Ge^I-Ge^I Coupling Reaction Induced by a Mixture of CoBr₂ and a Seven-Membered N-Heterocyclic Carbene

A new digermylene has been synthesized through the reaction of a six-membered cyclic radical germylene precursor with a mixture of CoBr₂ and a seven-membered N-heterocyclic carbene. The density functional theory simulation on the geometry of the digermylene agrees well with the experimental X-ray diffraction result. The digermylene possesses the shortest Ge^I-Ge^I bond [2.4853(6) Å] compared to the known singly bonded analogues, which can be attributed to σ → π* conjugation. In addition, it is revealed that a stable dative bond cannot form for the reductive radical germylene with the oxidative metal centers.