[54161-21-6] · C6H5Cl3W · Phenyltrichlorotungsten · (MW 367.31)
(transition metal catalyst for the alkene metathesis reaction)
Physical Data: brown crystalline solid; diamagnetic; mp >108 °C (dec).
Solubility: slightly sol toluene, diethyl ether.
Preparative Method: from the reaction of Tungsten(VI) Chloride with 2 equiv of Ph4Sn in refluxing pentane.
Handling, Storage, and Precautions: highly air sensitive; reacts vigorously with water or alcohols to liberate benzene.
Phenyltrichlorotungsten in combination with Aluminum Chloride is one of a large number of transition metal catalysts3 for the alkene metathesis reaction (eq 1). The mechanism has been extensively studied.4
The phenyltrichlorotungsten-aluminum chloride catalyst is extremely air sensitive and must be prepared in oxygen-free conditions. Typically, phenyltrichlorotungsten (1 mmol) is added to a centrifuge tube fitted with a rubber septum containing aluminum chloride (1 mmol) in an inert atmosphere of nitrogen. Oxygen-free chlorobenzene (25 mL) is then added and the mixture is shaken for 0.5 h and centrifuged. The supernatant liquid contains the active catalyst. Reaction of 1,7-octadiene with the above catalyst for ca. 21 h gives cyclohexene and ethylene (eq 2).5
In general, although cyclobutanes are not products from the alkene metathesis reaction, Gassman and Johnson6 have found that treatment of a strained diene, 11,12-bis(trifluoromethyl)-(i,o)-bicyclo[8.2.2]tetradeca-11,13-diene, with the above catalyst for 5 min results in equilibration with the corresponding, less strained, cyclobutane derivative (eq 3). Both 2,3-bis(trifluoromethyl)bicyclo[2.2.1]hepta-2,5-diene and 2,3-bis(trifluoromethyl)bicyclo[2.2.2]octa-2,5-diene, are unreactive under these conditions; however, the reverse reactions are readily achieved (eqs 4 and 5).
Treatment of 1-alkylcyclopropanes with a catalytic quantity of phenyltrichlorotungsten-aluminum chloride in a sealed Carius tube at rt in dimethyl ether-chlorobenzene (5:1) results principally in the formation of the corresponding 1-alkene through loss of a methylene fragment (eq 6). Similar treatment of bicyclo[2.1.0]pentane with PhWCl3/EtAlCl2 gives cyclobutene (eq 7).7
Treatment of a mixture of ethylcyclopropane and ethyl acrylate with catalytic phenyltrichlorotungsten-aluminum trichloride results in the formation of ethyl cyclopropanecarboxylate in low yield (eq 8). By using Ethylaluminum Dichloride rather than aluminum trichloride, the yield is slightly improved.8
Glaxo Research & Development, Stevenage, UK