Two-Way Street Transformation of Boronium and Borane Complexes Facilitated by Amino-Linked N-Heterocyclic Carbene

We have obtained boronium complexes upon reaction of an amino-NHC lithium bromide adduct with borane. Unexpectedly, the treatment of the boronium complexes with silver triflate led to the isolation of a bis-borane compound containing two chemically different boron centers. The bis-borane and boronium complexes can interconvert via a four-membered intermediate metallacycle consisting of a three-center, two-electron B-H-B bonding motif assisted by the pendant amine arm.