Anion binding at the core of branched ferrocene derivatives

Abstract

The anion binding ability of two ferrocenoyl amide derivatives with bulky branched substituents has been determined. NMR titration experiments indicated that in each case, the ability of these molecules to bind anions at the core through hydrogen bonding was poor as a consequence of the steric bulk of the substituents. Electrochemical experiments, however, indicated that anion binding could occur in the oxidised ferrocenium form as a consequence of electrostatic interactions. This binding was evidenced by the onset of EC mechanistic behaviour in the presence of halide anions. Square wave voltammetry was used to report on halide anion binding via a decrease in the peak current and a cathodic shift in the apparent redox potential of the receptors. The magnitude of this shift was dependent on the degree of dendritic functionalisation—indicating the ability of dendritic branching to act as a steric shield, hindering the penetration of guest anions. These results have implications for the design of sensors based on encapsulated binding sites.