First Synthesis and Structure of β-Ketoimine Calix[4]arenes: Complexation and Extraction Studies

The synthesis of a new series of β-ketoimine calix[4]arene derivatives is described. The reaction of calix[4]arene or p-tert-butylcalix[4]arene with bromoacetonitrile or bromobutyronitrile afforded di-, tri-, and tetranitrile calixarene derivatives (3−8, 3a), which were then reduced into the corresponding amine (9−13, 3b). The condensation of these aminocalixarenes with acetylacetone led to six β-ketoimine calix[4]arene derivatives (14−18, 3c) as a class of selective receptors toward transition metals. Molecular structures of 4, 7, and 17 have been determined by X-ray diffraction. The packing of 17 revealed a network of intramolecular and intermolecular hydrogen bonds. The complexation properties of receptors 15, 17, and 3c toward different metal ions have been investigated by UV−vis titrations in organic media. The stoichiometries of complexes with 17 were determined by both the mole ratio method and Job plots. These novel receptors selectively complex Cu²⁺, Hg²⁺, and Ag⁺. Moreover, the extraction properties of 17 toward cations have been studied by liquid−liquid extraction and atomic absorption spectrometry. Compound 17 has good affinity and selectivity toward Pb²⁺.