Anion recognition and anion-mediated self-assembly with thiourea-functionalised fused [3]polynorbornyl frameworks

Abstract

Three conformationally preorganised host molecules based on the [3]polynorbornyl framework and incorporating di-urea receptors were synthesised and their interaction with a series of anions investigated by ¹H NMR spectroscopy. A high affinity of each host molecule for dihydrogenphosphate (H₂PO₄⁻) and dihydrogenpyrophosphate (H₂P₂O₇²⁻) was identified. In addition to binding to the urea receptors of the host molecules, evidence for an interaction involving the non-polar C–H groups within the binding cavity of the framework and guest anions was also discovered. Furthermore, an unusual 2 : 1 host-to-anion stoichiometry was indicated when binding H₂P₂O₇²⁻, and a model for the anion-mediated self-assembly of this complex species is proposed.