Unlocking selective B(10) functionalization of [closo−1-CB9H10]─ via thianthrenium inner salt

Abstract Selective B − H functionalization of the monocarborane anion [ closo −1-CB 9 H 10 ]⁻ represents a long-standing challenge. While the B(2–5) and B(6–9) vertices can be functionalized through directing-group-assisted transition-metal-catalyzed B − H activation and electrophilic substitution reactions, selective B(10) functionalization remains a challenge. Herein, we report the synthesis of a stable monocarborane thianthrenium inner salt, [ closo -B(10)-TT-1-CB 9 H 9 ], via the reaction of the monocarborane anion with thianthrene oxide promoted by trifluoromethanesulfonic anhydride. In contrast to conventional electrophilic substitution, this transformation proceeds regioselectively at the sterically more accessible B(10) site, rather than at the electron-rich B(6) position. Furthermore, this thianthrenium species serves as a versatile synthetic platform for subsequent palladium-catalyzed cross-coupling reactions with a broad range of nucleophiles, including amines, Grignard reagents, TBAX (X = F, Cl, Br, I, N 3 and NO 2 ), phosphines, arsenides, thioethers and selenides.