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

Abstract

New palladium(II) and platinum(II) complexes with two families of chiral dithioether ligands, (−)-1-benzyl-3,4-bis(methylsulfanyl)pyrrolidine (−)-degusMe₂, (−)-1-benzyl-3,4-bis(isopropylsulfanyl)pyrrolidine (−)-degusPrⁱ₂, (+)-1-benzyl-3,4-bis(phenylsulfanyl)pyrrolidine (+)-degusPh₂, (−)-2,2-dimethyl-4,5-bis(methylsulfanylmethyl)-1,3-dioxolane (−)-diosMe₂ and (−)-4,5-bis(isopropylsulfanylmethyl)-2,2-dimethyl-1,3-dioxolane (−)-diosPrⁱ₂, have been prepared and characterised by NMR. The complexes [PdCl₂{(−)-degusMe₂}], [PdCl₂{(+)-degusPh₂}] and [PdCl₂{(−)-diosMe₂}] 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){(−)-diosMe₂}][BF₄]₂ is extremely fluxional and its diastereomers did not show isolated NMR resonances even at −90 °C. The complexes [PdCl₂{(−)-degusPrⁱ₂}], [PdCl₂{(−)-diosPrⁱ₂}] and [Pt(cod){(−)-diosPrⁱ₂}][BF₄]₂, which contain a more hindered ligand, seem to be well suited for use in enantioselective catalysis because only one diastereomer is present.