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 PdII pre-catalysts to Pd0 active species has been demonstrated. The non-innocent behavior of the PPh3 ligands of the [Pd(PPh3 )2 Cl2 ] 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 Pd0 active species, which led us to synthesize related (η3 -indenyl)Pd-monophosphine catalysts which show improved catalytic performances under mild conditions. A complete mechanistic proposal to aid future catalyst developments is provided.
Keywords: acylboranes; borylation; borylzinc; cross-coupling; palladium.
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