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.