Dimers, dicobalt porphyrin

One such reaction that has been studied is the electrocatalytic reduction of oxygen directly to water.25,27 The electrocatalysts for this process are often based on metal porphyrins and phthalo-cyanins. Thus a graphite electrode whose surface was modified by the irreversible adsorption of a cofacial dicobalt porphyrin dimer was able to reduce oxygen under conditions where the reduction did not occur on the bare electrode itself. Similarly, a catalytic chemically modified electrode for the oxidation of chloride to chlorine has been prepared28 where the active catalyst was reported to be a ruthenium dimer, [(bipy)2(OH)RulvORuvO(bipy)2]4+, which was reduced to the corresponding [Rum-RuIV] dimer during the reaction. 

Figure 3.64 Dicobalt porphyrin dimers with wide and narrow bites.

Collman, J.P, M. Marrocco, P. Denisevich, C. Koval, and F.C. Anson (1979). Potent catalysis of the electroreduction of oxygen to water by dicobalt porphyrin dimers adsorbed on graphite electrodes. J. Electroanal. Chem. 101, 117-122. 

The discussion of porphyrin complexes in the activation of dioxygen in solution can be readily subdivided into discussions of monomeric systems and dimeric systems. The dimeric systems (cofacial metallodi-porphyrins) have recently been reviewed by Collman, Wagenknecht, and Hutchison (73). That review highlights the significant amount of research stimulated by the initial discovery by Collman and co-workers (74), confirmed later by Chang and co-workers (75), that dicobalt cofacial diporphyrins can promote the direct four-electron reduction of dioxygen to water. 

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