Synthesis and functionalization of novel unsaturated thiacrown ethers and related compounds

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The 6-, 9-, 12-, 15-, 18-, 21-, 24-, and 27-membered unsaturated thiacrown ethers were synthesized by reacting cis-dichloroethene with sodium sulfide in acetonitrile. The crystal structures were determined by X-ray crystallography, and it was found that there are cavities in these molecules. The reactions of 18- and 21-membered unsaturated thiacrown ethers, 18-UT-6 and 21-UT-7, with CF_3COOAg in acetone afforded novel silver(I) complexes Ag^1(18-UT-6)(CF_3COO) and Ag^1_2(21-UT-7)(CF_3COO)_2, respectively. The stoichiometry for complexation of 15-UT-5, 18-UT-6, and 21-UT-7 with CF_3COOAg in solution was examined by ^1H NMR measurement. The titration plots of 15-UT-5 and 21-UT-7 showed a distinct break point at the 1:1 and 2:1 metal/macrocycle ratio, respectively, while the plots of 18-UT-6 gradually changed at the range of 1:1-2:1. From these results, 15-UT-5 and 21-UT-7 were found to include selectively one and two silver ions, respectively, and 18-UT-6 showed low selectivity for the inclusion number. The complexation of 18-UT-6 with 1 equiv of HgCl_2 in acetone afforded mercury complex Hg^<11>(18-UT-6)Cl_2. The complexations of 18-membered saturated thiacrown ether, 18S6, with 1 equiv of each HgCl_2 and CdCl_2 in acetone afforded Hg^<11>(18S6)Cl_2 and Cd^<11>(18S6)Cl_2, respectively. The crystal structure of Hg^<11>(18-UT-6)Cl_2 revealed that the mercury atom was inside the cavity of the macrocycle and the geometry around the mercury atom was an eight-coordinate hexagonal bipyramidal arrangement. ORTEP drawing of Hg^<11>(18S6)Cl_2 revealed the existence of mercury atom outside the cavity of the ring. ^1H NMR study of Hg^<11>(18-UT-6)Cl_2 in acetone-d_6 indicated that the interconversion between free 18-UT-6 and pure complex was slower than the NMR time scale. The titration experiment by ^1H NMR revealed that 18-UT-6 had inclusion selectivity for the number of mercury atoms.