Nickelacarborane-Supported Bis-N-heterocyclic Carbenes

Metallacarboranes have attracted significant attention due to their unique properties. Considerable efforts have been made on the reactions around the metal centers or the metal ion itself, while transformations of functional groups of the metallacarboranes have been much less explored. We presented here the formation of imidazolium-functionalized nickelacarboranes (2), their subsequent conversion to nickelacarborane-supported N-heterocyclic carbenoids (NHCs, 3), and the reactivities of 3 toward Au(PPh₃)Cl and Se powder, which resulted in the formation of bis-gold carbene complexes (4) and NHC selenium adducts (5). Cyclic voltammetry of 4 shows two reversible peaks, corresponding to the interconversion transformations Ni^II ↔ Ni^III and Ni^III ↔ Ni^IV. Theoretical calculations demonstrated relatively high-lying lone-pair orbitals, weak B-H···H-C interactions between the BH units and the methyl group, and weak B-H···π interactions between the BH groups and the vacant p-orbital of the carbene.