[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.

Alkene Metathesis.2

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).

Retro-Carbene Additions.

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

Cyclopropane-Alkene Cross Metathesis.

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

1. Grahlert, W.; Milowski, K.; Langbein, U. ZC 1974, 14, 287.
2. Haines, R. J.; Leigh, G. J. CSR 1975, 4, 155.
3. (a) Uchida, A.; Hata, K. J. Mol. Catal. 1982, 15, 111. (b) Bencze, L.; Thiele, K.-H.; Marquardt, V. RTC 1977, 96, 8. (c) Bencze, L.; Marko, L.; Opitz, R.; Thiele, K.-H. Hung. J. Ind. Chem. 1976, 4, 15.
4. Grubbs, R. H. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Volume 8, Chapter 54.
5. Grubbs, R. H.; Car, D. D.; Hoppin, C.; Burk, P. L. JACS 1976, 98, 3478.
6. Gassman, P. G.; Johnson, T. H. JACS 1976, 98, 861.
7. Gassman, P. G.; Johnson, T. H. JACS 1976, 98, 6057.
8. Gassman, P. G.; Johnson, T. H. JACS 1976, 98, 6058.

Malcolm Chandler

Glaxo Research & Development, Stevenage, UK

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.