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

摘要

New derivatives withthe 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'-(1-dicyclohexylphosphinopropanediyl)ferrocene, PP~(Cy)PF, 4 were synthesized from Pd_2(dba)_3·CHCl_3 and the appropriate ferrocnyl ligand. When an encess 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.