Acidic Ionic Liquid Anchored on PEG-Decorated Fe3O4 Nanoparticles: A Novel Heterogeneous and Magnetically Recoverable Organic-Inorganic Catalyst for the Efficient Synthesis of Pyrimidine Derivatives Running head: Magnetic nanohybrid acidic catalyst

A robust and sustainable catalytic system was developed by immobilizing a Brønsted acidic ionic liquid (BAIL) onto Fe ₃ O ₄ @PEG-SO₃H nanoparticles for the efficient synthesis of tetrazolopyrimidine derivatives. The fabrication of the catalyst commenced with the formation of an N-butyl sulfonate zwitterion via the reaction of N-methylimidazole with 1,4-butanesultone. Subsequently, Fe ₃ O ₄ @PEG-SO₃H core-shell nanoparticles were synthesized and functionalized by anchoring the zwitterion onto their surface through a reflux-assisted grafting process in ethanol. The resulting hybrid material was meticulously characterized using advanced analytical techniques, including FTIR, ¹H NMR, XRD, SEM, TEM, BET and EDX confirming its structural integrity, thermal stability, and magnetic properties. The catalytic efficacy of the hybrid was demonstrated in a one-pot multicomponent reaction involving aromatic aldehydes, active methylene compounds, and 5-aminotetrazole. Under optimized conditions, the catalyst exhibited exceptional performance, delivering high yields (85–95%) within remarkably short reaction times (15–35 minutes) at a minimal loading of 5 mol%. Furthermore, the catalyst's magnetic properties facilitated facile recovery, while its remarkable reusability was evidenced by sustained activity over four consecutive cycles with negligible loss in yield. Moreover, the introduced anchored BAIL combines the advantages of both heterogeneous and homogeneous catalysis while overcoming the limitations associated with free BAIL