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 NiII 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 NiIII , however, is required to trigger reductive elimination. The binuclear NiIII -NiIII intermediate lacks a Ni-Ni bond. Each NiIII undergoes separate, but fast reductive elimination, giving rise to NiI species. The reactivity of these binuclear Ni complexes highlights the fundamental difference between Ni and Pd in mediating bond-formation processes.