Binuclear, High-Valent Nickel Complexes: Ni−Ni Bonds in Aryl–Halogen Bond Formation

Metal–metal bonds play a vital role in stabilizing key intermediates in bond-formation reactions. We report that binuclear benzo[h]quinoline-ligated Ni^II complexes, upon oxidation, undergo reductive elimination to form carbon–halogen bonds. A mixed-valent Ni(2.5+)–Ni(2.5+) intermediate is isolated. Further oxidation to Ni^III, however, is required to trigger reductive elimination. The binuclear Ni^III–Ni^III intermediate lacks a Ni−Ni bond. Each Ni^III undergoes separate, but fast reductive elimination, giving rise to Ni^I species. The reactivity of these binuclear Ni complexes highlights the fundamental difference between Ni and Pd in mediating bond-formation processes.