Reactions of a chromium(III)-superoxo complex and nitric oxide that lead to the formation of chromium(IV)-oxo and chromium(III)-nitrito complexes

The reaction of an end-on Cr(III)-superoxo complex bearing a 14-membered tetraazamacrocyclic TMC ligand, [Cr^III(14-TMC)(O₂)(Cl)] ⁺, with nitric oxide (NO) resulted in the generation of a stable Cr(IV)-oxo species, [Cr^IV(14-TMC)(O)(Cl)]⁺, via the formation of a Cr(III)-peroxynitrite intermediate and homolytic O-O bond cleavage of the peroxynitrite ligand. Evidence for the latter comes from electron paramagnetic resonance spectroscopy, computational chemistry and the observation of phenol nitration chemistry. The Cr(IV)-oxo complex does not react with nitrogen dioxide (NO₂), but reacts with NO to afford a Cr(III)-nitrito complex, [Cr^III(14-TMC)(NO₂)(Cl)] ⁺. The Cr(IV)-oxo and Cr(III)-nitrito complexes were also characterized spectroscopically and/or structurally.