Electrochemical and Spectroelectrochemical Investigations of Mono‐ and Binuclear Cobalt( II ) Complexes of “Figure‐Eight” Octapyrrolic Macrocycles

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Abstract In this paper, electrochemical investigations of a set of three cyclooctaphyrin complexes containing divalent cobalt are reported. These complexes are the homodinuclear cobalt‐cobalt complex Co2L1 with the ligand H4L1, the mononuclear cobalt complex CoH2L2 and the heterodinuclear copper(II)‐cobalt complex CoCuL2 with the ligand H4L2. All of these species undergo two reduction and three oxidation processes, all of which are reversible one‐electron transfers. The two reduction and first two oxidation steps are ligand‐centered, as confirmed by spectroelectrochemical investigations. In contrast, the third oxidation corresponds to a metal‐centered reversible one‐electron transfer. The metal‐centered oxidation steps occur at lower potentials than the third oxidation steps of the free bases. UV/Visible spectral changes observed during oxidation confirm a metal‐centered oxidation generating a cobalt(III) cation, which is rather unusual when compared with cobalt porphyrin complexes, in which the oxidation of the metal usually occurs before the oxidation of the ligand. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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