Catalytic Insertion of Pd-Vinylidenes Into B─H Bonds.

An unprecedented palladium (Pd)‑catalyzed insertion of unsaturated carbenes into B─H bonds is described. Using alkynyl hypervalent iodine reagents as carbene precursors and amine-borane adducts as boron sources, this method delivers a broad range of E‑configured alkenyl monoborinates in good-to-high yields with exceptional stereoselectivity (>20:1 E/Z). The reaction proceeds under mild conditions, tolerates diverse aromatic, heteroaromatic, and aliphatic substituents, and is readily scalable to gram quantities. The resulting monoboronate products participate efficiently in a variety of C─X bond‑forming transformations, underscoring their synthetic versatility. Initial mechanistic investigations and DFT calculation support the formation of an unsaturated Pd-vinylidene intermediate, with stereocontrol influenced by ligand coordination at the palladium center. Collectively, this work establishes a mechanistic and conceptual bridge between unsaturated carbene chemistry and organoboron synthesis, expanding the reactivity landscape of Pd‑-carbene intermediates.