Alkali metal complexation properties of resorcinarene bis-crown ethers: effect of the crown ether functionality and preorganization on complexation

The synthesis and characterization of tetramethoxy resorcinarene tribenzo-bis-crown ethers, m- and p-TBBC6, are described. The effect of the added aromatic functionality in the crown ether bridge on the alkali metal complexation properties was investigated and compared to the properties of tetramethoxy resorcinarene bis-crown-5 (BC5) by means of 1H NMR spectroscopy and X-ray crystallography. It was found that BC5 and m-TBBC6 were capable of binding alkali metal cations (K+, Rb+, and Cs+), with the highest affinity toward Cs+ cation, while no binding was observed in the case of p-TBBC6, which confirms the significance of the complementarity and preorganization for complexation affinity.