Spectroscopic Evidence for Acid-Catalyzed Disproportionation Reaction of Oxoiron(IV) Porphyrin to Oxoiron(IV) Porphyrin π-Cation Radical and Iron(III) Porphyrin.

The disproportionation reaction of oxoiron(IV) porphyrin complex () to oxoiron(IV) porphyrin π-cation radical complex () and iron(III) porphyrin complex () have been proposed in various reactions. However, there have been no report that clarifies the disproportionation reaction spectroscopically. Here, we show direct evidence for the disproportionation reaction of with absorption, H NMR, and EPR spectroscopy. Kinetic study of the disproportionation reaction with stopped flow technique can be analyzed as the second-order reaction for the concentration of proton and the first-order for the concentration of . These results allow us to propose the mechanism of the disproportionation reaction, involving the sequential addition of two protons to the oxo ligand of , to give an iron(III) porphyrin π-cation radical species, which reacts with another to afford and .