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A triphenylphosphine-stabilized Ir/SiO 2 catalyst modified by a chiral diamine was synthesized with four silica spheres as support for the asymmetric hydrogenation of aromatic ketones. The H-bond between substrate and silanols and the interaction between substrate and modifier commonly affected the steric configuration of asymmetric hydrogenation of aromatic ketones. With the silanols increasing, the activity of asymmetric hydrogenation significantly increased. This is the first report of heterogeneous asymmetric hydrogenation of aromatic ketones enhanced by silanols on highly monodispersed silica spheres with > 99.9% ee and > 99% conversion.

New 3rd generation designer ansa-ruthenium(II) complexes featuring N,C-alkylene-tethered N,N-dialkylsulfamoyl-DPEN/η6-arene ligands, exhibited good catalytic performance in the asymmetric transfer hydrogenation (ATH) of various classes of (het)aryl ketones in formic acid/triethylamine mixture. In particular, benzo-fused cyclic ketones furnished 98 to >99.9% ee using a low catalyst loading.

Ruthenium encapsulated in an aluminium oxyhydroxide-support was investigated for the transfer hydrogenation of aldehydes and ketones with potassium formate as a sustainable green hydrogen donor. The entrapped ruthenium were narrowly distributed with mean diameters of 1.5–1.8 nm. XPS studies show that the ruthenium was present as Ru 0 and Ru 3+ . The catalysts showed high activity even at low metal loadings of 0.5–2 wt.%. The maximum TOF for benzaldehyde hydrogenation was over 1 wt.% Ru. The reduction of aromatic and aliphatic aldehydes was facile and occurred with 100% yield. In comparison, ketones were less readily reduced although moderate to excellent yields could be obtained after a longer reaction time. No leaching of ruthenium was observed in contrast to a catalyst prepared by wet impregnation. Washing of the used catalyst with water and ethanol effectively removed the deposited bicarbonate co-product and the recycled catalyst maintained its activity up to five runs.

The hydrogenation of 4-nitroacetophenone (4-NAP) and 4-aminoacetophenone (4-AAP) was examined over rhodium/silica catalysts. The reactions were carried out using isopropanol as the solvent under a range of temperatures (303–333 K) and pressures (1–5 barg). An activation energy of 50 ± 4 kJ mol−1 was determined for 4-NAP hydrogenation and 48 ± 2 kJ mol−1 for 4-AAP hydrogenation. Orders of reaction were obtained for 4-NAP (zero order) and hydrogen (first order) and a kinetic isotope effect of 3.0 was observed for 4-NAP hydrogenation and ∼1.4 for 4-AAP hydrogenation when deuterium was used. Under specific conditions high yields (∼94%) to 4-aminoacetophenone and 1-(4-aminophenyl) ethanol could be obtained from 4-NAP hydrogenation. An antipathetic metal crystallite particle size effect was observed for both reactants.

Imines and their derivatives are versatile synthetic intermediates for the industrial preparation of both bulk and fine chemicals and for pharmaceuticals, but preparing these compounds efficiently through direct hydrogenation of nitriles are hindered by overhydrogenation to secondary amines. Here we report a highly efficient multifunctional catalyst system for selective hydrogenation coupling of nitriles to secondary imines using a heterogeneous Pt catalyst that was deposited on a nickel-based metal-organic framework (MOF) containing DABCO. The catalyst showed excellent synergy in promoting the hydrogenation of a variety of nitriles, giving significantly improved activity and selectivity (up to >99% yield) even under atmospheric pressure of H2. It is suggested that the Lewis base (DABCO) sites on the Ni-MOF inhibit further hydrogenation of the imines. The influence of H2 pressure, reactant concentration, stirring speed, and reaction temperature was investigated. The kinetics and mechanism of hydrogenation of benzonitrile (BN) by the Pt/Ni-MOF catalyst has been studied. The reaction showed a first-order dependence on both BN concentration and H2 pressure. A kinetic model was proposed based on the mechanism of nitriles hydrogenation and compared with experimental observations. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3565–3576, 2014

