The oxidation of ethylbenzene by dioxygen catalysed by supported iron porphyrins derived from iron(III) tetrakis(pentafluorophenyl)porphyrin

Abstract

Chloromethylated poly(styrene) and chloropropylated silica gel have been reacted with α,ω-diamines to give diamine modified catalyst supports which have then been covalently attached to iron(III) tetrakis(pentafluorophenyl)porphyrin (FeTF₅PP). In this way the diamino groups provide a simple linker/spacer unit between the support and the catalyst. The diamino-silica has been further modified using trimethylsilyl chloride and by acetylation or acid washing. The polarities of the modified inorganic and organic supports have been measured using Reichardt’s dye. Spectroscopic studies reveal that with all the supported catalysts, except that on acid washed diamino-silica where the amines are protonated, the diamino groups reduce the iron(III) porphyrin to iron(II). The supported iron porphyrins have been used to catalyse the oxidation of ethylbenzene by dioxygen. These reactions give the same three products, 1-phenylethyl hydroperoxide, 1-phenylethanol and acetophenone, as the analogous homogeneous oxidation using FeTF₅PP, suggesting that they proceed by the same mechanism, however, in general they are slower. The overall product yields are limited by the stability/activity of the iron porphyrin and these in turn are very dependent on the length of the linker, the catalyst loading and the microenvironment provided by the support. The role of the diamino groups in the oxidations is discussed.