Oxygen transfer from Ph4PHSO5 to manganese porphyrins: kinetics and mechanism of the formation of the oxo species in homogeneous solution

Abstract

The kinetics and mechanism of the oxygenation of Mn(TMP)Cl, Mn(TDCPP)Cl and Mn(Br₈TMP)Cl by Ph₄PhSO₅ has been investigated in 1,2-dichloroethane and acetonitrile. In both solvents the reaction takes place only in the presence of species acting as axial ligands of the manganese porphyrins, e.g. imidazole or 4-tert-butylpyridine whose association constants to the metal have been measured. The rates of disappearance of the manganese porphyrin and of the appearance of the oxo-species, obtained by the stopped-flow technique, are identical within the experimental error. This finding, together with the determination of the kinetic law of the reaction allows us to suggest that the oxygen transfer process may be a simple bimolecular reaction or that, if an intermediate is formed, it is rather short lived.