Chemoselective hydrogenation of various aldehydes and ketones with methylamine borane (MeAB) in neat water was investigated. MeAB is suitable for green organic reactions, for MeAB is a nontoxic, environmentally benign, and easily handled reagent. Aldehydes were selectively and rapidly hydrogenated in excellent yields (86–97%) for 30 min, but hydrogenation of aromatic ketones needed over 20 h at room temperature because of their poor water solubility and steric hindrance. Thus we investigated polyethylene glycol (PEG400) and acidic cation-exchange D072 resin as catalysts to accelerate the hydrogenation reaction of aromatic ketones and achieved excellent yields within several hours. PEG 400 and D072 resin are both suitable for green organic reactions. The D072 resin was reused up to four times without any significance loss in activity.

A chiral ( R ) key intermediate of the biologically active form of terutroban has been prepared by asymmetric hydrogenation. The catalysts are based on very easily accessible ruthenium complexes modified by chiral phosphorous ligands. The use of the chiral catASium ® T ligands family allowed us to realize this transformation efficiently in terms of yield and enantioselectivity (ee up to 92%) with high substrate/catalyst ratios.

The first demonstration of the hydrogenation of sulfoxides under atmospheric H2 pressure is reported. The highly efficient reaction is facilitated by a heterogeneous Ru nanoparticle catalyst. The mild reaction conditions enable the selective hydrogenation of a wide range of functionalized sulfoxides to the corresponding sulfides. The high redox ability of RuO(x) nanoparticles plays a key role in the hydrogenation.

Asymmetric hydrogenation of unprotected NH imines catalyzed by rhodium/bis(phosphine)-thiourea provided chiral amines with up to 97% yield and 95% ee. (1)H NMR studies, coupled with control experiments, implied that catalytic chloride-bound intermediates were involved in the mechanism through a dual hydrogen-bonding interaction. Deuteration experiments proved that the hydrogenation proceeded through a pathway consistent with an imine.

When activated with base, the iron(II) complexes with tetradentate amine(imine)diphosphine ligands, (S,S)-trans-[FeCl(CO)(PAr2-NH-N-PAr′2)]BF4 (1: Ar, Ar′ = Ph; 2: Ar = Ph, Ar′ = 4-MeC6H4; 3: Ar, Ar′ = 3,5-Me2C6H3), are very active for the asymmetric transfer hydrogenation (ATH) of ketones in KOtBu/2-propanol. For ATH, better enantioselectivity, but lower catalytic activity, was observed in general when using catalyst precursors with the bulkier dixylylphosphino groups compared to those with diphenylphosphino groups. The complexes were much less active for the pressure hydrogenation of ketones, where 1 and 2 produced racemic product alcohols, while 3 yielded chiral alcohols with an enantiomeric excess of up to 70% (R) at turnover frequencies up to 80 h–1 and turnover numbers of 100 for a range of ketones at 50 °C and 20 atm H2. This is a rare example of asymmetric pressure hydrogenation using an iron complex. Unlike the case of ATH, there is no effect on the rate upon the addition of KOtBu beyond the 2 eq...

FexOy@C nanocomposites were synthesized and used as carriers for depositing Pt nanoparticles. Catalytic properties of the nanocomposites were investigated for the hydrogenation of p-chloronitrobenzene at room temperature and balloon hydrogen pressure. The catalyst Pt/FexOy@C was extremely active for the hydrogenation of p-chloronitrobenzene. Completely conversion of p-chloronitrobenzene was achieved with a selectivity of 99.7 % in ethanol-water mixture in a reaction time of 40 min. Moreover, it can be reused four times without loss of any activity.

Hydrogenation of esters is vital to the chemical industry for the production of alcohols, especially fatty alcohols that find broad applications in consumer products. Current technologies for ester hydrogenation rely on either heterogeneous catalysts operating under extreme temperatures and pressures or homogeneous catalysts containing precious metals such as ruthenium and osmium. Here, we report the hydrogenation of esters under relatively mild conditions by employing an iron-based catalyst bearing a PNP-pincer ligand. This catalytic system is also effective for the conversion of coconut oil derived fatty acid methyl esters to detergent alcohols without adding any solvent.

