Cu(II) immobilized on guanidinated epibromohydrin-functionalized γ-Fe2O3@TiO2 (γ-Fe2O3@TiO2-EG-Cu(II)): A highly efficient magnetically separable heterogeneous nanocatalyst for one-pot synthesis of highly substituted imidazoles

A simple, efficient and eco-friendly procedure has been developed using Cu(II) immobilized on guanidinated epibromohydrin-functionalized γ-Fe2O3@TiO2 (γ-Fe2O3@TiO2-EG-Cu(II)) for the synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles, via the condensation reactions of various aldehydes with benzil and ammonium acetate or ammonium acetate and amines, under solvent-free conditions. High-resolution transmission electron microscopy analysis of this catalyst clearly affirmed the formation of a γ-Fe2O3 core and a TiO2 shell, with mean sizes of about 10–20 and 5–10 nm, respectively. These data were in very good agreement with X-ray crystallographic measurements (13 and 7 nm). Moreover, magnetization measurements revealed that both γ-Fe2O3@TiO2 and γ-Fe2O3@TiO2-EG-Cu(II) had superparamagnetic behaviour with saturation magnetization of 23.79 and 22.12 emu g−1, respectively. γ-Fe2O3@TiO2-EG-Cu(II) was found to be a green and highly efficient nanocatalyst, which could be easily handled, recovered and reused several times without significant loss of its activity. The scope of the presented methodology is quite broad; a variety of aldehydes as well as amines have been shown to be viable substrates. A mechanism for the cyclocondensation reaction has also been proposed.