Heteroditopic ligands based on ferrocenyl benzimidazoles fused to an additional diaza heterocyclic ring system

Abstract

The synthesis of ferrocene-based heteroditopic receptors in which the ferrocene moiety is attached to an imidazo[4,5-e]benzothiadiazole or imidazo[4,5-f]quinoxaline is reported. These nitrogen-rich ferrocene derivatives show remarkable ion-sensing properties because of the presence of the redox active ferrocene unit and the polyazaheteroaromatic ring systems which act as a dual binding site for anions and metal cations. They display an anodic shift of the oxidation wave (ΔE_1/2 = 67–200 mV) upon complexation with metal cations and a strong cathodic shift (ΔE_1/2 = −82 to −100 mV) in the presence of F⁻ and HP₂O₇³⁻ anions. For the Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ metal cations tested, the change in the absorption spectra is accompanied by a dramatic colour change which allows the potential for “naked eye” detection.