[14040-11-0] · C6O6W · Hexacarbonyltungsten · (MW 351.91)
Alternate Name: tungsten hexacarbonyl.
Physical Data: dec. 150 °C; bp 175 °C.
Solubility: slightly sol alcohol, benzene, ether.
Form Supplied in: white crystals; commercially available.
Purification: recrystallized from diethyl ether or sublimed in vacuo at 65-70 °C. For most purposes, hexacarbonyltungsten is used without further purification.
Handling, Storage, and Precautions: highly toxic.
Treatment of sulfides or thiols with hexacarbonyltungsten leads to cleavage of the carbon-sulfur bond. Reactions proceed readily if the sulfur is in the benzylic position. For example, reaction of methyl 2-naphthylmethyl sulfide (1) with hexacarbonyltungsten in refluxing chlorobenzene provides dimeric compound (2) and the reduced compound 2-methylnaphthalene (3) (eq 1).4 The reaction is thought to proceed via tungsten-induced homolytic cleavage of the carbon-sulfur bond. The resulting benzylic radical then either undergoes radical-radical coupling or hydrogen abstraction.
Desulfurization of dithioacetals by hexacarbonyltungsten results in dimerization and alkene formation (eq 2). Dithioacetals derived from ketones, aldehydes, and ketenes (eq 3) are all effective in this transformation. The reaction is believed to involve a carbene intermediate, which undergoes dimerization. In cases where the dimerization is inhibited by steric effects, a sizable amount of the thioketone (7) is observed (eq 4).5 The mechanism for thioketone formation involves tungsten-induced homolysis of the carbon-sulfur bond, followed by elimination of ethylene. In addition, the alkene (10) was also observed and results from a C-C insertion of the carbene intermediate (8).
Treatment of geminal benzylic dihalides with hexacarbonyltungsten leads to dehalogenation-dimerization (eq 5).2 The reaction proceeds through a carbene or carbenoid intermediate, and leads to the more stable alkene stereoisomer. This transformation can also be effected using Tungsten(VI) Chloride and Lithium Aluminum Hydride. Benzylic alcohols undergo deoxygenation-dimerization under similar conditions (eq 6).
Irradiation of 2-pentene in the presence of hexacarbonyltungsten in carbon tetrachloride solution leads to a 2:1:1 mixture of 2-pentene, 3-hexene, and 2-butene (each compound is predominantly the trans isomer) (eq 7).3 The true alkene metathesis catalyst is generated from irradiation of hexacarbonyltungsten in carbon tetrachloride, and has not been unequivocally determined.6
James W. Herndon
University of Maryland, College Park, MD, USA