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FeV=O in Bio-inspired Olefin Epoxidation Catalysis.

Recent Research from the group of Professor Lawrence Que.

Nearly quantitative conversion of cyclooctene to its epoxide (200 turnovers) can be obtained within one minute at 0 oC using H2O2 as oxidant and [FeII(TPA)(NCMe)2]2+ (for structure of TPA, see scheme) as catalyst (0.5 mol% in 1:2 CH3CN/HOAc solvent). These results by postdoctoral associate Ruben Mas-Balleste will soon appear in the Journal of the American Chemical Society as part of an effort to discover efficient methods for catalytic epoxidation using inexpensive oxidants. The approach in Prof. Larry Que’s laboratory is inspired by iron enzymes that activate O2. Insight into the nature of the active species has been gleaned from spectroscopic experiments at low temperature. In the absence of substrate, FeIII-OOH and FeIV=O intermediates can be observed, but neither is kinetically competent as the active epoxidizing agent. Several lines of evidence support the hypothesis that HOAc binds to the FeIII-OOH moiety and promotes by protonation the heterolysis of the O-O bond to form an O=FeV-OAc oxidant. Such a proton-assisted O-O bond cleavage is generally accepted to be the key step in generating the active oxidant in the cytochrome P450 mechanism.



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