Ultrafine palladium nanoparticles immobilized into poly(4-vinylpyridine)-based porous monolith for continuous-flow Mizoroki–Heck reaction

• Porous monoliths containing highly dispersed Pd nanoparticles.
• SEM and TEM microscopies of very small Pd NPs across the monolith.
• Efficient catalysts for Mizoroki–Heck cross-coupling reactions under continuous-flow conditions.

Ultrafine Pd nanoparticles (dm = 2.3 nm), obtained by metal vapor synthesis technique, were immobilized into a poly(4-vinylpyridine)-based porous monolith by means of a new synthetic approach. The synthesis involves stabilization of Pd nanoparticles with 4-vinylpyridine ligand and their subsequent immobilization into the monolith by radical co-polymerization of the resulting metal-embedding monomer with ethylene glycol dimethacrylate in presence of porogenic agents (i.e. DMF and PEG-400) inside stainless-steel columns (HPLC type). The hybrid monolithic reactors containing highly dispersed Pd nanoparticles were effectively used as catalyst for Mizoroki–Heck cross-coupling reactions carried out under continuous-flow conditions. The devices showed long life-time (>65 h) and very low Pd leaching (<2 ppm).

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