Electrocatalytic Reduction of Oxygen by Cofacial Porphyrin

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1,2-Phenylene-bridged dicobalt diporphyrin 1 catalyzed efficiently the four-electron reduction of dioxygen to water in acidic solution. The catalytic activity of the dioxygen is strongly affected by the substitutents on the phenyl rings attached to the porphyrin macrocycles. Namely, the Koutecky-Levich plot of (limiting current)^<-1> vs (rotation rate)^<-1/2> confirms that the four electron pathway is the major for the dioxygen reduction : the number of the electrons consumed in the process determined from the slop of the polt is 3.8, while similar analysis indicates the numbers of electrons in the corresponding reduction reaction of 2 and 3 are 1.9 and 2.7, respectively. Thus, we have revealed that such a subtle structural perturbation on the porphyrin catalysts leads to significant change in the reduction pathway.