A methodology is described for the preparation of Pd@CeO(2) core-shell nanostructures that are easily dispersible in common organic solvents. The method involves the synthesis of Pd nanoparticles protected by a monolayer of 11-mercaptoundecanoic acid (MUA). The carboxylic groups on the nanoparticle surfaces are used to direct the self-assembly of a cerium(IV) alkoxide around the metal particles, followed by the controlled hydrolysis to form CeO(2). The characterization of the nanostructures by means of different techniques, in particular by electron microscopy, allowed us to demonstrate the nature of core-shell systems, with CeO(2) nanocrystals forming a shell around the MUA-protected Pd core. Finally, an example of the use of these nanostructures as flexible precursors for the preparation of heterogeneous catalysts is reported by investigating the reactivity of Pd@CeO(2)/Al(2)O(3) nanocomposites toward CO oxidation, water-gas shift (WGS), and methanol steam reforming reactions. Together with CO adsorption data, these observations suggest the accessibility of the Pd phase in the nanocomposites.

Well-defined surfaces of Pt have been extensively studied for various catalytic processes. However, industrial catalysts are mostly composed of fine particles (e.g., nanocrystals), due to the desire for a high surface to volume ratio. Therefore, it is very important to explore and understand the catalytic processes both at nanoscale and on extended surfaces. In this report, a general synthetic method is described to prepare Pt nanocrystals with various morphologies. The synthesized Pt nanocrystals are further purified by exploiting the "self-cleaning" effect which results from the "colloidal recrystallization" of Pt supercrystals. The resulting high-purity nanocrystals enable the direct comparison of the reactivity of the {111} and {100} facets for important catalytic reactions. With these high-purity Pt nanocrystals, we have made several observations: Pt octahedra show higher poisoning tolerance in the electrooxidation of formic acid than Pt cubes; the oxidation of CO on Pt nanocrystals is structure insensitive when the partial pressure ratio p(O2)/p(CO) is close to or less than 0.5, while it is structure sensitive in the O(2)-rich environment; Pt octahedra have a lower activation energy than Pt cubes when catalyzing the electron transfer reaction between hexacyanoferrate (III) and thiosulfate ions. Through electrocatalysis, gas-phase-catalysis of CO oxidation, and a liquid-phase-catalysis of electron transfer reaction, we demonstrate that high quality Pt nanocrystals which have {111} and {100} facets selectively expose are ideal model materials to study catalysis at nanoscale.

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A synthesis of variably functionalized thiol-protected palladium nanoparticles (Pd-NPs) is presented. The nanoparticle syntheses are performed in acetoneÀwater or tetrahydrofuranÀwater solutions, without making use of either phase-transfer agents or complex purification procedures of the as-synthesized nanoparticles. Small and mostly monodisperse thiol-protected Pd nanoparticles (Pd-NPs ∼ 2 nm) have been prepared with 11-mercaptoundecanoic acid (MUA), 9-mercapto-1-nonanol (MN), 1-dodecanethiol (DT), or mixtures thereof, and a simple scale-up synthesis is also proposed. The role of Pd II -thiolate species as metal precursors in the stage of nanoparticle synthesis and the influence of the reaction parameters on the final Pd-NPs size and size distribution are discussed. The formation of mixed-monolayer protected nanoparticles is achieved, with the final monolayer composition dictated by the thiols, initial molar ratio. Overall, the procedure presented here allows the preparation of functionalized nanoparticles with a high density of functional groups at the edge of the monolayer, with no need of place-exchange reactions. Specific postfunctionalization procedures conducted at the acid groups of the MUA-Pd monolayer are reported so as to widen the potential applicability of these amphiphilic nanoparticle precursors with respect to different applications in the field of material science. Finally, the successful use and the easy recycling/reuse of the Pd-NPs in a model Suzuki cross-coupling reaction are presented.

A series of low-valent ruthenium complexes bearing 2,6-bis(imino)pyridyl ("[N 3 ]") ligands has been synthesized and characterized. Reduction of [N 3 ) with hydridosilanes in an arene solvent such as toluene yields new 18eη 6 -arene complexes [κ 2 -N 3 ]Ru(η 6 -MeC 6 H 5 ), 2a,b,c, in which the [N 3 ] ligand is bidentate and only one imine group is coordinated to the metal. The arene ligand can be displaced with dinitrogen in non-arene solvents to yield the binuclear, four-coordinate, formally Ru(0) complexes {[N 3 ]Ru} 2 (μ-N 2 ), 3a,b,c. Pyrophoric complex 3c is a rare example of a structurally characterized Ru(0) dinitrogen complex. Treatment of low-valent complexes 2 or 3 with donor ligands generates five-coordinate complexes [N 3 xyl ]RuL 1,2 (L 1,2 =C 2 H 4 , 4a; L 1,2 =PMe 3 , 5a; L 1,2 =CO, 6a; L 1 =PMe 3 , L 2 =CO, 7a). Complexes 2a, 3c, 5a, 6a, and 7a are diamagnetic and have been structurally characterized by single-crystal X-ray diffraction methods. New six-coordinate Ru(II) complexes [N 3 xyl ]RuCl 2 (L) (L=PMe 3 , CO) were also isolated and structurally characterized. The infrared data, observed geometrical parameters, and reactivity patterns of the formally Ru(0) centers suggest varying degrees of electron delocalization to the "non-innocent" bis(imino)pyridyl, but probably not to the extent implied by the valence tautomeric [N 3 ] 2-/Ru(II) canonical form. Although the [N 3 ] -/Ru(I) representation may portray the electron distribution more accurately than "Ru(0)", the inherent odd electron counts on both ligand and metal;and requisite antiferromagnetic coupling;provides little in the way of "useful" distinctions or predictive value for the low-valent [N 3 ]Ru(L) 2 complexes with strong-field co-ligands such as CO and PMe 3. These five-coordinate adducts seem to be adequately described as Ru(0) complexes of the neutral [N 3 ] ligand. However, "non-innocent" valence tautomeric canonical forms such as [N 3 ] -/Ru þ may be more applicable to the four-coordinate dinitrogen complexes {[N 3 ]Ru} 2 (μ-N 2 ).