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Terminal acetylenes RC-CH are transformed catalytically into metathesis products RC=CR and C2H2 on the carbyne complex [W(CBU~)(OSU~)~], a process which is rapidlyfollowed by a polymerization of the alkyne; in the case of sterically hindered ButC-CH, a stoichiometric reaction is observed, by which a dinuclear compound p-C2H2[W(OBut)& 1 and the deprotiotungstenacyclobutadiene [ W C 3 ( B ~f ) 2 ( 0 B ~t ) 2 ] 2 are formed.

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Two new norbornene complexes of tungsten(0), W(CO) 5 (η 2 -C 7 H 10 ) (1) and trans-W(CO) 4 -(η 2 -C 7 H 10 ) 2 (2), have been obtained and characterized by IR and NMR spectroscopy, and initial studies of their reactivity are reported here. The molecular structure of compound 1, relatively unstable in solution, was established by single-crystal X-ray diffraction studies. Complex 1 can, depending on reaction conditions, give rise to different types of reactions: in a pure polychloromethane solution, it transforms to a species initiating the ring-opening metathesis polymerization of norbornene (ROMP), whereas in the presence of alcohol (ca. 1%), it leads to catalytic C-C bond formation with selective addition of polychloromethane to the olefinic bond of norbornene. The two-electron chemical oxidation of stable trans-W(CO) 4 -(η 2 -C 7 H 10 ) 2 (2) by SnCl 4 gives a very labile norbornene complex of tungsten(II) (3). The latter compound decomposes in CDCl 3 solution to give chloronorbornane, whereas in benzene-d 6 or toluene-d 8 solution the products of the hydroarylation of norbornene are formed. The identities of the organometallic and organic products were established by IR, NMR, ESI-MS, and GC-MS studies.