TiO₂ nanotube-supported Cu(II)-Schiff base complex as an efficient heterogeneous catalyst for A³ coupling reactions under solvent-free conditions.

A novel Cu(II)-Schiff base complex supported on TiO₂ nanotubes was successfully synthesized through a multi-step procedure. The resulting nanocatalyst was characterized using powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The catalytic activity of the synthesized material was evaluated in the three-component (A³) coupling reaction involving aldehydes, amines, and alkynes under solvent-free conditions. The catalyst demonstrated excellent activity, affording good to excellent yields across a range of tested substrates. The optimal reaction conditions were established, and the catalyst's reusability was investigated. However, a leaching test revealed significant Cu species in the solution, suggesting potential homogeneous catalysis. Despite this, the catalyst showed promising recyclability over multiple runs. Further analysis, including ICP-MS or AAS, could be useful to quantify the leached Cu and confirm the catalyst's stability in longer cycles.