Synthesis and alkali metal picrate extraction capabilities of novel, cage-functionalized diaza(l7-crown-5) ethers

The syntheses of novel cage-annulated diaza (17-crown-5) lariat crown ethers, i.e. 10-16 are reported. A series of alkali metal picrate extraction experiments have been performed by using this new class of synthetic ionophores in order to evaluate the effects of cage-annulation and the influence of N-pivot side-arms upon complexation properties. The results thereby obtained indicate that complexation of these lariat crown ethers with alkali metal cations is influenced by both of these structural features. In particular, the cage-annulated diaza crown ether 11 displays much greater avidity toward all alkali metal cations studied than does the corresponding model system (1). It was observed that ligands 11 and 13 display bimodal behavior toward extraction of alkali metal picrates, whereas ligands 15 and 16 behave as relatively non-selective alkali metal picrate extractants. A cage-annulated cryptand, 19, was prepared, and its alkali metal picrate extraction profile was obtained. Highly preorganized cryptand 19 displays particularly high avidity toward complexation of K+ and Rb+ picrates in solution. (C) 1999 Elsevier Science Ltd. All rights reserved.