OXIDATION OF HYDROCARBONS WITH DIOXYGEN

Activation of molecular oxygen by binding to an appropriate transition-metal centre at the surface of a solid and in a complex, as well as the properties of the active, oxygen-containing species, are compared. At oxide surfaces metal-oxo groups show strongly nucleophilic properties, whereas in porphyrin complexes their character may be modified from nucleophilic to electrophilic by introduction of appropriate substituents and axial ligands. The activities of some metalloporphyrin catalysts in the liquid-phase epoxidation and hydroxylation of hydrocarbons are given. The influence of such factors as type of metal centre and character of the peripheral substituents and axial ligands on the electrophilic and nucleophilic behaviour of the metal-oxo species is shown and discussed.