Functionalized Cellulose-supported Catalysts And Their Applications In Suzuki Reactions

Cellulose and its derivatives are one of the most important natural polymers in nature,because they are not only environmentally-friendly,but also can meet the requirements of green chemistry.Cellulose and its derivatives contain hydroxyl groups and other groups,making them easy to modify and to achieve functionalization.In addition,this kind of natural polymer as solid supports for heterogeneous catalyst depending on its high catalytic efficiency,cheapness,easy separation,recovery and other characteristics,which meet green chemistry trend,has been widely used.Among these reactions,the Suzuki coupling reaction in the syntheses of biaryl compounds plays an increasingly important role such as medicine,cosmetics,chemical and other industries.Thus,the development of cellulose and its derivatives as support materials for various heterogeneous catalysts are of far reaching impact in synthesis of such compounds.In chapter 2,cellulose was used as raw material to synthesize cellulose p-tosylate,then replaced with diethylenetriamine and coordinated with palladium acetate to prepare diethylenetriamine functionalized cellulose-supported catalyst.Moreover,the optimum conditions and catalytic performance in Suzuki coupling reaction were investigated.Results showed that the catalyst showed efficient catalytic activity for most of substrates employed except chlorobenzene.Compared to other nitrogen-containing ligands,carbene?NHC?exhibit binding metal ability strongly,non-toxic,high stability,excellent performance in the catalytic reaction.In chapter 3,carboxymethyl cellulose was used as scaffold to synthesize carboxymethyl p-tosylate,and then N-methylimidazole was coordinated with palladium acetate by coordinate bond to prepare N-methylimidazole functionalized carboxymethylcellulose-supported palladium trifunctional catalyst CMC-NHC-Pd,which is a heterogeneous supported catalyst possesing trifunctional?-COO-,-OH and N-methylimidazoles?catalytic properties.Then,parameters of temperature,the amount of catalyst,and base were examined by using Suzuki coupling reaction as the model reaction of p-bromoanisole and phenylboronic acid.The optimum reaction conditions were observed:C₂H₅OH:H₂O?1:1?was solvent,K₂CO₃ was the base,the amount of catalyst was 0.80%,and the reaction was at 60�C.Under the optimized conditions,various representative substrates were extended and most of the reaction could be an excellent yield to obtain the corresponding product except for aryl chloride due to its inertia.This catalyst can effectively prevent the release of palladium,and can be separated by simple filtration centrifugation process via the cooperative interaction of trifunctional catalytic capturing sites-COO^-,-OH and N-Methylimidazole with palladium nanopariticles.In addition,in the consecutive reaction,the yield gradually decreased,and can be recovered with 4 cycles in the recovery experiment.The aggregation of palladium nanoparticles could account for the decrease of catalytic activity.Finally,a plausible trifunctional catalyst complex was proposed based on ¹³C-NMR analysis.