Acylperoxo-iron(III) porphyrin complexes: A new entry of potent oxidants for the alkene epoxidation

Article abstract of DOI:10.1021/ja00130a007

Competitive epoxidation of norbomylene and α-methylstyrene by peracids in the presence of iron porphyrins has been carried out in methylene chloride and toluene at -78 °C. When (TMP)FeIII(RCO₂) (TMP = 5, 10, 15, 20-tetramesitylporphyrin) is used as a catalyst in methylene chloride, selectivity of norbomylene oxide over α-methylstyrene oxide is almost identical even though a variety of peracids are used, since O=Fe^IVTMP π-cation radical 2a is the common oxidant in the reactions. On the other hand, the selectivity in the epoxidations catalyzed by (TDCPP)Fe^III(X) (TDCPP: 5, 10, 15, 20-tetrakis(2,6-dichlorophenyl)porphyrin) is found to be dependent on the structure of peracids. The latter type of the results is also obtained for the reactions catalyzed both by (TMP)Fe^III(X) and by (TDCPP)Fe^III(X) in toluene. The dependence of the selectivity in the epoxidation on the structure of peracids is attributed to the alteration of the oxidant from 2 to peracid-Fe(III) complexes 1. The direct involvement of 1 in the epoxidation has been further confirmed by spectroscopic studies of the reactions. Under the catalytic epoxidation conditions at low temperature, the participation of 1 and 2 as the active species is controlled either by electronic structure of iron porphyrin complexes (push-pull effect) or by alteration of the solvent.