Electrochemistry and Spectroelectrochemistry of Cobalt Bis(phenolate)Dipyrrins

Three cobalt bis(phenolate)dipyrrins with different meso-tetraaryl groups were synthesized and characterized by UV−visible spectroscopy, 1H NMR spectroscopy and mass spectrometry in nonaqueous media. The structures of the investigated compounds are shown in Chart 1. The redox potentials for each electrode reaction of the above compounds were measured by cyclic voltammetry in CH2Cl2, PhCN, DMSO and pyridine containing 0.1 M TBAP and the spectra of the electroreduced and electroxidized species were obtained by thin-layer UV-visible spectroelectrochemistry under the same solution conditions. The electrochemical and spectroelectrochemical data were then analyzed as a function of the metal oxidation state, solvent properties, meso-substituents and non-innocence (or innocence) of the dipyrrin ligand. The axial ligand binding properties with the solvent (e.g. PhCN, DMSO or pyridine) and other small molecules (e.g. CO or NH3) were investigated and comparisons were made with related four-, five- and six-coordinate cobalt corroles under the same solution conditions. An X-ray crystal structure for the F5Ph derivative, compound 1, with two axial NH3 ligands is also presented. Figure 1