Hydrogen-Bonding Amidoindoles in the Presence of Anions: An X-ray Structure of a Receptor at the Acid–Base Half-Equivalence that Binds an Anion

Hydrogen-bonding catalysts based on (thio)amidoindole moieties were evaluated in the presence of anions as potent anion receptors and/or acidic partners involved in acid–base reactions. In particular, we focused on their behavior at the acid–base half-equivalence point in the presence of basic anions such as fluoride and benzoate salts. Among three isolated X-ray structures, an amidoindole in the presence of fluoride and hexafluorophosphate salts formed, at the acid–base half-equivalence point, an unprecedented sandwich complex between two receptors and a PF6– anion.