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

Reactions of NHC-BH 2 X (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-BH 3 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.