Tri-substituted hexahomotrioxacalix[3]arene derivatives bearing imidazole units: synthesis and extraction properties for cations and chromate anions

The article describes the synthesis and extraction properties of the new hexahomotrioxacalix[3]arene-based derivatives cone- and partial-cone-2 bearing 1-methyl-1H-imidazole moieties at the lower rim. It has been demonstrated that O-alkylation of the flexible macrocycle 1 with 2-(chloromethyl)-1-methyl-1H-imidazole hydrochloride affords tri-O-alkylated products with a cone or partial-cone conformation. Alkali metal salts such as NaH and Cs2CO3 can play an important role in the conformer distribution via a template effect. The conformation of receptors 2 has been confirmed by X-ray crystallographic analysis. Furthermore, the complexation properties of receptors 2 toward selected alkali/transition metal cations and alkylammonium ions are reported. The new 1-methyl-1H-imidazole-substituted hexahomotrioxacalix[3]arene frameworks are also efficient extractors of HCr2O7−/Cr2O72− anions at low pH.