A series of N-heterocyclic carbene copper(I) and rare copper(II) complexes (NHCCuCI or NHCCuCl2) were covalently immobilized directly on the surface of magnetic nanoparticles (MNPs) for the first time. The physicochemical properties were investigated by a broad range of techniques, including SEM and TEM microscopy, and TG analysis. The supported complexes exhibited excellent activity in the Huisgen cycloaddition with in situ generated azides. Unexpectedly, a direct comparison of NHCCuCl and NHCCuCl2 complexes anchored to the magnetic nanoparticles confirmed the higher activity of the latter for the formation of 1,2,3-triazoles, also under ascorbate-free conditions. (C) 2018 Elsevier Inc. All rights reserved.