Surface processes occurring at the catalytic chiral surface of a cinchona-modified Pt catalyst during the asymmetric hydrogenation of activated ketones have been monitored for the first time using operando ATR-IR spectroscopy. Fundamental information about this catalytic system could be gained, including the chiral modification process of the catalyst, the surface interaction of reactant ketone with preadsorbed chiral modifier, the role of hydrogen as well as the influence of the product enantiomers in the catalytic cycle. The formation of a diastereomeric transient surface complex between ketone and chiral modifier was found to be related to the ketone consumption. Among the studied activated ketones, a correlation between stereoselection and the strength of the intermolecular hydrogen bond was identified. Dissociated hydrogen from the catalytic surface is found to play a crucial role in the formation of the diastereomeric surface complex.

A chiral phosphoric acid catalyzed asymmetric transfer hydrogenation of aromatic amines, quinolin-3-amines, was successfully developed with up to 99% ee. To supplement our previous work on the Ir-catalyzed asymmetric hydrogenation of 2-alkyl substituted quinolin-3-amines, a number of 2-aryl substituted substrates were reduced to provide a series of valuable chiral exocyclic amines with high diastereo- and enantioselectivities.

In this report, a new series of C2-symmetric bis(sulfonyl) tetraaza ligands were synthesized from (1S,2S)-1,2-diarylethylenediamine analogues and tested in the asymmetric transfer hydrogenation (ATH) of aromatic ketones by complexing with [Ru(η 6-p-cymene)Cl2]2 employing sodium formate as hydrogen source in neat water. A moderate to excellent conversion (~99.8 %) and overall satisfying enantioselectivity (~92.8 %) were obtained with varied electronic and steric effects of the substituents on ligands and substrates. A new series of C2-symmetric bis(sulfonyl) tetraaza ligands was synthesized from (1S,2S)-1,2-diarylethylenediamine analogues and tested in the asymmetric transfer hydrogenation of aromatic ketones by complexing with [Ru(η6-p-cymene)Cl2]2 employing formate sodium as hydrogen source in neat water. A moderate to excellent conversion (~99.8 %) and overall satisfying enantioselectivity (~92.8 %) were obtained with varied electronic and steric effects of the substituents on ligands and substrates.

The efficient and highly enantioselective catalytic asymmetric hydrogenation of β-acetylamino acrylosulfone has been achieved by employing Rhodium-TangPhos as catalyst. A series of β-amido sulfone products are obtained with excellent yields and good enantioselectivities.

A chiral catalyst, Cp*RhTsDPEN (Cp* = pentamethyl cyclopentadiene, TsDPEN = substitutive phenylsulfonyl-1,2-diphenylethylenediamine), was synthesized and immobilized at the surface of glass. The immobilized catalyst exhibited good catalytic efficiency for asymmetric transfer hydrogenation of aromatic ketones in water with HCOONa as hydrogen source.

A bifunctional catalyst generated in situ from a ruthenium complex, chiral amine alcohol and isopropyl alcohol renders possible the transfer hydrogenation of ketimines (I) in excellent yields with high enantioselectivities.

Recent advance on asymmetric hydrogenation of aromatic carbocyclic rings and thiophenes has been described with the chiral ruthenium catalyst. It represents a great breakthrough in the area of asymmetric hydrogenation as well as opens up a new pathway for the facile synthesis of valuable optically active carbocyclic rings and dihydro- and tetrahydrothiophenes.

Ru-B/γ-Al2O3 catalyst was prepared by reductant impregnation method, which was applied in the selective hydrogenation of ethyl 1H-indole-2-carboxylate for producing ethyl 2,3,3a,7a-tetrahydro-1H-indole-2-carboxylate with hydrogen as reductant. Furthermore, we discussed the influences of substrate concentration, reaction solvent, hydrogenation temperature, initial hydrogen pressure and reaction time on the catalytic performance of the as-prepared catalyst. The obtained Ru-B/γ-Al2O3 catalyst showed a high-efficiency for the selective hydrogenation of ethyl 1H-indole-2-carboxylate(>99% conversion and selectivity) in i-propanol used as solvent at a concentration of 10%(mass fraction) of ethyl 1H-indole-2-carboxylate, a pressure of hydrogen of 6 MPa and a reaction temperature of 373 K.

