Renewable SiO2 as support for NiO catalyst for regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles from azide-alkyne cycloaddition in aqueous media

SiO2 derived from rice husk (SiO2-RH) has been used as a support for NiO catalyst for azide-alkyne cycloaddition in aqueous media at 60 ?. The 10wt%NiO/SiO2-RH catalyst was found to be an efficient and reusable catalyst for the regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles with broad substrate scope that included carbohydrate triazoles and one-pot synthesis of triazoles. The reaction mechanism followed through a nickel pi-complex on the surface of the NiO/SiO2-RH catalyst. The catalyst was recycled up to four times that showed consistent activity and selectivity. The structure-activity correlation and mechanistic studies were established by BET-SA, H-2-TPR, NH3-TPD, SEM-EDX, XPS, XRD,Si- 29 SS MAS NMR and H-2-pulse chemisorption studies and a plausible reaction mechanism has been proposed.