SYNTHETIC IONOPHORES - PART-18 - AG+ SELECTIVE TRITHIABENZENAPYRIDINACYCLOPHANES AND DITHIABENZENAPYRIDINACYCLOPHANES

The phase transfer catalysed nucleophilic displacement of 1,3-bis(brom omethyl)benzene, 2-methoxy-5-methyl-1,3-bis(bromomethyl)benzene (2) an d 1,4-bis(bromomethyl)benzene with 2-mercaptoethanol gives the respect ive diols 3, 4 and 12 (80-85%), which undergo intermolecular cyclodehy drochlorination with thiodiglycolyl dichloride and pyridine2,6-dicarbo nyl dichloride . HCl to provide m-phenylene (7-10) and p-phenylene (13 -14) based crownophanes. The single crystal X-ray structures of crowno phanes 8 and 13 and their NMR studies show that the m-phenylene and p- phenylene rings remain in plane and perpendicular to the macrocyclic r ing both in solution and solid phases. These crownophanes offer three soft coordinating sites (3 x S or 2 x 8 and 1 N) conducive to complexa tion with Ag+ and the steric restrictions imposed by m-and p-phenylene rings restrict 2:1 (L: M) sandwich complexation required for complexa tion with the borderline soft Pb2+ cation. The crownophanes 7 and 9 ex tract Ag+ 172 and 602 times, respectively, more than Pb2+.