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 reagent 7 is reported. The bis- and mono-crown systems 9 and 12 function as efficient ligands in the voltammetric and UV/Vis spectroscopic recognition of Na+ and Ag+. Solution electrochemical studies reveal that metal complexation to the crown unit(s) leads to a significant positive shift in the potential of the first, two-electron oxidation wave of 9 and 12 [maximum shift E1ox = 115 mV for 9 in the presence of Ag+ (ca. 10 molar equivalents)]. Considerably smaller shifts (< 30 mV) were observed for complexation of Li+, K+ and Ba2+. UV/Vis spectrophotometric studies of metal binding (Na+ and Ag+) to 9 are consistent with the simultaneous formation of 1:1 and 1:2 complexes. The X-ray crystal structures of compounds 10 and 12-CH2Cl2 are reported. The anthracenediylidene moiety of 12 is U-shaped due to the boat conformation of the central (quinodimethane) ring and folding of both 1,3-dithiole rings, providing an overall saddle conformation. The folding in 10 is reduced as steric crowding is relieved by removal of one of the 1,3-dithiole units. © Wiley-VCH Verlag GmbH, 2001