Thiamacrocyclic Lactones: New Ag(I)-Ionophores

The syntheses of novel adamantane thialactones 5−12 are reported, and the results of the heavy- and transition-metal cation extraction experiments are described. The results are compared with those obtained with similar thiamacrocyclic ligands that have flexible chains of methylene groups incorporated into the macrocyclic framework as in 13−20. The results show that most of the hosts studied are very good in complexing the Ag⁺ ion. The formation of complexes has also been demonstrated using NMR titration experiments for macrocycles 13 and 14 with AgTFA. Introduction of a single polycyclic molecule into the 15- to 18-membered rings increases the rigidity and preorganizes the ligand for complexation. However, two adamantane molecules embedded in the ring usually diminish the complexing ability of the ligand, primarily due to sterical effects of the bulky adamantane moiety that obstructs formation of an optimal geometry for binding the desired metal ion. The structures of macrocycles 5, 7, 9, 11, and 19 were determined by X-ray structure analysis, and their conformational properties are discussed. In the solid state, 7, 11, and 19 are organized into tubular fashion using C−H···O interactions. Also, two silver complexes with thialactone 13, Ag13 and Ag(13)₂, were prepared and characterized. The structure analysis of Ag13 and Ag(13)₂ reveals the formation of mononuclear and binuclear species with silver in ambivalent, tetrahedral coordination via sulfur and oxygen from trifluoroacetate anion.