Supported Palladium Catalysts for Suzuki Reactions: Structure-Property Relationships, Optimized Reaction Protocol and Control of Palladium Leaching

Palladium on metal oxides and on activated carbon with particular properties (high palladium dispersion, low degree of reduction, water content) are shown to be highly active (tunrover number, TON=20,000; turnover frequency, TOF=16,600), selective and robust catalysts for Suzuki cross-couplings of aryl bromides and activated aryl chlorides. Catalysts and reaction protocol offer combined advantages of high catalytic efficiency under ambient conditions (air and moisture), easy separation and reuse and quantitative recovery of palladium. The palladium concentration in solution during the reaction correlates clearly with the progress of the reaction and indicates that dissolved molecular palladium is in fact the catalytically active species. Dissolved palladium is redeposited onto the support at the end of the reaction. Additional minimization of the palladium content in solution (down to 0.1 ppm) could be achieved by simple procedures which meet the requirements of pharmaceutical industry.