Palladium-nanoparticles on end-functionalized poly(lactic acid)-based stereocomplexes for the chemoselective cinnamaldehyde hydrogenation: Effect of the end-group

Differently carboxylic acid end-functionalized poly(lactic acid) (PLA)-based stereocomplexes were used as polymer support to stabilize Pd-nanoparticles (NPs) generated by the metal vapor synthesis technique. The dispersion of Pd was strongly dependent on the end-group present in the polymer structure, as shown by HRTEM measurements. 2,2′-Bipyridine- and pyridine-based stereocomplexes showed high metal dispersion (i.e. well-separated Pd-NP size of 2.0 ± 0.6 nm), whereas stereocomplexes bearing benzyl and carboxylic acid end groups exhibited strong Pd-NPs aggregation. The heterogenous catalysts were employed to chemoselectively hydrogenate the CC double bond in cinnamaldehyde, showing for Pd-NPs, stabilized by the 2,2′-bipyridine-modified polymer support, the best performance in terms of chemoselectivity (99%) and recyclability in THF solution. Even under bulk cinnamaldehyde hydrogenation conditions, chemoselectivity for 3-phenylpropanal of 90% at 88% conversion was obtained.