Triazolyl Alkoxy Fischer Carbene Complexes in Conjugation with Ferrocene/Pyrene as Sensory Units: Multifunctional Chemosensors for Lead(II), Copper(II), and Zinc(II) Ions

The regioselective 1,3-dipolar cycloaddition reaction of alkoxy alkynyl Fischer carbene complex 1 with azidomethyl ferrocene 2 and with azidomethyl pyrene 4 under solvent-free conditions yielded the triazolyl Fischer carbene complexes 3 (C₂₇H₂₁O₆N₃FeW) and 5 (C₃₃H₂₁O₆N₃W), respectively. The cation complexation properties of these receptors have been systematically studied using electrochemical and spectroscopic techniques. The exceptional structural feature existing in these receptors is the presence of a Fischer carbene moiety, connected to the ferrocene or pyrene moiety through a 1,2,3-triazole ring. Receptor 3 contains a redox-active ferrocene moiety and is highly selective toward Pb²⁺ ion, whereas receptor 5, having a fluorescent pyrene unit, selectively recognizes Zn²⁺ and Cu²⁺ ions. The binding ability of receptor 3 can be inferred either from the redox shift (the anodic shift ΔE_1/2 = 55 mV) or the highly visual output response for Pb²⁺ ion. Receptor 5 displays considerable chelation-enhanced fluorescence (CHEF) upon binding with Zn²⁺ and Cu²⁺ ions in an aqueous environment. Further, the proposed binding modes of these receptors and their metal cation complexation properties have been supported by ¹H NMR titration and MALDI-MS and a DFT study.