Chromocene

Chromocene
Chromocene
Identifiers
CAS number 1271-24-5
ChemSpider 71485
ChEBI CHEBI:30677
RTECS number GB7600000
Jmol-3D images Image 1
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
EU classification Irritant Xi
R-phrases R20/21/22, R36/37/38
S-phrases S26, S37/39, S45
Main hazards pyrophoric
NFPA 704
NFPA 704.svg
0
1
0
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 references

Chromocene is an organochromium compound with the formula Cr(C5H5)2, often abbreviated Cp2Cr. This sandwich compound is structurally similar to ferrocene but does not follow the 18-electron rule because it only has 16 electrons.[1] It also paramagnetic and highly reducing. Also like structurally related metallocenes, chromocene sublimes readily in a vacuum and is soluble in non-polar organic solvents.

It is prepared from chromium(II) chloride and cyclopentadienylsodium:

CrCl2 + 2 NaC5H5 → Cr(C5H5)2 + 2 NaCl

Such syntheses are typically conducted in THF solution. The structure of the compound has been verified by X-ray crystallography; the average Cr-C bond length is 215.1(13) pm.[2]

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 in chromacene. Thus, chromocene in combination with silica gel gives the Union Carbide 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.

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.

References

  1. ^ C. Elschenbroich, A. Salzer ”Organometallics : A Concise Introduction” (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7
  2. ^ Kevin R. Flower, Peter B. Hitchcock "Crystal and molecular structure of chromocene (η5-C5H5)2Cr" Journal of Organometallic Chemistry, 1996, volume 507, p. 275-277. doi:10.1016/0022-328X(95)05747-D.

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