Selective semi-hydrogenation of internal alkynes catalyzed by Pd¿CaCO3 clusters

[EN] The de-novo synthesis of soluble or solid-supported Pd-(CaCO3)(n) clusters (n = 2-13) and their high catalytic activity for the semi-hydrogenation of internal alkynes compared to terminal alkynes, is presented. Mechanistic studies show that this reactivity, i.e. internal alkynes more reactive than terminal alkynes, comes from the higher electrophilicity of the Pd-(CaCO3)(n) cluster compared to the nanoparticulated Lindlar catalyst, which unveils the advantages of isolating the minimum catalytic unit of a solid catalyst. Translating solid active sites into soluble catalysts turns around the classical approach and constitutes a paradigmatic shift in catalyst design