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

A set of cobalt porphyrins containing alkyl substituents in their meso sites were synthesized and compared as catalysts for the electroreduction of O2 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 O2 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 O2 molecules as previously observed for the unsubstituted and tetramethyl analogs. Copyright © 2001 John Wiley & Sons, Ltd.