esign and synthesis of Fe₃O₄@Chitosan-Ru(II) complex for efficient Suzuki-Miyaura cross-coupling: Optimization, and reusability in green organic transformations

Abstract

n this work a magnetic nanocatalyst, Fe₃O₄@CS-Ru NPs, was synthesized by first preparing Fe₃O₄ nanoparticles, followed by chitosan (CS) surface functionalization, and finally immobilizing an organometallic Ruthenium (II) (Ru(II)) complex as the catalytic species. The Ru(II) complex is a cationic half-sandwich complex with cymene, bipyridine-NO and chloride ligands. The CS-coated magnetite support provides strongly coordinating σ-donor – NH2 groups that bind efficiently to the Ru(II) center, while the – OH functional groups offer a secondary, albeit weaker, coordination site for the Ru metal center. This duaFl coordination capability contributes to the formation of a stable, highly active, and magnetically recoverable catalytic system. This architecture yields a robust, magnetically recoverable nanocomposite with high catalytic efficiency. This design enhances stability and recyclability in catalytic applications. Advanced characterization techniques, including FE-SEM, TEM, EDX, EDX- Mapping, XRD, VSM, BET, FT-IR, UV-DRS, and TGA, were employed to confirm the structural and chemical properties of the nanocatalyst. The results provided strong evidence for the successful synthesis of a core-shell magnetic nanocatalyst with desirable surface properties and excellent stability. The synthesized nanocatalyst was employed in the Suzuki-Miyaura cross-coupling (SMCC) reaction to form C– C bonds. The optimized reaction conditions included an EtOH/H2O solvent system, 0.003 g of the nanocatalyst, K2CO3 as the base, a reaction temperature of 50 ◦ C, and a reaction time of 2 h. The Fe3O4@CS-Ru NPs exhibited high catalytic efficiency, demonstrating excellent performance with various aromatic halides and arylboronic acids. The structural identities of the synthesized compounds were confirmed using C nuclear magnetic resonance (NMR) spectroscopy. Furthermore, the catalyst showed remarkable recyclability, retaining its activity even after seven reaction cycles. A hot filtration test confirmed the heterogeneous nature of the catalyst, as no leaching was observed during the reaction. A comparison with other reported methods showed that the presented approach offers shorter reaction times and requires smaller catalyst amounts, making it a more cost-effective and environmentally friendly alternative for C– C bond formation in cross-coupling reactions.