Philippus F, Engel was born in Utrecht, The Netherlands, in 1965. He was educated in the State University of Utrecht and specialized in Organometallic Chemistry with Professor G. van Koten in 1989. He then moved to Strasbourg where he obtained his These de I'Universile Louis Pasteur in 1993. The subject of his Ph.D. thesis was on the organometallic chemistry of "Fischer-type" melallacarbynes. He recently joined Shell Research in Amsterdam, The Netherlands, as an associate research chemist.Michel Pfeffer was bom in Alsace in 1948 and he received his Doctorat d'Etal from the Universite Louis Pasteur in 1975. In 1976 he spent one year wth Professor F. G. A. Stone at the University of Bristol. Since 1973 he has held a position in the CNRS at ULP Strasbourg where he became Directeur de Recherche in 1985. His main research interests are in the field of organomelallic chemistry with an emphasis on metalmediated syntheses of carbon-carbon and carbon-heteroatom bonds.

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The carbyne carbon atom of metallacarbynes such as (^-CsHgXCOlaM^CR (where = Mo, W and R = p-tolyl, 4-iert-butylphenyl, 2,6-dimethylphenyl, 1-cyclopentenyl) is readily coupled with the palladated carbon atom of various cyclopalladated compounds. This reaction affords good to excellent yields of novel µ-alkylidene complexes whose structure is maintained irrespective of the palladated ligand employed. For example, the reaction of (^-CsHsXCO^-Mo=C-p-Tol with [2-Me2NCH2C6H4PdCl]2 affords [2-Me2NCH2C6H4(?73-{p-C(p-Tol)Mo(p-CO)}-C5H5(CO)PdCl].

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Reaction of Group 6 metallacarbynes with cyclopalladated dimers leads t o C-C bond formation, for which reaction an intermediate has been characterized b y X-ray diffraction methods; both structural data and extended Huckel calculations suggest the metallacarbyne to be yl-bonded to Pd via the carbyne carbon atom.The isolbal analogy between Group 6 metallacarbynes and actual C-C bond formation.*J We have found that treating the alkynes has been used extensively for the synthesis of cyclopalladated dimer 1 with 2 equivalents of Cp(OC)2M-Cpolymetallic compounds, by adding L(OC)*M=CR (L = 5e C6H4.pMe (M = Mo, W) at room temp. in dichloromethane ligand) to coordinatively unsaturated metal complexes.1 Very for 1-3 h affords the bimetallic species 2 in more than 65% few studies though report the use of this concept for obtaining yield (eqn. 1). The structures of 2a and b are based upon their