Three C2-symmetric dialkyne systems with internally conjugated 1,3-diyne (5a and 4b), and terminal alkynes (3b) as the principal functionality of interest and phenolphthalein as fluorophore and ferrocene as redox moiety, have been synthesized via microwave-assisted Cu-catalyzed Glaser−Hay coupling in neat condition for the first time. All of the three compounds were 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 receptors, whereas Hg2+ binds with each of the receptors strictly following the HSAB principle. The oxidation and binding phenomena were investigated by optical and electrochemical analyses. Furthermore, the binding site of Hg2+ ion with our designed probes were confirmed by 1H, 13C NMR and IR titrations, which indicated that the conjugated dialkyne units in 5a and 4b interact with Hg2+ ion by a favorable soft−soft interaction in the ratio 1:2 and 1:1 respectively, whereas the terminal alkynes in 3b interact with Hg2+ ion in 1:2 ratio. All the alkyne units in the three ligand systems participate in Hg2+-binding by extending its π-cloud and do not undergo any chemical transformation. Both ligands and their metal complexes are stable in the physiological pH range (pH = 6−7) and thermally stable up to 78°C for 5a and 60°C for 3b and 4b. The experimental results of metal binding have been further supported by quantum chemical calculations (DFT), which explore the favourable geometry of the free ligands as well as their Hg2+-complex.

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

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27th CRSI National Symposium in Chemistry

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