[{SiNDipp}MgNa]2: A Potent Molecular Reducing Agent

The bimetallic species, [{SiN^Dipp}MgNa]₂ [{SiN^Dipp} = {CH₂SiMe₂N(Dipp)}₂; (Dipp = 2,6-i-Pr₂C₆H₃)], is shown to be a potent reducing agent, able to effect one- or two-electron reduction of either dioxygen, TEMPO, anthracene, benzophenone, or diphenylacetylene. In most cases, the bimetallic reaction products imply that the dissimilar alkaline metal centers react with a level of cooperativity. EPR analysis of the benzophenone-derived reaction and the concurrent isolation of [{SiN^Dipp}Mg(OCPh₂)₂], however, illustrate that treatment with such reducible, but O-basic, species can also result in reactivity in which the metals provide independent reaction products. The notable E-stereochemistry of the diphenylacetylene reduction product prompted a computational investigation of the PhC≡CPh addition. This analysis invokes a series of elementary steps that necessitate ring-opening via Mg⁺ → Na⁺ amido group migration of the SiN^Dipp ligand, providing insight into the previously observed lability of the bidentate dianion and its consequent proclivity toward macrocyclization.