GroupII metal complexes of the germylidendiide dianion radical and germylidenide anion

The two-electron reduction of a Group14-element(I) complex [RË ] (E=Ge, R=supporting ligand) to form a novel low-valent dianion radical with the composition [RË:]^.2- is reported. The reaction of [LGeCl] (1, L=2,6-(CH=NAr)₂C₆H₃, Ar=2,6-iPr₂C₆H₃) with excess calcium in THF at room temperature afforded the germylidenediide dianion radical complex [LGe]^.2- Ca(THF)₃²⁺ (2). The reaction proceeds through the formation of the germanium(I) radical [LGe ], which then undergoes a two-electron reduction with calcium to form 2. EPR spectroscopy, X-ray crystallography, and theoretical studies show that the germanium center in 2 has two lone pairs of electrons and the radical is delocalized over the germanium-containing heterocycle. In contrast, the magnesium derivative of the germylidendiide dianion radical is unstable and undergoes dimerization with concurrent dearomatization to form the germylidenide anion complex [C₆H₃-2-{C(H)=NAr}Ge-Mg-6-{C(H)-NAr}] ₂ (3).