Mechanism of nickel-catalyzed direct carbony-Heck coupling reaction the crucial role of

    We present a detailed DFT mechanistic study on the first Ni-catalyzed direct carbonyl-Heck coupling of aryl triflates and aldehydes to afford ketones. The precatalyst Ni(COD)2 is activated with the phosphine (phos) ligand, followed by coordination of the substrate PhOTf, to form [Ni(phos)(PhOTf)] for intramolecular PhOTf to Ni(0) oxidative addition. The ensuing phenyl-Ni(II) triflate complex substitutes benzaldehyde for triflate by an interchange mechanism, leaving the triflate anion in the second coordination sphere held by Coulomb attraction. The Ni(II) complex cation undergoes benzaldehyde CvO insertion into the Ni–Ph bond, followed by β-hydride elimination, to produce Ni(II)-bound benzophenone, which is released by interchange with triflate. The resulting neutral Ni(II) hydride complex leads to regeneration of the active catalyst following base-mediated deprotonation/reduction. The benzaldehyde CvO insertion is the rate-determining step. The triflate anion, while remaining in the second sphere, engages in electrostatic interactions with the first sphere, thereby stabilizing the intermediate/transition state and enabling the desired reactivity. This is the first time that such second-sphere interaction and its impact on crosscoupling reactivity has been elucidated. The new insights gained from this study can help better understand and improve Heck-type reaction.