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

New CoIII–nitrosyl complexes bearing N-tetramethylated cyclam (TMC)
ligands, [(12-TMC)­CoIII(NO)]2+ (1) and [(13-TMC)­CoIII(NO)]2+ (2), were synthesized via [(TMC)­CoII(CH3CN)]2+ + NO­(g) reactions. Spectroscopic and structural characterization
showed that these compounds bind the nitrosyl moiety in a bent end-on
fashion. Complexes 1 and 2 reacted with
KO2/2.2.2-cryptand to produce [(12-TMC)­CoII(NO2)]+ (3) and [(13-TMC)­CoII(NO2)]+ (4), 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.