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 leads to alkyne−alkyne coupling to yield W(CO)(PhC⋮CPh) 2 (η 4 -C 4 Ph 4 ) ( 2 ), W(CO)(PhC⋮CPh)(η 5 -C 3 Ph 3 (C 5 Ph 5 )) ( 3 ), and W(CO)(PhC⋮CPh)(η 6 -C 3 Ph 3 (C 5 Ph 5 )) ( 4 ) together with the tungstenocene oligomer [W(C 5 Ph 5 ) 2 ] x ( 5 ). Oxidation of 5 by diiodine affords W(η 5 -C 5 Ph 5 ) 2 (I) 2 ( 6 ), which is converted into the oxo complex W(η 5 -C 5 Ph 5 ) 2 ( O) ( 7 ) by treating with AgBF 4 in wet dichloromethane solution. Reaction of W(NCMe)(PhC⋮CPh) 3 ( 8 ) and 1 equiv of diphenylacetylene produces W(NCMe)(PhC⋮CPh) 2 (η 4 -C 4 Ph 4 ) ( 9 ), whereas a similar reaction in the presence of excess diphenylacetylene gives mainly the metallacyclic complex W(PhC⋮CPh)(η 8 -C 8 Ph 8 ) ( 10 ). Compound 10 reacts with carbon monoxide to afford 3 and 4, while thermolysis of pure 10 results in 5 exclusively. The reaction mechanism has been explored by C-13 labeling experiments. The structures of 7 and 10 have been established by an X-ray diffraction study. The bonding of pentaphenylcyclopentadienyl ligands of 7 is best described as a localized η 3:η 2 fashion. Compound 10 contains a tungstenacyclononapentaene ring with two tungsten−carbon double bonds.