Reactions of Co(III)–Nitrosyl Complexes with Superoxide and Their Mechanistic Insights

New Co^III–nitrosyl complexes bearing N-tetramethylated cyclam (TMC) ligands, [(12-TMC)­Co^III(NO)]²⁺ (<b>1</b>) and [(13-TMC)­Co^III(NO)]²⁺ (<b>2</b>), were synthesized via [(TMC)­Co^II(CH₃CN)]²⁺ + NO­(g) reactions. Spectroscopic and structural characterization showed that these compounds bind the nitrosyl moiety in a bent end-on fashion. Complexes <b>1</b> and <b>2</b> reacted with KO₂/2.2.2-cryptand to produce [(12-TMC)­Co^II(NO₂)]⁺ (<b>3</b>) and [(13-TMC)­Co^II(NO₂)]⁺ (<b>4</b>), respectively; these possess O,O′-chelated nitrito ligands. Mechanistic studies using ¹⁸O-labeled superoxide (¹⁸O₂^•–) showed that one O atom in the nitrito ligand is derived from superoxide and the O₂ produced comes from the other superoxide O atom. Evidence supporting the formation of a Co–peroxynitrite intermediate is also presented