title: Cobalt(III) corroles as electrocatalysts for the reduction of dioxygen: reactivity of a monocorrole, biscorroles, and porphyrin-corrole dyads.
abstract: Three series of cobalt(III) corroles were tested as catalysts for the electroreduction of dioxygen to water. One was a simple monocorrole represented as (Me(4)Ph(5)Cor)Co, one a face-to-face biscorrole linked by an anthracene (A), biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or dibenzothiophene (S) bridge, (BCY)Co(2) (with Y = A, B, X, O or S), and one a face-to-face bismacrocyclic complex, (PCY)Co(2), containing a Co(II) porphyrin and a Co(III) corrole also linked by one of the above rigid spacers (Y = A, B, X, or O). Cyclic voltammetry and rotating ring-disk electrode voltammetry were both used to examine the catalytic activity of the cobalt complexes in acid media. The mixed valent Co(II)/Co(III) complexes, (PCY)Co(2), and the biscorrole complexes, (BCY)Co(2), which contain two Co(III) ions in their air-stable forms, all provide a direct four-electron pathway for the reduction of O(2) to H(2)O in aqueous acidic electrolyte when adsorbed on a graphite electrode, with the most efficient process being observed in the case of the complexes having an anthracene spacer. A relatively small amount of hydrogen peroxide was detected at the ring electrode in the vicinity of E(1/2) which was located at 0.47 V vs SCE for (PCA)Co(2) and 0.39 V vs SCE for (BCA)Co(2). The cobalt(III) monocorrole (Me(4)Ph(5)Cor)Co also catalyzes the electroreduction of dioxygen at E(1/2) = 0.38 V with the final products being an approximate 50% mixture of H(2)O(2) and H(2)O.
authors.affiliation: Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA. kkadish@uh.edu
authors.forename: Karl M
authors.initials: KM
authors.lastname: Kadish
authors.forename: Laurent
authors.initials: L
authors.lastname: Frémond
authors.forename: Zhongping
authors.initials: Z
authors.lastname: Ou
authors.forename: Jianguo
authors.initials: J
authors.lastname: Shao
authors.forename: Chunnian
authors.initials: C
authors.lastname: Shi
authors.forename: Fred C
authors.initials: FC
authors.lastname: Anson
authors.forename: Fabien
authors.initials: F
authors.lastname: Burdet
authors.forename: Claude P
authors.initials: CP
authors.lastname: Gros
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Barbe
authors.forename: Roger
authors.initials: R
authors.lastname: Guilard