Manganese catalysis epoxidation

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

On the other hand, in homogeneous epoxidation catalysis, De Vos et al. [6] have explored the properties of manganese (II) salts in the presence of triazacyclononane derivatives and... 

In the catalytic epoxidation of alkenes by a manganese porphyrin with phase-transfer catalysis and hypochlorite, the yield of epoxide also decreases with decreasing alkene concentration363 dibenzo-18-crown-6 has been shown to have an effect on the reaction364. 

One of the most important aspects of those listed above is catalysis. A great deal of research has been carried out in the investigation of catalysts for the epoxidation of alkenes. The oxidation of a-pinene to a-pinene epoxide (Equation 1) is one of the standard trial reactions for catalyst identification. The Jacobsen manganese complex catalyst, based on a salen derivative, shows brilliant enantioselectivity, whereas the use of related indole derivatives provides greater structural variety and powerful catalysis, but so far shows poorer enantioselectivity (Figure 2). Such catalysts can sometimes be effectively embedded in zeolites. ... 

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. 

Oxo-transfer from metal complexes to olefins results in a net two-electron reduction at the metal center. As a result, only metals capable of shuttling between oxidation states can be effective oxo-transfer catalysts. Iron, manganese, ruthenium, and chromium have proven effective for catalytic epoxidation via oxo-transfer [8,9], and in synthetic systems studied thus far for enantioselective catalysis, these metals are most commonly coordinated by tetradentate porphyrin (1) and salen (2) ligand frameworks (Fig. 1). 

Gross Z, Golubkov G, Simkhovich L (2000) Epoxidation catalysis by a manganese corrole and isolation of an oxomanganese(V) corrole. Angew Chem Int Ed 39 4045 1047... 

Cobalt tetraarylporphyrins with fluorine-containing substituents were active in epoxidation of alkenes using fluorous catalysis in the presence of oxygen and 2-methylpropanal [167,170-171]. Manganese and cobalt complexes of perfluorinated tetraazocyclonone catalyzed allylic oxidation of alkenes with r-BuOOH/Oa [172]. The complex with the salen ligand 57 was active in alkene epoxidation under Mikayama s conditions, and indene was epoxidated at a high stereospecificity [173]. 

Among such oxidations, note that liquid-phase oxidations of solid paraffins in the presence of heterogeneous and colloidal forms of manganese are accompanied by a substantial increase (compared with homogeneous catalysis) in acid yield [3]. The effectiveness of n-paraffin oxidations by Co(III) macrocomplexes is high, but the selectivity is low the ratio between fatty acids, esters, ketones and alcohols is 3 3 3 1. Liquid-phase oxidations of paraffins proceed in the presence of Cu(II) and Mn(II) complexes boimd with copolymers of vinyl ether, P-pinene and maleic anhydride (Amberlite IRS-50) [130]. Oxidations of both linear and cyclic olefins have been studied more intensively. Oxidations of linear olefins proceed by a free-radical mechanism the accumulation of epoxides, ROOH, RCHO, ketones and RCOOH in the course of the reaction testifies to the chain character of these reactions. The main requirement for these processes is selectivity non-catalytic oxidation of propylene (at 423 K) results in the formation of more than 20 products. Acrylic acid is obtained by oxidation of propylene (in water at 338 K) in the presence of catalyst by two steps at first to acrolein, then to the acid with a selectivity up to 91%. Oxidation of ethylene by oxygen at 383 K in acetic acid in... 

Renoud, J.P., P. Battioni, J.E. Bartoli, and D. Mansuy (1985). A very efficient system for alkene epoxidation by hydrogen peroxide catalysis by manganese-porphyrins in the presence of imidazole. J. Chem. Soc., Chem. Common. 13, 888-889. 

The application of fluorinated media seems to be a flourishing new area in homogeneous catalysis (103). However, until now enantioselective catalytic reactions in this alternative solvent are very rare. Chiral perfluoroalkylated SALEN-manganese complexes have been used for asymmetric epoxidation (104). 

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