Electrochemical and spectroelectrochemical investigations of mono- and binuclear cobalt(II) complexes of "Figure-Eight" octapyrrolic macrocycles

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. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.