A new copper complex of 1-(1H-benzo[d]imidazol-2-yl)guanidine on magnetic Fe3O4 nanoparticles as a green, reusable, robust and homoselective nanocatalyst in the synthesis of tetrahydrobenzo[b]pyrans.

In this work, magnetic Fe3O4 nanoparticles were encapsulated using a silica layer via a sol-gel method, giving SiO2@Fe3O4. Then, the surface of the SiO2@Fe3O4 was modified using 3-iodopropyltrimethoxysilane (3-IPTMS), giving IPTMS@SiO2@Fe3O4. Additionally, 1-(1H-benzo[d]imidazol-2-yl)guanidine ligand (BimG) was synthesized from the condensation of cyanoguanidine and benzene-1,2-diamine under acidic conditions. Then, a new copper complex of BimG was anchored on the surface of IPTMS@SiO2@Fe3O4 to produce Cu-BimG@SiO2@Fe3O4. The obtained nanocatalyst was characterized using TGA, BET, WDX, EDS, FTIR, XRD, SEM, AAS, and VSM. Cu-BimG@SiO2@Fe3O4 was investigated as an effective, homoselective and reusable nanocatalyst for synthesizing tetrahydrobenzo[b]pyrans through a multicomponent reaction. The homoselectivity of this catalyst was confirmed by NMR spectroscopy. This Cu-BimG@SiO2@Fe3O4 catalyst showed good reusability over several runs without a meaningful loss of catalytic performance. The recovered Cu-BimG@SiO2@Fe3O4 nanocatalyst was characterized by SEM, EDS, WDX, and FTIR techniques, which matched with the fresh catalyst.