Microwave-Assisted Neat Synthesis of a Ferrocene Appended Phenolphthalein Diyne: A Designed Synthetic Scaffold for Hg2+ Ion

摘要

A C-2-symmetric internally conjugated 1,3-dialkyne system 5, containing phenolphthalein as a fluorophore and ferrocene as a redox moiety, has been synthesized via a microwave-assisted synthetic procedure. Compound 5 was synthesized by Cu-catalyzed Glaser-Hay coupling using a microwave reactor in neat condition for the first time. Compound 5 was found to be highly selective toward Fe3+, Cu2+, and Hg2+ ions via multichannels. Interestingly, Fe3+ and Cu2+ ions simply promote the oxidation of ferrocene unit to ferrocenium ion without binding to the receptor, whereas Hg2+ binds with the receptor 5 (Delta E-1/2 = 71 mV). The oxidation and binding phenomena were investigated by optical and electrochemical analyses. Furthermore, the binding site of Hg2+ ion with our designed probe was confirmed by H-1, C-13 NMR and IR titration, which indicated that conjugated dialkyne unit interacts with Hg2+ ion by a favorable soft-soft interaction. Both receptor 5 and its metal complex, [5.2Hg(2+)], are stable in the physiological pH range (pH = 6-7) and thermally stable up to 78 degrees C. The experimental results of metal binding have been further supported by quantum chemical calculations (DFT), which explore the favorable geometry of the free ligand as well as its Hg2+ complex.