Three face-to-face linked porphyrin−corrole dyads were investigated as to their electrochemistry, spectroelectrochemistry, and chloride-binding properties in dichloromethane or benzonitrile. The same three compounds were also investigated as to their ability to catalyze the electroreduction of dioxygen in aqueous 1 M HClO₄ or HCl when adsorbed on a graphite electrode. The characterized compounds are represented as (PCY)H₂Co, where P = a porphyrin dianion; C = a corrole trianion; and Y = a biphenylenyl, 9,9-dimethylxanthenyl, or anthracenyl spacer, which links the two macrocycles in a face-to-face arrangement. An axial binding of one or two Cl^- ligands to the cobalt center of the corrole is observed for singly and doubly oxidized (PCY)H₂Co, with the exact stoichiometry of the reaction depending upon the spacer size and the concentration of Cl^- added to solution. No Cl^- binding occurs for the neutral or reduced forms of the dyad, which contrasts with what is seen for the monocorrole, (Me₄Ph₅Cor)Co, where a single Cl^- ligand is added to the Co(III) corrole in PhCN. The Co(III) form of the corrole in (PCY)H₂Co also appears to be the catalytically active species in the electroreduction of dioxygen, which occurs at potentials associated with the Co(IV)/Co(III) reaction, that is, 0.35 V in 1 M HClO₄ as compared to 0.31−0.42 V for the same three dyads in PhCN and 0.1 M TBAP. The potential for the catalytic electroreduction of O₂ in HCl shifts negatively by 60 to 70 mV as compared to E_1/2 values in 1 M HClO₄, consistent with the binding of Cl^- to the Co(IV) form of the corrole and its rapid dissociation after electroreduction to Co(III) at the electrode surface.

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