Synthesis of oligomeric calix[4]arene-crowns as novel ionophores for alkali and transition metals

Two different oligomeric calix[4]arene-crowns (2b and 3b) were synthesized (via) the condensation reaction of p-tert-butylcalix[4]arene-oxacrown-4 (2a) and p-tert-butylcalix[4]arene-thiacrown-4 (3a) (calix[4]arene-crown monomers) with 1,5-dibromopentane. In these oligomerization reactions, it has been found that only three or four calix[4]arene-crowns-4 units have been linked together through alkyl bridges. Their comparative complexing properties with selected alkali and transition metals are reported here. It has been deduced that the selectivity of monomer 2a toward alkali metals has not been reserved, but a pronounced increase in its complexing ability was observed after the oligomerization. However, the selectivity of the monomer 3a toward Cu2+, Hg2+, and Ph2+ has also been lost after oligomerization, and it has been found that oligomer 3b is an efficient extractant for the transition metal cations employed in the two-phase extraction systems.