Unravelling the Mechanism of Nickel Mediated Cross‐Electrophile‐ Electrophile Coupling Between Katritzky Salts and Acid Chlorides

Abstract

AbstractModern nickel‐mediated cross‐electrophile coupling reactions devoid of organometallic nucleophiles have garnered a great deal of interest due to their ability to enhance functional group compatibility. Despite the recent advances in the field, various mechanistic pathways, such as radical chain and sequential oxidative addition, in addition to finding the active nickel species and reductant, render the reaction complex. Although the reduction of Ni(II) complexes by heterogeneous Mn could produce either Ni(I) or Ni(0) species, the latter is more generally proposed as an active species. Likewise, Ni(I) mediated reduction of pyridinium salts is commonly invoked to generate the transient alkyl radicals. In stark contrast, we present a comprehensive mechanistic examination and experimental evidence for the intermediacy of Ni(I) species, a synergistic reduction of pyridinium salts by Ni(I) and Mn. Using a combination of kinetic analysis, control experiments, and spectroscopic methods, the rate‐limiting reductive alkylation and resting state Ni(II) species have been identified.