Palladium-Catalyzed Cross-Coupling Reactions In Aqueous Media

Palladium-catalyzed cross-coupling reactions are the important methods for the selective construction of the carbon-carbon bonds. However, many of these transformations were conducted in harmful organic solvents. As a result, the development of some environmental benign palladium-catalyzed cross-coupling processes is becoming a very urgent project for chemist. In this dissertation, we have developed two green modified protocols for the palladium-catalyzed cross-coupling reactions based on solvent and catalyst.1. PEG-400 [poly (ethylene glycol-400)] was found to improve the Pd(OAc)₂/DABCO-catalyzed aqueous Suzuki-Miyaura and Stille cross-coupling reactions. In the presence of Pd(OAc)₂, DABCO and PEG-400, a variety of aryl halides were coupled with arylboronic acids or organotin compounds efficiently to afford the corresponding cross-coupled products in moderate to excellent yields. The turnover numbers was up to 900,000 for the Suzuki-Miyaura reaction and up to 9800 for the Stille reaction. The catalyst system was also effective for Heck and Sonogashira cross-coupling reactions to some extent.2. Polymer-supported DABCO-palladium complex was observed as an efficient and reusable catalytic system for the Suzuki-Miyaura,Stille and Hiyama cross-coupling reaction. In the presence of 0.25 mol% of the polymer-supported DABCO-palladium complex, a variety of aryl bromides were coupled with arylboronic acids efficiently in an aqueous ethanol at room temperature under air. Moreover, the reaction was very rapid, and the catalyst could be recovered and reused at least five times from the reaction by simple filtration. It was also found that the Stille, Hiyama reactions in aqueous solvent and vinyl halides, aryl chlorides coupled with arylboronic acids in DMF could be carried out efficiently to afford the cross-coupled products in moderate to excellent yields.