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 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 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.
cross-coupling
,borylation
,palladium
,acylboranes
,borylzinc
