Chromium hexacarbonyl

Chromcarbonyl

White crystals

Fixed

1.77 g · cm -3 ( 20 ° C)

149-150 ° C

Decomposition

Practically insoluble

Risk

230 mg · kg -1 ( LD50, mouse, oral)

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Chromium hexacarbonyl is a chemical compound with the formula Cr (CO ) 6 This colorless compound is molybdenum and tungsten as its analogs, a volatile, relatively air- stable complex of chromium in the zero oxidation state.

Representation

Chromium hexacarbonyl is represented by the reduction of chromium (III ) chloride ( CrCl3 ) in benzene under Kohlenstoffmonoxiddruck. It succeeds in good yield even in large amounts in the autoclave.

Also possible is the use of triethyl aluminum instead of aluminum.

Properties and Structure

The chromium atom in the complex is octahedrally surrounded by six carbonyl ligands ( Oh). The dipole moment of the complex is 0 Debye. The Cr - C distance is 191 pm. The wavenumber of the CO stretching vibration of the free νCO carbon monoxide is 2000 cm -1. It is a stable 18- Valenzelektronenkomplex which melts without decomposition at 150 ° C, and may decompose explosively when heated rapidly to temperatures exceeding 210 ° C.

Chromium hexacarbonyl is a colorless, volatile, air-stable, crystalline and toxic compound. In addition, the suspicion of a carcinogenic effect exists. Like all metal carbonyls is chromium hexacarbonyl from improper handling of a source of volatile metal and carbon monoxide. It is insoluble in water and sparingly soluble in organic solvents. His solution is light and sensitive to oxidation.

Reactions

The carbonyl ligands can be oxidatively cleaved photolytically or thermally. The resulting free coordination sites are occupied by solvent molecules. Thus is formed by heating in aromatic solvents by elimination of three carbonyl ligands, a new complex which has an aromatic ligands.

The formation of such complexes is favored for electron-rich aromatics.

Other solvents which are capable of co-ordination, can co-ordinate a labile ligand in the complex.

Use

Chromium hexacarbonyl can be used to view of chromium Fischer carbenes. For this purpose, it is reacted with carbon nucleophiles such as alkyllithium compounds, which add to the carbonyl carbon. An important application is the Dötz reaction In the synthesis of aromatic compounds, such as vitamin K, vitamin E or a meaning.