Click dendrimers:: Synthesis, redox sensing of Pd(OAc)2, and remarkable catalytic hydrogenation activity of precise Pd nanoparticles stabilized by 1,2,3-triazole-containing dendrimers

Click dendrimers containing 1,2,3-triazolyl ligands that coordinate to Pd-II(OAc), have been synthesized in view of catalytic applications. Five of these dendrimers contain ferrocenyl termini directly attached to the triazole ligand in order to monitor the number of Pd-II that are introduced into the dendrimers by cyclic voltammetry. Reduction of the Pd-II-triazole dendrimers by using NaBH, or methanol yields Pd nanoparticles (PdNPs) that are stabilized either by several dendrimers (G(0), DSN) or by encapsulation inside a dendrimer (G(1) and G(2): DEN), as confirmed by TEM. Relative to PAMAM-DENs (PAMAM=poly(amidoamine)), the "click" DSNs and DENs show a remarkable efficiency and stability for olefin hydrogenation under ambient conditions of various substrates. ne influence of the reductant of Pd bound to the dendrimers is dramatic, reduction with methanol leading to much higher catalytic activity than reduction with NaBH4. The most active NPs are shown to be those derived from dendrimer G(1), and variation of its termini groups (ferrocenyl, alkyl, phenyl) allowed us to clearly delineate, optimize, and rationalize the role of the dendrimer frameworks on the catalytic efficiencies. Finally, hydrogenation of various substrates catalyzed by these PdNPs shows remarkable selectivity features.