Alkene epoxidation with dioxygen

In the presence of methyl, tert-butyl, or (-)-menthyl esters of 2-oxocyclopentanecarboxylic acids, the cobalt(II)-salen type complexes and Jacobsen-type manganese(ni) complexes shown in Figure 17 are active catalysts for alkene epoxidation with dioxygen . 

Introduction of mesityl groups at the porphyrin ring can prevent the formation of the dimeric products and the reaction with dioxygen now leads to ruthenium(VI)-dioxo complexes of TMP (tetramesitylporphyrin) [35], The tram-Ru(VI)02-TM P species can catalyse the epoxidation of alkenes as well as whole range of other oxidation reactions. After transfer of one oxygen atom to an organic substrate Ru(IV)0-TMP is formed, which disproportionates to an equilibrium of Ru02 and llu ). 

The kinetics of the catalytic oxidation of cyclopentene to glutaraldehyde by aqueous hydrogen peroxide and tungstic acid have been studied and a compatible mechanism was proposed, which proceeds via cyclopentene oxide and /3-hydroxycyclopentenyl hydroperoxide. " Monosubstituted heteropolytungstate-catalysed oxidation of alkenes by t-butyl hydroperoxide, iodosobenzene, and dioxygen have been studied a radical mechanism was proved for the reaction of alkenes with t-BuOOH and O2, but alkene epoxidation by iodosobenzene proceeds via oxidant coordination to the catalyst and has a heterolytic mechanism. ... 

Mononuclear peroxo complexes, such as MoO(02)2(HMPT), show a more electrophilic character in their reactions. This particular complex may be used for the epoxidation of alkenes.176 Much interest has been shown in the reaction of small molecules with dioxygen complexes of this type with a view to catalytic oxidation. These reactions and their products are sumarized in Table 10. The... 

A dinuclear ruthenium complex with both ruthenium in 2+ oxidation states catalyzes the oxidation of adamantane to hydroxy adamantane and alkene to epoxide by dioxygen. Suggest a possible mechanism. 

T. Iwahama, G. Hatta, S. Sakaguchi, Y. Ishii, Epoxidation of alkenes using alkyl hydroperoxides generated in situ by catalytic autoxidation of hydrocarbons with dioxygen, Chem. Commun. (2000) 163. 

Recently, Hulsken et al. have employed STM to probe the mechanism by which manganese porphyrin complexes achieve epoxidation of alkenes with dioxygen [69]. Importantly, this study demonstrates the positive role of solid-support immobilization in precluding the formation of inactive oxido-bridged catalyst dimers (a common deactivation pathway). 

This enzyme [EC 1.14.13.25] catalyzes the reaction of methane with NAD(P)H and dioxygen to produce methanol, NAD(P), and water. This enzyme is reported to exhibit a broad specificity. Many alkanes can be hydrox-ylated and alkenes are converted into the corresponding epoxides. Carbon monoxide is oxidized to carbon dioxide, ammonia is oxidized to hydroxylamine, and some aromatic compounds and cyclic alkanes can also be hy-droxylated, albeit not as efficiently. 

The gas-phase oxidation of ethylene to ethylene oxide over a supported silver catalyst was discovered in 1933 and is a commercially important industrial process. Using either air or oxygen, the ethylene oxide is produced with 75% selectivity at elevated temperatures (ca. 250 °C). Low yields of epoxides are obtained with propylene and higher alkenes so that other metal-based catalysts are used. A silver-dioxygen complex of ethylene has been implicated as the active reagent.222... 

Biological systems overcome the inherent unreactive character of 02 by means of metalloproteins (enzymes) that activate dioxygen for selective reaction with organic substrates. For example, the cytochrome P-450 proteins (thiolated protoporphyrin IX catalytic centers) facihtate the epoxidation of alkenes, the demethylation of Al-methylamines (via formation of formaldehyde), the oxidative cleavage of a-diols to aldehydes and ketones, and the monooxygenation of aliphatic and aromatic hydrocarbons (RH) (equation 104). The methane monooxygenase proteins (MMO, dinuclear nonheme iron centers) catalyze similar oxygenation of saturated hydrocarbons (equation 105). ... 

The reaction with molecular oxygen gives an jj -peroxy complex, [Pt(jj -02)(PPh3)2], in which the oxygen is reactive, and the complex can oxidize PPhs, RNC, and alkenes to OPPh3, RNCO, and the epoxide. SO2, NO2, NO, and CO2 react to give the sulphate, dinitrato, dinitro, and carbonate complexes. The dioxygen complex is planar and seems to have substantial Pt character. ... 

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