Direct aerobic liquid phase epoxidation of propylene catalyzed by Mn(iii) porphyrin under mild conditions: evidence for the existence of both peroxide and Mn(iv)-oxo species from in situ characterizations

Abstract

Manganese(iii) porphyrin exhibited excellent activity for the selective oxidation of propylene. Experimental evidences that the generation of peroxide and Mn(iv) oxo species, which was well confirmed by in situ IR, in situ UV and MS.

Mechanism of Propylene Epoxidation via O2 with Co‐Oxidation of Aldehydes by Metalloporphyrins

“…On the other hand, in the later stage of reaction, the PO yield with metalloporphyrins began to decline due to the change in reaction rate of main reaction and secondary reaction for the variation in the amount of acrolein and PO (Table , entry 1 and 2). It was also reported that the yield of PO was extremely low in the absence of co‐reductant, which was vitally important in this reaction, and the similar conclusion was obtained in this study (Table S1, entry 1). Therefore, the co‐reductant aldehydes play an important role in propylene epoxidation.…”

“…According to the previous studies,, , the characteristic peak of metalloporphyrins could be detected during the whole reaction under warm conditions. High‐valent oxo metalloporphyrins had been indeed detected directly in propylene epoxidation through in situ UV and GC–MS, but the peak was weak and couldn't be stable during the whole reaction process, and so did the metalloporphyrins . And in this study, there is no characteristic peak of porphyrin after the reaction initiated (Figure ).…”

“…Ji et al deduced the mechanism of cyclohexene epoxidation by metalloporphyrins in which the active species is high‐valent oxo metalloporphyrins, which was well confirmed by the biomimetic kinetics. However, the reaction conditions in propylene epoxidation are harsher than higher alkenes and cyclic alkenes, and metalloporphyrins and its high‐value oxo intermediates cannot exist for a long time after the reaction was initiated . According to the results above, the primary active species would be peroxy acid or other intermediates rather than the high‐valent oxo metalloporphyrins.…”

“…epoxidation of alkenes with oxygen, for its excellent property in activating oxygen . But in order to obtain excellent performance in direct epoxidation of olefins with oxygen, aldehyde as the co‐reductant is also essential to transfer oxygen to metalloporphyrins for the generation of high‐valent oxo metalloporphyrins which have been proposed as the active species in the epoxidation of olefins , . And corresponding reaction paths are proposed, including high‐valent oxo metalloporphyrins and peroxy acid served as active species respectively, but which is the predominant active species has not reached consensus .…”

Olefins oxidation with molecular O2 in the presence of chiral Mn (III) salen complex supported on magnetic CoFe2O4@SiO2@CPTMS

“…Based on the literature review, the epoxidation reaction in the presence of chiral Mn (III) salen complex with molecular oxygen and aldehyde oxidation is a free radical reaction (scheme ) . As it can be seen, by H abstraction from aldehyde, in the presence of Mn (III) salen complex, an acyl radical was generated.…”