Synthesis, characterization and catalytic applications of palladium nanoparticle-cored dendrimers stabilized by metal-carbon bonds

摘要

The synthesis and characterization of four generations of palladium nanoparticle-cored Fréchet-type dendrimers (Pd-G _n) possessing direct palladium-carbon bonds are reported. These core-shell materials have been synthesized by the simultaneous reduction of different generation diazodendrons and Pd ~(II) in an organic medium. The resulting organic-inorganic hybrid materials were characterized by IR, NMR and UV/Vis spectroscopic techniques. The formation of nearly spherical particles of 2-4 nm diameter was confirmed by TEM studies. The efficiency of one member of this series, Pd-G _1, in catalysing important C-C bond-forming reactions such as Suzuki, Stille and Hiyama coupling reactions was investigated. The results clearly show that Pd-G _1 can efficiently catalyse the cross-coupling of arylboronic acids, aryl stannanes and organosilicon compounds with differently substituted aryl halides in addition to efficiently catalysing hydrogenation reactions. The catalyst exhibited good recovery and recyclability in Suzuki coupling reactions. The study suggests that a single catalyst capable of catalysing several reactions can be designed. Palladium nanoparticle-cored dendrimers synthesized by the reduction of Pd II in the presence of diazodendrons find use as efficient catalysts for different cross-coupling reactions with good recyclability.