PENTACARBONYL (TELLUROBENZALDEHYDE)TUNGSTEN - PRODUCTION, THERMOLYSIS AND REACTIONS WITH CONJUGATED DIENES

Benzylidene(pentacarbonyl)tungsten reacts with tellurocyanate, [TeCN]-, by insertion of the tellurium atom into the benzylidene-tungsten bond to give pentacarbonyl(tellurobenzaldehyde)tungsten (3). The complex 3 is thermally very labile. When thermolyzed the binuclear tellurobenzaldehyde-bridged complex [(CO)5W]2{mu-2-eta-1,eta-2-Te = C(Ph)H} (4) is formed. The reaction of 3 with 2,3-dimethyl-1,3-butadiene affords (CO)5W[T activated eC(Ph)HCH2CMe = CMeCH2] (7). In solution, isomers of 7 are detectable, the phenyl group occupying the equatorial position in both. The [4 + 2]-cycloaddition of cyclopentadiene to 3 is stereoselective. Two isomers, exo-8 [Ph exo and (CO)5W endo] and endo-8 [Ph endo and (CO)5W exo], are formed in the ratio 11/1. The structure of the main isomer exo-8 is confirmed by an X-ray analysis.