Metal-Free Synthesis of Unsymmetrical B–B Bond via Pyridyl-Directed m -Carborane Borylation

Constructing B–B single bonds has long challenged boron chemists, as diboranes serve as crucial precursors for B–X bond formation. Traditional routes rely on strongly reducing metals for homocoupling, leaving unsymmetrical B–B bonds inaccessible. We report herein a metal-free strategy for regioselective B(2)–H borylation of m-carboranes with BBr3, forging unsymmetrical B–B bonds. Cooperative dual pyridyl moieties promote in situ generation of intramolecular Lewis pairs, driving B–H bond activation and borylation. The resulting B(2)–BBr2-m-carboranes are bench-stable and function as versatile intermediates, enabling synthesis of diverse B–BR2 derivatives (R = H, Me, Ph, OH, etc.).