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

Magnesium(I) halides (Mg^IX; 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 Mg^II (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 [Mg^IBr(NⁿBu₃)]₂ ( 1 ). The phosphanes [ClP(μ‐NTer)]₂ ( 2 ) and (Me₃Si)₂N‐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 Mg^I chelate complex L¹Mg?MgL¹ containing a strong Mg?Mg σ‐bond.