Synthesis of a bistriazolyl-phenanthroline-Cu(ii) complex immobilized on nanomagnetic iron oxide as a novel green catalyst for synthesis of imidazoles via annulation reactions

We designed and prepared a novel N-heterocycle-based nanocatalyst by a post synthetic method, namely the [Fe₃O₄@DAA-BTrzPhen-Cu(ii)] composite. In this method, bistriazolyl-phenanthroline groups were stepwise synthesized on an Fe₃O₄ substrate and used as a tetradentate nitrogenous ligand for coordinating to copper ions. The obtained nanocomposite was well characterized using FT-IR, PXRD, TGA, EDAX, ICP-OES, EDX-mapping, SEM, TEM, VSM and BET analyses, which confirm the formation of a thermostable crystalline spherical particle morphology with the particle size in the range of 17 nm to 25 nm and a magnetization value of 42 emu g⁻¹. Also, the catalytic activity of [Fe₃O₄@DAA-BTrzPhen-Cu(ii)] as a novel and magnetically separable heterogeneous nanocatalyst was evaluated in preparing various tetrasubstituted imidazole derivatives from one-pot four-component condensation of anilines, aldehydes, 1,2-diketones and ammonium acetate, and favorable products were produced with excellent yields. The stability, low Cu leaching, and heterogenous nature of the nanocatalyst were confirmed by hot-filtration and leaching tests. The copper based nanocatalyst could be easily recovered by magnetic field separation and recycled at least 8 times in a row without noticeable loss in its catalytic activity.