versus Magnesium Metal: Differences in Reaction Energy and Reactivity Monitored in Reduction Processes of P-Cl Bonds.

Abstract

Magnesium(I) halides (MgI X; X=Cl, Br, I), as high temperature molecules, are trapped and finally stored at -80 °C in toluene/donor solutions. These solutions provide insights into the fundamental mechanism of reduction reactions using activated magnesium metal as a prototype for every base metal. The most important example of such a reaction is the preparation of Grignard reagents (RMgX). The details of this highly complex mechanism especially of intermediates between Mg metal and MgII (RMgX) remain unknown until today. The same is true for the reaction of bulk magnesium with Group 15 halide compounds that give biradicaloid species. We investigate the reduction of P-Cl bonds with solutions of [MgI Br(Nn Bu3 )]2 (1). The phosphanes [ClP(μ-NTer)]2 (2) and (Me3 Si)2 N-PCl2 (3), were chosen as they had successfully been reduced by Mg metal before. Furthermore, reactions of both 1 and Mg metal are compared with an MgI chelate complex L1 Mg-MgL1 containing a strong Mg-Mg σ-bond.