Synthetic ionophores. Part 18: Ag⁺ selective trithiabenzena-and dithiabenzenapyridinacyclophanes

Abstract

The phase transfer catalysed nucleophilic displacement of 1,3-bis(bromomethyl)benzene, 2-methoxy-5- methyl-1,3-bis(bromomethyl)benzene (2) and 1,4-bis(bromomethyl)benzene with 2-mercaptoethanol gives the respective diols 3, 4 and 12 (80-85%), which undergo intermolecular cyclodehydrochlorination with thiodiglycolyl dichloride and pyridine-2,6-dicarbonyl dichloride?HCl to provide m-phenylene (7-10) and p-phenylene (13-14) based crownophanes. The single crystal X-ray structures of crownophanes 8 and 13 and their NMR studies show that the m-phenylene and p-phenylene rings remain in plane and perpendicular to the macrocyclic ring both in solution and solid phases. These crownophanes offer three soft coordinating sites (3 × S or 2 × S and 1 N) conducive to complexation with Ag⁺ and the steric restrictions imposed by m- and p-phenylene rings restrict 2 :1 (L :M) sandwich complexation required for complexation with the borderline soft Pb²⁺ cation. The crownophanes 7 and 9 extract Ag⁺ 172 and 602 times, respectively, more than Pb²⁺.