Метилтриоксорений

Description

Methyltrioxorenium (MTO) is an organometallic compound of rhenium in the highest oxidation state: the rhenium(VII) atom is bonded to three oxygen atoms by double bonds and to the methyl group by a metal-carbon bond. The geometry is tetrahedral, hence the catalog entry “rhenium, methyltrioxo-, (T-4)-”. The second name is methylrhenium trioxide. Colorless or pale gray crystals, soluble in water. One of the most versatile compounds in oxidation catalysis.

Basic Attributes

• CAS No: 70197-13-6; additional registration 795290-22-1
• Chemical formula: CH3O3Re
• Molecular weight: 249.24
• Exact weight: 249.963821
• BRN number: 3927932
• UNII: 883D8RDD5Q
• DSSTox ID: DTXSID40370077
• HS code: 2914190090
• PSA specifications: 51.2
• XLogP3: 0.2274
• EU number: the field is not filled in on the card

Physico-chemical properties

• Appearance: Colorless or pale gray crystal
• Density: d²³ 4.21
• Melting point: 111 °C (literature data)
• Boiling point: 65 °C at reduced pressure (on the card - write “65 °C 0 mm”)
• Solubility in water: soluble
• Packaging level (group): II

The high density of 4.21 is explained by the mass of the rhenium atom: there are 186 units of metal per 249.24 units of molecular weight. Sublimation at 65 °C in a vacuum is the standard method for purifying the drug.

Catalytic Application

Methyltrioxorenium activates hydrogen peroxide, forming rhenium mono- and bisperoxo complexes, which transfer oxygen to the substrate. Hence the main directions of use.

• Epoxidation of alkenes. The catalyst works in tandem with an oxidizing agent, most often aqueous hydrogen peroxide. Effective technique: 0.5 mol. % MTO, a complex of urea with hydrogen peroxide as a stoichiometric oxidizing agent and a catalytic amount of a heterocyclic aromatic base - pyrazole. The base inhibits the opening of the epoxy ring and dramatically increases the yield.
• Olefin metathesis. When supported on acidic supports, a typical Al₂O₃–SiO₂ aluminosilicate MTO system, the compound catalyzes the metathesis of functionalized olefins—allyl halides, allylsilanes, unsaturated carboxylates, and nitriles. Cocatalysts are not required, which distinguishes the system from classical rhenium-, molybdenum-, and tungsten-containing metathesis catalysts.
• Olefination of aldehydes. Reaction with diazo compounds and phosphines allows the aldehyde group to be converted into an alkene group.
• Other oxidative transformations. Oxidation of sulfides to sulfoxides and sulfones, oxidation of amines, reactions involving rhenium peroxo complexes.

Heterogenization and materials

The complex is fixed on mesoporous aluminosilicate supports - the immobilized catalyst is easier to separate from the products and return to the cycle. A separate page in the history of the compound relates to materials science: MTO forms the first described polymeric organometallic oxide, which expanded the understanding of structures of this class.

General scope of application

• Fine organic synthesis: selective oxidation under mild conditions
• Production of epoxides from olefins with hydrogen peroxide, an oxidizing agent that produces only water as a by-product
• Metathesis of functionalized olefins on supported systems
• Research in organometallic catalysis and materials science

Storage and handling

Rhenium(VII) compounds with a methyl group are sensitive to heat and bases: in an alkaline environment, the rhenium-carbon bond is destroyed. The product is stored in a tightly closed container, in a cool, dry place, protected from light, away from alkalis and reducing agents. Work is carried out with gloves, safety glasses and under a hood, dust is excluded. The card does not contain any separate hazard or warning phrases; only packaging level II is indicated—handling is based on the general rules for organometallic reagents. Considering the cost of rhenium, catalyst residues and spent solutions are collected separately for subsequent extraction of the metal.