Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the frontier between homogeneous and heterogeneous catalysis, and progress has been made in the efficiency and selectivity of reactions and recovery and recyclability of the catalytic materials. Usually NP catalysts are prepared from a metal salt, a reducing agent, and a stabilizer and are supported on an oxide, charcoal, or a zeolite. Besides the polymers and oxides that used to be employed as standard, innovative stabilizers, media, and supports have appeared, such as dendrimers, specific ligands, ionic liquids, surfactants, membranes, carbon nanotubes, and a variety of oxides. Ligand-free procedures have provided remarkable results with extremely low metal loading. The Review presents the recent developments and the use of NP catalysis in organic synthesis, for example, in hydrogenation and C--C coupling reactions, and the heterogeneous oxidation of CO on gold NPs.

Nanoparticles as Recyclable Catalysts: The Frontier between Homogeneous and Heterogeneous Catalysis

N-Heterocyclic Carbenes in Late Transition Metal Catalysis

Protic Ionic Liquids: Properties and Applications

2.5. Stabilization of IL Emulsions by Nanoparticles 2623 3. Hydrogenations in ILs 2623 3.1. Hydrogenation on IL-Stabilized Nanoparticles 2623 3.1.1. Hydrogenation of 1,3-Butadiene 2623 3.1.2. Hydrogenation of Alkenes and Arenes 2624 3.1.3. Hydrogenation of Ketones 2624 3.2. Homogeneous Catalytic Hydrogenation in ILs 2624 3.3. Hydrogenation of Functionalized ILs 2625 3.3.1. Selective Hydrogenation of Polymers 2625 3.4. Asymmetric Hydrogenations 2626 3.4.1. Enantioselective Hydrogenation 2626 3.5. Role of the ILs Purity in Hydrogenation Reactions 2628

Catalysis in ionic liquids

A wide array of forms of palladium has been utilized as precatalysts for Heck and Suzuki coupling reactions over the last 15 years. Historically, nearly every form of palladium used has been described as the active catalytic species. However, recent research has begun to shed light on the in situ transformations that many palladium precatalysts undergo during and before the catalytic reaction, and there are now many suggestions in the literature that narrow the scope of types of palladium that may be considered true “catalysts” in these coupling reactions. In this work, for each type of precatalyst, the recent literature is summarized and the type(s) of palladium that are proposed to be truly active are enumerated. All forms of palladium, including discrete soluble palladium complexes, solid-supported metal ligand complexes, supported palladium nano- and macroparticles, soluble palladium nanoparticles, soluble ligand-free palladium, and palladium-exchanged oxides are considered and reviewed here. A considerable focus is placed on solid precatalysts and on evidence for and against catalysis by solid surfaces vs. soluble species when starting with various precatalysts. The review closes with a critical overview of various control experiments or tests that have been used by authors to assess the homogeneity or heterogeneity of catalyst systems.

On the Nature of the Active Species in Palladium Catalyzed Mizoroki–Heck and Suzuki–Miyaura Couplings – Homogeneous or Heterogeneous Catalysis, A Critical Review

The antitumor activity of the organometallic ruthenium(II)−arene complexes, RuCl2(η6-arene)(PTA), (arene = p-cymene, toluene, benzene, benzo-15-crown-5, 1-ethylbenzene-2,3-dimethylimidazolium tetrafluoroborate, ethyl benzoate, hexamethylbenzene; PTA = 1,3,5-triaza-7-phosphaadamantane), abbreviated RAPTA, has been evaluated. In vitro biological experiments demonstrate that these compounds are active toward the TS/A mouse adenocarcinoma cancer cell line whereas cytotoxicity on the HBL-100 human mammary (nontumor) cell line was not observed at concentrations up to 0.3 mM, which indicates selectivity of these ruthenium(II)−arene complexes to cancer cells. Analogues of the RAPTA compounds, in which the PTA ligand is methylated, have also been prepared, and these prove to be cytotoxic toward both cell lines. RAPTA-C and the benzene analogue RAPTA-B were selected for in vivo experiments to evaluate their anticancer and antimetastatic activity. The results show that these complexes can reduce the growth of lung m...

In Vitro and in Vivo Evaluation of Ruthenium(II)−Arene PTA Complexes

Some of the recent developments concerning the synthesis, properties and applications of functionalised ionic liquids are highlighted. Various strategies are presented, including functionalisation of the cation, anion or both cation and anion in the same ionic liquid, leading to what has been termed dual-functionalised ionic liquids. Particular attention is given to the application of functionalised ionic liquids as reaction media, to stabilise nanoparticles/modify surfaces and to generate porous materials.

