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() tetrakis(pentafluorophenyl)porphyrin (FeTF 5 PP). 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() porphyrin to iron(). 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 FeTF 5 PP, 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.

Homogeneous and Heterogeneous Free-Based Porphyrins Incorporated to Silica Gel as Fluorescent Materials and Visible Light Catalysts Mimic Monooxygenases

“…Numerous proposals have appeared: the use of cross-linked polymers Ribeiro et al, 2008), clays and layered materials (Bedioui, 1995;Evans & Lindsay Smith, 2001), biopolymers (Huanga et al, 2005), cationic ionexchange resins (Campestrini, S. & Meunier, 1992); silanized kaolinite (Nakagaki et al, 2004); different types of zeolites (Skrobot et al, 2003;Haber et al, 2004), modified silica (Milaeva et al, 2007), and also microporous porphyrin framework solids (Suslick et al, 2005). Noteworthy results for the immobilized porphyrins have been obtained with ionic porphyrins immobilized on cationically functionalized polystyrene (Inbaraj et al, 2003), porphyrins copolymerized with polystyrene (Griesbeck et al, 2004), a soluble polyethylene glycol-supported tetrahydroxyphenyl porphyrin (Benaglia et al, 2002), photosensitizers ionically bound at polymeric ion-exchanging resins (Gerdes et al, 2001), and a cross-linked polyacrylamide hydrogel serve as a scaffold for the photosensitizer hematoporphyrin (Rogers et al, 2005) and as well with chitosan-supported metallotetraphenylporphyrin complexes (Huanga et al, 2005).…”

Hydrocarbon oxidation catalyzed by iron and manganese porphyrins anchored on aminofunctionalized supports

“…This reaction was performed under argon atmosphere and magnetic stirring, at 80 °C. 18 After 14 h, the reaction mixture was filtered; the white solid was washed with toluene, acetone and water until neutral pH, and dried in a vacuum pump at 140 °C. Aminofunctionalization of the 3-chloropropyl silica was carried out by mixing the 3-chloropropylsilica (1.0 g) with 1,6-diaminohexane (6.0 g) and toluene (30 mL), under argon atmosphere and magnetic stirring, at 80 °C.…”

“…100 mg) with distilled acetic anhydride (15 mL) for 21 h. 18 The resulting solids were washed with deionized water up to neutral pH. The solids were subsequently washed with dichloromethane and then methanol in a Soxhlet apparatus, and dried under vacuum.…”

Modified silicas covalently bounded to 5,10,15,20-tetrakis(2-hydroxy-5-nitrophenyl)porphyrinato iron(III): synthesis, spectroscopic and EPR characterization. Catalytic studies

“…420 nm) and bands at < 340 nm, suggesting the presence of Fe II porphyrin, besides Fe III porphyrin in agreement with a previous report of Evans and Lindsay Smith. 23 It is expected that metalloporphyrins containing electron withdrawing substituents, such as the -NO 2 group, can have the metal centre reduced in the presence of bases (Scheme 1). 7,23 In this sense, it is likely that the coordinating solvent DMF is responsible for some reduction (Fe III /Fe II ) seen in the spectrum of the homogeneous complex 1, the same also occurring for 1-CPS ( Figure 5C) prepared in DMF, in which some amount of Fe II with Fe III coexists.…”

“…23 It is expected that metalloporphyrins containing electron withdrawing substituents, such as the -NO 2 group, can have the metal centre reduced in the presence of bases (Scheme 1). 7,23 In this sense, it is likely that the coordinating solvent DMF is responsible for some reduction (Fe III /Fe II ) seen in the spectrum of the homogeneous complex 1, the same also occurring for 1-CPS ( Figure 5C) prepared in DMF, in which some amount of Fe II with Fe III coexists. For the supported catalyst 1-SiN(IPG) (Figure 5B), in turn, the presence of imidazole coordinated to Fe III also facilitates some reduction as already reported previously.…”