Reactions of Boron-Substituted N-Heterocyclic Carbene Boranes with Triflic Acid. Isolation of a New Dihydroxyborenium Cation

Reactions of NHC-BH2X (where X = Cl, OTf and NHC = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) with 1 equiv of triflic acid provide the stable products of acid/base reactions NHC-BH­(OTf)2 and NHC-BH­(OTf)­Cl. Further reactions of these compounds with additional triflic acid (or direct reactions of NHC-BH3 with excess triflic acid) produce the isolable dihydroxyborenium triflate [NHC-B­(OH)2]+TfO–. This first-in-class ligated borenium ion has been characterized by NMR spectroscopy and X-ray crystallography.