Redox properties of copper tetra(4-N,N′,N″-trimethylanilinium)porphyrin. Electrochemical and spectral studies

The redox behaviour of the copper tetra(4-N,N′,N″-trimethylanilinium)porphyrin (abbreviated as CuTMAP) has been studied in acetonitrile and aqueous solutions using differential pulse polarography, cyclic voltammetry, a rotating ring-disc electrode and spectroelectrochemical methods. The reduction of Cu^II is characterized by a two-step one-electron reduction. The Cu^II/Cu^ITMAP and Cu^II/Cu^IIITMAP couples show reversible redox behaviour in acetonitrile and have redox potentials of -0.18 and +0.45 V, respectively. In aqueous solutions and at low concentrations, the Cu^IITMAP complex is characterized by a Soret band at 412 nm and is reduced at (-0.56-0.057 pH) V, while a band in the 393-398 nm range and a reduction peak at (-0.79-0.057 pH) V predominate at high CuTMAP concentrations. E_1/2 for the oxidation of Cu^IITMAP is +0.87 V in aqueous solutions and is independent of pH. The decomposition of water is described in terms of a catalytic cycle which involves the Cu^IIITMAP complex.