Chromium hexacarbonyl

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Chromium hexacarbonyl
Cr(CO)6.png
Names
IUPAC name
Hexacarbonylchromium
Other names
Chromium carbonyl
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.032.579
RTECS number GB5075000
Properties
Cr(CO) 6
Molar mass 220.057 g/mol
Appearance colorless crystals
Density 1.77 g/cm3, solid
Melting point 90 °C (194 °F; 363 K)
Boiling point 210 °C (410 °F; 483 K) (decomposes)
insoluble
Solubility soluble in organic solvents
Structure
orthrhombic
octahedral
0 D
Hazards
Main hazards Toxic
Safety data sheet Oxford MSDS
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oilHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
1
2
0
Flash point 210 °C (410 °F; 483 K)
Lethal dose or concentration (LD, LC):
150 mg/kg (oral, mouse)
230 mg/kg (oral, rat)
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 1 mg/m3[1]
REL (Recommended)
TWA 0.5 mg/m3[1]
IDLH (Immediate danger)
250 mg/m3[1]
Related compounds
Other cations
Molybdenum hexacarbonyl
Tungsten hexacarbonyl
Related compounds
Vanadium hexacarbonyl
Dimanganese decacarbonyl
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Chromium carbonyl, also known as chromium hexacarbonyl, is the chemical compound with the formula Cr(CO)6. At room temperature the solid is stable to air, although it does have a high vapor pressure and sublimes readily. Cr(CO)6 is zerovalent, meaning that Cr has an oxidation state of zero, and it is a homoleptic complex, which means that all the ligands are identical. The complex is octahedral with Cr–C and C–O distances of 1.91 and 1.14 Å, respectively.[2]

Reactions[edit]

When heated or photolyzed in tetrahydrofuran (THF) solution, Cr(CO)6 converts to Cr(CO)5(THF) with loss of one CO ligand. Similarly, heating a solution of Cr(CO)6 in an aromatic solvent results in replacement of three CO ligands:

Cr(CO)6 + C6H5R → Cr(CO)3(C6H5R) + 3 CO

Such reactions proceed particularly well with electron-rich arenes such as anisole, either as the neat reagent or using a mixture of THF and dibutyl ether, the latter to increase the boiling point of the mixture. The products adopt a "piano-stool" structure. These species are typically yellow solids, which dissolve well in common organic solvents. The arene can be liberated from the chromium with iodine or by photolysis in air. In general, substituted derivatives of Cr(CO)6 decompose upon exposure to air.

Alkyl and aryl organolithium reagents RLi add to a carbonyl ligand to give anionic acyl complexes.[3] These species react with alkylating agents such as Me3O+ to form (OC)5Cr=C(OMe)R,[4] an example of a Fischer carbene. When R = vinyl or aryl, the resulting carbene complex can react with acetylenes to form (arene)Cr(CO)3 derivatives.

UV-irradiation of frozen solutions of chromium hexacarbonyl affords a variety of labile adducts.[5]

Safety[edit]

In common with many of the other homoleptic metal carbonyls (e.g. nickel carbonyl and iron carbonyl), chromium hexacarbonyl is toxic and thought to be carcinogenic. Its vapor pressure is relatively high for a metal complex, 1 mmHg (130 Pa) at 36 °C).[6]

References[edit]

  1. ^ a b c "NIOSH Pocket Guide to Chemical Hazards #0141". National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ Whitaker, A.; Jeffery, J. W. (1967). "The Crystal Structure of Chromium Hexacarbonyl". Acta Crystallogr. 23: 977–984. doi:10.1107/S0365110X67004153. 
  3. ^ Elschenbroich, C. (2006). Organometallics. Weinheim: Wiley-VCH. ISBN 978-3-527-29390-2. 
  4. ^ Herndon, James W. (2001). "Pentacarbonyl(methoxyphenylcarbene)chromium(0)". e-EROS Encyclopedia of Reagents for Organic Synthesis. 
  5. ^ Perutz, Robin N.; Turner, James J. (1975). "Photochemistry of the Group 6 Hexacarbonyls in Low-Temperature Matrixes. III. Interaction of the Pentacarbonyls with Noble Gases and Other Matrixes". Journal of the American Chemical Society. 97: 4791–800. doi:10.1021/ja00850a001. 
  6. ^ Patnaik, Pradyot (2003). "Chromium hexacarbonyl". Handbook of Inorganic Chemicals. McGraw-Hill Professional. pp. 222–223. ISBN 978-0-07-049439-8. 

External links[edit]