ALKYNE-ALKYNE COUPLING REACTIONS WITH W(CO)(PHC-CPH)(3) AND W(NCME)(PHC-CPH)(3)

Heating W(CO)(PhC=CPh)(3) (1) and diphenylacetylene in a sealed tube l eads to alkyne-alkyne coupling to yield W(CO)(PhC=CPh)(2)(eta(4)-C4Ph4 ) (2), W(CO)(PhC=CPh)(eta(5)-C3Ph3(C5Ph5)) (3), and W(CO)(PhC=CPh)(eta (6)-C3Ph3(C5Ph5)) (4) together with the tungstenocene oligomer [W(C5Ph 5)(2)](x) (5). Oxidation of 5 by diiodine affords W(eta(5)-C5Ph5)(2)(I )(2) (6), which is converted into the oxo complex W(eta(5)-C5Ph5)(2)(= O) (7) by treating with AgBF4 in wet dichloromethane solution. Reactio n of W(NCMe)(PhC=CPh)(3) (8) and 1 equiv of diphenylacetylene produces W(NCMe)(PhC=CPh)(2)(eta(4)-C4Ph4) (9), whereas a similar reaction in the presence of excess diphenylacetylene gives mainly the metallacycli c complex W(PhC=CPh)(eta(8)-C8Ph8) (10). Compound 10 reacts with carbo n monoxide to afford 3 and 4, while thermolysis of pure 10 results in 5 exclusively. The reaction mechanism has been explored by C-13 labeli ng experiments. The structures of 7 and 10 have been established by an X-ray diffraction study. The bonding of pentaphenylcyclopentadienyl l igands of 7 is best described as a localized eta(3):eta(2) fashion. Co mpound 10 contains a tungstenacyclononapentaene ring with two tungsten -carbon double bonds.