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Pacman dinuclear Co II triphenylporphyrin-tri(pentafluorophenyl)porphyrin 1 and dinuclear Co II bis-tri(pentafluorophenyl)porphyrin 2 , anchored at the two meso -positions of a benzene linker, are synthesized and examined as electrocatalysts for the oxygen reduction reaction (ORR). Both dinuclear Co bisporphyrins are more efficient and selective than corresponding mononuclear Co II tetra(pentafluorophenyl)porphyrin 3 and Co II tetraphenylporphyrin 4 for the four-electron electrocatalytic reduction of O 2 to water. Significantly, although the ORR selectivities of the two dinuclear Co bisporphyrins are similar to each other, 1 outperforms 2 , in terms of larger catalytic ORR currents and lower overpotentials. Electrochemical studies showed different redox behaviors of the two Co sites of 1 : the Co III /Co II reduction of the Co-TPP (TPP = triphenylporphyrin) site is well-behind that of the Co-TPFP (TPFP = tri(pentafluorophenyl)porphyrin) site by 440 mV. This difference indicated their different roles in the ORR: Co II -TPFP is likely the O 2 binding and reduction site, while Co III -TPP, which is generated by the oxidation of Co II -TPP on electrodes, may function as a Lewis acid to assist the O 2 binding and activation. The positively charged Co III -TPP will have through-space charge interactions with the negatively charged O 2 -adduct unit, which will reduce the activation energy barrier for the ORR. This effect of Co-TPP closely resembles that of the Cu B site of metalloenzyme cytochrome c oxidase (C c O), which catalyzes the biological reduction of O 2 . This work represents a rare example of asymmetrical dinuclear metal catalysts, which can catalyze the 4e reduction of O 2 with high selectivity and significantly improved activity.

Significantly improved electrocatalytic oxygen reduction by an asymmetrical Pacman dinuclear cobalt(ii) porphyrin–porphyrin dyad