Single Turnover Epoxidation of Propylene by α-Complexes (Fe^III–O^•)_α on the Surface of FeZSM-5 Zeolite

Abstract

Single turnover epoxidation of propylene by α-complexes (FeIII–O•)α on the surface of FeZSM-5 zeolite was studied in the temperature range from +25 °C to −60 °C. After extraction, the reaction products were identified by gas chromatography (GC), gas chromatography–mass spectrometry (GC-MS), and nuclear magnetic resonance (NMR). The reaction C3H6 + (FeIII–O•)α was shown to proceed in a similar way as the oxidation of propylene by the enzyme methane mono-oxygenase sMMO, i.e., via the addition of active oxygen over C═C bonds to yield propylene oxide, not affecting a weakly bound allylic hydrogen. This result, together with the previous results on the hydroxylation of methane and other hydrocarbons, shows the (FeIII–O•)α to be the unique functional model of compound Q, the key intermediate of sMMO. In another aspect, the results relate to the low selectivity problem of the silver catalyst in propylene epoxidation and raise doubts about the presently accepted mechanism explaining an adverse effect of allylic hydrogen.