Polyvinylpolypyrrolidone-Stabilized Copper Nanoparticles as an Efficient and Recyclable Heterogeneous Catalyst for the Click of 1,2,3-Triazoles in Water

A simple, efficient, inexpensive, and friendly benign route for the preparation of highly stable monodisperse copper nanoparticles with an average of 4-5 nm is developed by using polyvinylpolypyrrolidone (PVPP) as a stabilizer. Chemical reaction of PVPP and copper(II) sulfate followed by the thermal chemical reduction of embedded copper(II) ions with ascorbic acid afford copper nanoparticles-polyvinylpolypyrrolidone (CuNPs-PVPP) nanocatalyst, which is systematically characterized by FT-IR, Raman, transmission electron microscopy, X-ray powder diffraction, scanning electron microscopy, dispersive X-ray spectroscopy, and atomic absorption spectroscopy. The CuNPs-PVPP system efficiently catalyzes the click chemistry reaction of azides-alkynes as well as one-pot three-component reactions to regioselectively produce the 1,4-disubstituted-1,2,3-triazole isomer in excellent yields in water under mild reaction conditions. CuNPs-PVPP is successfully recycled up to five times without significant loss of its catalytic efficiency and selectivity. Moreover, a mechanistic study is performed through density functional theory type calculations in order to explain the observed selectivity of CuNPs catalyst in copper(I)-catalyzed azide-alkyne cycloaddition reactions. The cheap, simple work-up, recoverability/reusability, and negligible residual traces in the final product (0.5 ppm) of this novel nanocatalyst are the significant features of this eco-friendly green protocol.