The potential of bimetallic Pt–Co catalysts for production of higher alcohols in high pressure CO hydrogenation has been assessed. Two catalysts (Pt3Co/SiO2 and PtCo/SiO2) were tested, and the existing literature on CO hydrogenation over Pt–Co catalysts was reviewed. It is found that the catalysts produce mainly methanol in the Pt-rich composition range and mainly hydrocarbons (and to a modest extent higher alcohols) in the Co-rich composition range. The transition between the two types of behavior occurs in a narrow composition range around a molar Pt:Co ratio of 1:1.

The development of catalysts capable of promoting hydrogenation of aromatics while being resistant to poisoning by nitrogen- and sulfur-containing species is of much interest in connection with hydrotreating of fossil fuels. We report a catalyst composed of ruthenium nanoparticles supported on magnesia, designed to promote heterolytic hydrogen splitting and surface ionic hydrogenation pathways. The catalyst, prepared through a one-pot procedure, promotes the hydrogenation of mono- and poly-cyclic arenes, as well as N- and S-heteroaromatics representative of fossil fuels components. Of particular significance are the superior activity and wider substrate scope of the catalyst, in relation to other known supported noble metals, and the excellent recyclability and long catalyst lifetime. Based on our experimental data, a dual-site catalyst structure and an associated dual-pathway mechanism are proposed, which may have interesting implications for the development of new poison-tolerant noble metal catalytic systems.

A method for the preparation of a composite iron oxide catalyst on a carbon support is described in this work. The hydrogenation of model polyaromatic compounds in the presence of iron-containing catalysts was studied.

Chiral 9-amino epi-cinchonine was anchored on external surface passivated SBA-15 as well as calcined SBA-15. The two resulting materials were used as catalysts for the asymmetric transfer hydrogenation of aromatic ketones after complexing with [Ir(COD)Cl]2. Higher enantioselectivities were obtained over the passivated SBA-15 supported catalyst compared with the catalyst based on calcined SBA-15 as well as the homogeneous counterpart. Especially for the substrate of acetophenone, an obviously high enantiomeric excess (ee) of 74% (homogeneous ee: 60%) was achieved with comparable conversion to the homogeneous catalyst (97% vs. 98%). Furthermore, the passivated SBA-15 supported catalyst demonstrated higher stability during the asymmetric transfer hydrogenation reaction as compared with the catalyst based on calcined SBA-15.

This review describes our recent works on the diastereo- and enantioselective synthesis of anti-β-hydroxy-α-amino acid esters using transition-metal-chiral-bisphosphine catalysts. A variety of transition metals, namely ruthenium (Ru), rhodium (Rh), iridium (Ir), and nickel (Ni), in combination with chiral bisphosphines, worked well as catalysts for the direct anti-selective asymmetric hydrogenation of α-amino-β-keto ester hydrochlorides, yielding anti-β-hydroxy-α-amino acid esters via dynamic kinetic resolution (DKR) in excellent yields and diastereo- and enantioselectivities. The Ru-catalyzed asymmetric hydrogenation of α-amino-β-ketoesters via DKR is the first example of generating anti-β-hydroxy-α-amino acids. Complexes of iridium and axially chiral bisphosphines catalyze an efficient asymmetric hydrogenation of α-amino-β-keto ester hydrochlorides via dynamic kinetic resolution. A homogeneous Ni-chiral-bisphosphine complex also catalyzes an efficient asymmetric hydrogenation of α-amino-β-keto ester hydrochlorides in an anti-selective manner. As a related process, the asymmetric hydrogenation of the configurationally stable substituted α-aminoketones using a Ni catalyst via DKR is also described.

