Synthesis and stereochemical study of new complexes of Pd and Pt with chiral dithioether ligands

摘要

New palladium(II) and platinum(II) complexes with two families of chiral dithioether ligands, (-)-1-benzyl-3, 4-bis(methylsulfanyl)pyrrolidine (-)-degusMe_2, (-)-1-benzyl-3, 4-bis(isopropylsulfanyl)pyrrolidine (-)-degusPr_2~i, (+)-1-benzyl-3, 4-bis(phenylsulfanyl)pyrrolidine (+)-degusPh_2, (-)-2, 2-dimethyl-4, 5-bis(methylsulfanylmethyl)-1, 3-dioxolane (-)-diosMe_2 and (-)-4, 5-bis(isopropylsulfanylmethyl)-2, 2-dimethyl-1, 3-dioxolane (-)-diosPr_2~i, have been prepared and characterised by NMR. The complexes [PdCl_2{(-)-degusMe_2}], [PdCl_2{(+)-degusPh_2}] and [PdCl_2{(-)-diosMe_2}] show a mixture of two diastereomers in solution at room temperature. VT-NMR indicates that there is no interconversion between diastereomers at room temperature. Complex [Pt(cod){(-)-diosMe_2}][BF_4]_2 is extremely fluxional and its diastereomers did not show isolated NMR resonances even at -90 deg C. The complexes [PdCl_2{(-)-degusPr_2~i}], [PdCl_2{(-)-diosPr_2~i}] and [Pt(cod){(-)-diosPr_2~i][BF_4]_2, which contain a more hindered ligand, seem to be well suited for use in enantioslective catalysis beacuse only one diastereomer is present.