Reduced Graphene Oxide-Supported CuPd Alloy Nanoparticles as Efficient Catalysts for the Sonogashira Cross-Coupling Reactions

Monodisperse CuPd alloy nanoparticles (NPs) were prepared by using a typical high-temperature organic solution phase protocol comprising the coreduction of copper(II) acetylacetonate and palladium(II) acetylacetonate by morpholineborane complex in oleylamine and 1-octadecene solution at 80 degrees C. The presented synthesis protocol allows us to control the composition of CuPd alloy NPs by simply tuning the initial ratio of metal precursors and the Cu-rich Cu75Pd25 NPs and Pd-rich Cu32Pd68 were synthesized besides the Cu48Pd52 NPs. Transmission electron microscopy studies revealed that most of the CuPd alloy NPs are polyhedral with an average diameter of 3.0 +/- 0.3 nm. The alloy structure of CuPd NPs was confirmed by the detailed X-ray diffraction and X-ray photoelectron spectroscopy analysis. As-prepared CuPd NPs were deposited on reduced graphene oxide (rGO) by using a liquid self-assembly method (rGO-CuPd) and used as catalysts in the Sonogashira cross-couplings of various aryl iodides or bromides and phenyl acetylene under the optimized reaction conditions. Among the three compositions of CuPd alloy NPs tested in the Sonogashira couplings, the rGO-Cu48Pd52 gave the best yields in shorter reaction times and therefore it was used for further coupling reactions. The results demonstrated that rGO-Cu48Pd52 were efficient catalysts for the Sonogashira reaction of various aryl halides with phenylacetylene. The coupling reactions proceeded smoothly with both electron-rich and electron-deficient aryl iodides and aryl bromides, affording the desired biaryl products in high yields. This is the first example of the employment of monodisperse CuPd alloy NPs with composition control in the Sonogashira cross-coupling reactions.