Methyltrioxorhenium , formation

Immediately upon addition of the urea-hydrogen peroxide adduct to the solution containing methyltrioxorhenium, a yellow color develops due to formation of the catalytically active rhenium peroxo complexes.3... 

Methyltrioxorhenium (MTO) has proven to he a useful oxidant for a number of reactions. A problem with the use of MTO in epoxidation is the acidity of the reagent, which leads to diol formation. Several different methods have previously been reported in an attempt to solve this problem. The use of microeneapsulated Lewis base adducts of MTO appears to be a good solution <05T1069>. Another modification of MTO is (PPhjljlReCNCS) ] with H Oj as an oxidant <05TL339>. 

Miscellaneous Reactions of Phosphines.- The basicities of a series of bidentate phosphines have been determined by a study of their enthalpies of protonation with trifluoromethanesulphonic acid in 1,2-dichloroethane. Ring-opening of sultones via nucleophilic attack by nitrogen occurs on treatment with tri-(2-pyridyl)phosphine, with the formation of the water-soluble phosphine systems (91). A novel aldehyde-olefination procedure is afforded by the reactions of aldehydes, diazomethanes, and tertiary phosphines in the presence of a catalytic amount of the powerful Lewis acid methyltrioxorhenium. Attempts to prepare carboxyphenylphosphines by the ring metallation of triphenylphosphine followed by... 

A recent improvement to this type of reaction often selects for the formation of tetroxanes over the trimeric hexaoxonane analogs. The use of fluorinated alcohols such as trifluoroethanol (TEE) or, often better, HFIP, as solvent and methyltrioxorhenium (MTO) as catalyst, as well as a substrate concentration of 1 M, are considered important for success (Equation (26) Table 3) <2003TL6309, 2006T1479, 2006BMC7790>. 

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. 

Methyltrioxorhenium(VII) (MTO), CHaReOs, has been shown to be an organo-metallic compound with a broad variety of catalytic properties. Two synthetic pathways have been established the direct alkylation of dirhenium heptoxide (Re207) with tetramethyltin yielding 50% of unreactive trimethylstannyl perrhe-nate, and the alkylation with tributyhnethyltin in the presence of trifluoroacetic anhydride. In the latter case, the formation of the rhenium-containing byproduct can be avoided. The disadvantage of both methods is that the Re207 is extremely moisture-sensitive. 

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