Stabilization of Nanoparticles Produced by Hydrogenation of Palladium–N-Heterocyclic Carbene Complexes on the Surface of Graphene and Implications in Catalysis

Abstract

Palladium nanoparticles (NPs) have been obtained by decomposition of well-defined palladium complexes noncovalently anchored onto the surface of reduced graphene oxide. Morphological analysis by microscopy showed the presence of small palladium NPs homogeneously distributed on the support. Characterization by X-ray photoelectron spectroscopy confirmed that palladium NPs contain Pd(2+) and Pd(0) oxidation states and the presence of N-heterocyclic carbene and bromo ligands. The catalytic properties of the NPs with and without the support have been evaluated in the hydrogenation of alkynes. Supported palladium NPs showed increased activity versus the nonsupported ones and could be recycled up to 10 times without the loss of catalytic activity. The composition of the palladium NPs is different for each catalytic cycle indicating a dynamic process and the formation of different catalytic active species. On the contrary, the unsupported palladium NPs showed limited activity caused by decomposition and could not be recycled. The role of the support has been investigated. The results indicate that the support influences the stability of palladium NPs.

Palladium‐Based Catalysts Supported by Unsymmetrical XYC–1 Type Pincer Ligands: C5 Arylation of Imidazoles and Synthesis of Octinoxate Utilizing the Mizoroki–Heck Reaction

“…The dominant Pd 3d5/2 peak shifted to the binding energy at 343.4 eV from 342.9 eV and 3d3/2 peak shifted at 337.9 eV from 337.7 eV which could be assigned to new Pd(II) species. Two different new peaks at 342.6 eV and 337.2 eV which consigned Pd 3d5/2 and Pd 3d3/2 of Pd(0) species , . This peak confirms that both Pd(II) and Pd(0) species were involved during the catalytic cycle.…”

The non-innocent role of graphene in the formation/immobilization of ultra-small gold nanoparticles functionalized with N-heterocyclic carbene ligands

“…We have previously evidenced that graphene stabilizes PdNPs and also that control the size and morphology. [60] XPS analysis confirms the presence of NHC ligands and anions (OTf -) at the surface of the AuNPs by the assignment of the core-level peaks of N (400.7 eV) and F (688.0 eV). The Au 4f region of 2-rGO-NPs shows a doublet peak (4f7/2 and 4f5/2) at a binding energy of 88.8 and 85.1 eV, suggesting the presence of Au(I) at the surface of the AuNPs (Figure 2d).…”

Organometallic Nanoparticles Ligated by NHCs: Synthesis, Surface Chemistry and Ligand Effects

“…The formation of chemical bonds between the organic ligands and surface metal atoms results in a strong electronic stabilization, which leads to important modifications of the chemical reactivity of MNPs. In this context, NHCs have demonstrated to be a family of versatile stabilizing ligands that are able to modify the electronic or steric properties of MNPs by modifying their N-substituents or imidazolium structure [12][13][14][15][16]45]. Another key parameter to take into account in MNP synthesis is the stabilizer, which can be a polymer [37,38], ligand [39], ionic liquid (IL) [40], solvent [41] or even a solid support [42][43][44].…”

“…As excellent ligands for transition metal complexes, they have been applied in some of the most important catalytic processes in chemistry. The above-mentioned characteristic of NHCs not only make them perfect candidates for the formation of homogeneous catalysts, but also allow their use in MNP synthesis, showing a great ability to stabilize MNPs [12][13][14][15][16]. Indeed, during the last 10 years, NHC ligands have been employed to stabilize a considerable number of MNPs of different metals, such as Au [17], Pd [18,19], Ru [20] and Ir [21].…”