Ag@Pd core-shell nanoparticles

1308-1317Colloids of silver and palladium nanoparticles have been prepared by the Solvated Metal Atom Dispersion method. The as-prepared Ag colloid consisting of polydisperse nanoparticles is transformed into a monodisperse colloid by the digestive ripening process which involves refluxing the as-prepared colloid in the presence of a surfactant. In addition to the monodisperse nanoparticles, a small amount of an Ag-thiolate complex is also formed. Refluxing a mixture of the as-prepared Ag and Pd colloids results in Ag@Pd core–shell nanoparticles. The core-shell structure has been established using a combination of techniques such as UV-visible spectroscopy, high resolution electron microscopy, energy filtered electron microscopy, energy dispersive X-ray analysis, high angle annular dark field imaging and powder X-ray diffraction

Dynamic processes of H-atom site exchange in <i>trans </i>dihydrogen hydride complex of ruthenium

27-33A new dihydrogcn hydride complex of ruthenium of the type trans-[(dppm )Ru (H)(η2-H2)(PPh3)2][BF4] (1) (dppm =Ph2PCH2PPh2) has been prepared by protonating the precursor dihydride complex cis- -[(dppm )Ru (H)2( (PPh3)2] using HBF4.Et2O. The fmmulation of (1) as a dihydrogen complex has been based upon the variable temperature T<span style="mso-bidi-font-style: italic">1 measurements (T1 (min) = 12.4 ms at 273 K, ClCD2CD2Cl, 400 MHz) and the observation of a substantial H-D coupling constant (J(H,D) = 32 Hz, 243 K, ClCD2CD2Cl) for the corresponding HD isotopomer trans <i style="mso-bidi-font-style: normal">-[(dppm )Ru (H)(η2-HD) (PPh3)2][BF4]. The T1 and the H-D coupling constant measurements have been carried out in the temperature range 243- 283 K. The dihydrogen and the hydride ligands of (<b style="mso-bidi-font-weight: normal">1) show dynamic behavior and undergo rapid H-atom site exchange at 343 K. At 273 K (1) shows a static structure. The dynamics of (1) involving a trihydride intermediate has been studied by variable temperature NMR spectroscopy. The barrier to site exchange of the H-atom bet ween the dihydrogen with the hydride (∆Gǂ) has been determined to be 14.4 kcal/mol at 303 K. Compound (1) has been found to be stable up to 343 K in solution and no loss of the H2 ligand has been observed at that temperature; in addition, the compound is stable in solution at room temperature for a period of two days

Photolysis of arene chromium tricarbonyl complexes in presence of amine-boranes: Observation of sigma-borane complexes in solution

Activation of the B-H sigma-bond of amine-boranes on the chromium(0) center of arene chromium tricarbonyl complexes (eta(6)-arene) Cr(CO)(3) (arene = fluorobenzene, 1a; benzene, 1b and mesitylene, 1c) has been studied. Photolysis of 1b in presence of ammonia-borane (H3N center dot BH3, AB) and tert-butylamine-borane ((BuH2N)-Bu-t center dot BH3, TBAB) resulted in H-2 evolution and precipitation of a BNHx polymer. On the other hand, photolysis in the presence of trimethylamine-borane (Me3N center dot BH3, TMAB) resulted in the formation of a sigma-borane complex (2) along with Cr(CO)(5)(eta(1)-HBH2 center dot NMe3) (3). The sigma-borane complexes (eta(6)-arene) Cr-( CO)(2)(eta(1)-HBH2 center dot NMe3) (arene = fluorobenzene, 2a; benzene, 2b and mesitylene, 2c) were characterized in solution by H-1, B-11, and C-13 NMR spectroscopy. Electron withdrawing substituents on the arene ring provide the more stable sigma-borane moiety in this series of complexes. (C) 2011 Elsevier B.V. All rights reserved

From (Au₅Sn + AuSn) physical mixture to phase pure AuSn and Au₅Sn intermetallic nanocrystals with tailored morphology: digestive ripening assisted approach

Here we present digestive ripening facilitated interatomic diffusion for the phase controlled synthesis of homogeneous intermetallic nanocrystals of Au–Sn system. Au and Sn metal nanoparticles synthesized by a solvated metal atom dispersion (SMAD) method are employed as precursors for the fabrication of AuSn and Au₅Sn which are Au-rich Au–Sn intermetallic nanocrystals. By optimizing the stoichiometry of Au and Sn in the reaction mixture, and by employing growth directing agents, the formation of phase pure intermetallic AuSn and Au₅Sn nanocrystals could be realized. The as-prepared Au and Sn colloidal nanoparticles and the resulting intermetallic nanocrystals are thoroughly characterized by powder X-ray diffraction, transmission electron microscopy (TEM and STEM-EDS), and optical spectroscopy. The results obtained here demonstrate the potential of solution chemistry which allows synthesizing phase pure Au–Sn intermetallics with tailored morphology

Ag@Pd core-shell nanoparticles

Colloids of silver and palladium nanoparticles have been prepared by the Solvated Metal Atom Dispersion method. The as-prepared Ag colloid consisting of polydisperse nanoparticles is transformed into a monodisperse colloid by the digestive ripening process which involves refluxing the as-prepared colloid in the presence of a surfactant. In addition to the monodisperse nanoparticles, a small amount of an Ag-thiolate complex is also formed. Refluxing a mixture of the as-prepared Ag and Pd colloids results in Ag@Pd core-shell nanoparticles. The core-shell structure has been established using a combination of techniques such as UV-visible spectroscopy, high resolution electron microscopy, energy filtered electron microscopy, energy dispersive X-ray analysis, high angle annular dark field imaging and powder X-ray diffraction

