Neutral Anion Receptors with Multiple Urea‐Binding Sites

The synthesis of macrocyclic and acyclic cleft-like anion receptors in which four hydrogen bond donating urea moieties are present in a preorganized fashion is described. NMR spectroscopy shows the complex formation with H2PO4− and Cl −. Cleft-like receptors bind H2PO4− in a 2:1 guest-host stoichiometry (Ka = 107M−2) in DMSO, whereas Cl − is bound in a 1:1 stoichiometry (Ka = 103M−1). The macrocyclic receptors form a 1:1 complex with H2PO4− (Ka = 103M−1 in DMSO) with a 100-fold selectivity for H2PO4− over Cl −.