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

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

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