Electrochemical anion recognition with ferrocene functionalised macrocycles

The syntheses and characterization of two new redox active cyclam ligands ferrocenylmethyl-(6-methyl-1,4,8,11-tetraazacyclotetradec-6-yl)-amine (L3) and 1,1'-ferrocenylmethyl-bis(6-methyl-1,4,8,11-tetraazacyclotetradec-6-yl)-amine (L4) are reported. The compounds each possess a ferrocenyl group bearing one (L3) or two (L4) appended macrocycles linked by their exocyclic amino groups and the crystal structures of both compounds have been determined. Anion binding of L3 and L4 was investigated by electrochemical titrations where H-bonding to each macrocycle causing a shift in the Fc+/0 redox potential was used as a reporter of guest binding. The Zn(II) complex of L3 has also been isolated and characterized structurally. These compounds were analysed for their capacity to electrochemically recognize anions in both aqueous and non-aqueous solution. We have found that L3, L4 and ZnL3]2+ sense Cl- and AcO- anions in MeCN-CH2Cl2, a function that is lost in aqueous solution.