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

Abstract 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(H 2 )=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.