Asymmetric syntheses, structures and co-ordination chemistry of palladium(II) complexes containing a chiral P,S hybrid bidentate ligand

Abstract

The chiral palladium complex (+)₅₈₉-di-µ-chloro-bis{(S)-1-[1-(dimethylamino)ethyl]-2-naphthyl-C²,N}dipalladium(II) has been used successfully to promote the asymmetric [4 + 2] Diels–Alder reaction between 3,4-dimethyl-1-phenylphosphole and phenyl vinyl sulfide. The cycloaddition product (–)-(1α,4α,5α,7R)-2,3-dimethyl-7-phenyl-5-(phenylsulfanyl)-7-phosphabicyclo[2.2.1]hept-2-ene was formed stereoselectively on the chiral palladium template and behaves as a bidentate ligand via its phosphorus and sulfur donor atoms. The chiral naphthylamine auxiliary and the new P,S bidentate ligand can be selectively released with retention of chirality by treatment with hydrochloric acid or 1,2-bis(diphenylphosphino)ethane respectively. The optical purity of the liberated heterobidentate compound has been confirmed by NMR spectroscopic studies. The absolute stereochemistries and the co-ordination properties of the enantiomerically pure P,S compound and its oxidized derivative have been established by single-crystal X-ray analyses.