Abstract
Here, we report a comparative study of nitric oxide oxidation (NOO) reactions of CoIII-peroxo (CoIII–O22–) and Co-nitrosyl ({CoNO}8) complexes bearing the same N4-donor ligand (HMTETA) framework. In this regard, we prepared and characterized two new [(HMTETA)CoIII(O22–)]+ (2, S = 2) and [(HMTETA)Co(NO)]2+ (3, S = 1) complexes from [(HMTETA)CoII(CH3CN)2]2+ (1). Both complexes (2 and 3) are characterized by different spectroscopic measurements, including their DFT-optimized structures. Complex 2 produces CoII-nitrato [(HMTETA)CoII(NO3–)]+ (CoII–NO3–, 4) complex in the presence of NO. In contrast, when 3 reacted with a superoxide (O2•–) anion, it generated CoII-nitrito [(HMTETA)CoII(NO2–)]+ (CoII–NO2–, 5) with O2 evolution. Experiments performed using 18/16O-labeled superoxide (18O2•–/16O2•–) showed that O2 originated from the O2•– anion. Both the NOO reactions are believed to proceed via a presumed peroxynitrite (PN) intermediate. Although we did not get direct spectral evidence for the proposed PN species, the mechanistic investigation using 2,4-di-tert-butylphenol indirectly suggests the formation of a PN intermediate. Furthermore, tracking the source of the N-atom in the above NOO reactions using 15N-labeled nitrogen (15NO) revealed N-atoms in 4 (CoII–15NO3–) and 5 (CoII–15NO2–) derived from the 15NO moiety.
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