(Benzene)chromium tricarbonyl

(Benzene)chromium(0) tricarbonyl

Names
IUPAC name (benzene)tricarbonylchromium
Other names benzene tricarbonyl chromium, (benzene)chromium tricarbonyl, Benchrotrene, pi-benzenetricarbonylchromium
Identifiers
CAS Number	12082-08-5
ChemSpider	9130108
Jmol interactive 3D	Image
InChI InChI=1S/C6H6.3CO.Cr/c1-2-4-6-5-3-1;3*1-2;/h1-6H;;;; Key: WVSBQYMJNMJHIM-UHFFFAOYSA-N InChI=1/C6H6.3CO.Cr/c1-2-4-6-5-3-1;3*1-2;/h1-6H;;;; Key: WVSBQYMJNMJHIM-UHFFFAOYAR
SMILES [Cr].[O+]#[C-].[O+]#[C-].[O+]#[C-].c1ccccc1
Properties
Chemical formula	Cr(C6H6)(CO)3
Molar mass	214.14 g/mol
Appearance	solid yellow crystals
Melting point	163 to 166 °C (325 to 331 °F; 436 to 439 K)
Solubility in water	nonsoluble
Solubility	THF, ether, benzene
Structure
Coordination geometry	tetrahedral, "piano stool"
Hazards
Main hazards	Harmful through inhalation, contact with skin, or swallowed
R-phrases	20/21/22
S-phrases	36/37
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

(Benzene)chromium tricarbonyl is an organometallic compound with the formula Cr(C₆H₆)(CO)₃. This yellow crystalline solid compound is soluble in common nonpolar organic solvents. The molecule adopts a geometry known as “piano stool” because of the planar arrangement of the aryl group and the presence of three CO ligands as "legs" on the chromium-bond axis.^[1]

Preparation

(Benzene)tricarbonylchromium was first reported in 1957 by Fischer and Öfele, who prepared the compound by the carbonylation of bis(benzene)chromium.^[2] They obtained mainly chromium carbonyl (Cr(CO)₆) and traces of Cr(C₆H₆)(CO)₃. The synthesis was optimized through the reaction of Cr(CO)₆ and Cr(C₆H₆)₂. For commercial purposes, a reaction of Cr(CO)₆ and benzene is used:

Cr(CO)₆ + C₆H₆ → Cr(C₆H₆)(CO)₃ + 3 CO

Applications

The aromatic ring of (benzene)tricarbonylchromium is substantially more electrophilic than benzene itself, allowing it to undergo nucleophilic addition reactions.^[3]

It is also more acidic, undergoing lithiation upon treatment with n-butyllithium. The resulting organolithium compound can then be used as a nucleophile in various reactions, for example, with trimethylsilyl chloride:

(Benzene)tricarbonylchromium is a useful catalyst for the hydrogenation of 1,3-dienes. The product alkene results from 1,4-addition of hydrogen. The complex does not hydrogenate isolated double bonds.

References

1. Gilbert T. M. Bauer C. B., Rogers R. D. (1996). "Structures of (η⁶-benzene dimethylacetal)- and (η⁶-benzene diethylacetal)chromium tricarbonyl: structural evidence for the near-electroneutrality of the dialkylacetal substituent". Journal of Chemical Crystallography 26 (5): 355. doi:10.1007/BF01677100.
2. Fischer, Ernst Otto; Őfele, Karl. (1957). “Über Aromatenkomplexe von Metallen, XIII Benzol-Chrom-Tricarbonyl,” Chemische Berichte, 90, 2532-5. doi:10.1002/cber.19570901117.
3. Herndon, James W; Laurent, Stéphane E. (2008). “(η⁶-Benzene)tricarbonylchromium,” in Encyclopedia of Reagents for Organic Synthesis, John Wiley & Sons, Chichester, 2008. doi:10.1002/047084289X.rb025.pub2. Article Online Posting Date: March 15, 2009