Dirhenium heptoxide

Diplatinavinyl complexes, 5, 417 Dirhenates, nonahalo-, 4,176 Dirhenium heptoxide, 4,197 Diselenides... 

An explosive red/orange solid, obtained from dirhenium heptoxide and hydrogen peroxide reacting in ether as solvent. 

W. A. Herrmann, J. G. Kuchler, J. K. Felixberger, E. Herdtweck, and W. Wagner, Methylrhenium Oxides Synthesis from Dirhenium Heptoxide and Catalytic Activity in Olefin Metathesis, Angew. Chem. Int. Ed. Engl. 27, 394-396 (1988). 

The aqueous chemistry of rhenium(VII) is dominated by the great stability of the [Re04] ion.1 Dirhenium heptoxide (RejO-,) is a yellow volatile crystalline compound which dissolves in water to... 

Octene was mixed with the dirhenium heptoxide catalyst (0.1 mol % to 2 mol % based of olefin), cooled, and the oxidizing solution (in the reagent ratio range of 1 2 to 1 14 olefin/peroxide) added. After the reaction was complete, the reaction was filtered, cooled, unreacted peroxide removed by addition of sodium sulfite, and desiccant added to remove water. The product was isolated by vacuum distillation. 

In addition to dirhenium heptoxide, methylrhodium trioxide and cyclopentadienyl- and cyclopropylrhodium trioxide were also effective as oxidation catalysts and are described by the author. 

The direct conversion of alkenes to carboxylic acids using dirhenium heptoxide in a solution of acetic anhydride and dioxane is illustrated below for the oxidative cleavage of 1-octene to form n-heptanoic acid (2) ... 

The established synthesis routes for MTO and its congeners are the direct alkylation of dirhenium heptoxides with Sn(CH3)4, tetraalkyltin or dialkylzinc reagents yielding highly pure alkylrhenium trioxides (eq. (3)), and the alkylation of Rc207 in the presence of trifluoro- or trichloroacetic or carboxy anhydrides (eq. (4)) [6]. 

MTO is generated by methylation of oxidic Re " precursor compounds under nonreducing conditions. Thus, dimethylzinc and methyl Grignard compounds are not very well suited for this purpose. The first commonly applied synthesis started from dirhenium heptoxide using the toxic tetramethyltin as methylating reagent (eq. (1)). The major drawback in this otherwise excellent approach is the loss of half of the Re due to formation of the low-reactivity trimethylstannyl perrhenate [2]. 

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. 

The flask is charged with dirhenium heptoxide (commercial product, 1.22 g, 2.5 mmol) imder nitrogen and suspended in hexamethyldisiloxane added via syringe through the septum (dry commercial product, 10 g, 62 mmol, excess). The mixture is refluxed for 30 min to give a clear colorless solution. Upon cooling and reducing the volume of the solvent/reactant to 10 mL, colorless crystals separate from the mother liquor. Removal of all solvent in a vacuum leaves a colorless product yield 1.62 g, 99.6% based on dirhenium heptoxide. The product is stable in dry air but sensitive to moisture. 

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