Asymmetric syntheses, structures and reactions of palladium(II) complexes containing thiolato- and sulfinyl-substituted P chiral phosphines

Abstract

The palladium complex (–)589-di-µ-chlorobis{(R)-1-[1-(dimethylamino)ethyl]-2-naphthyl-C 2,N}dipalladium(II) has been used successfully as the chiral template to promote the asymmetric [4 + 2] Diels–Alder reaction between 3,4-dimethyl-1-phenylphosphole and divinyl sulfoxide. A pair of diastereomeric exo-cycloadducts (1α,4α,5α,7S)-2,3-dimethyl-7-phenyl-5-(R/S-vinylsulfinyl)-7-phosphabicyclo[2.2.1]hept-2-ene were formed on the cationic palladium template with both behaving as bidentate ligands via their phosphorus and sulfinyl-oxygen donor atoms. Treatment of both diastereomeric template complexes with hydrochloric acid removed the chiral naphthylamine auxiliary from the template and resulted in the unexpected reductive cleavage of the S–O and the vinylic S–C bonds from the co-ordinating exo-cycloadducts to give a single optically pure thiolato-substituted phosphine P,S palladium chelate. In the absence of hydrochloric acid, the Pd–naphthylamine auxiliary and Pd–P bonds in both diastereomeric sulfinyl-substituted phosphine complexes are stable but their Pd–O bonds are easily displaced by any ionic chloride to give the corresponding neutral chloro complexes in which the sulfoxide functions are not involved in metal complexation. In these chloro complexes, the sulfinyl-substituted phosphines behave as monodentate ligands via their phosphorus donor and in contrast to their cationic counterparts the two neutral diastereomers could be separated efficiently by silica column chromatography.