Anion recognition by phosphoric triamide-based receptors

Abstract A series of phosphoric triamides were employed as a new class of anion receptor. The binding abilities for anions were evaluated by means of ultraviolet-visible and nuclear magnetic resonance spectral titrations. Receptor 1a ((PhNH)3P=O), which has 3 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 using density functional theory calculations.