Unsaturated Selenacrown Ethers: Synthesis, Structure, and Formation of Silver Complexes

The unsaturated selenacrown ethers, (Z,Z,Z,Z,Z)-1,4,7,10,13-pentaselenacyclopentadeca-2,5,8,11,14-pentaene (15-US-5) (2), (Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16-hexaselenacyclooctadeca-2,5,8,11,14,17-hexaene (18-US-6) (3), (Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19-heptaselenacycloheneicosa-2,5,8,11,14,17,20-heptaene (21-US-7) (4), (Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22-octaselenacyclotetracosa-2,5,8,11,14,17,20,23-octaene (24-US-8) (5), and (Z,Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22,25-nonaselenacycloheptacosa-2,5,8,11,14,17,20,23,26-nonaene (27-US-9) (6), were obtained together with 1,4-diselenin (1) by reacting sodium selenide with cis-dichloroethene in the presence of a phase-transfer catalyst. The crystal structures of 2−5 were determined by X-ray crystallographic analysis. The UV spectra of the selenacrown ethers showed absorption maximums in the range of 251−262 nm, which were assigned to n→π* transitions. The cyclic voltammograms indicated that the large unsaturated selenacrown ethers were oxidized more easily than the small ones. The thermal reactions of the unsaturated selenacrown ethers afforded 1,4-diselenin (1) along with polymeric materials, whereas 1 was thermally stable even at 100 °C. The reactions of 1 or unsaturated selenacrown ethers 2−5 with silver ion yielded various novel silver complexes, Ag(C4H4Se2)(CF3COO) (7), Ag(C4H4Se2)2(CF3COO) (8), Ag(15-US-5)(CF3COO) (9), Ag5(18-US-6)3(CF3COO)5 (10), Ag7(21-US-7)(CF3COO)5 (11), Ag(24-US-8)2(CF3COO) (12), Ag2(24-US-8)(CF3COO)2 (13), Ag3(24-US-8)2(CF3COO)3 (14), Ag(15-US-5)NO3 (15), and Ag(21-US-7)BF4 (16). The stoichiometry for the complexation with silver trifluoroacetate in solution was examined by 1H NMR measurement. The titration plots of 2 and 5 under the dilution conditions showed a distinct inflection point at the 1/1 metal/macrocycle ratio, whereas the plots of 1 and 3 showed gradual change.