Cerium(IV)-driven oxidation of water catalyzed by mononuclear ruthenium complexes

This paper reviews results from study of mononuclear ruthenium complexes capable of catalyzing the oxidation of water to molecular oxygen. These catalysts may be classified into three groups, with different rate laws associated with O₂ evolution. In one class, O₂ evolution proceeds via radical coupling of the oxygen atom of an Ru^V=O species with a hydroxocerium(IV) ion. O₂ evolution catalyzed by the second class occurs via acid–base reaction of the oxygen atom of an Ru^V=O species with a water molecule. In the third group, the dominant mechanism is oxo–oxo radical coupling between two Ru^V=O species. Several significant properties of the oxidant Ce(IV) are also discussed, including the singlet biradical character of the hydroxocerium(IV) ion.