Chromium carbonyl
2483127
196734531
2008-03-08T10:12:51Z
Axiosaurus
3399137
corrected IUPAC name
{{Chembox new
| Name = Chromium carbonyl
| ImageFile = Cr(CO)6.png
| ImageSize = 150px
| ImageName =
| IUPACName = hexacarbonylchromium(0)
| OtherNames = chromium carbonyl
| Section1 = {{Chembox Identifiers
| CASNo = 13007-92-6
| RTECS = GB5075000
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>6</sub>CrO<sub>6</sub>
| MolarMass = 220.06 g/mol
| Appearance = colorless crystals
| Density = 1.77 g/cm<sup>3</sup>, solid
| Solubility = insoluble
| Solvent = other solvents
| SolubleOther = soluble in [[benzene]], [[THF]]
| MeltingPt = 150 °C (decomposition)
| BoilingPt = sublimes
}}
| Section3 = {{Chembox Structure
| Coordination = octahedral
| CrystalStruct = orthrhombic
| Dipole = 0 [[Debye|D]]
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = CO source
| RPhrases = {{R22}}
| SPhrases = {{S53}} {{S36}} {{S45}}
}}
| Section8 = {{Chembox Related
| Function = compounds
| OtherFunctn = [[Vanadium carbonyl|V(CO)<sub>6</sub>]], [[Iron pentacarbonyl|Fe(CO)<sub>5</sub>]]<sub>-</sub>]], [[Chromium(III) chloride|CrCl<sub>3</sub>]]
}}
}}
'''Chromium carbonyl''', also known as '''chromium hexacarbonyl''', is the [[chemical compound]] with the [[chemical formula|formula]] Cr(CO)<sub>6</sub>. At [[room temperature]] the solid is stable to air, although it does have a high [[vapor pressure]] and [[Sublimation (chemistry)|sublime]]s readily. Cr(CO)<sub>6</sub> is [[Valence (chemistry)|zerovalent]], meaning that Cr has a [[formal charge]] of zero, and it is called a [[homoleptic]] complex, which means that all the [[ligand]]s are the same. The complex is [[octahedral]] with Cr-C and C-O distances of 1.92 and 1.17 Å, respectively.<ref>Whitaker A.; Jeffery, J. W. “The Crystal Structure of Chromium Hexacarbonyl” Acta Crystallographica 1967, volume 23, pp. 977-984. {{doi|10.1107/S0365110X67004153}}.</ref>
==Reactions==
When heated or photolyzed in [[tetrahydrofuran]] (THF) solution, Cr(CO)<sub>6</sub> converts to Cr(CO)<sub>5</sub>(THF) with loss of one CO ligand. Similarly, heating a solution of Cr(CO)<sub>6</sub> in an [[aromatic]] solvent results in replacement of three CO ligands:
:Cr(CO)<sub>6</sub> + C<sub>6</sub>H<sub>5</sub>R → Cr(CO)<sub>3</sub>(C<sub>6</sub>H<sub>5</sub>R) + 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 "[[Sandwich compound|piano-stool]]" structure. These species are typically [[yellow]] solids, which dissolve well in common organic [[solvent]]s. The arene can be liberated from the chromium with [[iodine]] or by photolysis in [[air]]. In general, substituted derivatives of Cr(CO)<sub>6</sub> decompose upon exposure to air.
Alkyl and aryl [[organolithium reagent]]s RLi add to a carbonyl ligand to give anionic [[acyl]] complexes.<ref>Elschenbroich, C. ”Organometallics” (2006) Wiley-VCH: Weinheim. ISBN 978-3-29390-6</ref> These species react with alkylating agents such as [[Meerwein salt|Me<sub>3</sub>O<sup>+</sup>]] to form (OC)<sub>5</sub>Cr=C(OMe)R, an example of a [[Transition metal carbene complex|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).
==References==
<references/>
==External links==
* [http://www.npi.gov.au/database/substance-info/profiles/24.html National Pollutant Inventory - Chromium (III) and compounds fact sheet]
[[Category:Chromium compounds]]
[[Category:Carbonyl complexes]]
[[ar:سداسي كربونيل كروم]]