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

Abstract

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 pre-catalysts to Pd active species has been demonstrated. The non-innocent behavior of the PPh ligands of the [Pd(PPh)Cl] pre-catalyst under activation conditions has been probed both experimentally and computationally, revealing the formation of a trimetallic Pd species bearing bridging phosphide (PPh ) ligands. Our studies also reveal the monoligated formulation of the Pd active species, which led us to synthesize related (η-indenyl)Pd-monophosphine catalysts which show improved catalytic performances under mild conditions. A complete mechanistic proposal to aid future catalyst developments is provided.