Alkenes reaction with activated iodosylbenzene

In pursuit of biomimetic catalysts, metaUoporphyrins have been extensively studied in attempts to mimic the active site of cytochrome P450, which is an enzyme that catalyzes oxidation reactions in organisms. In recent decades, catalysis of alkene epoxidation with metaUoporphyrins has received considerable attention. It has been found that iron [1-3], manganese [4,5], chromium [6], and cobalt porphyrins can be used as model compounds for the active site of cytochrome P450, and oxidants such as iodosylbenzene, sodium hypochlorite [7,8], hydrogen peroxide [9], and peracetic acid [10] have been shown to work for these systems at ambient temperature and pressure. While researchers have learned a great deal about these catalysts, several practical issues limit their applicability, especially deactivation. 

Oxidation of ]V-MeTTPFenCl (46, 52). Catalytic alkene oxidation by iron N-alkylporphyrins requires that the modified heme center can form an active oxidant, presumably at the HRP compound I level of oxidation. To show that iron N-alkyl porphyrins could form highly oxidized complexes, these reactive species were generated by chemical oxidation and examined by NMR spectroscopy. Reaction of the (N-MeTTP)FenCl with chlorine or bromine at low temperatures results in formation of the corresponding iron(III)-halide complex. Addition of ethyl- or t-butyl-hydroperoxide, or iodosylbenzene, to a solution of N-MeTTPFenCl at low temperatures has no effect on the NMR spectrum. However, addition of m-chloroperoxybenzoic acid (m-CPBA) results in the formation of iron(III) and iron(IV) products as well as porphyrin radical compounds that retain the N-substituent. 

Cobalt-catalyzed epoxidation of alkenes has been carried out with the cobalt derivative of (174), employing iodosylbenzene as the oxidant. Epoxidation of cfa- -methylstyrene furnishes exclusively the cis-epoxide (equation 62). The reaction proceeds through an active oxo-cobalt(IV) species, and is mote selective than reactions proceeding through oxo-chromium or oxo-manganese species. The catalyst can be recovered unchanged by simple filtration. 

In the MOF PIZA-3 (PIZA, porphyrinic Illinois zeolite analog), Mn(III) is found both in the porphyrin struts and as a structural metal node. The framework is structurally stable and is used for the oxidation of cycUc alkanes and alkenes with iodosylbenzene or peracetic acid as the oxidant [117]. Reaction is found to take place at the outer surface, which is justified by the authors by the unfavorable hydrophilic properties of the pore interior. Yields were similar to those obtained with homogeneous Mn(III) porphyrin systems or those immobilized inside inorganic supports as heterogeneous catalysts. Less than 0.1 mM of metalloporphyrin or degradation products were observed in the reaction mixtures, with no loss of oxidation activity observed in a second run when peracetic acid was used. 

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