| Abstract
| - 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 werealso investigated as to their ability to catalyze the electroreduction of dioxygen in aqueous 1 M HClO4 or HCl whenadsorbed on a graphite electrode. The characterized compounds are represented as (PCY)H2Co, where P = aporphyrin 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 thecobalt center of the corrole is observed for singly and doubly oxidized (PCY)H2Co, with the exact stoichiometry ofthe reaction depending upon the spacer size and the concentration of Cl- added to solution. No Cl- bindingoccurs 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 atpotentials 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 forthe same three dyads in PhCN and 0.1 M TBAP. The potential for the catalytic electroreduction of O2 in HCl shiftsnegatively by 60 to 70 mV as compared to E1/2 values in 1 M HClO4, consistent with the binding of Cl- to theCo(IV) form of the corrole and its rapid dissociation after electroreduction to Co(III) at the electrode surface.
- Three face-to-face free-base porphyrin−cobalt corrole dyads with different spacers were characterized by electrochemistry and UV−visible spectroelectrochemistry, and their reactivity with Cl- or O2 was investigated.
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