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

Abstract

Palladium nanoparticles (Pd‐NPs) were synthesized under green conditions in water by chemical reduction of PdCl2 with NaOH and supported by Fe3O4‐Lignin. Fe3O4‐Lignin is an organic–inorganic hybrid core‐shell was synthesized by sonication of a mixture of Fe3O4‐NPs (20 nm) and alkali lignin. The new materials Fe3O4‐Lignin and Fe3O4‐Lignin@Pd‐NPs were characterized by PXRD, SEM and FT‐IR spectroscopy. The Fe3O4‐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 Fe3O4‐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 Fe3O4‐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.