Anion Recognition by Phosphoric Triamide-Based Receptors

A series of phosphoric triamides were employed as a new class of anion receptors. The binding abilities for anions were evaluated by means of UV-vis and NMR titrations. Receptor 1a ((PhNH)3P=O), which has three aryl N-H groups, showed remarkable binding ability for anions comparable to the corresponding N, N’-diphenylurea 2. The orders of the association constants of receptors 1a, 1b ((BuNH)(PhNH)2P=O), and 1c ((BuNH)2(PhNH)P=O) for anions are basically dependent on the charge, Hofmeister series, and size of anions. The order of the binding ability of receptors for anions is 1a > 1b > 1c, indicating that the hydrogen bond ability of aryl substituted phosphoryl amide N-H is stronger than that of alkyl substituted phosphoryl amide. The properties were confirmed by DFT calculations.