Ni-rGO-zeolite nanocomposite: an efficient heterogeneous catalyst for one-pot synthesis of triazoles in water

An important group of pharmaceutical materials, 1,2,3-triazoles, has been synthesised using a Ni-based nanocomposite catalyst (Ni-rGO-zeolite) through azide alkyne cycloaddition (NiAAC). First, a GO-zeolite hybrid was prepared through protonation of a Na-Y-zeolite by H⁺ ions originating from the -COOH groups of GO. Subsequently the GO-zeolite was treated with Ni-acetate solvothermally in the presence of NaBH₄ (reducing atmosphere). Under the solvothermal conditions a significant part of the incorporated Ni ions in the GO-zeolite were reduced to Ni(0) and simultaneously GO was transformed into rGO. The resulting ternary nanocomposite, Ni-rGO-zeolite, serves as a highly efficient heterogeneous catalyst, and shows excellent regioselectivity forming 1,4-disubstituted-1,2,3-triazoles as the sole product at a low loading of the nickel (similar to 2.6 mol% with respect to the substrate) with recyclability, and without any significant leaching of the metal. In addition, the Ni-rGO-zeolite exhibits enhanced efficiency under aqueous conditions, proficiency with varying substrates and overcomes some of the shortcomings of the previously reported limited number of Ni-based and other catalysts. The catalytic process is believed to involve the active Ni(0) species, which is stabilized by electron rich rGO that is supported on the microporous high-surface-area zeolite.