ANION RECOGNITION BY REDOX-RESPONSIVE DITOPIC BIS-COBALTOCENIUM RECEPTOR MOLECULES INCLUDING A NOVEL CALIX[4]ARENE DERIVATIVE THAT BINDS A DICARBOXYLATE DIANION

A series of novel ditopic bis-cobaltocenium receptor molecules containing alkyl, aryl, and calix[4]arene spacers have been synthesized via the reaction of the new synthon 1-(ethylcarboxy)-1'-(chlorocarbonyl)cobaltocenium chloride (3) or 1-(chloro carbonyl)cobaltocenium chloride (9) with the appropriate diamine. Proton NMR halide anion coordination studies reveal that the ethyl- (4), propyl- (5), and butyl-linked (6) derivatives form 1:1 stoichiometric complexes in acetonitrile solutions. Stability constant determinations suggest that the ethyl derivative 4 exhibits selectivity for the chloride anion in preference to bromide or iodide. Receptors containing larger aryl (7,8,10) and alkylamino (11) spacers form complexes of2:1 halide anion:receptor stoichiometry. An X-ray crystal structure of the bis-cobaltocenium calix[4]arene derivative 15 is described. This receptor forms extremely stable 1:1 anion complexes with chloride, bromide, and H2PO4- in dimethylsulfoxide solutions and with the dicarboxylate dianion adipate in acetone. Ah the bis-cobaltocenium systems were found to display electrochemical recognition of varied anion guests, as shown by cyclic voltammetric experiments. Receptor 15 was also found to redox-respond to the presence of adipate.