Organometallics pendent non-hydrogen atoms were found with program MULTAN and subsequent Fourier difference syntheses. Refinement of their coordinates and thermal parameters, first isotropic and then anisotropic, led to the final R values reported in Table IV. For the compound 9a, the coordinates of the hydrogen atoms were computed and their contributions introduced in the refinement with thermal parameters equal to those of the atoms to which they were bonded. For the compound 11, the hydrogen atoms were not introduced into the refinement because of the large R and R, values; in this case, the last Fourier difference synthesis did not show any residual electronic density except for peaks at 1.5 e A-3 close to the Pd or I atoms.A c k n o w l e d g m e n t . W e t h a n k Mr. R. Hueber for recording t h e mass spectra, Dr. A. Dedieu for helpful discussions, t h e CNRS for a grant (to F.M.), a n d t h e "Commission of t h e European Communities" for financial support of this work (Contract No. ST 2J-0090-1-F). (39) Frenz, B. A. Computing in Crystallography; Schenk, H., 01-thof-Hazelkamp, R., van Konigsveld, H., Bassi, G. C., Eds.; Delft University Press: HollandSupplementary Material Available: Tables of atomic coordinates, thermal parameters, and bond distances and bond angles including all atoms for 901 and 11 (15 pages); listings of observed and calculated structure factors for 90 and 11 (43 pages). Ordering information is given on any current masthead page. The Pd-C bond of the compound containing a six-membered palladocyclic ring [(Pd(BP)(pCl)],] (1) (BP = C6H4CH2C5H4N-2-(2-picolyl)phenyl) reacted with one alkyne unit (R1C=CR2 in which R1 and f or R2 = Me, Ph, or C 0 2 R and R = Me or Et) t o afford regioselectively [(Pd(C(R2)=C-(R1)C6H4CH2C5H4N)(~-C1))2] (2a-0. The geometry of these eight-membered ring containing complexes was determined by an X-ray diffraction study of one of their corresponding monomers, [Pd(C(Ph)=C-(CO2Et)C6H4CH2C5H4N)(2-MeC5H4N)Cl] (3"a), obtained by reaction of 2a with 2-methylpyridine. The structure revealed that the carbon and the nitrogen atom bonded to the palladium are cis to each other.It also showed that the more electron-withdrawing group of the alkyne (R' = C02Et) is close to the benzyl ring of the B P ligand. The iodide-bridged derivative 1* reacted with diphenylacetylene in refluxing chlorobenzene t o afford a mixture of two products, 7a and Sa, which contain the heterocyclic cation [C(Ph)=C(Ph)C6H4CH2C5H4N] with a Pd216 dianion or an iodide ion, respectively. Compounds 2c, 2d, and 2f underwent insertion of a second alkyne (R1, R2 = Me, Ph) leading to the series of compounds 4a-g.The X-ray diffraction of 4a revealed the cyclization of two alkyne molecules with one carbon atom of the benzyl unit. This led t o a spiro junction between a tetraphenylcyclopentadiene and a hexadienyl ring. This latter is q3-bonded t o Pd. Compound 4a rearranged in refluxing chlorobenzene leading to a thermodynamically more stable isomer, 5a. The reaction between the ionic compound [Pd(C(C02Me)=C-(C0...
