Design of Schiff base modified guar gum supported palladium complex with multiple coordinated sites and its application towards aryl halides cyanation reaction.

As a significant polysaccharide, owing to fascinating properties, ease of availability and biocompatibility, natural guar gum (GG) has received extensive attention in foods, pharmaceuticals and industrial applications. However, the catalytic applications for GG were not fully explored. Additionally, traditional cyanation methods for preparing significant aryl nitriles often rely on highly toxic cyanide sources, prompting the need for greener alternatives. For exploring and extending full potentials of GG, it is essential that the design and study of this polysaccharide is deemed as new bio-support in heterogeneous catalysis through further chemical modification. In this study, a novel 5-hydroxymethylfurfural (HMF) modified GG supported Pd catalyst (GG-SB-Pd) was projected and synthesized by using multidentate coordinated functionalized GG as stabilizer agent for immobilizing palladium. The resulting catalyst could be utilized as an efficient catalyst in the construction of aryl nitriles in cyanation reactions with non-toxic cyanide sources. More importantly, dependent on the multiple coordinated sites (hydroxyl, furyl and imine moieties) with palladium on this polysaccharide, this catalyst was able to efficiently enhance catalytic performance and prevent metal leaching (<1%). In addition, it was proved that the Pd composite could be simply recollected by centrifugation for 5 cycles. A possibly cooperative multifunctional structure was also proposed. Accordingly, this study furnishes valuable insights into the design and fabrication of polysaccharides in potential application of organic transformations.