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 PPh3 ligands of the [Pd(PPh3)(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 (PPh2-) ligands. Our studies also reveal the monoligated formulation of the Pd-0 active species, which led us to synthesize related ((3)-indenyl)Pd-monophosphine catalysts which show improved catalytic performances under mild conditions. A complete mechanistic proposal to aid future catalyst developments is provided.