Multielectron Redox Afforded by a Pincer Ligand Promoting Kumada Cross‐Coupling Reactions

Abstract

AbstractThe redox‐active nature of a pincer has been exploited to conduct C−C cross‐coupling reactions under mild conditions. A nickel complex with a NNN pincer was dimeric in the solid state, and the structure displayed a Ni2N2 diamond core. In the dimeric structure, both ligand backbones house an electron, in the iminosemiquinonate form, to keep the metal's oxidation state at +2. In the presence of an aryl Grignard reagent, only 3 mol % loading the nickel complex generates a Kumada cross‐coupled product in good yield from a wide variety of aryl‐X (X= I, Br, Cl) substrates. That the ligand‐based radical remains responsible for promoting such a coupling reaction following a radical pathway is suggested by TEMPO quenching. Furthermore, a radical‐clock experiment along with tracing product distribution unambiguously supported the radical's involvement through the catalytic cycle. A series of thorough mechanistic probation, including computational DFT analysis, disclosed the cooperative action of both redox‐active pincer ligand and the metal centre to drive the reaction.