Pd and Rh nanoparticles onto ion-exchange borate monoliths: synthesis, characterization and application to selective hdrogenation reactions under continuous flow

Strong cation-exchange resins featured by low loading of noncoordinating B(C6H5)3- anions in styrene-divinylbenzene matrices at various cross-linking degree were synthesized via free radical bulk copolymerization with appropriate borate monomers. The polymerization mixture was tailored to obtain swellable materials for use as insoluble carriers of single-site heterogeneous catalysts. Having established an effective protocol for the synthesis of this material, we prepared an unconventional monolith (called MonoBor) featuring an homogeneous microstructure of interconnected macropores (10 ?m size) in situ, into a commercial glass column, so as to provide a monolithic mesoreactor perfectly suited for use under continuous flow.1 Palladium and Rhodium nanoparticles were immobilized onto the monolith and the resulting Pd or Rh@MonoBor catalyst was employed in the semihydrogenation reaction of alkynes 2 and selective hydrogenation of unsatured carbonyl compounds 3 under continuous flow by direct connection to a home-made reactor system. The macroporous monolith, showing excellent hydrodynamic properties and high chemical and mechanical stability, was successfully used under mild reaction conditions, without additives, with high performance in terms of space-to-time yield productivity, selectivity and catalyst durability.