Activation of small molecules by ambiphilic NHC-stabilized phosphinoborenium cation: formation of boreniums with B–O–C, B–O–B, and B–O–P structural motifs

The reactivity of the phosphinoborenium cation supported by a 1,3,4,5-tetramethylimidazolin-2-ylidene ligand toward small molecules was explored. The phosphinoborenium cation exhibited dual Lewis acid-base properties due to the presence of the Lewis acidic boron center and the Lewis basic phosphido ligand connected by a covalent bond. The reaction of the title cation with CO₂ led to the insertion of a CO₂ molecule into the P-B bond. The obtained borenium CO₂-adduct underwent hydrolysis, forming an N-heterocyclic carbene stabilized diborenium dication bearing a B-O-B functionality. The activation of N₂O proceeded <i>via</i> the insertion of an oxygen atom into the B-P bond of the parent cation, yielding a borenium cation with a phosphinite moiety. An alternative synthetic pathway to borenium cations with a B-O-P skeleton was achieved <i>via</i> the activation of secondary phosphine oxides by the phosphinoborenium cation. Furthermore, borenium cations and diborenium dications with B-O-C structural motifs were obtained from the reaction of the title compound with perfluorinated <i>tert</i>-butyl alcohol and hydroquinone, respectively. The structure of the obtained borenium cations is discussed based on multinuclear NMR spectroscopy, X-ray diffraction, and density functional theory calculations.