109997-09-3Relevant academic research and scientific papers
Stepwise insertion of one, two, and three alkyne molecules into the Pd-C bond of a six-membered palladocycle. One-pot synthesis of spirocyclic compounds
Maassarani, Fida,Pfeffer, Michel,Le Borgne, Guy
, p. 2043 - 2053 (2008/10/08)
The Pd-C bond of the compound containing a six-membered palladocyclic ring [{Pd(BP)(μ-Cl)}2] (1) (BP = C6H4CH2C5H 4N-2-(2-picolyl)phenyl) reacted with one alkyne unit (R1C≡CR2 in which R1 and/or R2 = Me, Ph, or CO2R and R = Me or Et) to afford regioselectively [{Pd(C(R2)=C-(R1)C6H4CH 2C6H4N)(μ-Cl)}2] (2a-f). 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)C6H4CH2C 5H4N}(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 (R1 = CO2Et) is close to the benzyl ring of the BP ligand. The iodide-bridged derivative 1* reacted with diphenylacetylene in refluxing chlorobenzene to afford a mixture of two products, 7a and 8a, which contain the heterocyclic cation [C(Ph)=C(Ph)C6H4CH2C5H4N] with a Pd2I6 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 to a spiro junction between a tetraphenylcyclopentadiene and a hexadienyl ring. This latter is η3-bonded to Pd. Compound 4a rearranged in refluxing chlorobenzene leading to a thermodynamically more stable isomer, 5a. The reaction between the ionic compound [Pd{C(CO2Me)=C-(CO2Me)C6H4CH 2C5H4N}(MeCN)2]SO3CF 3 (2e**) and dimethyl acetylenedicarboxylate (DMAD) afforded complex 6 in which three alkyne molecules have been found per Pd atom. The molecular structure of 6 has been determined by means of X-ray diffraction. It revealed that the two alkynes that have been added on 2e** formed again a cyclopentadiene ring with one quaternary carbon atom. The new terdentate ligand is chelating the Pd atom via the nitrogen, carbon, and oxygen atoms, defining thus two metalated rings containing seven and five atoms, respectively.
