NMR study on the coordination of dibenzylideneacetone to chiral palladium(0) units.: Fluxional behaviour including an intramolecular double bond exchange

New derivatives with the general formula Pd(L-L)(eta (2)-dba) (dba = dibenzylideneacetone), L-L = 1-diphenylphosphino-2,1'-(1-dimethylaminopropanediyl)ferrocene, PAPF, 1; 2-[1-(dimethylamino)ethyl]-1-(diphenylphosphino)ferrocene, PPFA, 2; N,N-dimethyl-1-[1',2-bis(diphenylphosphino)ferrocenyl]ethylamine, BPPFA, 3, 1-diphenylphosphino-2,1'-(I-dicyclohexylphosphinopropanediyl)ferrocene, (PPPF)-P-Cy, 4 were synthesized from Pd-2(dba)(3). CHCl3 and the appropriate ferrocenyl ligand. When an excess of PPFA was used, the complex Pd(PPFA)(3) with P-coordinated PPFA ligands was formed. The dba unit preferentially adopts an s-cis,trans conformation with the s-trans alkene coordinated to the Pd(L-L) fragment. Several intramolecular dynamic processes were identified: at room temperature a fast rotation of dba about the alkene-Pd bond, a Pd-N bond rupture process for complex 2 and, at elevated temperatures, an intramolecular diastereomer interconversion involving an alkene face exchange accompanied by an interchange between the coordinated and non-coordinated dba double bonds. The crystal structure of complex 2 was determined by X-ray diffraction.