Abstract: The synthesis of the non-classical ruthenium dihydrogen complexes [Ru(dtbpmp)H2(H2)] (PNP-pincer backbone) and [Ru(dtbpoet)(H2)H2] (POP-pincer backbone) with constrained geometries, their application in homogeneous catalysis and their reactivity towards small molecules like N2, CO2 and CO is described. The complexes with side-on bonded molecular hydrogen were analysed by NMR (T1-analysis), FT-IR and by means of DFT calculations. Ruthenium dihydrogen complexes have a great potential as catalysts for CH-activation, especially for H/Dexchange and hydrogen transfer processes. We successfully generated a ruthenium hydride catalyst for the H/D-exchange between (hetero)aromatic or olefinic protons and D2O (or C6D6)under mild conditions. The H/D-exchange processes included mechanistic investigation (NMR-kinetics and DFT calculations). Interestingly, it is also catalytically active in acceptorless dehydrogenation of alcohols to esters and some other reactions.
Abstract: A brief summary of selected pioneering and mechanistic contributions in the field of carbon-carbon cross-coupling reactions with palladium nanoparticles (Pd-NPs) in ionic liquids (ILs) is presented. Five exemplary model systems using the Pd-NPs/ILs approach are presented: Heck, Suzuki, Stille, Sonogashira and Ullmann reactions which all have in common the use of ionic liquids as reaction media and the use of palladium nanoparticles as reservoir for the catalytically active palladium species.
Abstract: The sputtering of gold foil onto 1-n-butyl-3-methylimidazolium tetrafluoroborate, hexafluorophosphate, bis(trifluoromethylsulfonyl)amide, or tris(fluoro)tris(perfluoroethane)phosphate ionic liquids (ILs) generates stable and well-dispersed gold nanoparticles (NPs) of 3-5 nm under conditions of 40 mA, 335 V, and 2 Pa Ar work pressure. The size and size distribution of these Au nanoparticles depends on various experimental parameters, particularly the surface composition of the IL and less so the surface tension and viscosity. Under the experimental conditions used here, both nucleation and NP growth seem to occur on the IL surface and the NP size changes with the changes in the IL surface composition, especially with the increase of the fluorinated content. Moreover, the NP size is independent of sputtering time but does depend on the discharge current. When higher discharge currents are used, more gold atoms hit the ionic liquid surface per unit time, changing the kinetics of particle growth on the surface of the IL.
Notes: J. Phys. Chem. C xD;ISI Document Delivery No.: 620NZ Times Cited: 0 Cited Reference Count: 47 Wender, Heberton de Oliveira, Luciane F. Migowski, Pedro Feil, Adriano F. Lissner, Elizeo Prechtl, Martin H. G. Teixeira, Sergio R. Dupont, Jairton CNPq ; FAPERGS ; MCT ; CAPES ; INCT-Catal. ; CME-UFRGS Thanks are due to the following Brazilian agencies for financial support: CNPq, FAPERGS, MCT, CAPES, INCT-Catal., and CME-UFRGS. AMER CHEMICAL SOC WASHINGTON
Abstract: Here we present the state-of-the-art for asymmetric catalysis using chiral ionic liquids (CILs) as source of chiral information. The current review covers reactions using typical homogeneous catalysts e. g. organocatalysts, transition metal complexes and solid catalysts for heterogeneous catalysis in solvent-systems with chiral ionic liquids.
Notes: Prechtl, Martin H. G. Scholten, Jackson D. Neto, Brenno A. D. Dupont, Jairton
Abstract: Ruthenium nanoparticles prepared in nitrile-functionalised ionic liquids (ILs) display unusual selectivities toward the hydrogenation of nitrile containing aromatic compounds. In particular, a selective catalytic hydrogenative coupling of nitriles was observed. In this transformation, nitrile groups are exclusively hydrogenated in the presence of arenes, which are typically hydrogenated by ruthenium nanoparticles in non-functionalised ILs. The catalyst material was characterised by means of TEM and EDS analysis. Furthermore, molecular species formed during the catalytic process were characterised by MS-analysis of the gaseous phase and the ionic liquid phase by ESI/MS Q-TOR. (C) 2009 Elsevier B.V. All rights reserved.
