Synthesis of an anthracenyl bridged porphyrin–corrole bismacrocycle. Physicochemical and electrochemical characterisation of the biscobalt μ-superoxo derivative

Dicobalt or heterobimetallic cofacial bisporphyrins are up till now amongst the very few molecular electrocatalysts able to promote the direct reduction of dioxygen to water via a four-electron process in acidic medium. Numerous studies have been devoted to elucidate the key steps of this catalytic reaction and an important result has revealed an unexpected high dioxygen affinity for a mixed valence Co(II)/Co(III) cofacial porphyrin, the key intermediate complex being a μ-superoxo derivative. At the same time, the great importance assumed by ‘Pacman’ porphyrins and the recent developments in corrole chemistry have provided the stimulation to synthesise porphyrin–corrole dyads which might also transport and/or activate dioxygen. In the present paper, we report the stepwise synthesis and characterisation of a cofacial porphyrin–corrole bearing an anthracenyl bridge, (PCA)H5 where PCA is the pentaanion of 1-(13,17-diethyl-2,3,7,8,12,18-hexamethylporphyrin–5-yl)-8-(7,8,12,13-tetramethyl-2,3,17,18-tetraphenylcorrol-10-yl) anthracene. The synthesis and characterisation of the μ-superoxo Co(III)/Co(III) complex 〚(PCA)Co2Im2〛(μ-O2) is also described.