Boron-modified Pd catalysts have shown excellent performance for the selective hydrogenation of alkynes experimentally. In the current work, we investigated the hydrogenation of acetylene on boron-modified Pd(111) and Pd(211) surfaces, utilizing density functional theory calculations. The activity of acetylene hydrogenation has been studied by estimating the effective barrier of the whole process. The selectivity of ethylene formation is investigated from a comparison between the desorption and the hydrogenation of ethylene as well as comparison between the ethylene and the 1,3-butadiene formation. Formation of subsurface carbon and hydrogen on both boron-modified Pd(111) and Pd(211) surfaces has also been evaluated, since these have been reported to affect both the activity and the selectivity of acetylene hydrogenation to produce ethylene on Pd surfaces. Our results provide some important insights into the Pd–B catalysts for selective hydrogenation of acetylene and also for more complex hydrogenation sy...

A series of efficient ruthenium catalysts has been developed for the asymmetric hydrogenation and transfer hydrogenation of ketones with high reactivities and selectivities. The new chiral bisdihydrobenzooxaphosphole (BIBOP)/diamine-ruthenium complexes catalyzed the enantioselective hydrogenation of substrates such as aryl and heteroaryl cyclic and alkyl ketones with substrate/catalyst (S/C) ratios of up to 100,000. The opposite sense of enantioselectivity can be obtained by proper selection of a diamine with a given chirality of the phosphine. The usefulness of the new system has been demonstrated in the asymmetric hydrogenation of a complex synthetic intermediate towards cholesteryl ester transfer protein (CETP) inhibitors at S/C 20,000 on large-scale operation.

Experimental evidences related to the proton transfer in the catalytic system Pt–cinchona alkaloids for enantioselective hydrogenation of activated ketones were collected and analyzed. Both new and earlier results indicate that in aprotic media direct transfer of proton from platinum to the substrate with the involvement of quinuclidine nitrogen as a general rule can be questioned.

Optically active medium-sized cyclic carbonyl compounds bearing an α-chiral carbon center are of interest in pharmaceutical sciences and asymmetric synthesis. Herein, SpinPhox/Ir(I) catalysts have been demonstrated to be highly enantioselective in the asymmetric hydrogenation of the CC bonds in the exocyclic α,β-unsaturated cyclic carbonyls, including a broad range of α-alkylidene lactams, unsaturated cyclic ketones, and lactones. It is noteworthy that the procedure can be successfully used in the asymmetric hydrogenation of the challenging α-alkylidenelactam substrates with six- or seven-membered rings, thus affording the corresponding optically active carbonyl compounds with an α-chiral carbon center in generally excellent enantiomeric excesses (up to 98 % ee). Synthetic utility of the protocol has also been demonstrated in the asymmetric synthesis of the anti-inflammatory drug loxoprofen and its analogue, as well as biologically important ε-aminocaproic acid derivatives.

Hydrogenation of prochiral ketones using chiral transition-metal catalysts represents the cleanest way to access enantiomerically enriched secondary alcohols, which are important building blocks in fine chemicals synthesis. Despite excellent activity, selectivity and compatibility of metal complexes with variety of functional groups, no universal catalysts exist. In this article we summarize the advances in catalyst systems for the asymmetric homogenous and heterogenous hydrogenation of ketones that have been made in past decade. The development of catalysts is oriented in reaching as high as activity with low catalyst loadings, using “greener’’ conditions, and ensuring good recyclability of catalysts. Even though ruthenium complexes represent the largest part of the catalysts, other metals rapidly penetrate this field.

A highly efficient ligand free catalytic system was developed for chemoselective transfer hydrogenation of α,β-unsaturated carbonyl compounds by palladium nanoparticles (PdNPs) in an aqueous reaction medium. The developed methodology offers chemoselective 1,4-reduction of various α,β-unsaturated carbonyl compounds such as carbonyls, amides, esters and nitriles with excellent chemoselectivity and effective catalyst recyclability.

A new efficient and highly enantioselective direct asymmetric hydrogenation of α-keto acids employing the Ir/SpiroPAP catalyst under mild reaction conditions has been developed. This method might be feasible for the preparation of a series of chiral α-hydroxy acids on a large scale.

