Synthesis and Sulfur Oxygenation of a (N₃S)Ni Complex Related to Nickel-Containing Superoxide Dismutase

A nickel(II) thiolate complex incorporating three N-donor types (amino, amido, and imidazole) has been synthesized and characterized. The (N3S)Ni complex, [N-{2-[(2-mercapto-2-methylpropyl)amino]ethyl}-1-methylimidazole-2-carboxamido]nickel(II) (1), is stable in the presence of O2 but readily forms the sulfinato (RSO2−) derivative 2 upon the addition of H2O2. Electrochemical investigations of 1 reveal an irreversible sulfur-based oxidation at +0.17 V vs Fc+/Fc (200 mV/s) that shifts to +0.81 V upon oxidation to 2. Density functional theory investigations of 1 reveal a highest occupied molecular orbital that is predominantly sulfur-based, consistent with the observed sulfur-based oxidation and O2 stability.