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Chromocene



Chromocene
IUPAC name Di(cyclopentadienyl)-
chromium(II)
Other names Chromocene,
Bis(cyclopentadienyl)-
chromium(II)
Identifiers
CAS number 1271-24-5
RTECS number GB7600000
Properties
Molecular formula C10H10Cr
Molar mass 182.18 g/mol
Appearance dark red crystals
Density 1.43 g/cm3, solid
Melting point

168-170 °C

Boiling point

sublimes (under vacuum)

Solubility in water decomposes in water
Structure
Coordination
geometry
pseudooctahedral
see Ferrocene
Dipole moment 0 D
Hazards
Main hazards pyrophoric
R-phrases 20/21/22-36/37/38
S-phrases 26-37/39
Related Compounds
Related compounds Fe(C5H5)2
Ni(C5H5)2
Chromium(II) acetate
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Chromocene is an organometallic compound with the formula Cr(C5H5)2. It is also often abbreviated Cp2Cr. This sandwich compound is structurally similar to ferrocene but paramagnetic and far more reactive. Also like structurally related metallocenes, chromocene sublimes readily in a vacuum and is soluble in non-polar organic solvents.

Additional recommended knowledge

It is prepared by the following route:

CrCl2 + 2 NaC5H5 → Cr(C5H5)2 + 2 NaCl

Such syntheses are typically conducted in THF solution. The strongly reducing analogue decamethylchromocene, Cr[C5(CH3)5]2, is prepared analogously from LiC5(CH3)5.

Like some other metallocenes, the C5H5 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 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

     
    This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Chromocene". A list of authors is available in Wikipedia.
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