1,3-Dimethylimidazol-2-ylidene borane (diMe-Imd-BH3)
NHC-trihydroboranes are white solids that are stable to air, water, and even chromatography. However, 1,3-dimethylimidazol-2-ylidene borane is a suprisingly good hydride donor that is comparable to anionic reagents such as NaCNBH3. The reagent can be used for reductive amination procedures and even for reduction of carbonyl compounds if silica gel is present. Besides, NHC-boranes are attractive reagents for radical, pericyclic and organometallic reactions.
NHC-boranes such as 1,3-dimethylimidazol-2-ylidine trihydridoborane serve as practical hydride donors for the reduction of aldehydes and ketones in the presence of silica gel to give alcohols in good yields under ambient conditions. Aldehydes are selectively reduced in the presence of ketones. The process is attractive because all the components are stable and easy to handle and because the isolation procedure is convenient.
T. Taniguchi, D. P. Curran, Org. Lett., 2012, 14, 4540-4543.
N-heterocyclic carbene boranes (NHC-boranes) are 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.
M. Horn, H. Mayr, E. Lacôte, E. Merling, J. Deaner, S. Well, T. McFadden, D. P. Curran, Org. Lett., 2012, 14, 82-85.