Tungsten Hexachloride
Tungsten hexachloride is the chemical compound of tungsten and chlorine with the formula WCl6. This dark violet blue species exists as a volatile solid under standard conditions. It is an important starting reagent in the preparation of tungsten compounds. WCl6 is a rare example of a charge-neutral hexachloride, another example being ReCl6. Better known than WCl6 is the still more volatile WF6.
As a d0 ion, W(VI) forms diamagnetic derivatives. The hexachloride is octahedral with equivalent W–Cl distances of 2.24–2.26 Å. In acceptor, the chloride ligands are donors in both sigma and pi sense.
Preparation
Tungsten hexachloride can be prepared by chlorinating tungsten metal in a sealed tube at 600°C:
W + 3 Cl2 → WCl6
Properties and Reactions
Tungsten (VI) chloride is a blue-black crystalline solid at room temperature. At lower temperatures, it becomes wine-red in color. A red form of the compound can be made by rapidly condensing its vapor, which reverts to the blue-black form on gentle heating. It is readily hydrolyzed in moist air, giving the orange oxychlorides WOCl4 & WO2Cl2, and subsequently, tungsten trioxide. WCl6 is soluble in carbon disulfide, carbon tetrachloride and phosphorus oxychloride.
Methylation with trimethylaluminium affords hexamethyl tungsten:
WCl6 +3 Al2(CH3)6 → W(CH3)6 + 3 Al2(CH3)4Cl2
Treatment with butyl lithium affords a reagent that is useful for deoxygenation of epoxides.
The chloride ligands in WCl6 can be replaced by many anionic ligands including: Br−, NCS−, and RO− (R = alkyl, aryl).Safety considerations
WCl6 is an aggressively corrosive oxidant, and hydrolyzes to release hydrogen chloride.
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