Selective Alkyne Semi-Hydrogenation by PdCu Nanoparticles Immobilized on Stereocomplexed Poly(lactic acid)

Polymer-supported PdCu alloy nanoparticles with a palladium to copper atom ratio of 1 have been synthesized upon: (i) Coordination of palladium/copper acetate to 2,2’-bipyridine-end functionalized poly(lactic acid) (PLA); (ii) Stereocomplexation of PLA-based macrocomplexes of opposite stereochemistry, and (iii) metal reduction with hydrogen. The obtained supported PdCu nanoparticles were successfully applied in the semi-hydrogenation of industrially important alkynols, such as 3-hexyn-1-ol and 2-butyne-1,4-diol leading to the corresponding cis-alkenol in high selectivity (98 %) under mild reaction conditions (i. e. ethanol, T (25 °C), p(H2)=3 bar) in the absence of any further additive. From a comparison of the catalytic performance of supported PdCu nanoparticles with those of Pd and Cu, located in the same chemical environment, emerged a clear alloy effect (i. e. high chemoselectivity for the alkene at high alkyne conversion). Recycling experiments conducted with the PdCu-based catalyst proved the stability of the catalyst with time, even by its recovering in air atmosphere.