PREPARATION OF PALLADIUM COLLOIDS IN BLOCK-COPOLYMER MICELLES AND THEIR USE FOR THE CATALYSIS OF THE HECK REACTION

Colloidal dispersions of nanometer sized palladium colloids with very high stability were prepared in block copolymer micelles of polystyren e-b-poly-4-vinylpyridine and analyzed by electron microscopy and X-ray analysis. The resulting polymer/metal hybrids can easily be dissolved and handled in standard organic solvents such as toluene, tetrahydrof uran, and cyclohexane. They were successfully used for the Pd-catalyze d carbon(-) carbon coupling of aryl halides with alkenes (Heck reactio n). Such block copolymer stabilized palladium colloids exhibit about t he same reactivity as low molecular weight Pd complexes classically us ed for the Heck reaction, but show a much higher stability: in most re actions, the hybrids remain catalytically active even after 50000 turn -over cycles, Reaction rates were significantly controlled by the reac tivity of the educts, but also respond to micelle architecture and dis persity of the palladium. Other advantages of the block copolymer stab ilizer are that they are more simple and readily accessible than the p hosphor-containing chelates, and that they dissolve even in ''simple'' solvents such as toluene (instead of amidic solvents).