Electrochemical and binding properties of a novel ferrocene-containing redox-active basket-shaped host molecule

A novel basket-shaped host based on the rigid molecule diphenylglycoluril {3a,6a-diphenyltetrahydroimidazo[4,5-d]imidazole-2,5(1H,3H)-dione} has been synthesized and characterised. It is able to bind cations in its crown ether rings and neutral organic substrates in its cavity. Differential pulse voltammetry experiments showed that the host is redox-responsive to cations. It forms 1:1 complexes with K+ and NH4+ ions and 1:2 host-guest complexes with Na+ ions. On addition of(di)ammonium salts, protonation of the host occurs. A complex was formed between the host and model substrate olivetol (5-pentylbenzene-1,3-diol). In the absence of additives, this complex is stabilised via hydrogen bonds and pi-pi stacking interactions. In the presence of Na+ ions a complex consisting of the host, the diol, and 2 Na+ ions was formed, in which hydrogen bonds are no longer present. In the presence of 2 Na+ ions a four-fold increase in association constant has been found. Spectroscopic (NMR and IR) experiments have been used to elucidate the mode of co-operative co-ordination between the host, diol substrate and Na+ ions.