A Combined Experimental/Computational Study of the Mechanism of a Palladium‐Catalyzed Bora‐Negishi Reaction. Issue 51 (10th August 2017) - Campos, Jesús
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 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. Abstract : The introduction of borylzinc reagents in palladium‐catalyzed borylations led to the first systematic method for the synthesis of acylboranes, a rare class of organoboron compounds. Here a critical mechanistic insight into this new bora‐Negishi methodology is offered by combining experimental and computational efforts. The studies demonstrate the monoligated nature of the Pd active species and guided the access to related Pd precursors with improved performance.