Aqueous Phase Synthesis of Palladium Tripod Nanostructures for Sonogashira Coupling Reactions

In this work, palladium tripod nanocrystals have been synthesized by mixing an aqueous solution of cetyltrimethylammonium bromide (CTAB) surfactant, Na2PdCl4, copper acetate, and ascorbic acid at 30 degrees C for 3 h. Addition of a small amount of copper ion source is critical to the formation of these tripods with a pod length reaching 100 nm. The incorporation of Cu atoms into the Pd tripods has been verified. The entire Pd tripod is single-crystalline with their branches growing along the [111] and [200] directions. Formation of side branches can be observed in some tripods. Triangular nanoplates are initially formed and evolved into the tripod structure in 20-30 min of reaction. Further growth leads to elongation of the pods. The large Pd tripods can serve as active and recyclable catalysts for a broad range of Sonogashira coupling reactions in water using a variety of aromatic halides containing electron-donating and -withdrawing substituents.