A comparison of several meso-tetraalkyl cobalt porphyrins as catalysts for the electroreduction of dioxygen

A set of cobalt porphyrins containing alkyl substituents in their meso sites were synthesized ani compared as catalysts for the electroreduction of O-2 when adsorbed on the surface of graphite electrodes. The meso substituents examined included ethyl, propyl, n-butyl and n-pentyl. All but the last exhibited high catalytic activity for the electroreduction of O-2 by four electrons. The catalytic activity was attributed to spontaneous aggregation of the porphyrins to produce structures in which pairs of cobalt centers could be bridged by O-2 molecules as previously observed for the unsubstituted and tetramethyl analogs. Copyright (C) 2001 John Wiley & Sons, Ltd.