Chromium(IV)–Peroxo Complex Formation and Its Nitric Oxide Dioxygenase Reactivity

The O2 and NO reactivity of a Cr­(II) complex bearing a 12-membered tetraazamacrocyclic N-tetramethylated cyclam (TMC) ligand, [CrII(12-TMC)­(Cl)]+ (1), and the NO reactivity of its peroxo derivative, [CrIV(12-TMC)­(O2)­(Cl)]+ (2), are described. By contrast to the previously reported Cr­(III)–superoxo complex, [CrIII(14-TMC)­(O2)­(Cl)]+, the Cr­(IV)–peroxo complex 2 is formed in the reaction of 1 and O2. Full spectroscopic and X-ray analysis revealed that 2 possesses side-on η2-peroxo ligation. The quantitative reaction of 2 with NO affords a reduction in Cr oxidation state, producing a Cr­(III)–nitrato complex, [CrIII(12-TMC)­(NO3)­(Cl)]+ (3). The latter is suggested to form via a Cr­(III)–peroxynitrite intermediate. [CrII(12-TMC)­(NO)­(Cl)]+ (4), a Cr­(II)–nitrosyl complex derived from 1 and NO, could also be synthesized; however, it does not react with O2.