Hydrogenation Of Various Substrates Research Articles

Ni2P Nanoalloy as an Air‐Stable and Versatile Hydrogenation Catalyst in Water: P‐Alloying Strategy for Designing Smart Catalysts

AbstractNon‐noble metal‐based hydrogenation catalysts have limited practical applications because they exhibit low activity, require harsh reaction conditions, and are unstable in air. To overcome these limitations, herein we propose the alloying of non‐noble metal nanoparticles with phosphorus as a promising strategy for developing smart catalysts that exhibit both excellent activity and air stability. We synthesized a novel nickel phosphide nanoalloy (nano‐Ni2P) with coordinatively unsaturated Ni active sites. Unlike conventional air‐unstable non‐noble metal catalysts, nano‐Ni2P retained its metallic nature in air, and exhibited a high activity for the hydrogenation of various substrates with polar functional groups, such as aldehydes, ketones, nitriles, and nitroarenes to the desired products in excellent yields in water. Furthermore, the used nano‐Ni2P catalyst was easy to handle in air and could be reused without pretreatment, providing a simple and clean catalyst system for general hydrogenation reactions.

Supported ruthenium nanoparticles on ordered mesoporous carbons using a cyclodextrin-assisted hard-template approach and their applications as hydrogenation catalysts

The present study is concerned with the preparation of ordered mesoporous carbons containing uniform dispersions of ruthenium nanoparticles by a hard-template method, based on the use of RuCl3 and cyclodextrin as respective sources of metal and carbon. The influence of chemical structure of the parent CD [randomly methylated-β-CD (RAME-β-CD) and 2-hydroxypropyl-β-CD (HP-β-CD)] and loading of the ruthenium source are studied in detail. The catalysts are carefully characterized by N2-adsorption, TEM, XRD, CO pulse chemisorption, TG-MS and H2-TPR. The most outstanding effect is obtained when HP-β-CD is used, allowing to stabilize small and reactive Ru particles (1–2 nm) in the carbon matrix, with a good compromise between immobilization, surface availability and hydrogen spillover effect. The catalytic systems prepared from HP-β-CD display remarkably high catalytic activities in the liquid-phase hydrogenation of various substrates while their reusability and robustness are also demonstrated.

Ru‐Catalyzed Transfer Hydrogenation of Nitriles, Aromatics, Olefins, Alkynes and Esters

AbstractThis paper reports the preparation of new ruthenium(II) complexes supported by a pyrazole‐phosphine ligand and their application to transfer hydrogenation of various substrates. These Ru complexes were found to be efficient catalysts for the reduction of nitriles and olefins. Heterocyclic compounds undergo transfer hydrogenation with good to moderate yields, affording examples of unusual hydrogenation of all‐carbon‐rings. Internal alkynes with bulky substituents show selective reduction to olefins with the unusual E–selectivity. Esters with strong electron‐withdrawing groups can be reduced to the corresponding alcohols, if ethanol is used as the solvent. Possible mechanisms of hydrogenation and olefin isomerization are suggested on the basis of kinetic studies and labelling experiments.

Ester Hydrogenation Catalyzed by CNN-Pincer Complexes of Ruthenium

Ruthenium complexes supported by two new CNN-pincer ligands were synthesized. Both were tested as catalysts for the hydrogenation of esters under mild conditions (105 °C, 6 bar H2). A striking dependence on ligand structure was observed, as a dimethylamino-substituted ligand gave a nearly inactive catalyst, while a diethylamino-substituted variant gave up to 980 catalytic turnovers for the hydrogenation of benzyl benzoate. This system catalyzes the hydrogenation of various substrates including ethyl, benzyl, and hexyl esters, but is surprisingly unreactive toward methyl esters. Experiments demonstrate that base-catalyzed transesterification is rapid under the reaction conditions and that methyl esters are effectively hydrogenated when benzyl alcohol is added to the reaction mixture. The reverse reaction, dehydrogenation of primary alcohols to give esters, was tested as well; up to 920 catalytic turnovers were observed for the dehydrogenation of 1-hexanol to hexyl hexanoate.

Active hydrogenation Rh nanocatalysts protected by new self-assembled supramolecular complexes of cyclodextrins and surfactants in water

New supramolecular assemblies as protective agents of rhodium(0) nanoparticles for hydrogenation of various substrates in water.

