Bacterial Cellulose-supported Pd Catalyst For Heck And Suzuki Coupling Reactions

Palladium-catalyzed Heck and Suzuki reactions are important organic reactions in constructing C=C and C-C bond. These reactions have attracted wide attention from chemical industry. Homogeneous palladium catalyst has found to be difficult in separation and recycling. Hence, it is very important to develop heterogeneous palladium (Pd) catalyst systems with high activity and selectivity, long lifetime, as well as easy separation and reclycing.In this paper, a new heterogeous Pd catalyst has been developed by employing bacterial cellulose (BC) nanofibers as scaffold. Fermented by Acetobactes xylinum, BC nanofibers boast unique spatial structure, good mechanical properties, good chemical stability, high purity, high crystallinity, and good intermiscibility. The Pd/BC catalyst was prepared by depositing Pd nanoparticles (NPs) onto BC nanofibers using hydrothermal and in-situ reduction reaction. The catalyst was structurally characterized and its catalytic performance for Suzuki and Heck reactions was further explored. The main research results are as follows:(1) The as-prepared catalyst was characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), fourier transform infrared spectroscopy analysis (FTIR), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy analysis (XPS) respectively. The results revealed that Pd NPs (-20 nm in diameter) embedded on BC nanofibers with slight aggregation. With a Pd load of 20%, Pd/BC catalyst exhibited good thermal stability, with a decomposition temperature reaching 300℃. Pd NPs were found to deposit onto BC nanofibers via physical adsorption rather than chemical adsorption, with no change of BC original structure found after Pd embedding. With a valance of zero, Pd NPs presented perfect fcc crystal structure without any impurities.(2) With Pd/BC catalyst in hand, its catalytic performance for Heck and Suzuki reaction was evaluated. With a model coupling of styrene and iodobenzene, the optimized Heck reaction conditions were found as:120℃temperature, DMF solvent, triethylamine as base, 0.1 mol% catalyst. With model coupling of benzyl boronic acid and iodobenzene, the aqueous Suzuki reaction conditions were optimized to be 85℃, K2CO3 as base,0.1 mol% catalyst. Under the optimized reaction conditions, a large variety of substrates with different functionality have been explored in these couplings. The results indicated the as-prepared Pd/BC catalyst showed goof functional compatibility, high catalytic performance, and good reclyclability. In addition, Pd source [Pd(NO3)2 or PdCl2] exerted neglible effect on the catalytic performance of Pd catalyst.In conclusion, the Pd/BC catalyst in this thesis features high catalytic performance, easy handling, facile post-treatment, and good recyclability. The Pd/BC catalyst developed in this paper may be a good alternative for heterogeneous Pd catalyst systems.