A Combined Experimental/Computational Study of the Mechanism of a Palladium‐Catalyzed Bora‐Negishi Reaction

Experimental and computational efforts are reported which illuminate the mechanism of a novel boron version of the widespread Negishi coupling reaction that offers a new protocol for the formation of aryl/acyl C−B bonds using a bulky boryl fragment. The role of nucleophilic borylzinc reagents in the reduction of the Pd II pre‐catalysts to Pd 0 active species has been demonstrated. The non‐innocent behavior of the PPh 3 ligands of the [Pd(PPh 3 ) 2 Cl 2 ] pre‐catalyst under activation conditions has been probed both experimentally and computationally, revealing the formation of a trimetallic Pd species bearing bridging phosphide (PPh 2 − ) ligands. Our studies also reveal the monoligated formulation of the Pd 0 active species, which led us to synthesize related (η 3 ‐indenyl)Pd‐monophosphine catalysts which show improved catalytic performances under mild conditions. A complete mechanistic proposal to aid future catalyst developments is provided.