Operando Analysis of Nickel Catalyst Speciation in Reductive Biaryl Synthesis Using Thin Layer Electrochemistry and a Microelectrode

Operando insights into nickel speciation during nickel-catalyzed cross-electrophile coupling reactions could play a major role in advancing these reactions, but analytical methods capable of providing such insights have not yet been developed. In this study, we integrate a thin-layer electrode (TLE) platform with microelectrode (ME) voltammetry to enable operando monitoring of nickel species during the reductive homocoupling of aryl halides. This approach allows for identification and quantitation of Ni-based intermediates, yielding insight into the temporal evolution of catalyst speciation and their kinetic profiles. The methodology reveals previously unrecognized patterns in nickel speciation, including accumulation of both mono- and bisaryl Ni^II species during the reactions and variation in the predominant Ni oxidation state (Ni⁰/Ni^II) with different quantities of the bipyridyl ligand. These results establish the utility of this technique and provide a foundation for its adaptation to other metal-catalyzed reactions.