REMARKABLE EFFECTS OF METAL, SOLVENT, AND OXIDANT ON METALLOPORPHYRIN-CATALYZED ENANTIOSELECTIVE EPOXIDATION OF OLEFINS

Three metal complexes of one particular homochiral porphyrin were inve stigated as catalysts for enantioselective epoxidation of unfunctional ized olefins under various reaction conditions. Much better results we re obtained with the iron and ruthenium complexes than with the mangan ese derivative. The absence of any effect of amines on the iron porphy rin-catalyzed reaction in benzene, as well as the superior results in aromatic as opposed to both more and less polar nonaromatic solvents, suggest that specific association of aromatic molecules to the metallo porphyrin affects its solution structure. Strong evidence for the invo lvement of active oxidants that are more selective than trans-dioxorut henium(VI) porphyrin is provided by the significant effect of primary oxidants on the ruthenium porphyrin-catalyzed reactions. Preliminary r esults with the iron complex of an only slightly modified porphyrin wi der the optimized reaction conditions found in this study resulted in epoxidation of styrene and 4-chlorostyrene to their epoxides with enan tiomeric excesses identical to the best ever reported. These results w ere obtained with an unprecedented large number of catalytic turnovers , requiring only 0.01 mol % of catalyst.