Microwave-Assisted Aqueous Carbon-Carbon Cross-Coupling Reactions of Aryl Chlorides Catalysed by Reduced Graphene Oxide Supported Palladium Nanoparticles

The utilization of environmentally friendly heterogeneous catalytic system for efficiently promoting low cost and readily available starting materials to valuable chemicals have drawn significant research focus. Palladium-catalyzed carbon-carbon bond formations were discovered almost 50 years ago. But, activating aryl chlorides to practical useful products in mild conditions by supported Pd nanoparticles still remains a challenge. Herein, a simple and green in-situ assembly and reduction approach was developed for the fabrication of reduce graphene oxide supported palladium nanoparticles (Pd/rGO). Owing to the abundant surface functional groups, Pd NPs were uniformly dispersed on the sheets of rGO with the average size of around 2.0 nm. Interestingly, under microwave irradiation, Pd/rGO can efficiently promote Ullmann and Suzuki coupling reactions by using aryl chlorides as the reactants in aqueous media, which displayed even better catalytic performances than homogenous catalytic system. Notably, this mild reaction system can be demonstrated in the gram-scale synthesis of 4’-methyl-2-biphenylcarbonitrile and 2-nitro-3’,4’,5’-trifluoro-1,1’-biphenyl, which are important pharmaceutical intermediates of Sartans and Fluxapyroxad, respectively. On the basis of material characterizations and the control experiments, this remarkable catalytic performance could be ascribed to its robust microwave absorption capability, efficient electron transfer and unique two-dimensional structure. Furthermore, it was easily recycled and used repetitively for at least six times without the significant loss of its activity.