Hybrid organic-inorganic Cu(II) iminoisonicotine@TiO2@Fe3O4 heterostructure as efficient catalyst for cross-couplings

Two novel mononuclear copper (II) complex catalysts were synthesized from a new tridentate iminoisonicotine ligand (HL) by coordination with Cu(II) ion, with (CuL@TiO2@Fe3O4) and without (CuL) immobilization on TiO2-coated nanoparticles of Fe3O4. The ester moiety on the back of the ligand was utilized for immobilization on nanoparticles of Fe3O4. Both ligand and CuL complex were fully characterized by using alternative spectral techniques (nuclear magnetic resonance, infrared, ultraviolet-visible and mass spectroscopy, and elemental analyses). Different analytical techniques were used to identify the structural feature and morphology of the immobilized copper catalyst (CuL@TiO2@Fe3O4) shell-shell-core system. The structural analysis revealed that the catalyst system is composed of both agglomerated nanospheres and deformed nanorods. Both copper catalysts, immobilized CuL@TiO2@Fe3O4 and un-immobilized CuL were studied in heterogeneous and homogeneous catalysis, respectively, for Suzuki-Miyaura (C-C) and Buchwald-Hartwig (C-N) cross-coupling reactions of various heteroaryl halides. Both catalysts showed good catalytic potential under the controlled optimal reaction conditions. In contrast to the homogeneous catalyst (CuL), the heterogeneous catalyst (CuL@TiO2@Fe3O4) showed slightly better catalytic performance. The characteristic obtains supported the catalytic potential of the current samples. Reusability/recycling of both catalysts was also investigated in C-C cross-coupling reactions. It was found that the homogeneous catalyst (CuL) could be only recycled up to three times, whereas the heterogeneous one (CuL@TiO2@Fe3O4) could be reused up to seven times with good efficiency.