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

Abstract

Magnesium(I) halides (MgIX; 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 [MgIBr(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 MgI chelate complex L1Mg−MgL1 containing a strong Mg−Mg σ‐bond.

N-Heterocyclic Carbene-Supported Aryl- and Alk- oxides of Beryllium and Magnesium

“…The molecular compounds described thus far continue to play an important role in Ae-mediated bond activation and catalysis, and this is consistent with the recent surge in interest regarding the study of Ae metal complexes as cost-effective mediators for important organic transformations [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. Indeed, compounds containing Ae-R functionalities also facilitate energy-relevant bond activation events.…”

Chemistry of alkaline earth metals: It is not all ionic and definitely not boring!

“…Mg + -halides have been studied in comparison with magnesium metal as reducing agents, for instance in the reaction with P-Cl bonds [26]. The same reference mentions also relatively stable (with respect to disproportionation into Mg 0 and Mg 2+ species) biradical species such as [MgBr(N n Bu 3 )] 2 and metalloid clusters like the anionic [Mg 16 Cp* 8 Br 4 K] -, whose proposed structure was calculated to possess multiple Mg-Mg bonds.…”

An Isolable Magnesium(II)-Radical Dianion Complex

“…Since their isolation, the magnesium­(I) complexes have been demonstrated to be powerful reducing reagents in small-molecule activation and organometallic synthesis . Mononuclear magnesium­(I) species are proposed as intermediates in the formation of the Mg–Mg compounds and in small-molecule activation. , Until now, no stable mononuclear magnesium­(I) compounds have been isolated, although Schnöckel et al showed that the metastable donor-stabilized magnesium­(I) halides could be obtained in solution at low temperature. , …”

“…6,17 Until now, no stable mononuclear magnesium(I) compounds have been isolated, although Schnockel et al showed that the metastable donor-stabilized magnesium(I) halides could be obtained in solution at low temperature. 18,19 Very recently, Ren et al 20,21 and Gilliard et al 22 reported the magnesium-bipyridine and -diazo complexes D−G. Analyses of the electronic structures reveal that the bipyridine and diazo ligands are in a radical anion state due to the redox-active properties, and the magnesium center is essentially in the +2 oxidation state.…”