Influence of organic ligands on the stabilization of palladium nanoparticles

The synthesis of palladium nanoparticles is performed by hydrogenation of a precursor, Pd2(dba)3 (1) or [Pd(C3H5)Cl]2 (2) in the presence of either a weakly coordinating ligand (hexadecylamine, HDA) or good ligands (polyphosphines). It is shown in the case of 1 that good ligands lead to stable spherical nanoparticles of small size (near 2 nm) whereas the protective effect of HDA depends on the amount of ligand added as a result of equilibria present at the surface of the particles as monitored by solution NMR spectroscopy. The decomposition of 2 being very fast, the particle growth cannot be controlled except in the case of the use of a large excess of HDA which leads to spongelike particles resulting from the agglomeration of initially obtained nanocrystallites.