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, [Cr^II(12-TMC)­(Cl)]⁺ (1), and the NO reactivity of its peroxo derivative, [Cr^IV(12-TMC)­(O₂)­(Cl)]⁺ (2), are described. By contrast to the previously reported Cr­(III)–superoxo complex, [Cr^III(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, [Cr^III(12-TMC)­(NO₃)­(Cl)]⁺ (3). The latter is suggested to form via a Cr­(III)–peroxynitrite intermediate. [Cr^II(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.