Chromocene
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206518067
2008-04-18T16:32:53Z
Benjah-bmm27
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[[skeletal formula]] added
{{Chembox new
| Name = Chromocene
| ImageFileL1 = Chromocene-2D-skeletal.png
| ImageSizeL1 = 100px
| ImageNameL1 = Chromocene
| ImageFileR1 = Chromocene-3D-balls.png
| ImageSizeR1 = 150px
| ImageNameR1 = Chromocene
| IUPACName = chromocene
| OtherNames = Chromocene,<br />Bis(cyclopentadienyl)-<br />chromium(II)
| Section1 = {{Chembox Identifiers
| SMILES =
| CASNo = 1271-24-5
| RTECS = GB7600000
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>10</sub>H<sub>10</sub>Cr
| MolarMass = 182.18 g/mol
| Appearance = dark red crystals
| Density = 1.43 g/cm<sup>3</sup>, solid
| Solubility = decomposes in water
| MeltingPt = 168-170 °C
| BoilingPt = sublimes (under vacuum)
}}
| Section3 = {{Chembox Structure
| Coordination = pseudooctahedral<br /> see [[Ferrocene]]
| CrystalStruct =
| Dipole = 0 [[Debye|D]]
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = pyrophoric
| FlashPt =
| RPhrases = 20/21/22-36/37/38
| SPhrases = 26-37/39
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Ferrocene|Fe(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>]]<br />[[Nickelocene|Ni(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>]]<br /> [[Chromium(II) acetate]]
}}
}}
'''Chromocene''' is an [[Organometallic chemistry|organometallic]] compound with the formula Cr(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>. It is also often abbreviated Cp<sub>2</sub>Cr. This sandwich compound is structurally similar to [[ferrocene]] but paramagnetic and far more reactive. Also like structurally related [[metallocene]]s, chromocene sublimes readily in a vacuum and is soluble in non-polar organic solvents.
It is prepared by the following route:
:[[Chromium(II) chloride|CrCl<sub>2</sub>]] + 2 Na[[Cyclopentadienyl complex|C<sub>5</sub>H<sub>5</sub>]] → Cr(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + 2 NaCl
Such syntheses are typically conducted in [[THF]] solution. The strongly reducing analogue decamethylchromocene, Cr[C<sub>5</sub>(CH<sub>3</sub>)<sub>5</sub>]<sub>2</sub>, is prepared analogously from [[Pentamethylcyclopentadiene|LiC<sub>5</sub>(CH<sub>3</sub>)<sub>5</sub>]].
Like some other metallocenes, the C<sub>5</sub>H<sub>5</sub> ligands are displaceable. Thus, chromocene in combination with [[silica gel]] gives the Phillips catalyst for the polymerization of [[ethylene]], although other preparations exist for this important catalyst. The chromocene decomposes on the silica surface to generate high reactive organometallic centers that are responsible for the catalysis. A large percentage of the industrial production of polyethylene is attributable to such chromium-based catalysts.
==Safety==
Chromium compounds are toxic, although [[Chromate|Cr(VI)]] species are usually considered more dangerous than reduced chromium compounds. Chromocene is highly reactive toward air and could inflame upon exposure to the atmosphere.
==General reading==
C. Elschenbroich, A. Salzer ”Organometallics : A Concise Introduction” (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7
==References==
{{Unreferenced|date =September 2007}}
<references/>
[[Category:Chromium compounds]]
[[Category:Metallocenes]]
[[ar:كروموسين]]
[[ca:Plantilla:Chembox]]
[[es:Plantilla:Chembox]]
[[fr:Modèle:Chimiebox général]]