Phosphinoborenium cations stabilized by -heterocyclic carbenes: synthesis, structure, and reactivity.

Phosphinoborenium cations stabilized by -heterocyclic carbenes (NHCs) were synthesized the reaction of bromo(phosphino)boranes with NHCs. Their structures were investigated by heteronuclear magnetic resonance spectroscopy, X-ray diffraction, and density functional theory calculations. They possess a planar trigonal boron center directly bonded with the pyramidal phosphanyl group (PR) and can be treated as cationic phosphinoboranes. The reactivity of the selected NHC-phosphinoborenium cation was tested toward AuCl·SMe and PhPCl. In both reactions, the titled compound acted as a phosphido group donor under heterolytic cleavage of the P-B bond. Control experiments with parent phosphinoborane emphasized differences between the reactivity of low-coordinate neutral and cationic species with P-B functionality.