Functionalized cellulose with multiple binding sites for a palladium complex catalyst: synthesis and catalyst evaluation in Suzuki–Miyaura reactions

Abstract

Due to their eco-friendly nature, polysaccharides are desirable supporting materials in organic transformations. Nevertheless, as is the case for other supports, polysaccharides have to face the issue of seeking more binding sites via multifunctional structures to capture metal species in the catalyst, which enhance stability and promote catalytic performance in aforementioned process. In this paper, an environmentally-friendly and multifunctional cellulose supported Pd(II)-Schiff base complex is fabricated and applied in the formation of different biaryls under mild ambient conditions. The results of thermal analysis reveal that the composite has high thermal stability. The as-prepared catalyst demonstrates to be a robust and efficient catalyst with more than 90% yields in H2O: EtOH (1:1) at 70 °C by using 0.30 mol% of catalyst under air towards the coupling of various substituted aryl halides and phenylboronic acids. Moreover, identified by ICP-OES analysis, the green Pd(II) catalyst displays higher metal content (1.93%) in comparison with the direct deposition of Pd particles on cellulose (0.93%), and prevents the metal leaching (< 1%) via the coordination interaction of multiple capturing sites (–OH, Schiff base and pyridyl moieties) with palladium. The resultant catalyst is characterized by FT-IR, TGA, XRD, SEM, TEM, XPS, CP/MAS 13C-NMR, and ICP-OES examination. Also, this green catalyst is able to be retrieved in five cycles with simple centrifugation. Notably, we propose a plausible multifunctional catalyst complex. The present study offers a novel and effective supported catalyst, which broadens the contributions of polysaccharides in green catalysis.