Oxidative Addition of Aryl Halides to a Ni(I)-Bipyridine Complex

The oxidative addition of aryl halides to bipyridine- or phenanthroline-ligated nickel(I) is a commonly proposed step in nickel catalysis. However, there is a scarcity of complexes of this type that both are well-defined and undergo oxidative addition with aryl halides, hampering organometallic studies of this process. We report the synthesis of a well-defined Ni(I) complex, [(CO2Etbpy)NiCl]4 (1). Its solution-phase speciation is characterized by a significant population of monomer and a redox equilibrium that can be perturbed by π-acceptors and σ-donors. 1 reacts readily with aryl bromides, and mechanistic studies are consistent with a mechanism proceeding through an initial Ni(I) → Ni(III) oxidative addition. Such a process was demonstrated stoichiometrically for the first time, affording a structurally characterized Ni(III) aryl complex.