Notes: Prechtl, Martin H. G. Scholten, Jackson D. Dupont, Jairton
Abstract: The reduction of [Ru(COD)(2-methylallyl) 2] (COD = 1,5-cyclooctadiene) dispersed in various room-temperature ionic liquids (ILs), namely, 1- n-butyl-3-methylimidazolium (BMI) and 1- n-decyl-3-methylimidazolium (DMI), associated with the N-bis(trifluoromethanesulfonyl)imidates (NTf 2) and the corresponding tetrafluoroborates (BF 4) with hydrogen gas (4 bar) at 50 degrees C leads to well-dispersed immobilized nanoparticles. Transmission electron microscopy (TEM) analysis of the particles dispersed in the ionic liquid shows the presence of [Ru(0)] n nanoparticles (Ru-NPs) of 2.1-3.5 nm in diameter. Nanoparticles with a smaller mean diameter were obtained in the ILs containing the less coordinating anion (NTf 2) than that in the tetrafluoroborate analogues. The ruthenium nanoparticles in ionic liquids were used for liquid-liquid biphasic hydrogenation of arenes under mild reaction conditions (50-90 degrees C and 4 bar). The apparent activation energy of E A = 42.0 kJ mol (-1) was estimated for the hydrogenation of toluene in the biphasic liquid-liquid system with Ru-NPs/BMI.NTf 2. TEM analysis of the ionic liquid material after the hydrogenation reactions shows no significant agglomeration of the [Ru(0)] n nanoparticles. The catalyst ionic liquid phase can be reused several times without a significant loss in catalytic activity.
Abstract: The synthesis and characterisation of nonclassical ruthenium hydride complexes containing bidentate PP and tridentate PCP and PNP pincer-type ligands are described. The mononuclear and dinuclear ruthenium complexes presented have been synthesised in moderate to high yields by the direct hydrogenation route (one-pot synthesis) or in a two-step procedure. In both cases [Ru(cod)(metallyl)(2)] served as a readily available precursor. The influences of the coordination geometry and the ligand framework on the structure, binding, and chemical properties of the M--H(2) fragments were studied by X-ray crystal structure analysis, spectroscopic methods, and reactivity towards N(2), D(2), and deuterated solvents.
Abstract: The potential of pincer complexes [M(H)(2)(H(2))(PXP)] (M=Fe, Ru, Os; X=N, O, S) to coordinate, activate, and thus catalyze the reaction of N(2) with classical or nonclassical hydrogen centers present at the metal center, with the aim of forming NH(3) with H(2) as the only other reagent, was explored by means of DF (density functional) calculations. Screening of various complexes for their ability to perform initial hydrogen transfer to coordinated N(2) showed ruthenium pincer complexes to be more promising than the corresponding iron and osmium analogues. The ligand backbone influences the reaction dramatically: the presence of pyridine and thioether groups as backbones in the ligand result in inactive catalysts, whereas ether groups such as gamma-pyran and furan enable the reaction and result in unprecedented low activation barriers (23.7 and 22.1 kcal mol(-1), respectively), low enough to be interesting for practical application. Catalytic cycles were calculated for [Ru(H)(2)(H(2))(POP)] catalysts (POP=2,5-bis(dimethylphosphanylmethyl)furan and 2,6-bis(dimethylphosphanylmethyl)-gamma-pyran). The height of activation barriers for the furan system is somewhat more advantageous. Formation of inactive metal nitrides has not been observed. SCRF calculations were used to introduce solvent (toluene) effects. The Gibbs free energies of activation of the numerous single reaction steps do not change significantly when solvent is included. The reaction steps associated with the formation of the active catalyst from precursors [M(H)(2)(H(2))(PXP)] were also calculated. The otherwise inactive pyridine ligand system allows for the generation of the active catalyst species, whereas the ether ligand systems show activation barriers that could prohibit practical application. Consequently the generation of the active catalyst species needs to be addressed in further studies.
Abstract: Under palladium dichloride catalysis, vinylic tellurides couple efficiently with alkynes with retention of the double-bond geometry. Herein we show that the amount of the PdCl2 catalyst can be reduced from 40 mol % to 10 mol % by using copper(II) chloride as an oxidizing agent. Under these conditions, an inert atmosphere is no longer required and the reaction occurs quite efficiently in the presence of air, leading to the enynes in 40−82% isolated yields. Mass and tandem mass spectrometric experiments using electrospray ionization were performed, and Pd−Te cationic intermediates were, for the first time, intercepted and transferred to the gas phase for structural characterization. An expanded catalytic cycle for this important method for enyne synthesis is proposed.
