Studies On Palladium Nanoparticle-Catalyzed Carbonylative And Carboxylative Coupling Reactions

Nano-metal catalysts stabilized by appropriate additives are usually better than the corresponding molecular catalysts on catalytic activity and selectivity. Therefore, the research on the application of nano-metal catalysts in organic synthesis has attracted considerable attention. In this thesis, palladium nanoparticles generated in situ in the presence of quaternary ammonium salts were used in carbonylative and carboxylative coupling reactions under ligand-free conditions.In the first part, carbonylative Stille coupling reaction of benzyl chlorides with allyltributylstannane was successfully conducted by using palladium nanoparticles as the catalyst and tetraoctylammonium bromide (TOAB) as an additive under the phosphine ligand-free conditions. ?, ?-Unsaturated ketones were obtained with various benzyl chlorides, and the yield was up to 90%; the yields of trans-isomers were higher than those of cis-isomers. Transmission electron microscopy (TEM) image showed the presence of (1.97±0.50) nm-sized palladium nanoparticles in the reaction mixture. No generation of Pd-Sn alloy was confirmed by Energy Dispersive X-ray Spectroscopy (EDX).In the second part, three-component coupling reactions of five-membered (chloromethyl)heteroarenes, allyltributylstannane, and carbon dioxide were successfully conducted by using palladium nanoparticles as the catalyst.?,?-Unsaturated esters were obtained in 63%-89% yields with various five-membered (2-chloromethyl)heteroarenes, such as (2-chloromethyl)thiophenes, (2-chloromethyl)furans and (2-chloromethyl)pyrroles. The target reactions showed good functional group tolerance, such as bromo atom, alkyl, aryl, and alkynyl groups could existed on the substrates. The morphology and particle size of palladium nanoparticles were not changed during the target reaction proceeding, which indicated that the palladium nanoparticle catalyst was very stable. The mercury poisoning tests demonstrated the reaction occurred on the surface of palladium nanoparticles. Cations and anions in quaternary ammonium salts influenced the catalytic activity of palladium nanoparticles, and the palladium nanoparticles stabilized by tetrabutylammonium bromide (TBAB) proved to be the best catalyst. (2.23±0.58) nm-sized palladium nanoparticles generated in situ in the presence of TBAB [Pd(acac)2/TBAB= 1/30] showed high catalytic activity. Palladium nanoparticles could be recycled for four times without significant loss in catalytic activity.In the last part, carboxylative Suzuki coupling reactions of (chloromethyl)arenes with pinacol allylboronate were successfully conducted by using palladium nanoparticles as the catalyst and TBAB as an additive. The palladium nanoparticles formed in situ under ligand-free conditions. This method could avoid cumbersome processes for the preparation of catalysts and ligands. Pinacol allylboronate could be activated by the fluorine anion. These carboxylative coupling reactions were successfully extended to various (chloromethyl)arenes under the optimized conditions.