Chelating 1,2-Bis(2′-picolyl)-<i>o</i>-carborane as a Supporting Ligand for Pd-Catalyzed Selective B(3,6)–H Difunctionalization of <i>o</i>-Carboranes

Transition metal catalyzed selective cage B-H functionalization of carboranes has made significant progress in recent years, giving rise to the efficient synthesis of a large variety of cage B-functionalized carboranes including alkenylation, arylation, alkynylation, borylation, hydroxylation, acyloxylation, amination, and halogenation. However, the mechanisms of these catalytic B-X coupling reactions are not well understood. Herein, we describe the isolation and characterization of the catalytically relevant <i>o</i>-carborane based palladium(II) metallacycle, disclosing the details of Pd-catalyzed B-H functionalization of <i>o</i>-carboranes. As a result, highly selective catalytic B(3,6)-dihalogenation, -dimethylation, and -diarylation of <i>o</i>-carboranes have been achieved.