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A facile asymmetric transfer hydrogenation of ortho-substituted aryl N-heteroaryl ketones and non-ortho-substituted N-oxide of aryl N-heteroaryl ketones using a readily available oxo-tethered ruthenium complex as a catalyst and sodium formate as a hydrogen source in an aqueous solution has been discovered. A variety of chiral aryl N-heteroaryl methanols were obtained with up to 99.9% ee.

An efficient catalytic system containing [RuCl2(η6-p-cymene)]2 and one P,N ligand, N-diphenylphosphino-2-aminopyridine (L1) was loaded in catalyzing the alkylation of ketones with primary alcohols for a diverse array of substrates. Other five P,N ligands based on pyridin-2-amine and pyrimidin-2-amine were also examined in this reaction to explore the influence of steric hindrance and electronic effects. Monitoring by 1H NMR and ESI-MS reveals a stable cationic L1-coordinated ruthenium hydride intermediate, identified as [Ru(η6-p-cymene)(κ2-L1)H]+. Organic intermediates consistent with a three-step dehydrogenation, alkylation and hydrogenation pathway were also observed. The final step in this reaction, the ruthenium-catalysed transfer hydrogenation reduction of α,β-unsaturated ketone with benzyl alcohol was performed separately.

Rates of C3-C5 ketone hydrogenation are measured in the vapor phase over Ru/SiO2. Reaction kinetics are considered through a range of ketone partial pressures (0.3–30 Torr), hydrogen partial pressures (90–900 Torr), and reaction temperatures (322–456 K). Ketone hydrogenation is observed to be facile, with site time yields ranging from 0.14 s−1 for 2-pentanone to 0.37 s−1 for acetone at 322 K and 1.2 bar H2. At low temperatures, apparent reaction orders and kinetic barriers are similar for all ketones. During acetone hydrogenation at higher temperatures, (422 K), the ketone order increases from 0 to 0.4, while the hydrogen order increases from 0.5 to 0.9. Furthermore, the apparent barrier decreases from ≈50 kJ mol−1 at 322 K to ≈18 kJ mol−1. Apparent trends in hydrogenation rates are interpreted at an elementary level using a microkinetic analysis that is based on a Horiuti-Polanyi mechanism involving two distinct surface sites.

Manganese complexes of the types [Mn(PNP′)(Br)(CO)2] and [Mn(PNP′)(H)(CO)2] containing a tridentate ligand with a planar chiral ferrocene and a centro chiral aliphatic unit were synthesized, characterized, and tested in the enantioselective transfer hydrogenations of 13 ketones. The catalytic reactions proceeded with conversions up to 96 % and ee values up to 86 %. The absolute configuration of all products was determined to be (S). Notably, the presence of dihydrogen (up to 20 bar) did not affect the reduction. On the basis of DFT calculations, preliminary mechanistic details including the origin of the (S) selectivity are presented. The molecular structure of [Mn(PNP′)(Br)(CO)2] was studied by X-ray diffraction.

This paper reports results of a comparative study of the structure and activity of MgF 2 -supported metal (Me) catalysts containing 1 wt.% of platinum, iridium or ruthenium. Their activities for hydrogenation of toluene and selective hydrogenation of ortho-chloronitrobenzene to ortho-chloroaniline were compared with the hydrogenation performance of metal catalysts prepared by impregnation of a alumina which is one of the most widely used supports. The catalysts were characterized by using low-temperature nitrogen adsorption, TPR-H 2 and H 2 -chemisorption techniques. The nature of metal and support appeared to have a clear influence on metallic phase dispersion and it was reflected by the activity of Me/MgF 2 catalysts. The application of magnesium fluoride as a support has enabled to obtain catalysts showing high activities for hydrogenation of toluene at 323–498 K and selective hydrogenation of ortho-chloronitrobenzene (o-CNB) to ortho-chloroaniline (o-CAN) in the liquid-phase at 353 K under hydrogen pressure of 4 MPa. From among the catalysts studied, the highest activity for the both aforementioned reactions has been found in the case of MgF 2 -supported platinum catalyst and the highest selectivity (100%) in that of ruthenium-containing catalyst. The activity of magnesium fluoride-supported catalysts was several times higher than that of alumina-supported ones.

