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Conformationally flexible hexakis‐urea 1 was synthesized efficiently by condensing hexakis(aminomethyl)benzene with 4‐nitrophenyl‐(3,5‐di‐tert‐butylphenyl)carbamate. The hexakis‐urea 1 is unexpectedly soluble in organic solvents of low polarity due to intramolecular hydrogen bonding. The hexakis‐urea 1 recognizes chloride, bromide, and acetate in a 1:2 host‐guest ratio and in a positive allosteric manner in CDCl3. The ability of 1 to recognize dihydrogen phosphate is a unique outcome, and the structure of the associated complex, which contains four dihydrogen phosphate ions, was clarified by single‐crystal X‐ray structural analysis. However, in solution, a complex with three dihydrogen phosphate ions was identified. The dihydrogen phosphate association in CDCl3 proceeds in an amphoteric allosteric manner; in a positive allosteric manner (K1K3) in the subsequent step. [ABSTRACT FROM AUTHOR]

Cover Feature: Amphoteric Homotropic Allosteric Association between a Hexakis-Urea Receptor and Dihydrogen Phosphate (Chem. Eur. J. 71/2019) Keywords: allosteric cooperativity; anion recognition; host-guest system; hydrogen bonding; receptors Allosteric cooperativity, anion recognition, host-guest system, hydrogen bonding, receptors. [Extracted from the article]