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Molybdenum natural-health-informatio... | Molybdenum healthwalk.com | Molybdenum - The Antioxidant Mineral vitaminstohealth.com | Molybdenum?::?Minerals?::?Products H-O?::?Forrest Health Online forresthealth.com |
Molybdenum hexacarbonyl (also called molybdenum carbonyl) is the chemical compound with the formula Mo(CO)6. This colorless solid, like its chromium and tungsten analogues, is noteworthy as a volatile, air-stable derivative of a metal in its zero oxidation state.
[edit] Structure and propertiesMo(CO)6 adopts an octahedral geometry consisting of six rod-like CO ligands radiating from the central Mo atom. A recurring minor debate in some chemical circles concerns the definition of an "organometallic" compound. Usually, organometallic indicates the presence of a metal directly bonded via a M-C bond to an organic fragment, which must in turn have a C-H bond. By this strict definition, Mo(CO)6 is not organometallic. [edit] PreparationMo(CO)6 is prepared by the reduction of molybdenum chlorides or oxides under a pressure of carbon monoxide,[citation needed] although it would be unusual to prepare this inexpensive compound in the laboratory. The compound is somewhat air-stable and sparingly soluble in nonpolar organic solvents. [edit] OccurrenceMo(CO)6 has been detected in landfills and sewage plants, the reducing, anaerobic environment being conducive to formation of Mo(CO)6.[1] [edit] Applications in inorganic and organometallic synthesisMolybdenum hexacarbonyl is widely used in electron beam-induced deposition technique - it is easily vaporized and decomposed by the electron beam providing a convenient source of molybdenum atoms.[2] Mo(CO)6 is also a popular reagent in organometallic synthesis[3] because one or more CO ligands can be displaced by other donor ligands.[4] For example, Mo(CO)6 reacts with 2,2'-bipyridine to afford Mo(CO)4(bipy). UV-photolysis of a THF solution of Mo(CO)6 gives Mo(CO)5(THF). Many metal carbonyls are similarly photo-activatable. [edit] [Mo(CO)4(piperidine)2]The thermal reaction of Mo(CO)6 with piperidine affords Mo(CO)4(piperidine)2. The two piperidine ligands in this yellow-colored compound are labile, which allows other ligands to be introduced under mild conditions. For instance, the reaction of [Mo(CO)4(piperidine)2] with triphenyl phosphine in boiling dichloromethane (b.p. ca. 40 °C) gives cis-[Mo(CO)4(PPh3)2]. This cis- complex isomerizes in toluene to trans-[Mo(CO)4(PPh3)2]. [edit] [Mo(CO)3(MeCN)3]Upon heating in a solution of acetonitrile, Mo(CO)6 converts to its tris(acetonitrile) derivative. The resulting compound serves as a source of "Mo(CO)3". For instance treatment with allyl chloride gives [MoCl(allyl)(CO)2(MeCN)2], whereas treatment with KTp and sodium cyclopentadienide gives [MoTp(CO)3]- and [MoCp(CO)3]- anions. These anions can be reacted with electrophiles to form a wide range of products.[5] [edit] Applications in organic synthesisMo(CO)6, [Mo(CO)3(MeCN)3], and related derivatives are employed as catalysts in organic synthesis. For example, these catalysts can be used for alkyne metathesis and the Pauson–Khand reaction. [edit] Safety and handlingLike all metal carbonyls, Mo(CO)6 is dangerous source of volatile metal as well as CO. It diffuses readily into plastic stoppers. [edit] References
[edit] Further reading
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