The enantioselective hydrogenation of 3-aryl and 3-styryl-substituted-2H-1,4-benzoxazines was developed using the chiral cationic Ru(η6-cymene)(MsDPEN)(Ar2PO2) system in high yields with up to 99% ee. The counteranion was found to be critically important for the high enantioselectivity. Furthermore, the regioselectivity could be regulated by the counteranion of the catalyst in the asymmetric hydrogenation of 3-styryl-2H-1,4-benzoxazines.

Lutidine-derived bis-N-heterocyclic carbene (NHC) ruthenium CNC–pincer complexes (Ru-CNCs) were prepared. They showed various coordination modes of the two NHC ligands depending on the synthetic procedure, yielding normal (1, 2) or mixed normal/abnormal NHC-complexes (3). In the presence of phosphazene base, Ru-CNC complexes activate nitriles to give ketimino compounds 4-6. Nitrile adduct 4 shows reactivity towards strong bases to yield dearomatized complex 7, that heterolytically activate H2 to form the bis-hydrido complex 8. Finally, these Ru-CNCs are active in catalytic hydrogenation of CO2 to formate salts and, unlike the phosphine-containing Ru-PNP counterpart, they also catalyze the selective hydrogenation of esters to alcohols.

Hydrogenation of aromatic ketones with chiral bifunctional amidoiridium complexes proceeds in preference to transfer hydrogenation in methanol, in which the pressurised hydrogen can suppress unintended racemisation of the alcoholic product, leading to enhanced enantioselectivity.

A systematic study of solvent effects in low-temperature hydrogenation of various model oxygenates in bio-oils (such as 2-butanone, 2-pentanone, and phenol) with Ru/C catalyst is presented. Protic (e.g., water and C 1 –C 4 primary alcohols), aprotic polar (e.g., γ-butyrolactone, acetonitrile, and tetrahydrofuran), and aprotic apolar (e.g., cyclohexane and n -heptane) solvents were investigated. It was found that for 2-butanone hydrogenation, Ru/C catalyst shows the highest hydrogenation activity in water, followed by alcohols, while in aprotic apolar solvents (i.e., cyclohexane and n -heptane), a remarkably lower hydrogenation activity was observed. In sharp contrast, Ru/C catalyst shows little hydrogenation activity in aprotic polar solvents (i.e., γ-butyrolactone, acetonitrile, and tetrahydrofuran). To explain these dramatic effects, both classical measures of polarity and others based on different solvatochromic scales were considered. For 2-butanone hydrogenation, a clear correlation between the initial hydrogenation rate and hydrogen-bond donor capability ( α ) of the solvents was observed. This is consistent with previously reported hypothesis that the strong interaction between protic solvents and 2-butanone by hydrogen bonding lowers the activation energy barrier and leads to high hydrogenation rate. For aprotic polar solvents, it seems plausible that such solvents could strongly adsorb onto the catalyst surface and block the Ru active sites, thereby inhibiting the hydrogenation rate. In the case of aprotic apolar solvents, both solvent–substrate and solvent–catalyst interactions are insignificant, and thus, a reasonable hydrogenation rate was observed in these solvents. Kinetic modeling of 2-butanone hydrogenation in water as a solvent indicates that the power-law and Langmuir–Hinshelwood (with the second hydrogenation step as the rate-determining step) models provide the best fits to experimental rate data. Further, the estimated activation energy for 2-butanone hydrogenation in water is 33.4 kJ/mol, which is lower than the value of 68 kJ/mol reported from density functional theory (DFT) calculations that assume the formation of the hydroxybutyl intermediate and its subsequent hydrogenation as the rate-determining step.

Knolker's catalyst has prodigious applicability for the hydrogenation of aldehydes with various functional groups, such as organohalides, nitro groups and benzyl ethers. Density functional theory was used to explore the effect of the substituent on the hydrogen-transfer processes. The hydrogenation of a series of aldehydes with different substituents was analyzed using an outer-sphere concerted hydrogen transfer mechanism. Electron-donating substituents are kinetically and thermodynamically unfavorable for the hydrogenation of aldehydes whereas electron-withdrawing substituents are favorable for reductions. Furthermore, substituents with large steric hindrance have no significant influence on the hydrogenation of aldehydes. These conclusions drawn for the calculations are in good agreement with experimental results.

