Alkenes methyltrioxorhenium

The oxidation of alkenes and allylic alcohols with the urea-EL202 adduct (UELP) as oxidant and methyltrioxorhenium (MTO) dissolved in [EMIM][BF4] as catalyst was described by Abu-Omar et al. [61]. Both MTO and UHP dissolved completely in the ionic liquid. Conversions were found to depend on the reactivity of the olefin and the solubility of the olefinic substrate in the reactive layer. In general, the reaction rates of the epoxidation reaction were found to be comparable to those obtained in classical solvents. 

Methyltrioxorhenium, supported on silica functionalized with polyether tethers, catalyzed the epoxidation of alkenes with 30% aq H2O2 in high selectivity compared to the ring opening products observed in homogeneous media in the absence of an organic solvent.46... 

The low solubility of oxygen in most ionic liquids limits its application in oxidation catalysis in these liquids. However, oxidation by H2O2 or organoperoxide is not subject to this limitation when the ionic liquids are properly chosen. An example of catalytic oxidation is the methyltrioxorhenium (MTO)-catalyzed epox-idation of alkenes with the urea-H202 adduct in [EMIMJBF4 (228). High conversions and yields were obtained. 

Methyltrioxorhenium(VII) (MTO) absorbance spectroscopy, 130, 132 alkene epoxidation, catalysis with hydrogen peroxide... 

W. M. Adam, C. M. Mitchell, Methyltrioxorhenium(VII)-catalyzed epoxidation of alkenes with the urea/hydrogen peroxide adduct, Angew. Chem. Int. Ed. Engl. 35, 533— 535 (1996). 

H. Adolfsson, C. Coperet, J. P. Chiang, A. K. Yudin, Efficient epoxidation of alkenes with aqueous hydrogen peroxide catalyzed by methyltrioxorhenium and 3-cyano-pyridine, J. Org. Chem. 65, 8651-8658 (2000). 

Since its discovery in 1991, methyltrioxorhenium (MTO, 80) has attracted much interest as one of the most versatile catalysts for oxidation.When it is associated with a stoichiometric amount of H2O2, the system can efficiently transform alkene to epoxide, although formation of undesired diol can occur. Alternatively, water-free conditions, using urea hydrogen peroxide (UHP), allow the formation of the desired epoxide without byproducts. A maj or drawback of the MTO/UHP system is its insolubility in organic solvents, leading to a kinetically slow heterogeneous system. 

Neumann, R., and T.-J. Wang, Methyltrioxorhenium Supported on Silica Tethered with Polyethers as Catalyst for the Epoxidation of Alkenes with Hydrogen Peroxide, Chem. Commun., 1915-1916 (1997). 

The oxidized electron transfer mediator (ETMox). namely the peroxo complexes of methyltrioxorhenium (MTO) and vanadyl acetylacetonate [VO(acac)2] and flavin hydroperoxide, generated from its reduced form (Figure 1.1) and H2O2, recycles the N-methylmorpholine (NMM) to N-methylmorpholine N-oxide (NMO), which in turn reoxidizes the Os(VI) to Os(VIII). While the use of hydrogen peroxide as oxidant without any electron transfer mediators is inefficient and nonselective, various alkenes were oxidized to diols in good to excellent yields employing this mild triple catalytic system (Scheme 1.2). 

Epoxidation of Alkenes. In 1991, Hermann demonstrated that alkenes are efficiently converted to the corresponding epoxide using methyltrioxorhenium (MTO) as the catalyst and hydrogen peroxide as the co-oxidant4 A range of alkenes undergo epoxidation at ambient temperatures with a catalyst loading of 0.1 to 1 mol % (eq 1). 

Progress in rhenium chemistry reported in 1991 is reviewed.549 There is much important material in a review of methyltrioxorhenium catalysed alkene metathesis, oxidation and aldehyde alkenation, a review of the insertion of activated alkynes into the metal-metal bond of dinuclear manganese and rhenium carbonyl complexes. i a review of the reactions of [Cp(CO)2Mn=CPh]+ towards electron rich alkynes and nitriles552 and a review of the discovery of tRe(CBu )(CHBu ) OCMe(CF3)2 2l and recent results covering the metathesis of alkenes. s... 

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