Nickelacarborane-Supported Bis-N-heterocyclic Carbenes

Metallacarboraneshave attracted significant attention due to theirunique properties. Considerable efforts have been made on the reactionsaround the metal centers or the metal ion itself, while transformationsof functional groups of the metallacarboranes have been much lessexplored. We presented here the formation of imidazolium-functionalizednickelacarboranes (2), their subsequent conversion tonickelacarborane-supported N-heterocyclic carbenoids(NHCs, 3), and the reactivities of 3 towardAu(PPh3)Cl and Se powder, which resulted in the formationof bis-gold carbene complexes (4) and NHC selenium adducts(5). Cyclic voltammetry of 4 shows two reversiblepeaks, corresponding to the interconversion transformations Ni-II & LRARR; Ni-III and Ni-III & LRARR;Ni-IV. Theoretical calculations demonstrated relativelyhigh-lying lone-pair orbitals, weak B-H & BULL;& BULL;& BULL;H-Cinteractions between the BH units and the methyl group, and weak B-H & BULL;& BULL;& BULL;& pi;interactions between the BH groups and the vacant p-orbital of the carbene.