Molybdenum hexacarbonyl (also called molybdenum carbonyl) is the chemical compound with the formula Mo(CO)<sub>6</sub>. This colorless solid, like its chromium, tungsten, and seaborgium analogues, is noteworthy as a volatile, air-stable derivative of a metal in its zero oxidation state.
Mo(CO)<sub>6</sub> 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 MâÂÂC bond to an organic fragment, which must in turn have a CâÂÂH bond.
Like many metal carbonyls, Mo(CO)<sub>6</sub> is generally prepared by "reductive carbonylation", which involves reduction of a metal halide with under an atmosphere of carbon monoxide. As described in a 2023 survey of methods "most cost-effective routes for the synthesis of group 6 hexacarbonyls are based on the reduction of the metal chlorides (CrCl<sub>3</sub>, MoCl<sub>5</sub> or WCl<sub>6</sub>) with magnesium, zinc or aluminium powders... under CO pressures".
Mo(CO)<sub>6</sub> has been detected in landfills and sewage plants, the reducing, anaerobic environment being conducive to formation of Mo(CO)<sub>6</sub>.
Molybdenum hexacarbonyl is a popular reagent in research. One or more CO ligands can be displaced by other ligands. Examples:
(pip = piperidine) (MeCN = acetonitrile)
Some of these species are suited for substitution. For instance, the reaction of [Mo(CO)<sub>4</sub>(piperidine)<sub>2</sub>] with triphenyl phosphine gives cis- and trans-[Mo(CO)<sub>4</sub>(PPh<sub>3</sub>)<sub>2</sub>]. [Mo(CO)<sub>3</sub>(MeCN)<sub>3</sub> serves as a source of "Mo(CO)<sub>3</sub>". For instance treatment with allyl chloride gives [MoCl(allyl)(CO)<sub>2</sub>(MeCN)<sub>2</sub>], whereas treatment with KTp and sodium cyclopentadienide gives [MoTp(CO)<sub>3</sub>]<sup>âÂÂ</sup> and [MoCp(CO)<sub>3</sub>]<sup>âÂÂ</sup> anions, respectively. These anions react with a variety of electrophiles. A related source of Mo(CO)<sub>3</sub> is cycloheptatrienemolybdenum tricarbonyl.
Mo(CO)<sub>6</sub>, [Mo(CO)<sub>3</sub>(MeCN)<sub>3</sub>], and related derivatives are employed as catalysts or reagents in organic synthesis for example, alkyne metathesis and the PausonâÂÂKhand reaction. The hexacarbonyl can serve as a source of CO.
Molybdenum 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.
Like all metal carbonyls, Mo(CO)<sub>6</sub> is a dangerous source of volatile metal as well as CO.