Manganese porphyrin multilayer films assembled on ITO electrodes via zirconium phosphonate chemistry: Chemical and electrochemical catalytic oxidation activity

A supported manganese porphyrin-based oxidation catalyst was prepared by zirconium-phosphonate multilayer assembly with [5,15-bis(4-phenylphosphonic acid)porphyrinato] manganese(III) chloride (2) and zirconium(IV) ions on indium-tin oxide (ITO) electrodes. The multilayer assembly technique gave good control over the catalyst loading on the surface as evidenced by the consistent growth of the deposited porphyrin layers. When manganese porphyrin catalysts were supported on ITO, they were more resistant to degradation than their homogeneous counterpart, displaying longer lifetimes and higher turnover number for the epoxidation of styrene. Attempts to exploit the film-based catalysts electrochemically, using the solvent (water) as the source of oxygen for olefin epoxidation were only partially successful. Epoxide product was obtained electrocatalytically, but in competition with the electrocatalytic conversion of water to hydrogen peroxide, which, in turn, inactivated the catalyst by irreversibly oxidizing the porphyrin ligand.