Sol-gel TiO₂ nanostructures single doped with copper and nickel as nanocatalysts for enhanced performance for the Liebeskind–Srogl reaction

Design of nanostructured catalytic materials plays a strategic role in the synthesis of organic compounds with outstanding physicochemical properties. In this regard, titanium dioxide nanostructures doped with a single metal, namely, nickel and copper, were successfully prepared by a sol-gel method, and their phase structures, elemental compositions and morphologies were extensively characterised. In particular, X-ray diffraction (XRD) diffractograms and Raman spectra mainly revealed a rutile-phase structure for Cu-doped TiO₂ and a biphasic anatase–rutile structure for Ni-doped TiO₂. In addition, catalytic activities of Cu- and Ni-doped titanium dioxide nanostructures were evaluated for the synthesis of pyridopyrimidine derivatives from sulphur intermediates by the Liebeskind–Srogl reaction under UV illumination. Under the optimized reaction conditions, the target compounds were obtained in a yield of up to 87% by using the Cu-doped TiO₂ catalyst and with a slightly lower yield of up to 79% for Ni-doped TiO₂ in 12 h. Overall, the catalytic activity of Cu-doped TiO₂ was greater than that of Ni-doped TiO₂.