PHOTOCHEMICAL EPOXIDATION OF ALKENE BY VISIBLE-LIGHT IN A REDOX SYSTEM INVOLVING METALLOPORPHYRINS AND WATER

Visible light irradiation to the reaction mixture of metalloporphyrins such as antimony(V), phosphorus(V), tin(IV) and germanium(IV) tetraphenylporphyrins with methylviologen (MV2+), hydroxide ion (OH-), alkene in degassed acetonitrile-water induced reduction of MV2+ into its cation radical (MV.+) and epoxidation of the alkene. The oxygen atom of water was confirmed to be incorporated in the oxidation product epoxide by experiment using (H2O)-O-18. Detailed laser flash photolysis studies of the antimony(V) tetraphenylporphyrin system revealed that the hydroxy-coordinated antimony(V) tetraphenylporphyrin deprotonated in the triplet excited states followed by an electron transfer to MV2+ to produce MV.+ and oxo-type porphyrin complex which could transfer the oxygen atom to alkene to form the corresponding epoxide.