CHIRAL MODEL COMPLEXES FOR METHANE MONOOXYGENASE AND THEIR ASYMMETRICCATALYSIS OF STYRENE EPOXIDATION

Four chiral mu-phenolato dinuclear (VO)(2), Cr-2, Mn-2, and Fe-2 compl exes with a phenolic ligand bearing two L-phenylanalines as complexing arms have been synthesized and characterized. Asymmetric epoxidations of styrene with these complexes as chiral models of methane monooxyge nase (MMO) and iodosylbenzene as an oxygen atom donor have been studie d. The results reveal that the Mn-2 complex catalyzes asymmetric epoxi dation of styrene with the formation of R-(+)-styrene oxide in 42.8% e .e. Contrarily, the (VO)(2) analogue complex gives S-(-)-styrene oxide in 19.2% e.e. EPR investigations suggest that the catalyzed epoxidati ons with the Mn-2, Cr-2 and Fe-2 complexes proceed via high-valent oxo metal intermediates; while in the case of the (VO)(2) complex as catal yst, the epoxidation proceeds by a pathway that involves a complex of metal-iodine ligand. The catalytic activities of the complexes decreas e in a sequence of Mn-2 > Cr-2 > (VO)(2) > Fe-2.