Hydrazine-functionalized SiO2@Fe3O4 as a highly effective magnetic catalyst: applications in the synthesis of chromene-annulated heterocyclic scaffolds under mild conditions, assessment of antimicrobial activity, and a theoretical mechanism insight based on DFT analysis

The synthesis of chromene derivatives is a crucial focus in chemical research due to their significant pharmaceutical and biological relevance. In this work, we introduce a new, straightforward, and highly efficient magnetically retrievable nanocatalyst: hydrazine-immobilized SiO 2 @Fe 3 O 4 nanoparticles (2NHNH/(CH 2 ) 3 @SiO 2 @Fe 3 O 4 ). The nanocatalyst underwent extensive physicochemical characterization using FT-IR, VSM, SEM, TEM, XRD, BET, TGA, and EDX techniques. The XRD measurement indicates that the as-synthesized nanocatalyst possesses a crystallite size of approximately 33 nm. BET analysis reveals that the catalyst exhibits a mesoporous architecture with a relatively large specific surface area of 45.20 m 2 g − 1 . TEM observations confirm that the catalyst was synthesized in a spherical form, with particle sizes ranging from about 10 to 35 nm. The catalytic performance of the nanocatalyst was examined in a three-component synthesis of 4 H-chromene derivatives, combining aromatic aldehydes, various phenols, and malononitrile in ethanol as a green solvent under mild conditions, producing products with very high yields and excellent amounts. The simplicity of the procedure, environmentally friendly reaction conditions, short reaction times, and straightforward product separation collectively position this approach as an attractive alternative to previously reported methods. Additionally, a disk diffusion assay was employed to assess the antimicrobial activity of selected synthesized compounds against both Gram-positive and Gram-negative bacteria, revealing that compounds 4e, 6d, and 7d inhibited bacterial growth. Furthermore, Density Functional Theory (DFT) calculations were conducted to illuminate the reaction mechanism, using the total energies of reactants and products as the basis for the analysis.