1,4-Dihydroxyanthraquinone-copper(II) nanoparticles immobilized on silica gel: a highly efficient, copper scavenger and recyclable heterogeneous nanocatalyst for a click approach to the three-component synthesis of 1,2,3-triazole derivatives in water

High yielding preparation of structurally different β-hydroxy 1,4-disubstituted 1,2,3-triazole from the regio-selective reaction of epoxides 2a–2c with wide range of terminal alkynes 1a–1j, and sodium azide in the presence of catalytic amount, complexed form of homogeneous catalyst [bis 1,4-mono ester hydroxy anthraquinone copper(II)] (5.0 mol%), [AQ2Cu(II)] 7 at 25 °C in water has been described. To benefit from the recovery and reuse of the catalyst, a novel heterogeneous nanoparticles of catalyst [bis 1,4-mono ester hydroxy anthraquinone copper(II) aminopropyl silica gel] (5.0 mol%), [AQ2Cu(II)-APSiO2] 13 bearing oxygen anthraquinone ligands with strong copper(II) affinity was easily prepared by using silica gel as a suitable support. The heterogeneous catalyst was fully characterized by XRD, SEM, AFM, ICP, TG methods for analysis of nitrogen adsorption, and FT-IR techniques. The remarkable features of this protocol are high yields, short reaction times, a cleaner reaction profile in an environmentally benign solvent (H2O), one-pot procedure and the method is applicable to large-scale operation without any problem. Furthermore, the catalyst could be recovered and easily removed by simple filtration of the reaction mixture and it was recycled ten times showing negligible copper leaching. In their uncomplexed form of homogeneous catalyst [AQ2Cu(II)] 7 and heterogeneous catalyst [AQ2Cu(II)-APSiO2] 13, the anthraquinone ligand 6 and [AQ-APSiO2] 12 are very efficient copper scavengers able to catalyze the 1,3-dipolar cycloaddition reaction of azides with alkynes (CuAAC) without pre-synthesis of catalysts.