Palladiumimmobilized on chitosan nanofibers cross-linked by glutaraldehyde as an efficient catalyst for the Mizoroki–Heck reaction

Nonwoven chitosan (CS) nanofiber mats were successfully prepared by the electrospinning of the mixture of CS and poly(ethylene oxide) (PEO) in acetic acid aqueous solution. The CS/PEO fiber mats were treated with glutaraldehyde aqueous solution to stabilize fibers in solution. The concentration of glutaraldehyde is important for incorporating swelling properties in the cross-linked CS/PEO fiber mats. The cross-linked CS/PEO fibers (CCS/PEO fibers) were then used as supports for palladium catalysts in the Mizoroki–Heck reaction. The results of the study demonstrated that the catalytic activities of Pd catalyst supported on CCS/PEO fiber (Pd-CCS/PEO fiber) were highly dependent on the concentration of glutaraldehyde in the cross-linking process. Density functional theory (DFT) calculations indicated that the Schiff bond formed between CS and glutaraldehyde could reduce the energy needed to form a chelate complex between the CCS/PEO fibers and palladium active species. This in turn could decrease the activation energy of the Mizoroki–Heck reactions which occur in the presence of the Pd-CCS/PEO fiber catalysts. The optimized Pd-CCS/PEO fiber catalyst was very efficient and stable in the Mizoroki–Heck reaction of aromatic iodides with olefins.