The Ir/AlO(OH) catalyst was prepared by sol-gel method and used for selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroniamine (p-CAN). The mechanism of p-CNB hydrogenation over the catalyst was discussed. The hydrogen bond between the surface hydroxyl groups of the catalyst and the nitrogen present in p-CNB facilitated the hydrogenation of nitro group. On the other hand, the formation of hydrogen bond between the hydrogenation product and water promotes the rapid desorption of the hydrogenation product on the surface of the catalyst. Thus the activity and selectivity were greatly promoted.

The widespread precatalyst (prepared in-situ or ex-situ) (arene) RuTsDPEN advocated for highly effectual asymmetric transfer hydrogenation (ATH) reactions with 2-propanol as hydrogen donor at ambient conditions, is proven to be unstable under the strong reducing conditions prevailing in the reaction mixtures (blend of alcohol and a base such as KOH). We assert that the true catalysts are the ruthenium metal nanoclusters formed swiftly under the reducing conditions of these systems. The TsDPEN ligand plays a critical role in the generation and formatting of the active catalyst including wreaking chiral properties to the so formed catalytic nanoparticles. Kinetic measurements, NMR, UV-visible spectroscopy, circular dichroism (CD) and TEM analyses corroborate this argument.

Bis(isonitrile) iron(II) complexes bearing a C2-symmetric N2P2 macrocyclic ligand, which are easily prepared from the corresponding bis(acetonitrile) analogue, catalyze the asymmetric transfer hydrogenation (ATH) of a broad scope of ketones in excellent yields (up to 98%) and with high enantioselectivity (up to 91% ee).

Combined studies of adsorption and hydrogenation have been carried out using Pd black electrochemically deposited in a loose packed thin layer in order to avoid co-adsorption on a support. Pd black covered with a monomolecular layer of strongly adsorbed hydrogen and exposed to butadiene shows a very low hydrogenation rate, more than two orders of magnitude lower than the rate of hydrogenation of a mixture of butadiene and hydrogen. This result reveals that the second step of hydrogenation according to the reaction scheme of Horiuti and Polanyi via a semi-hydrogenated intermediate needs subsurface hydrogen loading. While the first step towards a surface alkyl requires a negatively charged surface hydride for nucleophilic attack the subsequent electrophilic attack proceeds with a positively charged hydrogen from the subsurface region. Strong support for this view is given by the kinetics of isomerization/hydrogenation of cis-2-butene which shows at low hydrogen pressure fast isomerization and slow hydrogenation rate. The access of hydrogen to the catalyst surface is regarded as rate determining step of butene respectively butadiene hydrogenation. The consequence of increased hydrogen access to the Pd surface is an enhanced diffusion of hydrogen from surface to subsurface positions thus leading to an increased hydrogenation rate. Furthermore in the state of selective hydrogenation of 1,3-butadiene towards butenes the surface is densely covered by butadiene.

The use of hydrogen as a fuel requires both safe and robust technologies for its storage and transportation. Formic acid (FA) produced by the catalytic hydrogenation of CO2 is recognized as a potential intermediate H2 carrier. Herein, we present the development of a formate-based H2 storage system that employs a Ru PNP-pincer catalyst. The high stability of this system allows cyclic operation with an exceptionally fast loading and liberation of H2. Kinetic studies highlight the crucial role of the base promoter, which controls the rate-determining step in FA dehydrogenation and defines the total H2 capacity attainable from the hydrogenation of CO2. The reported findings show promise for the development of practical technologies that use formic acid as a hydrogen carrier.

A new kind of chiral dendritic [RuCl2(BINAP)(DPEN)] catalysts with a ‘Sandwich’ multi-layer structure have been synthesized via metal coordination reactions with dendritic chiral diphosphines and dendritic chiral diamine ligands. The formation of the dendritic catalysts was confirmed by 31P NMR. The catalyst performance was then investigated in the asymmetric hydrogenation of simple aryl ketones, and comparable enantioselectivities were achieved with comparison to that of the corresponding small-molecular catalyst. In addition, the recyclable property of these homogeneous catalysts was studied with the third-generation catalyst, which was reused nine times by simple solvent precipitation without any loss of enantioselectivity.

