Crown-annelated 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene derivatives as cation sensors: Synthesis, X-ray crystal structures, voltammetric and spectroscopic monitoring of metal complexation

The synthesis of O4S2-crown annelated derivatives of 9,10-bis(1,3-dithiol-2 -ylidene)-9,10-dihydroanthracene using the novel Horner-Wadsworth-Emmons re agent 7 is reported. The bis- and mono-crown systems 9 and 12 function as e fficient Ligands in the voltammetric and UV/Vis spectroscopic recognition o f Na+ and Ag+. Solution electrochemical studies reveal that metal complexat ion to the crown unit(s) leads to a significant positive shift in the poten tial of the first, two-electron oxidation wave of 9 and 12 [maximum shift E -1(OX) = 115 mV for 9 in the presence of Ag+ (ca. 10 molar equivalents)]. C onsiderably smaller shifts (< 30 mV) were observed for complexation of Li+, K+ and Ba2+. UV/Vis spectrophotometric studies of metal binding (Na+ and A g+) to 9 are consistent with the simultaneous formation of 1:1 and 1:2 comp lexes. The X-ray crystal structures of compounds 10 and 12<bullet>CH2Cl2 ar e reported. The anthracenediylidene moiety of 12 is U-shaped due to the boa t conformation of the central (quinodimethane) ring and folding of both 1,3 -dithiole rings, providing an overall saddle conformation. The folding in 1 0 is reduced as steric crowding is relieved by removal of one of the 1,3-di thiole units.