Pd/C-Catalyzed Aqueous Suzuki Reaction And Sonogashira Reaction

The Suzuki reaction and the Sonogashira reaction have been the versatile and powerful methods for the formation of carbon-carbon bond, which play an important role in the synthesis of drug intermediates, natural products and advanced functional materials. Potassium organotrifluoroborates have become the common nucleophilic partners of the Suzuki reaction due to its characteristics of easily preparation, high stability and difficulty in carring out side reaction, which expands the application of the organoboron reagents. The recycling performance of the precious metal catalyst has always been an important part of the study in the catalytic reaction system. This paper will investigate the recycling performance of Pd/C in the different reaction systems.This paper contains following three parts:(1) A Pd/C-catalyzed ligand-free Suzuki reaction of potassium organotrifluoroborates with aryl halides in aqueous ethanol has been developed. In this catalytic system, the results demonstrated that oxygen played a positive role in the coupling reaction. The catalyst Pd/C could be easily separated by simple filtration and could be recycled seven times with the product yield no less than 90%. In addition, this catalytic system could be successfully applied to synthesize biaryl compounds containing a carbazole moiety, which are important photoelectric materials for OLEDs.(2) The Pd/C-EtOH/H2O system has been successfully expanded to the Sonogashira reaction, and a simple, efficient, copper-free approach for the Pd/C-catalyzed ligand-free Sonogashira reaction has been developed for the cross-couplings between various aryl iodides and terminal alkynes, providing the highest yield up to 98%. After simple filtration, the catalyst Pd/C could be recycled 5 times with the yield more than 90%.(3) A simple approach for the Pd/C-catalyzed ligand-free Suzuki reaction of potassium organotrifluoroborates in pure water has been developed. The results show that (i-Pr)2NH plays an important role in the reaction and a wide range of aryl bromides were reacted with different potassium organotrifluoroborates smoothly under the optimized conditions, affording the highest reaction yield up to 97%. Furthermore, Pd/C could be recycled 5 times with the yield more than 90%.