High selectivity for l-cysteine residue at axial solvated site of trigonal–bipyramidal palladium(II) complex with tripodal tetradentate phosphine

The five-coordinate trigonal–bipyramidal palladium(II) and platinum(II) complexes with sulfur-coordinated glutathione at the axial position, [Pd(gluta)(pp3)](BF4) and [Pt(gluta)(pp3)](PF6) (gluta = glutathionate, pp3 = tris[2-(diphenylphosphino)ethyl]phosphine), were prepared and characterized by 31P NMR spectroscopy. The dimeric square-planar platinum(II) complex [Pt(pp3)]2(PF6)4 gave the monomeric five-coordinate solvated complex, [Pt(pp3)(CH3CN)]2+, in acetonitrile. Extraction experiments for amino acids from the aqueous solution to the chloroform layer were carried out by using [Pd(pp3)(CH3CN)]2+, [Pt(pp3)(CH3CN)]2+, and [Pd(p3)(CH3CN)]2+ (p3 = bis[2-(diphenylphosphino)ethyl]phenylphosphine) as extractants. High selectivity for the thiolate sulfur atom in l-cysteinate was observed at the solvated coordination site in [Pd(pp3)(CH3CN)]2+. The selectivity was applied to extraction of l-cysteinate from a mixture of some amino acids and, further, the reduced form of glutathionate from a mixture of the reduced and oxidized forms of glutathione.