Alkene epoxidation by iodosylbenzene catalysed by iron(III) 5, 10, 15, 20-tetra(2,6-dichlorophenyl)porphyrin coordinated to pyridine-modified silica

Le résumé fourni par la source

Six silicas, with different surface areas, pore sizes and pore volumes, have been surface modified with pyridine groups and used to support iron(III) 5, 10, 15, 20-tetra(2,6-dichlorophenyl)porphyrin (FeIIITDCPP) by ligation to the metal ion. Comparison of these materials (SiPy–FeIIITDCPP) as catalysts for the epoxidation of (Z)-cyclooctene by iodosylbenzene in dichloromethane reveals that all have essentially the same catalytic activity and that the heterogeneous reactions are significantly slower (ca. ten-fold) than the homogeneous analogue. In small scale repeat-use experiments the catalysts achieve 2200 catalyst turnovers without loss of activity, however, larger scale reactions (7900 turnovers) lead to catalytic oxidative bleaching and > 50% reduction in activity.A Hammett study of the epoxidation of styrene and 4-substituted styrenes gives ρ values (vs. σ+) of –0.95 and –0.98 for oxidations catalysed by FeIIITDCPP and a supported catalyst SiPy–FeIIITDCPP, respectively. The similarity of these values to each other and to values from other iron(III) porphyrin-catalysed epoxidations is discussed. A minor pathway in the oxidation of the styrenes in air that leads to benzaldehydes is attributed to dioxygen intercepting an intermediate in the reaction.Oxidations of (Z)- and (E)-4-methylpent-2-ene catalysed by FeIIITDCPP and by SiPy–FeIIITDCPP show a marked difference. With the former the relative reactivity of (Z)- to (E)-alkene is 13:1, whereas the latter fails to catalyse the epoxidation of the (E)-alkene and instead is converted into a green material; this is possibly an iron N-alkylporphyrin.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.