Methylated β‐Cyclodextrin‐Capped Ruthenium Nanoparticles: Synthesis Strategies, Characterization, and Application in Hydrogenation Reactions

AbstractColloidal suspensions of ruthenium nanoparticles (Ru0 NPs) stabilized by randomly methylated β‐cyclodextrins were easily prepared in aqueous solution by two comparative reductive approaches. The first method relies on a one‐step hydrogen reduction of ruthenium trichloride as a metal precursor in the presence of cyclodextrins (one‐pot method). The second method consists of the chemical reduction of metal salts by NaBH4, followed by the stabilization of ruthenium NPs by post‐addition of the methylated β‐cyclodextrins (cascade method). The modified β‐cyclodextrin‐capped ruthenium NPs obtained were characterized using TEM, DLS, and NMR techniques. The highly dispersed colloidal suspensions contain very small particles in the size range of 1–1.4 nm. Their catalytic performances were investigated in terms of activity and selectivity of their biphasic hydrogenation of various substrates (olefins, ketones, and disubstituted arenes) under mild conditions.

About the Use of Rhodium Nanoparticles in Hydrogenation and Hydroformylation Reactions

Even if rhodium is one of the rarest and the most costly metals, this noble metal has found many catalytic applications, particularly in hydrogenation and hydroformylation reactions owing to its specific catalytic properties. Tremendous research activities are thus carried out by the scientific community for the development of novel rhodium-based catalysts. This interest for rhodium catalysts concerns also the modern “nanocatalysis” area, situated at the frontier between heterogeneous and homogeneous ones, nanoparticles soluble in a liquid phase being considered as “pseudo homogeneous” systems. A high number of papers describe the preparation of diverse rhodium nanoparticles in suspension for their application as catalysts in hydrogenation of various substrates (mainly olefins and aromatic derivatives) in various catalytic conditions (mainly organic or biphasic phases). Concerning hydroformylation catalysis, it appears that only a few papers deal with rhodium metal nanoparticles for investigation in this reaction, although rhodium is well-known as highly active metal in hydroformylation reaction in homogeneous conditions. In this review, rhodium nanoparticle systems that have been prepared for investigation as nanocatalysts in liquid phase hydrogenation and hydroformylation reactions are described. This work is not comprehensive but provides an overview of the main methods used to synthesize rhodium nanoparticles for these selected catalytic applications. The objective of this review is to give to the readership an outlook of the recent advances in this field, as well as of the great potential of rhodium-based nanocatalysts for hydrogenation and hydroformylation reactions, two reactions of importance in organic synthesis. Keywords: Nanoparticle, Rhodium, Catalysis, Hydrogenation, Hydroformylation, Organic media, Aqueous media, Biphasic media, Polymer-protected Rhodium, poly(methyl vinyl ether) (PMVE)

Oxidation and Reduction of Various Substrates Over a Pd(II) Containing Post-Synthesis Metal Organic Framework

A palladium containing metal-organic framework (MOF) compound has been synthesized from MOF, (Zn4O)3(BDC–NH2)3(BTB)4 through Schiff base condensation reaction and complexation of Pd(II). Pd–MOF was found to be an effective heterogeneous catalyst for the oxidation and hydrogenation of various substrates under mild reaction conditions. This catalytic method is highly active and shape selective.

Continuous Flow Hydrogenation Using an On-Demand Gas Delivery Reactor

A continuous-flow approach to the hydrogenation of alkenes utilizing Wilkinson’s catalyst is reported. The approach relies on a newly developed coil design in which it is possible to load gas and heat the reaction mixture simultaneously. The hydrogenation of various substrates has been performed successfully on small scale and can be scaled up substantially.

Amphiphilic ionic liquid stabilizing palladium nanoparticles for highly efficient catalytic hydrogenation

The highly water-soluble palladium nanoparticles (NPs) were synthesized by using the amphiphilic poly(ethylene glycol)-functionalized dicationic imidazolium-based ionic liquid (C(12)Im-PEG IL) as a stabilizing agent. The aqueous dispersed palladium NPs in the range of 1.9 ± 0.3 nm were observed by transmission electron microscopy (TEM). The physicochemical properties of C(12)Im-PEG IL in aqueous phase have been characterized by electrical conductivity, surface tension and dynamic light scattering (DLS) measurements. It was demonstrated that the amphiphilic ionic liquid can form micelles above its critical micelle concentration (CMC) in aqueous solution and the micelles played a crucial role in stabilizing the palladium NPs and thus promoted catalytic hydrogenation. Furthermore, the dicationic ionic liquid can also act as a gemini surfactant and generated emulsion between hydrophobic substrates and the catalytic aqueous phase during the reaction. The aqueous dispersed palladium NPs showed efficient activity for the catalytic hydrogenation of various substrates under very mild conditions and the stabilizing Pd(0) nanoparticles (NPs) can be reused at least eight times with complete conservation of activity.

