Dioxygen moieties electron transfer

It was observed in a 2005 article that Co(II) porphyrin-Co(III) corrole dimers are more effective dioxygen reduction electrocatalysts than analogous Co(III)-Co(III) corrole dimers or monomeric Co(III) corroles [145], The heterodimers operated effectively at lower overpotentials and promote complete reduction to water (the average number of electrons transferred per 02 molecule approaches 4 in the best porphyrin-corrole catalyst). It was suggested that the inferior catalytic performance of the corrole homodimers could be due to a reduction in the basicity of the activated intermediate when two Co(III) moieties are involved, leading to a less favorable 4-electron reduction. Heterobimetallic catalysts containing formally Co (IV) corroles were also examined as potential dioxygen reduction catalysts [146]. 

Moreover, the 1 1 Co—O2 complexes are paramagnetic. From the small Co hyperfine splitting, it is deduced that the single unpaired electron resides primarily on the dioxygen moiety. " From other experiments it is apparent that net transfer of electron density from the metal onto the dioxygen varies... 

By determining the rate constants for the various steps in Scheme 8, it has been demonstrated [78] that electron or proton transfer to the metalloporphyrin-dioxygen moiety weakens the 0-0 bond, thereby... 

Planar tetradentate ligands afford the most active catalysts. Electron transfer from the aniline moiety to a hydroxocobalt(III) is believed to play a key role in the process [31]. Dioxygen probably reoxidizes the cobalt(II) complex formed. 

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