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.

Promotion of oxygen reduction by a bio-inspired tethered iron phthalocyanine carbon nanotube-based catalyst

“…Alongside the pyrolysis strategy, state-of-the-art synthetic techniques have been used to modify the geometric and electronic structure of metal macrocycles and its derivatives to improve its performance toward ORR 16,28,29 . However, most of the synthetic strategies focus on four-coordinated systems in an effort to change the accommodating space for oxygen molecules between cofacial porphyrins in its dyads and little attention has been paid to tuning the coordination environment of the Fe ion 30,31 .…”

Electrochemistry of Fe(IV) and Mn(IV) corroles containing meso-dichlorophenyl substituents and the use of these compounds as catalysts for the electroreduction of dioxygen in acid media

“…We have earlier examined numerous cobalt triarylcorroles 16,17,19,24,25 phenyl rings of a triarylcorrole will significantly affect the catalytic activity of these compounds towards the reduction of O 2 .…”

Efficient Two‐Step Synthesis of Face‐to‐Face meso‐Substituted Bis(corrole) Dyads

“…For many years, we have been interested in the synthesis and characterization of cofacial bis(porphyrin), bis(corrole), and porphyrin-corrole dyads, where the two tetrapyrrolic macrocycles are covalently linked by a rigid or a more flexible spacer. [9,14,16,[25][26][27][28][29][30][31][32][33] As a result of the close proximity of the two macrocycles, these dyads can be used in the reduction of oxygen to water, [34,35] in the oxidation of water to oxygen, [36] and probably in molecular recognition. In addition to this work, linear bis(corrole)s and porphyrin-corrole dyads have also been reported by other groups.…”

“…[27][28][29]33,[42][43][44] The ability of bis(cobalt) complexes of porphyrin-corrole and bis(corrole) dyads to catalyze efficiently the reduction of oxygen to water was more interesting. [34,35] Despite their enhanced catalytic activities, these β-substituted porphyrincorrole or bis(corrole) dyads suffered from multistep syntheses that afforded final complexes in less than 1 % overall yield. meso-Substituted porphyrins are readily available, in comparison to their β-substituted counterparts, from reactions of pyrrole or dipyrromethane derivatives.…”