Molybdenum hexacarbonyl

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Molybdenum hexacarbonyl
Stereo, skeletal formula of molybdenum hexacarbonyl Ball and stick model of molybdenum hexacarbonyl
Sample of molybdenum hexacarbonyl
Identifiers
CAS number 13939-06-5 YesY
PubChem 98885
ChemSpider 21428397 N
EC number 237-713-3
UN number 3466
MeSH Hexacarbonylmolybdenum
ChEBI CHEBI:30508 N
Gmelin Reference 3798, 562210
Jmol-3D images Image 1
Properties
Molecular formula C6MoO6
Molar mass 264.00 g mol−1
Appearance Vivid, white, translucent crystals
Density 1.96 g cm-3
Melting point 150 °C (302 °F; 423 K)
Boiling point 156 °C (313 °F; 429 K)
Structure
Crystal structure Orthogonal
Coordination
geometry
Octahedral
Dipole moment 0 D
Thermochemistry
Std enthalpy of
formation
ΔfHo298
-989.1 kJ mol-1
Std enthalpy of
combustion
ΔcHo298
-2123.4 kJ mol-1
Hazards
MSDS External MSDS
EU classification Very Toxic T+
R-phrases R26/27/28
S-phrases (S1/2), S36/37/39, S45
Related compounds
Related compounds Chromium hexacarbonyl

Tungsten hexacarbonyl

Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

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.

Structure and properties[edit]

Mo(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.

Preparation[edit]

Mo(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.

Occurrence[edit]

Mo(CO)6 has been detected in landfills and sewage plants, the reducing, anaerobic environment being conducive to formation of Mo(CO)6.[2]

Applications in inorganic and organometallic synthesis[edit]

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.[3] Mo(CO)6 is also a popular reagent in organometallic synthesis[4] because one or more CO ligands can be displaced by other donor ligands.[5] 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.

[Mo(CO)4(piperidine)2][edit]

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].[6]

[Mo(CO)3(MeCN)3][edit]

Upon refluxing in a solution of acetonitrile, Mo(CO)6 converts to its tris(acetonitrile) derivative. The resulting air-sensitive 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 respectively. These anions can be reacted with electrophiles to form a wide range of products.[7]

Applications in organic synthesis[edit]

Mo(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.

Safety and handling[edit]

Like all metal carbonyls, Mo(CO)6 is dangerous source of volatile metal as well as CO. It diffuses readily into plastic stoppers.

References[edit]

  1. ^ "Hexacarbonylmolybdenum (CHEBI:30508)". Chemical Entities of Biological Interest (ChEBI). UK: European Bioinformatics Institute. 
  2. ^ Feldmann, J. (1999). "Determination of Ni(CO)4, Fe(CO)5, Mo(CO)6, and W(CO)6 in Sewage Gas by Using Cryotrapping Gas Chromatography Inductively Coupled Plasma Mass Spectrometry". Journal of Environmental Monitoring 1 (1): 33–37. doi:10.1039/a807277i. 
  3. ^ Randolph, S. J.; Fowlkes, J. D.; Rack, P. D. (2006). "Focused, Nanoscale Electron-Beam-Induced Deposition and Etching". Critical Reviews of Solid State and Materials Sciences 31 (3): 55–89. doi:10.1080/10408430600930438. 
  4. ^ Faller, J. W.; Brummond, K. M.; Mitasev, B. (2006). "Hexacarbonylmolybdenum". In L. Paquette. Encyclopedia of Reagents for Organic Synthesis. New York: J. Wiley & Sons. doi:10.1002/047084289X.rh004.pub2. 
  5. ^ http://www.chm.bris.ac.uk/teaching-labs/inorganic2ndyear/2004-2005labmanual/Experiment3.pdf[dead link]
  6. ^ Darensbourg, D. J.; Kump, R. L. (1978). "A Convenient Synthesis of cis-Mo(CO)4L2 Derivatives (L = Group 5a Ligand) and a Qualitative Study of Their Thermal Reactivity toward Ligand Dissociation". Inorganic Chemistry 17 (9): 2680–2682. doi:10.1021/ic50187a062. 
  7. ^ Elschenbroich, C.; Salzer, A. (1992). Organometallics : A Concise Introduction (2nd ed.). Weinheim: Wiley-VCH. ISBN 3-527-28165-7. 

Further reading[edit]

  • Marradi, M. (2005). "SYNLETT Spotlight 119 Molybdenum Hexacarbonyl [Mo(CO)6]" (pdf). SYNLETT 2005 (7): 1195–1196. doi:10.1055/s-2005-865206. 
  • Feldmann, J.; Cullen, W. R. (1997). "Occurrence of Volatile Transition Metal Compounds in Landfill Gas: Synthesis of Molybdenum and Tungsten Carbonyls in the Environment". Environmental Science and Technology 31 (7): 2125–2129. doi:10.1021/es960952y. 
  • Feldmann, J.; Grümping, R.; Hirner, A. V. (1994). "Determination of Volatile Metal and Metalloid Compounds in Gases from Domestic Waste Deposits with GC/ICP-MS". Fresenius' Journal of Analytical Chemistry 350 (4–5): 228–234. doi:10.1007/BF00322474.