From dysfunction to bis-function: on the design and applications of functionalised ionic liquids

A series of relatively low-cost ionic liquids, based on the N-butyronitrile pyridinium cation [C(3)CNpy](+), designed to improve catalyst retention, have been prepared and evaluated in Suzuki and Stille coupling reactions. Depending on the nature of the anion, these salts react with palladium chloride to form [C(3)CNpy](2)[PdCl(4)] when the anion is Cl(-) and complexes of the formula [PdCl(2)(C(3)CNpy)(2)][anion](2) when the anion is PF(6)(-), BF(4)(-), or N(SO(2)CF(3))(2)(-). The solid-state structures of [C(3)CNpy]Cl and [C(3)CNpy](2)[PdCl(4)] have been established by single-crystal X-ray diffraction. The catalytic activity of these palladium complexes following immobilization in both N-butylpyridinium and nitrile-functionalized ionic liquids has been evaluated in Suzuki and Stille coupling reactions. All of the palladium complexes show good catalytic activity, but recycling and reuse is considerably superior in the nitrile-functionalized ionic liquid. Inductive coupled plasma spectroscopy reveals that the presence of the coordinating nitrile moiety in the ionic liquid leads to a significant decrease in palladium leaching relative to simple N-alkylpyridinium ionic liquids. Palladium nanoparticles have been identified as the active catalyst in the Stille reaction and were characterized using transmission electron microscopy.

Nitrile-functionalized pyridinium ionic liquids: Synthesis, characterization, and their application in carbon-carbon coupling reactions

Imidazolium chlorides with one or two carboxylic acid substituent groups, 1-methyl-3-alkylcarboxylic acid imidazolium chloride, [Me{(CH2)(n)COOH}im]Cl (n=l, 3), and 1,3-dialkylcarboxylic acid imidazolium chloride, [{(CH2)(n)COOH}(2)im]Cl (n=1, 3), have been synthesized via their corresponding acid esters. Deprotonation of the carboxylic acid functionalized imidazolium chlorides with triethylamine affords the corresponding zwitterions [Me{(CH2)(n)COO}im] (n=1, 3) and [{(CH2),COOH}{(CH2)(n)COO}im] (n= 1, 3). Subsequent reaction of the zwitterions with strong acids gives the new imidazolium salts [Me{(CH2)(n)COOH }im]X (n=1, 3; X=BF4, CF3SO3) and [{(CH2)(n)COOH)(2)im]X (n=1, 3; X=BF4, CF3SO3), which exhibit melting points as low as -61 degreesC. The solidstate structures of two of the carboxylic acid functionalized imidazolium salts have been determined by single-crystal X-ray diffraction analysis. Extensive hydrogen bonding is present between the chloride and the imidazolium, with eight (ClH)-H-... interactions below 3Angstrom. The pK(a) values of all the salts, determined by potentiometric titration, lie between 1.33 and 4.59 at 25 degreesC.

Brønsted Acidic Ionic Liquids and Their Zwitterions: Synthesis, Characterization and pKa Determination

The synthesis of a novel imidazolium-tagged ruthenium complex, which represents a versatile precursor for aqueous and ionic liquid biphasic catalysis, is reported. Its utility is demonstrated in the highly enantioselective ionic liquid biphasic transfer hydrogenation of acetophenone and is compared to conventional (untagged) complexes.

A Versatile Ruthenium Precursor for Biphasic Catalysis and Its Application in Ionic Liquid Biphasic Transfer Hydrogenation: Conventional vs Task-Specific Catalysts

Tilmann J. Geldbach

Papers

In Vitro and in Vivo Evaluation of Ruthenium(II)−Arene PTA Complexes

From dysfunction to bis-function: on the design and applications of functionalised ionic liquids

Nitrile-functionalized pyridinium ionic liquids: Synthesis, characterization, and their application in carbon-carbon coupling reactions

Brønsted Acidic Ionic Liquids and Their Zwitterions: Synthesis, Characterization and pKa Determination

A Versatile Ruthenium Precursor for Biphasic Catalysis and Its Application in Ionic Liquid Biphasic Transfer Hydrogenation: Conventional vs Task-Specific Catalysts