Ligand-Assisted Electron Transfer Drives N−O Bond Cleavage Enabling Heteronuclear Copper Oxidative Addition

The redox pathways of the copper species are yet in dispute and a concerned subject in transition metal catalysis. Herein, a complex yet interesting reaction mechanism is proposed for the oxidative addition of N−O bonds in Cu(I)-catalyzed cross-coupling reactions of oxime esters. The calculations reveal that carboxylate counterions can function as bridging ligands to facilitate electron transfer and enable bimetallic Cu-mediated oxidative addition. Distinct from the conventional two-electron transfer pathway that oxidizes Cu(I) to Cu(III), bimetallic oxidative addition involves a stepwise single-electron transfer, and dinuclear Cu(I) centers are oxidized to Cu(II) asynchronously. Natural population analysis of charge and spin corroborate the electron transfer in the stepwise bimetallic oxidative addition and validate the proposed mechanism. These findings shed light on the intricate behavior of copper species and challenge the common mechanistic proposal for the reaction of Cu(I) with oxime acetates, thus providing fresh perspectives into the mechanistic aspect of the copper-catalyzed coupling reactions.