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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]
It is an early example of a cluster compound with metal-metal bonds. [30] Rhenium(III) bromide also adopts the same structure, and is a black lustrous crystalline solid. [31] [32] It can be obtained by the direct reaction between rhenium metal and bromine at 500 °C under nitrogen: [33] 6 Re + 9 Br 2 → 2 Re 3 Br 9
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(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]
Rhenium's main oxides are rhenium(IV) oxide and rhenium(VII) oxide. Rhenium(IV) oxide is a gray to black crystalline solid that can be formed by comproportionation. [21] At high temperatures it undergoes disproportionation. It is a laboratory reagent that can be used as a catalyst. It adopts the rutile structure.
Perrhenic acid is the chemical compound with the formula Re 2 O 7 (H 2 O) 2.It is obtained by evaporating aqueous solutions of Re 2 O 7.Conventionally, perrhenic acid is considered to have the formula HReO 4, and a species of this formula forms when rhenium(VII) oxide sublimes in the presence of water or steam. [2]