Catecholboryl-functionalized ferrocene based Lewis acid system: a selective probe for fluoride ion through multiple channels

Abstract

The design and synthesis of two new receptors, C₂₀H₁₉O₃BFe and C₂₀H₂₁O₃BFe and their anion sensing properties through multiple channels are reported. Both the receptors, having chelating boronic ester Lewis acidic centre as the sole binding site, selectively bind fluoride ion in micromolar concentration. The binding constant of C₂₀H₁₉O₃BFe with the fluoride ion has been found to be quite high [K = 106 M⁻¹], whereas it displays a negligible affinity towards other effective competitors, for example acetate and cyanide (K = 10 M₋₁) and no sensitivity towards other halide ions. Upon selective recognition of F⁻ in acetonitrile, the redox potential of C₂₀H₁₉O₃BFe shifted by ΔE = 200 mV and the fluorescence emission was quenched drastically. The considerable changes in their absorption spectra are accompanied by the appearance of a new low energy (LE) peak at 566 nm and by a strong colour change from yellow to deep green which allows the prospective for “naked eye” detection of F⁻ anion.