Kinetic and thermodynamic parameters of copper-dioxygen interaction with different oxygen binding modes

Kinetic and thermodynamic parameters for metal ion-O₂ interaction have been obtained for a variety of copper(I) complexes with different binding modes for dioxygen. In general, favorable binding enthalpies of up to 80 kJ mol^-1 are compensated by strongly negative reaction entropies up to -220 J K^-1 mol^-1 restricting the range of overall stabilities. Sequential formation of superoxo and peroxo complexes, as well as concomitant formation of η¹:η¹ and η²:η² μ-peroxo complexes has been established by low-temperature stopped-flow experiments. In several cases, pseudoreversible binding of dioxygen is followed by an irreversible oxidation of the organic ligand. A recent result is the identification of a rapid equilibrium between an η²:η² μ-peroxo complex and the isomeric bis-μ oxo compound with broken O-O bond which may be fundamental to several O₂ dependent redox enzymes.