The Ir-catalyzed asymmetric hydrogenation of olefins is widely used for production of value-added bulk and fine chemicals. The iridium catalysts with chiral spiro phosphine-oxazoline ligands developed in our group show high activity and high enantioselectivity in the hydrogenation of olefins bearing a coordinative carboxyl group, such as α,β-unsaturated carboxylic acids, β,γ-unsaturated carboxylic acids, and γ,δ-unsaturated carboxylic acids. Here we conducted detailed mechanistic studies on these Ir-catalyzed asymmetric hydrogenation reactions by using (E)-2-methyl-3-phenylacrylic acid as a model substrate. We isolated and characterized several key intermediates having Ir-H bonds under the real hydrogenation conditions. Particularly, an Ir(III) migratory insertion intermediate was first isolated in an asymmetric hydrogenation reaction promoted by chiral Ir catalysts. That this intermediate cannot undergo reductive elimination in the absence of hydrogen strongly supports the involvement of an Ir(III)/Ir(V) cycle in the hydrogenation. On the basis of the structure of the Ir(III) intermediate, variable-temperature NMR spectroscopy, and density functional theory calculations, we elucidated the mechanistic details of the Ir-catalyzed hydrogenation of unsaturated carboxylic acids and explained the enantioselectivity of the reactions. These findings experimentally and computationally elucidate the mechanism of Ir-catalyzed asymmetric hydrogenation of olefins with a strong coordinative carboxyl group and will likely inspire further catalyst design.

Hydrogenation catalysis is dominated by transition metals, but interest in alternative catalysts has been growing over recent years. Herein, a transition-metal-free catalyst is discussed consisting of carbon supported NaAlH4 as a selective catalyst for hydrogenation. This is illustrated using a range of substrates, and in more detail for the case of diphenylacetylene. Catalytic activity depends on the solvent utilized; in cyclohexane the activity is 2.3 mol (DPA) mol−1 (NaAlH4) h−1 at 100 bar H2, 150 °C with a slight preference for the formation of trans-stilbene. The catalyst selectivity is influenced by the loading, yielding a high selectivity toward the thermodynamically less stable cis-stilbene at low catalyst loadings. This proof of principle shows promise for using metal hydrides based on earth-abundant elements as effective hydrogenation catalysts.

This article provides an account of our group's efforts in developing aqueous-phase transfer hydrogenation reactions. It is comprised of mainly two parts. The first part concentrates on asymmetric transfer hydrogenation in water, enabled by Noyori–Ikariya catalysts, while the second part is concerned with the achiral version of the reaction catalysed by a new class of catalysts, iridacycles. A range of substrates are featured, including various carbonyl compounds and N-heterocycles.

CNN pincer ruthenium(II) and osmium(II) complexes of general formula RuCl(CNN)(dppb) (1 a-c) and OsCl(CNN)(dppb) (2 a,b) (dppb=Ph2P(CH2)4PPh2, HCNN=[6-(p-tolyl)-2-pyridyl]methylamine (4), N-methyl-[6-(p-tolyl)-2-pyridyl]methylamine (7) and N,N-dimethyl-[6-(p-tolyl)-2-pyridyl]methylamine (8)) were prepared and assessed as catalysts in the hydrogenation of a variety of imines. Among the examined complexes, the Ru-complex 1 a, RuCl(4)(dppb), showed the best activity, reducing N-aryl and N-alkyl imines to the related amines in high yields (up to 100 %) with a catalyst loading of 0.1-1 mol% and under mild conditions (5 atm H2, 40-70 °C). The Os-complexes exhibited a lower activity than their ruthenium analogues. Despite this, the Os-complex 2 a, OsCl(4)(dppb), was successful in the reduction of N-benzylideneaniline at 70 °C, affording a rare example of application of osmium complexes in the catalytic hydrogenation of imines.