Reaction of a Nitrosyl Complex of Co(II)-Porphyrin with Hydrogen Peroxide: Formation of a Porphyrin Radical Cation

A nitrosyl complex of Co(II)-porphyrinate, [Co^II(TTMPP^2-)(NO)], 1 [TTMPPH₂=5,10,15,20-tetrakis(3,4,5-trimethoxyphenyl)porphyrin] having {Co(NO)}⁸ configuration has been synthesized and characterized spectroscopically as well as structurally. Complex 1 in dichloromethane:acetonitrile (1 : 4, v/v) solution at -40 °C reacts with hydrogen peroxide (H₂O₂) to result in the corresponding nitrite (NO₂ ^-) complex, [Co^III(TTMPP^2-)(NO₂ ^-)], 2. The formation of a Co(III)-peroxynitrite intermediate is presumed in this reaction based on the characteristic phenol ring nitration test. From spectroscopic studies, formation of [Co^IV=O] species followed by a Co(III)-porphyrin radical complex was observed during the course of the reaction.