N-Heterocyclic carbene boranes are good hydride donors.

The nucleophilicity parameters (N) of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene borane and 1,3-dimethylimidazol-2-ylidene borane are 9.55 and 11.88. This places N-heterocyclic carbene boranes (NHC-boranes) among the most nucleophilic classes of neutral hydride donors. Reductions of highly electron-poor C═N and C═C bonds provide hydrogenation products along with new, stable borylated products. The results suggest that NHC-boranes have considerable untapped potential as neutral organic reductants.