Highly selective hydrogenation of quinolines promoted by recyclable polymer supported palladium nanoparticles under mild conditions in aqueous medium

• Polymer supported Pd catalyst (Pd-pol) promoted the quinoline hydrogenation.
• Pd-pol was active under mild conditions in aqueous medium.
• The catalyst could be reused at least nine times without loss of activity.
• Pd leaching did not occur.
• The in situ formed supported Pd nanoparticles were the true active species.

Polymer supported palladium catalyst, obtained by copolymerization of Pd(AAEMA)2 [AAEMA− = deprotonated form of 2-(acetoacetoxy)ethyl methacrylate] with ethyl methacrylate (co-monomer) and ethylene glycol dimethacrylate (cross-linker), exhibited excellent activity and selectivity for the hydrogenation of quinolines to 1,2,3,4-tetrahydroquinolines under mild temperature (80 °C) and H2 pressure (10 bar) in aqueous medium. Both the activity and selectivity could be maintained for at least nine reaction runs. No metal leaching into solution occurred during application. TEM analyses carried out on the catalyst showed that the active species were supported palladium nanoparticles having a mean size of 4 nm, which did not aggregate with the recycles.

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