Kinetics of the chemical oxidation of (5,10,15,20-tetraphenyl-21H,23H-porphinato)(chloro)(aqua)iridium(III)

Abstract

The oxidation of (Cl)(H₂O)IrTPP with atmospheric oxygen in the presence of concentrated H₂SO₄ accompanied by coordination of molecular O₂ and substitution of axial ligands was studied spectrophotometrically. In 16.785–18.09 М H₂SO₄ at 298–318 K, (Cl)(H₂O)IrTPP experienced two single-electron oxidations in sequence: with an increase in the oxidation state of the iridium cation and with formation of the π-radical cation form (HSO₄)Ir^IVTPP^•+ oxidized at the aromatic ligand (k²⁹⁸ = 7.2 × 10^–6 mol^–1 L s^–1). Referring to the literature data on the oxidation of (Cl)(H₂O)IrTPP in AcOH and CF₃COOH, it was shown that the medium acidity and the nature of the axial ligands affect the electron removal site in the chemical oxidation of (Cl)(H₂O)IrTPP with atmospheric oxygen in proton-donor solvents.