Oxidation of alkanes and alkenes by iodosylbenzene and hydrogen peroxide catalysed by halogenated manganese porphyrins in homogeneous solution and covalently bound to silica

Abstract

Manganese(III) 5-(pentafluorophenyl)-10,15,20-tri(2,6-dichlorophenyl)porphyrin, Mn(PFTDCPP), and manganese(II) 2,3,7,8,12,13,17,18-octachloro-5-(pentafluorophenyl)-10,15-20-tri(2,6-dichlorophenyl)porphyrin, Mn(PFTDCCl 8PP), have been synthesised and used as catalysts in hydrocarbon oxidations by iodosylbenzene and hydrogen peroxide both in solution and covalently bound to aminopropylated silica. The former shows higher efficiency in the epoxidation of alkenes by iodosylbenzene, whereas the perchlorinated manganese porphyrin is more efficient in the hydroxylation of alkanes by this oxidant. The supported manganese(III) porphyrin show the same activity as its homogeneous analogue. With hydrogen peroxide as oxygen donor, Mn(PFTDCPP) is a stable and effective catalyst in the presence of imidazole. The perchlorinated analogue is a poor catalyst with this oxidant. The eight additional chlorine atoms on the porphyrin ring stabilise Mn(II) and unfavour the formation of the active species, Mn VO.