- Chromium hexacarbonyl
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Chromium hexacarbonyl 
HexacarbonylchromiumOther namesChromium carbonylIdentifiers CAS number 13007-92-6 
PubChem 518677 ChemSpider 23855 ChEBI CHEBI:33031 RTECS number GB5075000 Jmol-3D images Image 1 - [Cr].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-].[O+]#[C-]
- InChI=1S/6CO.Cr/c6*1-2;
Key: KOTQLLUQLXWWDK-UHFFFAOYSA-N
InChI=1/6CO.Cr/c6*1-2;
Key: KOTQLLUQLXWWDK-UHFFFAOYAN
Properties Molecular formula C6CrO6 Molar mass 220.057 g/mol Appearance colorless crystals Density 1.77 g/cm3, solid Melting point 150 °C
Boiling point 210 °C (decomp)
Solubility in water insoluble Solubility soluble in ether, chloroform, tetrahydropyran (THP), methylene chloride Structure Crystal structure orthrhombic Coordination
geometryoctahedral Dipole moment 0 D Hazards MSDS Oxford MSDS EU Index Not listed Main hazards Toxic NFPA 704 
120Flash point 210 °C LD50 150 mg/kg (oral, mouse)
230 mg/kg (oral, rat)Related compounds Other cations Molybdenum hexacarbonyl
Tungsten hexacarbonylRelated compounds Vanadium hexacarbonyl
Dimanganese decacarbonyl
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)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 a formal charge of zero, and it is called a homoleptic complex, which means that all the ligands are the same. The complex is octahedral with Cr-C and C-O distances of 1.91 and 1.14 Å, respectively.[1]
Contents
Reactions
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.[2] These species react with alkylating agents such as Me3O+ to form (OC)5Cr=C(OMe)R, an example of a Fischer carbene. If the R group is a vinyl or an aryl group, then the resulting carbene complex can react with an acetylene to form a new benzene ring to which is bonded the chromium tricarbonyl fragment. The two acetylene carbon atoms become part of the new ring, as does a carbon from one of the carbonyl ligands. Also the three carbons from the vinyl carbene become part of the new benzene ring.
Safety
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 mm Hg ( 36 °C).[3]
References
- ^ Whitaker A.; Jeffery, J. W. “The Crystal Structure of Chromium Hexacarbonyl” Acta Crystallographica 1967, volume 23, pp. 977-984. doi:10.1107/S0365110X67004153.
- ^ Elschenbroich, C. ”Organometallics” (2006) Wiley-VCH: Weinheim. ISBN 978-3-29390-6
- ^ Patnaik, Pradyot (2003). "Chromium hexacarbonyl". Handbook of Inorganic Chemicals. McGraw-Hill Professional. pp. 222–223. ISBN 9780070494398. http://books.google.de/books?id=Xqj-TTzkvTEC&pg=PA222.
External links
Chromium compounds Categories:- Carbonyl complexes
- Octahedral compounds
- Organochromium compounds
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