Laser flash photolysis production of metal-oxo derivatives and direct kinetic studies of their oxidation reactions

Kinetic studies of oxidation catalysts in real time are necessarily limited by the high reactivity of the active form of the catalysts. One method for direct studies involves photochemical production of the transients in relatively large concentrations using laser flash photolysis methods and kinetic studies under single turnover conditions. Two photochemical entries to high-valent transition metal-oxo derivatives have been developed in our laboratory. In photo-oxidation reactions, irradiation of Compound II and analogues, porphyrin–iron(IV)-oxo species, gave Compound I and analogues, iron(IV)-oxo and porphyrin radical cations. In photo-induced ligand cleavage reactions, metals in n+ oxidation state with the oxygen-containing ligands perchlorate, chlorate, or nitrate were photolyzed. Homolytic cleavage of the OX bond in the ligand gives (n + 1)+ oxidation state metal-oxo species, and heterolytic cleavage gives (n + 2)+ oxidation state metal-oxo species.