Novel recyclable tridentate Schiff base Cr species based on Fe3O4 magnetic nanocatalyst for efficient multicomponent synthesis of mono and bis dihydro-benzoimidazopyrimidines

A novel magnetic nanocatalyst, Fe₃O₄@SiPr@OVASB@Cr, was synthesized, thoroughly characterized, and applied for the green synthesis of 2-amino-4-substituted-1,4-dihydro-benzo[4,5]imidazo[1,2-a]pyrimidine-3-carbonitriles. The catalyst was prepared via a multi-step strategy: Fe₃O₄ magnetic nanoparticles were functionalized with 3-chloropropyltrimethoxysilane, modified with a tridentate Schiff base ligand, and coordinated with Cr species as Lewis acidic sites. One-pot multicomponent cyclocondensation of aromatic monoaldehydes, malononitrile, and 2-aminobenzimidazole was efficiently carried out under solvent-free conditions at room temperature, providing excellent yields in short reaction times. Furthermore, symmetrical bis-aldehydes with flexible tetra- and hexa-methylene ether linkers were successfully employed, affording the corresponding two novel dihydro-benzoimidazopyrimidine derivatives in high yields. The catalyst was characterized by FT-IR, XRD, FE-SEM/TEM, EDX, VSM, TGA, and DSC, confirming its structure and properties. It exhibited good reusability over six cycles with minimal loss of activity, highlighting mild operational conditions, facile magnetic separation, and good efficiency. This work demonstrates a sustainable, economical, and environmentally friendly approach for the synthesis of functionalized heterocycles using magnetic nanocatalysis.