“Click” Dendrimers: Synthesis, Redox Sensing of Pd(OAc)2, and Remarkable Catalytic Hydrogenation Activity of Precise Pd Nanoparticles Stabilized by 1,2,3‐Triazole‐Containing Dendrimers

"Click" dendrimers containing 1,2,3-triazolyl ligands that coordinate to PdII(OAc)2 have been synthesized in view of catalytic applications. Five of these dendrimers contain ferrocenyl termini directly attached to the triazole ligand in order to monitor the number of PdII that are introduced into the dendrimers by cyclic voltammetry. Reduction of the PdII-triazole dendrimers by using NaBH4 or methanol yields Pd nanoparticles (PdNPs) that are stabilized either by several dendrimers (G0, DSN) or by encapsulation inside a dendrimer (G1 and G2: DEN), as confirmed by TEM. Relative to PAMAM-DENs (PAMAM=poly(amidoamine)), the "click" DSNs and DENs show a remarkable efficiency and stability for olefin hydrogenation under ambient conditions of various substrates. The influence of the reductant of PdII bound to the dendrimers is dramatic, reduction with methanol leading to much higher catalytic activity than reduction with NaBH4. The most active NPs are shown to be those derived from dendrimer G1, and variation of its termini groups (ferrocenyl, alkyl, phenyl) allowed us to clearly delineate, optimize, and rationalize the role of the dendrimer frameworks on the catalytic efficiencies. Finally, hydrogenation of various substrates catalyzed by these PdNPs shows remarkable selectivity features.

Efficient Synthesis of an Imidazole-Substituted δ-Amino Acid by the Integration of Chiral Technologies

Two methods to produce (2S)-5-amino-2-(1-n-propyl-1H-imidazol-4-ylmethyl)-pentanoic acid were investigated. Diastereoisomeric salt resolution, using the quinidine salt, gave the desired intermediate in 98% ee and 33% yield. Asymmetric hydrogenation of various substrates gave high conversions, with up to 83% ee. Integration of these two approaches via asymmetric hydrogenation of a quinidine salt substrate followed by crystallization provided the desired intermediate in 94% ee and 76% yield.

New Monodentate Chiral Phosphite Ligands for Asymmetric Hydrogenation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

New monodentate chiral phosphite ligands for asymmetric hydrogenation.

We report the synthesis of new chiral monodentate phosphite ligands with a biphenyl backbone, the axial chirality of which is introduced early in the synthesis and locked by a chiral alkylenedioxy bridge. We also describe results obtained with these ligands in rhodium-catalysed asymmetric hydrogenation of various substrates.

Asymmetric hydrogenation by an in situ prepared ( S)-BINAP–Ru(II) catalytic system

A catalytic system obtained by in situ mixing [RuCl 2(benzene)] 2 and ( S)-BINAP has been tested in the asymmetric hydrogenation of various substrates. The best results have been obtained working in methanol: excellent optical purities were achieved in the reduction of substrates such as tiglic acid (83%), geraniol (97%) and methyl 3-oxobutanoate (95%). Some investigations on the nature of the catalyst have been carried out.

Stereochemical Investigation on Asymmetrically Modified Raney Nickel Catalyst. Mode of Interaction between Modifying Reagent and Substrate in the Enantioface-differentiating Process

Abstract The mode of enantioface-differentiating hydrogenation with asymmetrically modified Raney nickel (MRNi) was investigated by using various sorts of modifying reagents and substrates. The optical yields (O.Y.) of the hydrogenation of methyl acetoacetate over MRNi for different modifying reagents occured in the following order: (Remark: Graphics omitted.), (Remark: Graphics omitted.). The hydrogenation of various substrates of the structure, (Remark: Graphics omitted.), over tartaric acid-modified Raney nickel (TA–MRNi), gave high optical yields only when the substituent –Y functioned as a good hydrogen bond acceptor like a carbonyl group, and two pairs of hydrogen bondings between substrate and two hydroxyl groups of tartaric acid were available. As for the stereochemistry of the reaction in such a case, (R,R)-TA–MRNi always gave (R)-product in excess. Based on the stereochemistry of the reaction and the role of hydrogen bonds between modifying reagent and substrate, a stereochemical model is proposed to elucidate the mode of enantioface-differentiating hydrogenation of prochiral ketones over TA–MRNi.