Monodisperse Ni@Pd Core@Shell Nanoparticles Assembled on Reduced Graphene Oxide as a Highly Efficient and Reusable Heterogeneous Catalyst for the C-H Bond Arylation of Imidazo[1,2-a]pyridine with Aryl Halides

We report herein, for the first time, the direct C-H bond arylation of imidazo[1,2-a]pyridine with aryl halides using monodisperse Ni@Pd core@shell nanoparticles assembled on reduced graphene oxide (rGO) as a highly efficient and reusable heterogeneous catalyst. Monodisperse Ni@Pd core@shell nanoparticles (NPs) were synthesized by using one-pot successive reduction of metal precursors in the presence of oleylamine and trioctyl phosphine and then assembled on rGO via a liquid-phase self-assembly method to yield rGO-Ni@Pd nanocatalyst. The structures of the colloidal Ni@Pd core@shell NPs and rGO-Ni@Pd nano catalyst were characterized by TEM, high-resolution TEM (HR-TEM), STEM-EDS, XPS, and ICP-MS. Next, rGO-Ni@Pd nanocatalysts as well as rGO-Ni and rGO-Pd counterparts were first tested in the direct C-H bond arylation of imidazo[1,2-a]pyridine with bromobenzene under tunable reaction conditions to find the optimum reaction conditions. Under the optimum reaction conditions, the substrate scope of rGO-Ni@Pd-catalyzed direct C-H arylation of irnidazo[1,2-a]pyridine was examined by performing the catalytic reactions with a variety of aryl halides. These studies showed for the first time that rGO-Ni@Pd nanocatalysts are highly efficient and reusable catalysts in the direct C-H bond arylation reactions and have a high potential to be applied in other C-H activation reactions.