SELECTIVE ION CLEFTS BASED ON A 3-BRIDGED [4(3)]CYCLOPHANE

A variety of new three-bridged cyclophanes,clefts 4-14, have been conv eniently prepared, and their cation-binding properties have been exami ned. Compounds 4-6 have a special affinity for alkali metal cations. E thyl ester 5 and methyl ester 4 selectively formed 2:1 complexes with K+ and Na+ ions, respectively. Clefts 11-13, which possess pyridyl gro ups, bind Ag+ cation exclusively. H-1 NMR titration studies confirmed that 11 or 12, having 2- or 3-pyridyl groups, form a 1:1 complex with Ag+ cation, while 13, with 4-pyridyl ligating groups, forms a 2:1 comp lex. Cleft 10, with aminimide groups, also shows an affinity for Ag+ c ation in a 2:1 ratio in a polar solvent, while it forms a 1:1 complex in a nonpolar solvent. The same solvent effect was observed for clefts 13 and 15c, which is discussed qualitatively.