Comparison of the electronic and vibrational spectra of complexes of protoporphyrin-IX, hemeoctapeptide, and heme proteins

We propose herein a bio-mimetic catalytic structure as a new approach to increase the oxygen reduction catalytic selectivity of transition metal complexes. As in biological systems, where there is a series of mediators between the active site and the surface, that lowers the activation energy of the overall reaction and increases its selectivity, we use here a structure where a molecular catalyst Fe(III)tetrakis(1-methyl-4-pyridyl) porphyrin is bonded to a surface via a benzimidazole mediator. Using electron paramagnetic resonance (EPR), UV–vis spectroscopy and electrochemical measurements, we compared the ORR activity of the molecular catalyst with and without benzimidazole and show that this ligand strongly influences the selectivity of the reaction and shifts it from the 2 to the 2+2-electron reduction.