Journal
MOLECULES
Volume 20, Issue 10, Pages 18661-18684Publisher
MDPI
DOI: 10.3390/molecules201018661
Keywords
polymer supported Pd nanoparticles; morphological analysis; TEM; micro-IR spectroscopy; recyclable catalyst; quinoline transfer hydrogenation; water solvent; nitrobenzene reduction; quinoline hydrogenation; Suzuki-Miyaura coupling
Funding
- Italian Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR) [2010FPTBSH_001]
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An insight into the nano- and micro-structural morphology of a polymer supported Pd catalyst employed in different catalytic reactions under green conditions is reported. The pre-catalyst was obtained by copolymerization of the metal-containing monomer Pd(AAEMA)(2) [AAEMA(-) = deprotonated form of 2-(acetoacetoxy) ethyl methacrylate] with ethyl methacrylate as co-monomer, and ethylene glycol dimethacrylate as cross-linker. This material was used in water for the Suzuki-Miyaura cross-coupling of aryl bromides, and for the reduction of nitroarenes and quinolines using NaBH4 or H-2, as reductants. TEM analyses showed that in all cases the pristine Pd(II) species were reduced in situ to Pd(0), which formed metal nanoparticles (NPs, the real active species). The dependence of their average size (2-10 nm) and morphology on different parameters (temperature, reducing agent, presence of a phase transfer agent) is discussed. TEM and micro-IR analyses showed that the polymeric support retained its porosity and stability for several catalytic cycles in all reactions and Pd NPs did not aggregate after reuse. The metal nanoparticle distribution throughout the polymer matrix after several recycles provided precious information about the catalytic mechanism, which was truly heterogeneous in the hydrogenation reactions and of the so-called release and catch type in the Suzuki coupling.
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