Electrochemical anion recognition with ferrocene functionalised macrocycles

Abstract

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.