Nanomaterials. Influence of the support on surface rearrangements of bimetallic nanoparticles in real catalysts.

Catalysts used for heterogeneous processes are usually composed of metal nanoparticles dispersed over a high-surface-area support. In recent years, near-ambient pressure techniques have allowed catalyst characterization under operating conditions, overcoming the pressure gap effect. However, the use of model systems may not truly represent the changes that occur in real catalysts (the so-called material gap effect). Supports can play an important role in the catalytic process by providing new active sites and may strongly affect both the physical and chemical properties of metal nanoparticles. We used near-ambient pressure x-ray photoelectron spectroscopy to show that the surface rearrangement of bimetallic (rhodium-palladium) nanoparticles under working conditions for ethanol steam reforming with real catalysts is strongly influenced by the presence of a reducible ceria support.

Synthesis of carbosilane dendrimers containing up to four metal layers.

Metallodendrimers are an important class of materials with valuable properties and applications in a large number of areas. Herein, we report a highly efficient route for the synthesis of carbosilane dendrimers containing multimetal layers. The procedure involves the use of heteroditopic and tritopic P,N ligands as connectors of the metal layers. The synthetic strategy is based on the ability of the latter ligands to react selectively with the metal complexes [AuCl(tht)] (tht: tetrahydrothiophene), [{RuCl(2)(p-cymene)}(2)] and [Pd(eta(3)-2-MeC(3)H(4))(cod)](OTf) (cod: 1,5-cyclooctadiene; OTf: triflate). In this way, metallodendrimers containing trimetallic Ru-Au-Pd or tetrametallic Ru-Au-Au'-Pd layers have been formed and characterized. The trimetallic dendrimer 9 can be selectively deconstructed by cleavage of the Ru-N or Au-N bonds by reaction with chloride or iodide salts, respectively.

Single and double metallic layer-containing ruthenium dendrimers. Synthesis and catalytic properties.

The reaction of a series of phosphanyl-terminated carbosilane dendrimers displaying only one phosphorus ligand per arm with [RuCl(2)(p-cymene)](2) resulted in the grafting of RuCl(p-cymene) moieties on the periphery of the dendrimer. In these species, the chloride ligand is easily displaced by the organic bases pyridine, 4-cyanopyridine and 4,4[prime or minute]-bipyridine to afford new cationic metallodendrimers. NMR studies have confirmed the chirality of the ruthenium centre. The species containing 4,4[prime or minute]-bipyridine reacts through the uncoordinated pyridyl nitrogen with a new equivalent of [RuCl(2)(p-cymene)](2) or [RhCl(CO)(2)](2) to lead to homo- or hetero-bimetallic layer-containing dendrimeric systems. The ruthenodendrimers were tested as catalysts in the transfer hydrogenation of cyclohexanone by propan-2-ol and their activity compared with that of some analogous mononuclear ruthenium(ii) complexes.

Unprecedented eight-palladium(I) crown-cycle with metal-metal unsupported bonds.

Tri(N-pyrrolyl)phosphine reacted with the sigma/pi complex [Pd(mu-Cl)(COD-MeO)]2 to give the octa-cycle [Pd(mu-Cl)[P(pyrl)3]]8 containing four Pd(I)-Pd(I) unbridged bonds.