From agricultural waste residue to wealth support: A magnetically N-heterocyclic carbene functionalized corn cob cellulose as a new stabilizer for Pd catalyst in Suzuki reaction.

Because of eco-friendliness, biodegradability and ease of modification, cellulose is deemed as alternative to unrenewable petroleum resources. Nonetheless, it is more indispensable to exploit corn cob cellulose produced from agricultural waste residue as supportive materials in green catalysis. In this study, a new magnetically benzimidazole functionalized cellulose/Fe3O4 derived from corn cob cellulose as a stabilizer agent (Fe3O4@CL-NHC) was prepared, and palladium was immobilized on this stabilizer (Fe3O4@CL-NHC-Pd). The catalyst was fully characterized by different techniques including TEM, SEM, and XPS analyses, etc. The abundant hydroxyl groups of cellulose provided uniform dispersion and high stability of palladium, while Fe3O4 as a support offered simple magnetic separation. High efficiency (up to 99 %) was demonstrated by this biocatalyst under green conditions in relatively short reaction times towards Suzuki reactions. Due to collaborative interactions of N-heterocyclic carbene and hydroxyl groups with palladium, the synthesized complex prevented metal leaching effectively (<1 %). Moreover, the magnetic property of this catalyst (43.0 emu g-1) provides facile recovery of this composite from the reaction mixture with great ease for several times, which overcomes issues of complicated work-up separation. This work offers a promising avenue to enriching the application of biopolymer from agricultural residue in the potential organic transformations.

Schiff base modified starch: A promising biosupport for palladium in Suzuki cross-coupling reactions.

Starch can be used in diverse fields because it is a readily available, non-toxic polysaccharide with adaptable functionality and biodegradability. In this study, taking the aforementioned characteristics into consideration, we designed a modified starch (Starch-SB), which serves as supporting material for palladium stabilization. This new air and moisture-stable robust palladium composite [Starch-SB-Pd(II)] was characterized by FT-IR, XRD, TGA, XPS, SEM, EDX, TEM, CP/MAS 13C NMR, and ICP-MS analytical techniques. The catalytic studies exhibit high activity (up to 99 %) and stability in Suzuki cross-coupling reactions for this starch supported catalytic system under mild conditions (lower reaction temperature and green solvents) because of the cooperative interactions of multifunctional capturing sites on starch (Schiff base, hydroxy and amine groups) with palladium species. The experiments on reusability demonstrate that Starch-SB-Pd(II), which was prepared from functionalized starch, could be readily recycled several cycles through centrifugation. Moreover, we proposed a possibly multifunctional complex structure. This work presents an appealing and intriguing pathway for the utilization of polysaccharide as crucial support in green chemical transformations.