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

Dicobalt or heterobimetallic cofacial bisporphyrins are up till now amongst the very few molecular electrocatalysts able to promote the direct reducti on of dioxygen to water via a four-electron process in acidic medium. Numer ous studies have been devoted to elucidate the key steps of this catalytic reaction and an important result has revealed an unexpected high dioxygen a ffinity for a mixed Valence Co(II)/Co(III) cofacial porphyrin, the key inte rmediate complex being a mu -superoxo derivative. At the same time, the gre at importance assumed by 'Pacman' porphyrins and the recent developments in corrole chemistry have provided the stimulation to synthesise porphyrin-co rrole dyads which might also transport and/or activate dioxygen. In the pre sent paper, we report the stepwise synthesis and characterisation of a cofa cial porphyrin-corrole bearing an anthracenyl bridge, (PCA)H-5 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. Th e synthesis and characterisation of the mu -superoxo Co(III)/Co(III) comple x [(PCA)Co(2)Im(2)](mu -O-2) is also described. (C) 2001 Academie des scien ces / Editions scientifiques et medicales Elsevier SAS.