Immobilization of a Pd(II) complex on hydrophilic graphite oxide and its catalytic investigation in the Heck coupling reaction

Abstract

Tetraamminepalladium(II) chloride monohydrate was heterogenized on hydrophilic graphite oxide (GO), synthesized by Brodie's method. Two samples, with Pd contents of 2% and 5%, referred to as Pd2 and Pd5, respectively, were prepared by a simple and scalable impregnation method and tested as catalysts in the Heck coupling reaction of styrene and bromobenzene. The reactions were carried out at 423 K for 3 hr by applying Na2CO3 as a base and N‐methylpirrolidone or dimethylformamide (DMF) as a solvent. The Pd complexes heterogenized on graphene oxide platelets proved to be highly active and selective catalysts, and Pd2 was more efficient than Pd5. The effect of quaternary ammonium salts (tetrabutylammonium bromide and tetrabutylammonium chloride, TBAC) as modifiers and that of an ionic liquid (1‐butyl‐3‐methylimidazolium bromide, bmim) was studied and the highest conversions were obtained when TBAC was employed. The selectivity for the formation of the main product, E‐stilbene, was in the range 91–96%. Catalyst recycling was investigated and the extent of leaching was found to depend on the solvent. DMF proved to be a highly feasible reaction medium because both catalysts could be recycled five times in this solvent without any significant loss of activity. A hot filtration test was performed and gave evidence that leaching of the active Pd species did not take place under the above reaction conditions. These results substantiate the fact that simple cationic Pd species can be efficiently immobilized on pristine GO surfaces without the requirement of the functionalization of GO with nitrogen‐containing mono or multidentate ligands as binding sites.

Immobilizing palladium on melamine‐functionalized magnetic nanoparticles: An efficient and reusable phosphine‐free catalyst for Mizoroki–Heck reaction

“…Immobilization of palladium on insoluble solid supports is a strategy used for the heterogenization of Pd catalysts. Various inorganic and organic supports including mesoporous silica, [ 17 ] nanostructured materials, [ 18,19 ] metal oxides, [ 20 ] graphitic carbon nitride, [ 21,22 ] ionic liquids [ 23 ] carbon nanotubes, [ 24 ] graphite oxide, [ 25 ] graphene, [ 26 ] and various polymers [ 27–29 ] have been explored. Moreover, as a means to combine the advantages of homogeneous and heterogeneous catalytic processes, nanoparticles have been widely employed recently due to their high surface area and facile recovery.…”