Identifying a Terminal Nickel–Oxygen Complex Bearing an Unsymmetrical β-Diketiminate Ligand

Nickel–oxygen species are proposed as key intermediates in various biological nickel-containing catalytic and enzymatic processes. We report the successful synthesis and crystallographic characterization of the first terminal nickel–oxygen complex featuring a tridentate N-aryl-N′-methylpyridyl β-diketiminate ligand. This species can be formally classified as either a nickel-oxo (NiIII=O) or nickel-oxyl (NiII–O•) species, exhibiting dual bonding characteristics. The experimental observations and DFT calculations suggest the bonding is best described as a resonance hybrid of NiIII=O and NiII–O• states, with the NiII–O• form likely predominant.