Factors influencing the redox reactions of iron porphyrins

The electrochemical research presented describes the interacting effects of porphyrin ring basicity and axial coordination on the standard redox potential for the metal centered reactions of a number of synthetic iron porphyrins. Elucidation of these factor effects was considered as the first step toward the characterization, prediction and control of metalloporphyrin reactivity. The redox potential of the Fe(III)/Fe(II) couple was 'tuned' over a 1300 mV potential range by appropriate selection of the Fe(III) counterion and/or nitrogenous base coordinated to either the Fe(III) or Fe(II) center. The redox potential as well as the stoichiometry of both the electrode reactant and product were modified by changing the solvent in which the redox reaction was carried out. Variations in these factors also produced systematic changes in the number of electrons transferred and changes in the electron transfer mechanisms.