Zinc(II) complex immobilized on amine functionalized silica gel: A novel, highly efficient and recyclable catalyst for multicomponent click synthesis of 1,4-disubstituted 1,2,3-triazoles

We report a highly efficient and recyclable heterogeneous zinc catalytic system via covalent immobilization of 2-hydroxyacetophenone (2-HAP) onto an amine functionalized silica gel followed by metallation with zinc chloride and its catalytic application in three component click synthesis of 1,4-disubstituted 1,2,3-triazoles. The structure of the synthesized organic-inorganic hybrid material (SiO 2 @APTES@2HAP-Zn) has been confirmed by various physico-chemical characterization techniques such as solid-state 13 C CPMAS NMR spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), atomic absorption spectroscopy (AAS), energy dispersive X-ray fluorescence spectroscopy (ED-XRF), and elemental analysis.

The newly designed catalyst works under mild reaction conditions and also exhibits excellent performance in terms of good product yield and high turnover number (TON). One of the most important attributes of the present methodology is that the catalyst can be recycled several times without appreciable loss in its activity as proved by FTIR spectroscopy and SEM analysis. Besides, the heterogeneity test also confirms that no leaching of active catalytic species occurs from the silica supported zinc catalyst which confirms its remarkable structural stability under the reaction conditions.