NITROGEN-BRIDGED MACROCYCLES - SYNTHESIS, STRUCTURES AND INCLUSION PHENOMENA

Synthetic methods of nitrogen-bridged macrocyclic host molecules such as highly symmetrical cage compounds 3-6 and their bond isomers 8, 10, azacalix[n]arenes 16, 18 and 20, and tetraaza[3(4)] cyclophanes 24 an d 31, are summarized. The new class of macrocycles 3-6 were designed a nd synthesi2ed by one-step coupling reactions. In the compounds, pyrid ine or benzene units are connected by four bridgehead nitrogens, and b oth pyridine and bridgehead nitrogen lone pairs are directed into the cavity. The bridgehead nitrogen inversion is inhibited by the rigid st ructure. Because of the preorganized structure of 5 and 6 with four an d six pyridine donors, respectively, they strongly bind alkali metal a nd ammonium ions, as exemplified by the fact that they are obtained as the K+ complexes in the coupling reactions. The compound 5 showed Rb selectivity among alkali metal ions, and the structure of its K+ comp lex was confirmed by X-ray structural analysis. The hosts 5 and 6 also form very stable proton cryptates (H+ subset of 5 . OH- or H+ subset of 6 . OH-). They are relatively stable, but very slowly changed into water cryptates (H2O subset of 5 or H2O subset of 6). The cation affin ity of the host can be controlled by attaching electron-donating or -w ithdrawing substituents on the pyridine rings. A Cl- ion formed the co mplex with 6 in acidic solution, but Br-, I- and other anions larger t han Cl- could not be encapsulated by 6. The azacalixarenes, a new fami ly of calix [n] arenes, have more rigid structure than the correspondi ng oxacalix[n]arenes and calix[n]arenes because of the strong intramol ecular hydrogen bonds between phenolic hydroxyl groups and nitrogen lo ne pairs.