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Rearrangement of the W(0) d6 ^-alkyne complex /ac-(dppe)(OC)3W(j/2-PhC=CH) (dppe = Ph2PCH2CH2PPh2) yields a meridional tricarbonyl tungsten vinylidene complex, zner-(dppe) (OC)3W=C=CHPh, which provides an M-C-C framework for further ligand-based transformations. Electrophilic addition at the 0-carbon of the vinylidene ligand generates a cationic tungsten carbyne, [wr-(dppe)(OC)3W5=CCH2Ph] [BF4]. This carbyne cation undergoes carbon monoxide substitution

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260ChemInform Abstract Substitution of acetone in the fac-W(0) complex (I) by the terminal alkynes (II) leads to the alkyne adducts (III). Chemical and spectroscopic properties indicate that the alkyne ligand is weakly bound in these labile octahedral d6 monomers. The phenylacetylene adduct (R: Ph) isomerizes cleanly to the vinylidene derivative mer-W(CO)3(Ph2PCH2CH2PPh2)(=C=CHPh). Internal alkyl and aryl alkynes do notyield clean products under similar conditions, but the electron poor ester substituted alkyne (IV) (DMAC) forms the bis-alkyne complex (V). A single-crystal X-ray study of this complex (space group P1, Z=2) confirms the trans alkyne-cis dicarbonyl geometry anticipated from spectroscopic data.