Dichlorotetracarbonyltungsten as a catalyst for olefin metathesis

The photolysis of hexacarbonyltungsten (I) in carbon tetrachloride yields a catalytic mixture for olefin metathesis. One of the principal products of this transformation is dichlorotetracarbonyltungsten (II). Chemical preparation of II from I and chlorine was carried out. Authentic II was shown to give catalysis of 2-pentene metathesis by either heating in chlorobenzene or chloroform or irradiation in chlorobenzene or carbon tetrachloride. The Dubois report of phosgene formation in the original irradiated mixture of I in carbon tetrachloride was shown to be an artifact.