Suzuki- and Heck-type cross-coupling with palladium nanoparticles immobilized on spherical polyelectrolyte brushes

We report on a systematic study of the use of palladium nanoparticles immobilized on spherical polyelectrolyte brushes - Pd@SPB - for Heck- and Suzuki-type coupling reactions. The spherical polyelectrolyte brush particles serving as carriers for the palladium nanoparticles consist of a solid polystyrene core with a radius of 46 nm onto which long chains of cationic polyelectrolytes are grafted. The palladium nanoparticles have directly been generated within this brush layer and the stabilization of the nanoparticles is effected by the colloidal carriers, no further surface stabilization is necessary. We demonstrate that these composite particles present robust catalysts for the Heck- and Suzuki-type coupling reactions. This was shown by carrying out the Suzuki- and Heck-type coupling reactions at relatively low temperatures (Suzuki reaction: 50 degrees C, Heck reaction: 70 degrees C). We demonstrate that the catalytic composite particles are not changed by these reaction conditions and retain their full activity for at least four runs. The yields obtained for both reactions are good to excellent. The mild operation conditions of the palladium nanoparticles are traced back to the absence of surface stabilization. Further mechanistic implications are discussed.