Green synthesis of CuO nanoparticles using aqueous extract of Thymus vulgaris L. leaves and their catalytic performance for N-arylation of indoles and amines

[Display omitted] •Green synthesis of CuO NPs using Thymus vulgaris L. leaf extract.•Ligand-free N-arylation of indoles and amines.•Characterization of CuO NPs by XRD, EDS, TEM, TGA/DTA, FT-IR and UV–vis.•The catalyst can be recovered and reused for further catalytic reactions with almost no loss in activity. Copper oxide (CuO) nanoparticles (NPs) were synthesized by biological method using aqueous extract of Thymus vulgaris L. leaves as a reducing and capping agent. The progress of the reaction was monitored using UV–visible spectroscopy. The advantages of this procedure are simple operation, use of cheap, natural, nontoxic and benign precursors, absence of toxic reagents and mild and environmentally friendly conditions. The green synthesized CuO NPs was characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). More importantly, the green synthesized CuO NPs was found to be an excellent heterogeneous catalyst for ligand-free N-arylation of indoles and amines. The N-arylated products were obtained in good to excellent yield and the catalyst can be recovered and reused for further catalytic reactions with almost no loss in activity.