Six-Membered Saturated NHC-Stabilized Borenium Cations: Isolation of a Cationic Analogue of Borinic Acid.

The reaction of six-membered saturated NHC [1,3-di(2,6-diisopropylphenyl) tetrahydropyrimidine-2-ylidene; henceforth abbreviated as 6-SIDipp] with PhBCl yields a Lewis base adduct, 6-SIDipp·PhBCl (), which readily undergoes nucleophilic substitution reaction with AgNO, leading to the single () and double () substitution of both chlorides with ONO moieties at the boron atom. The reaction of with 1 equiv of AlCl resulted in a borenium cation of composition [6-SIDipp·B(Ph)Cl] () with AlCl as the counteranion. Although borenium cations with different substituents on boron have been reported, a structurally characterized phenylchloroborenium cation remains unknown. Similarly, the reaction of with triflic acid provides the first representative of a new class of borenium cations bearing one hydroxyl and one phenyl group on boron (), a cationic analogue of borinic acid.