Structure and reactivity of germylene-bridged digold complexes

The bonding between gold and main-group metallic elements (M) featuring Au(δ−)−M(δ+) polarity, has been studied recently. The gold in the bonds is expected to have the oxidation number of −1, and hence, nucleophilic. However, the knowledge of the reactivity of the gold-metal bonds remains limited. Here, we report digold-substituted germanes of the form of R’(2)Ge(AuPR(3))(AuGeR’(2)) (3a; R = Me, 3b; R = Et), featuring two Au-Ge(IV) and one Au-Ge(II) bonds. DFT calculations of 3a revealed the existence of high-lying σ(Ge-Au) type HOMO and low-lying LUMO with germylene p(π) nature. A pendular motion of AuPR(3) group between Ge(IV) and Ge(II) of 3 occurs in the NMR time scale, suggesting that the Ge(II) center has an enhanced electrophilicity to be attacked by the nucleophilic gold (−I) atom. 3a reacts with nucleophilic Cl(−) and electrophilic MeOTf reagents at Ge(II) and Ge(IV) centers, respectively.