Axial ligand effects on the redox reactions of manganese porphyrins

A systematic study for the effect of axially coordinated monovalent anions on the electrode reactions of several manganese porphyrins in acetonitrile is presented. Potential shifts of the metal-centered reduction with changes in counterion were related to the degree of Mn(III)-counterion interaction . In the electrochemically induced ligand exchange, perchlorate anion repla ces the other anions as axial ligand coordinated to Mn(III) at oxidation po tential less than the first oxidation of manganese porphyrins. Formation co nstants for axial ligation of OH- are calculated. One-electron oxidation of dihydroxide coordinated manganese porphyrins generate oxomanganese(IV) por phyrin complexes electrochemically. O=(MnOEP)-O-IV(OH) is more thermodynami cally stable than O=(MnTPP)-T-IV(OH), while O-Mn(IV)TpFPP(OH) cannot be gen erated electrochemically. In the presence of styrene or cyclohexene, the ab sorption spectra of oxomanganese(IV) porphyrins are changed to form mangane se(III) porphyrins gradually, which indicates the oxygen atom transfer from oxomanganese(IV) porphyrins to the substrates.