Electrochemically active phenylenediamine probes for transition metal cation detection

Abstract

A novel family of tetraalkyl-p-phenylenediamine (TAPD)-based ligands has been efficiently prepared by reductive amination of heterocyclic aldehydes. The redox properties of these electrochemical active ligands change dramatically upon complexation of the transition metal cations Zn²⁺, Ni²⁺ and Cd²⁺ leading to large oxidation potential shifts of up to 950 mV depending on the nature of the ligand. Complexes with a metal to ligand ratio of 1 ∶ 2 were formed and ¹¹³Cd NMR revealed an octahedral coordination sphere of the metal. All pyridyl derivatives show a distinct chemoselectivity (Zn²⁺ > Cd²⁺ > Ni²⁺). The thiophenyl containing derivatives display a particularly high selectivity for zinc cations (Zn²⁺ ≫ Ni²⁺, Cd²⁺).