UO2-salenes: neutral receptors for anions with a high selectivity for dihydrogen phosphate

TL;DR: In this paper, the authors report a novel class of neutral receptors for anions that contain an immobilized Lewis acidic binding site (UO{sub 2}){sup 2+} and in which there are ample opportunities to introduce specific secondary binding sites.

Abstract: The design and synthesis of neutral macrocyclic receptors that complex cations in apolar solvents with a high degree selectivity are based on the ability to organize nucleophilic binding sites (Lewis bases) in a complementary array. Although macrocycles with quaternary ammonium salts are known to complex anions, selectivity is not simply introduced. Macrocyclic and acyclic ligands that contain Lewis acidic binding sites such as boron, silicon, tin, and mercury bind anions, but these structures lack the possibility of subtle structural variation that is the basis for the selectivity in cation complexation. In this communication we report a novel class of neutral receptors for anions that contain an immobilized Lewis acidic binding site (UO{sub 2}){sup 2+} and in which there are ample opportunities to introduce specific secondary binding sites. This concept leads to high thermodynamic stabilities combined with high selectivities. Neutral anion receptors are very important for application in sensors and membrane transport experiments. This unique combination of a Lewis acidic uranyl center and the presence of amide NH groups which can form a favorable H-bond with a coordinated anion guest, in a preorganized receptor, can lead to highly specific anion recognition. 20 refs., 2 figs., 1 tab.