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The olefin metathesis is the other reaction for which rhenium is used as catalyst. Normally Re 2 O 7 on alumina is used for this process. [73] Rhenium catalysts are very resistant to chemical poisoning from nitrogen, sulfur and phosphorus, and so are used in certain kinds of hydrogenation reactions. [23] [74] [75]
Rhenium can form in many oxidation states, and compounds are known for every oxidation state from -3 to +7 except -2, although the oxidation states +7, +4, and +3 are the most common. [1] Rhenium is most available commercially as salts of perrhenate, including sodium and ammonium perrhenates. These are white, water-soluble compounds. [2]
Rhenium(IV) oxide or rhenium dioxide is the inorganic compound with the formula ReO 2. This gray to black crystalline solid is a laboratory reagent that can be used as a catalyst . It adopts the rutile structure.
Formerly the reaction had been called "olefin disproportionation." In this reaction 2-pentene forms a rapid (a matter of seconds) chemical equilibrium with 2-butene and 3-hexene. No double bond migrations are observed; the reaction can be started with the butene and hexene as well and the reaction can be stopped by addition of methanol.
Hydrogen-bond catalysis is a type of organocatalysis that relies on use of hydrogen bonding interactions to accelerate and control organic reactions. In biological systems, hydrogen bonding plays a key role in many enzymatic reactions, both in orienting the substrate molecules and lowering barriers to reaction. [ 1 ]
Rhenium alloys are being used in electronic components, gyroscopes and nuclear reactors. Rhenium finds its most important use as a catalyst. It is used as a catalyst in reactions such as alkylation, dealkylation, hydrogenation and oxidation. However its rarity makes it the most expensive of the refractory metals. [28]
Salts of [Re 2 Cl 8] 2− feature a quadruple metal-metal bond. Although the highest rhenium chloride features Re(VI), fluorine gives the d 0 Re(VII) derivative rhenium heptafluoride. Bromides and iodides of rhenium are also well known. Like tungsten and molybdenum, with which it shares chemical similarities, rhenium forms a variety of oxyhalides.
Rhenium(VII) oxide is the inorganic compound with the formula Re 2 O 7. This yellowish solid is the anhydride of HOReO 3. Perrhenic acid, Re 2 O 7 ·2H 2 O, is closely related to Re 2 O 7. Re 2 O 7 is the raw material for all rhenium compounds, being the volatile fraction obtained upon roasting the host ore. [2]