Acid-catalyzed disproportionation of oxoiron(IV) porphyrins to give oxoiron(IV) porphyrin radical cations

Disproportionation of oxoiron(IV) porphyrin (Compound II) to oxoiron(IV) porphyrin radical cation (Compound I) was studied in three P450 model systems with different electronic structures. Direct conversion of Compound II to Compound I has been observed for 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin (TDCPP) in acid-catalyzed reactions in a mixed solvent of acetonitrile and water (1:1, v/v) containing excess m-CPBA oxidant, with a second-order rate constant of (1.3 ± 0.2) × 102 M− 1 s− 1. The acid-catalyzed disproportionation heavily depends on the electron demand of the substituted aryl groups on the porphyrin macrocycle. The disproportionation equilibrium constants show drastic change for the three porphyrin systems.