Synthesis and anion-selective complexation of cyclophane-based cyclic thioureas

Cyclic thiourea derivatives having three different types of cyclophane structure, ortho-meta, meta-meta, and meta-para, and a lariat-type thiourea, were synthesized, and their anion-binding ability was examined. The association constants for the complexation between the receptors and several anions in DMSO-d(6) were measured by the titration method using (1)H NMR spectroscopy. All receptors, except for the meta-para cyclophane, exhibit selective binding to the dihydrogenphosphate anion, which is stronger than that of the acyclic reference compound. The lariat-type receptor binds anions even more strongly than the cyclic receptors which do not possess the third binding site.