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

Abstract

Six silicas, with different surface areas, pore sizes and pore volumes, have been surface modified with pyridine groups and used t o support iron( 111) 5.1 0,15,2O-tetra(2,6-dichlorophenyl) porphyrin (Fe'I'TDCPP) by ligation t o the metal ion. Comparison of these materials (SiPy-Fe'I'TDCPP) 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 t o catalytic oxidative bleaching and > 50% reduction in activity.A Hammett study of the epoxidation of styrene and 4-substituted styrenes gives p values (vs. a ' ) of -0.95 and -0.98 for oxidations catalysed b y FelIlTDCPP and a supported catalyst SiPy-Fe"'TDCPP, respectively. The similarity of these values t o each other and to values from other iron( 111) porphyrin-catalysed epoxidations is discussed. A minor pathway in the oxidation of the styrenes in air that leads t o benzaldehydes is attributed t o dioxygen intercepting an intermediate in the reaction.

Anchored ironporphyrins?the role of talc-aminofunctionalyzed phyllosilicates in the catalysis of oxidation of alkanes and alkenes

“…These results are similar to those already reported for other homogeneous metalloporphyrins [38][39][40]. Aldehyde formation is explained in terms of aerobic oxidation of styrene involving the ironporphyrin and iodosylbenzene [13], and this assumption has been confirmed in this study with the significant decrease in the yield of this product when the reactions were carried out under argon. As the results in Fig.…”

“…Since developments in the catalytic area aim at achieving selective, stable and high-turnover catalytic systems [8], the combination of versatile metalloporphyrin homogeneous systems with the advantages of heterogeneous catalysis has enabled major advances in this area [9][10][11][12]. When compared to homogeneous catalysts, heterogeneous systems present many advantages such as easy separation and recovery of the catalyst from the reaction media, increase in the stability of the catalytic species, protection against catalyst destruction and ability to mime the protein active site of the enzyme [13]. A variety of solid supports has been tested, including inorganic matrices such as silica, alumina, zeolites, cationic and anionic clays, as well as organic polymers and resins [14][15][16].…”

A regenerable ruthenium tetraammine nitrosyl complex immobilized on a modified silica gel surface: Preparation and studies of nitric oxide release and nitrite-to-NO conversion

“…One possible strategy for preparing such materials could be the attachment of heterocyclic bases to the silica surface. In fact, silica gels bearing heterocyclic bases such as pyridine [67], 2-aminoethylpyridine [52], and imidazol [49] are already known.…”

A view on the mechanism of metalloporphyrin degradation in hydrogen peroxide epoxidation reactions

“…Some general ways for the catalyst degradation can be considered [14]. One possibility is the intramolecular decomposition of the highly active species (path a) by a process similar to the described ring destruction in supported metalloporphyrins [14,15]. Other processes of macrocycle destruction of intermolecular nature are the oxidation of another molecule of catalyst by the active oxidant species (path b) or the generation of oxygen radical's by interaction with H 2 O 2 , which can destroy the catalyst (path c) [8,16] (Scheme 1).…”