Dynamic processes of H-atom site exchange in trans dihydrogen hydride complex of ruthenium

A new dihydrogcn hydride complex of ruthenium of the type trans-[(dppm )Ru (H)(&#951;2-H2)(PPh3)2][BF4] (1) (dppm =Ph2PCH2PPh2) has been prepared by protonating the precursor dihydride complex cis- -[(dppm )Ru (H)2( (PPh3)2] using HBF4.Et2O. The fmmulation of (1) as a dihydrogen complex has been based upon the variable temperature T1 measurements (T1 (min) = 12.4 ms at 273 K, ClCD2CD2Cl, 400 MHz) and the observation of a substantial H-D coupling constant (J(H,D) = 32 Hz, 243 K, ClCD2CD2Cl) for the corresponding HD isotopomer trans -[(dppm )Ru (H)(&#951;2-HD) (PPh3)2][BF4]. The T1 and the H-D coupling constant measurements have been carried out in the temperature range 243- 283 K. The dihydrogen and the hydride ligands of (1) show dynamic behavior and undergo rapid H-atom site exchange at 343 K. At 273 K (1) shows a static structure. The dynamics of (1) involving a trihydride intermediate has been studied by variable temperature NMR spectroscopy. The barrier to site exchange of the H-atom bet ween the dihydrogen with the hydride (&#916;G&#8800;) has been determined to be 14.4 kcal/mol at 303 K. Compound (1) has been found to be stable up to 343 K in solution and no loss of the H2 ligand has been observed at that temperature; in addition, the compound is stable in solution at room temperature for a period of two days

Synthesis and characterization of Pd(0), PdS, and Pd@PdO core-shell nanoparticles by solventless thermolysis of a Pd-thiolate cluster

Colloids of palladium nanoparticles have been prepared by the solvated metal atom dispersion (SMAD) method. The as-prepared Pd colloid consists of particles with an average diameter of 2.8 +/- 0.1 nm. Digestive ripening of the as-prepared Pd colloid, a process involving refluxing the as-prepared colloid at or near the boiling point of the solvent in the presence of a passivating agent, dodecanethiol resulted in a previously reported Pd-thiolate cluster, Pd(SC12H25)(2)](6) but did not render the expected narrowing down of the particle size distribution. Solventless thermolysis of the Pd-thiolate complex resulted in various Pd systems such as Pd(0), PdS, and Pd@PdO core-shell nanoparticles thus demonstrating its versatility. These I'd nanostructures have been characterized using high-resolution electron microscopy and powder X-ray diffraction methods. (C) 2010 Elsevier Inc. All rights reserved

Metal and Alloy Nanoparticles by Amine-Borane Reduction of Metal Salts by Solid-Phase Synthesis: Atom Economy and Green Process

A new solid state synthetic route has been developed toward metal and bimetallic alloy nanoparticles from metal salts employing amine-boranes, as the reducing agent. During the reduction, amine-borane plays a dual role: acts as a reducing agent and reduces the metal salts to their elemental form and simultaneously generates a stabilizing agent in situ which controls the growth of the particles and stabilizes them in the nanosize regime. Employing different amine-boranes with differing reducing ability (ammonia borane (AB), dimethylamine borane (DMAB), and triethylamine borane (TMAB)) was found to have a profound effect on the particle size and the size distribution. Usage of AB as the reducing agent provided the smallest possible size with best size distribution. Employment of TMAB also afforded similar results; however, when DMAB was used as the reducing agent it resulted in larger sized nanoparticles that are polydisperse too. In the AB mediated reduction, BNHx polymer generated in situ acts as a capping agent whereas, the complexing amine of the other amine-boranes (DMAB and TMAB) play the same role. Employing the solid state route described herein, monometallic Au, Ag, Cu, Pd, and Ir and bimetallic CuAg and CuAu alloy nanoparticles of <10 nm were successfully prepared. Nucleation and growth processes that control the size and the size distribution of the resulting nanoparticles have been elucidated in these systems

A capping agent dissolution method for the synthesis of metal nanosponges and their catalytic activity towards nitroarene reduction under mild conditions

We report a general strategy for the synthesis of metal nanosponges (M = Ag, Au, Pt, Pd, and Cu) using a capping agent dissolution method where addition of water to the M@BNHx nanocomposite affords the metal nanosponges. The B-H bond of the BNHx polymer gets hydrolysed upon addition of water and produces hydrogen gas bubbles which act as dynamic templates leading to the formation of nanosponges. The rate of B-H bond hydrolysis has a direct impact on the final nanostructure of the materials. The metal nanosponges were characterized using powder XRD, electron microscopy, XPS, and BET surface area analyzer techniques. The porous structure of these nanosponges offers a large number of accessible surface sites for catalytic reactions. The catalytic activity of these metal nanosponges has been demonstrated for the reduction of 4-nitrophenol where palladium exhibits the highest catalytic activity (k = 0.314 min(-1)). The catalytic activity of palladium nanosponge was verified for the tandem dehydrogenation of ammonia borane and the hydrogenation of nitroarenes to arylamines in methanol at room temperature. The reduction of various substituted nitroarenes was proven to be functional group tolerant except for a few halogenated nitroarenes (X = Br and I) and >99% conversion was noted within 30-60 min with high turnover frequencies (TOF) at low catalyst loading (0.1 mol%). The catalyst could be easily separated out from the reaction mixture via centrifugation and was recyclable over several cycles, retaining its porous structure