An electrochemical study in acetonitrile of macrocyclic or open-chain ferrocene-containing oxa-aza or polyaza receptors in the presence of protons, metal cations and anions

Electrochemical studies on redox-active macrocyclic and open-chain ferrocene-containing oxa-aza or polyaza receptors were carried out in acetonitrile in the presence of protons, cations and anions. Electrochemical studies in the presence of H+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ with L4 (1,15-diferrocenyl-2,5,8,11,14-pentaazapentadecane) and L5 (1,4,7,10,13-penta(ferrocenylmethyl)-1,4,7,10,13-pentaazacyclopentadecane) resulted in shift of the ferrocene oxidation wave to more positive potentials with maximum shifts for L4 in the presence of Zn2+ and for L5 in the presence of Ni2+, Cu2+ and Hg2+ of 80 mV. In contrast, L1 (10-ferrocenylmethyl-1,4,7-trioxa-10-azacyclododecane), L2 (1,8-bis[bis(ferrocenylmethylamino)]-3,6-dioxaoctane) and L3 7,13-bis(ferrocenylmethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane) show a two-wave behaviour for H+, Pb2+ and Hg2+ allowing the amperometric titration of these metal cations. The maximum oxidation peak shift of 290 mV was found for L1 in the presence of Hg2+. Electrochemical behaviour with anions (H2PO4−, HSO4−, Br− and Cl−) in acetonitrile show that L2 and L6 (1,8-bis(ferrocenylmethylamino)-3,6-dioxaoctane) electrochemically sense H2PO4−. For L2 a cathodic shift of the oxidation peak of 190 mV and a shift of 346 mV to lower potential for the reduction peak was found. L6 shows a similar behaviour. This electrochemical sense of H2PO4− was observed even in the presence of excess of other anions (HSO4− or Cl−) in anion competition experiments.