Palladium Nanoparticles Supported on Smopex-234(R) as Valuable Catalysts for the Synthesis of Heterocycles

Supported catalysts are important tools for developing green-economy-based processes. Palladium nanoparticles (NPs) that are immobilized on two fibers developed as metal scavengers (i.e., Smopex(R)-234 and Smopex(R)-111, 1% w/w) have been prepared and tested in copper-free cyclocarbonylative Sonogashira reactions. Their catalytic activity has been compared with that of a homogeneous catalyst (i.e., PdCl2(PPh3)(2)). Pd/Smopex(R)-234 showed high activity and selectivity in the synthesis of functionalized heterocycles, such as phthalans and isochromans, even when working with a very low amount of palladium (0.2-0.5 mol%). The extension of Pd/Smopex(R)-234 promoted cyclocarbonylative reactions to propargyl and homopropargyl amides afforded the corresponding isoindoline and dihydrobenzazepine derivatives. A preliminary test on Pd NPs leaching into the solution (1.7 x 10(-3) mg) seems to indicate that, at the end of the reaction, almost all of the active metal is present on the fiber surface.