Molybdenum hexacarbonyl

Molybdenum hexacarbonyl
IUPAC name

Hexacarbonylmolybdenum(0)
Systematic name

Hexacarbonylmolybdenum[1]
Identifiers
CAS number 13939-06-5 Y
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 g mol−1
Exact mass 265.874895578 g mol-1
Appearance Vivid, white, translucent crystals
Density 1.96 g cm-3
Melting point

150 °C, 423 K, 302 °F
Boiling point

156 °C, 429 K, 313 °F
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 T+
R-phrases R26/27/28
S-phrases (S1/2), S36/37/39, S45
Related compounds
Related compounds Chromium hexacarbonyl

Tungsten hexacarbonyl
 N (verify) (what is: Y/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.

Contents

Structure and properties

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

Mo(CO)6 is prepared by the reduction of molybdenum chlorides or oxides under a pressure of carbon monoxide, 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

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

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]

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]

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

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

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

References

  1. ^ "Hexacarbonylmolybdenum (CHEBI:30508)". Chemical Entities of Biological Interest (ChEBI). UK: European Bioinformatics Institute. https://www.ebi.ac.uk/chebi/searchId.do?chebiId=30508. 
  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.; Fowlkes, J.; Rack, P. (2006). "Focused, Nanoscale Electron-Beam-Induced Deposition and Etching". Critical Reviews of Solid State and Materials Sciences 31 (3): 55. doi:10.1080/10408430600930438. 
  4. ^ Faller, J. W. "Hexacarbonylmolybdenum" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289.
  5. ^ http://www.chm.bris.ac.uk/teaching-labs/inorganic2ndyear/2004-2005labmanual/Experiment3.pdf
  6. ^ Darensbourg, Donald J.; Kump, Robin 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". Inorg. Chem. 17 (9): 2680–2682. doi:10.1021/ic50187a062. 
  7. ^ Elschenbroich, C.; Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) (1992) Wiley-VCH: Weinheim. ISBN 3-527-28165-7

Further reading