Fe3O4-Lignin@Pd-NPs: A highly efficient,magnetically recoverable and recyclable catalyst for Mizoroki-Heck reaction under solvent-free conditions

Palladium nanoparticles ( Pd-NPs ) were synthesized under green conditions in water by chemical reduction of PdCl₂ with NaOH and supported by Fe ₃ O ₄ -Lignin . Fe ₃ O ₄ -Lignin is an organic–inorganic hybrid core-shell was synthesized by sonication of a mixture of Fe ₃ O ₄ -NPs (20 nm) and alkali lignin. The new materials Fe ₃ O ₄ -Lignin and Fe ₃ O ₄ -Lignin@Pd-NPs were characterized by PXRD, SEM and FT-IR spectroscopy. The Fe ₃ O ₄ -Lignin@Pd-NPs was further confirmed by UV–Visible spectroscopy, TEM, EDX, HRICP-AES and TGA/DTA. The average size of Pd-NPs determined from PXRD was 5–10 nm. The amount of palladium loaded on Fe ₃ O ₄ -Lignin obtained from EDX analysis was 26.63% by mass. The amount of Fe and Pd present in the catalyst obtained from HRICP-AES was 11.88 (wt. %) and 10.90 (wt. %) respectively per gram of lignin. The catalytic potential of Fe ₃ O ₄ -Lignin@Pd-NPs was evaluated in Mizoroki-Heck C-C coupling reaction. During the optimization studies of reaction between iodobenzene and n-butyl acrylate in various solvents and under solvent-free but aerobic conditions using various inorganic and organic bases, the product n-butyl 3-phenylprop-2-enoate ( 1a ) obtained was as high as 95% in highly polar solvents as short as in 10 min and 99% under solvent-free conditions in 3 min at 140 °C using n-Pr₃N as base. The scope of the above catalyst was investigated in the Mizoroki-Heck reaction of various aryl/heterocyclic halides and n-butyl acrylate/styrene under optimized solvent-less conditions. The corresponding products were obtained in high yields (73–99%). The catalyst recovered by magnetic decantation was reused for five times in the C-C coupling reaction between iodobenzene and n-butyl acrylate which yielded 90–95% of the desired product, 1a .