Approaches towards the enantioselective recognition of anionic guest species using chiral receptors based on rhenium(i) and ruthenium(ii) with amide bipyridine ligands

Abstract

The syntheses of chiral anion receptors based on rhenium(I) and ruthenium(II) with amide bipyridine ligands are reported. The rhenium(I) hosts were prepared in moderate to high yields by co-ordinating chiral bipyridine ligands to a Re(CO)₃Br centre. The ruthenium(II) receptors were synthesised via the chiral building blocks Λ- and Δ-[Ru(bpy)₂(py)₂]²⁺ or by chromatographic resolution on a SP Sephadex C-25 cation exchanger. Chiral purity was determined by ¹H NMR and circular dichroism spectroscopy and lanthanide shift experiments. ¹H NMR titration studies showed that these receptors bind chiral carboxylate anions in DMSO-d₆, although significant chiral discrimination was not observed.