New PHOX ligands, derived in three steps from (1R,2S,3R,5R)-3-amino-apopinan-2-ol 1 and (1R,2R,3S,5R)-3-amino-pinan-2-ol 2 were applied as chiral ligands for the formation of ruthenium catalysts. The catalysts were used in asymmetric transfer hydrogenations of prochiral ketones producing the corresponding alcohols in moderate to high yields and enantioselectivity.

A series of Ru(II)-benzene organometallic compounds (1–6) constructed from [RuCl2(η6-benzene)]2 and chiral aroylthiourea ligands (L1-L6) obtained from D/L-phenylalanine, was fully characterized. The chiral complexes along with 2-propanol and NaOH effected the asymmetric hydrogenation of aromatic ketones at 82 °C within 8–10 h. The reduction reactions proceeded with excellent conversions and enantiomeric excesses (up to 99%).

International audience; A catalytic hydrogenation of carbonyl derivs. with a manganese pre-catalyst has been developed. The key feature is the use of an air stable cationic manganese pre-catalyst bearing a tridendate ligand with a 2,6-(diaminopyridinyl)diphosphine scaffold. Under 50 bar of H2, at 130°, various ketones were reduced to the corresponding alcs. with moderate to good yield.

A series of phenanthroline based NHC and pyridine containing NNC and NNN pincer Ru(II) complexes were synthesized and fully characterized by various spectroscopic techniques. Comparative studies revealed that Ru(II)-NHC complexes were much more active than the Ru(II)-NNN complexes in both transfer hydrogenation (TH) of ketones and nitroarenes. Wingtip groups and counter anions modulated the impact of NHC complexes in both the reactions. The complexes with PF6- counter anion were found to be more active in TH of ketones while complexes with Cl- counter anion were superior towards the nitroarenes reduction. To the best of our knowledge this is the first example of counter anion controlled reactivity alteration between TH of ketones and nitroarenes.

New ionic Schiff-base ligands have been synthesized by condensation of (3-formyl-4-hydroxybenzyl)triphenylphosphonium and 3-(3-formyl-4-hydroxybenzyl)-1-methyl-1H-imidazol-3-ium chloride and hexafluorophosphate salts with N,N-dimethylethylenediamine. Treatment of the dimeric derivative [{RuCl(μ-Cl)(η6-p-cymene)}2] with two equivalents of these ligands allowed the preparation of novel mononuclear water-soluble Ru(II) complexes, which proved to be catalytically active in the transfer hydrogenation of ketones and aldehydes under aqueous conditions.

The catalytic hydrogenation of nitriles to primary amines constitutes an environmentally benign and atom-economical methodology in synthetic organic chemistry. However, selective hydrogenation can be challenging, and usually elevated pressure and the use of various additives is requited. Herein the hydrogenation of aromatic and aliphatic nitriles to form primary amines catalyzed by ruthenium pincer complexes is described. The reactions are conducted at low H2 pressure, low catalytic loadings and, in case of a variety of benzonitriles, under neutral conditions and without any additives. Mechanistic insight is provided.

Long chain α–ω diols were readily accessed from renewable fatty acid methyl esters following an orthogonal tandem self-metathesis–ester hydrogenation protocol. By adding a base and a bidentate ligand, the metathesis catalysts were transformed in situ into efficient ester hydrogenation catalysts. The selectivity of the hydrogenation reaction was tuned towards the exclusive formation of either the unsaturated or the saturated diol by modifying the ligand/catalyst ratio. An orthogonal tandem cross-metathesis–ester hydrogenation reaction was also applied for the synthesis of a fragrance compound.

We successfully applied tridentate f-amphox ligands to the iridium-catalytic asymmetric hydrogenation of various α-hydroxy ketones to afford the corresponding chiral 1,2-diols with excellent results (almost all products up to 99% yield and >99% ee). The resulting chiral 1,2-diols and their derivatives are important synthetic and pharmaceutical intermediates. Our catalytic system displayed extremely high activity, achieving up to 1 000 000 turnover number (TON). The great performance of this asymmetric hydrogenation makes the preparation of various chiral 1,2-diols highly practical with great potential.

Novel chiral multidentate P3N4-type ligand has been synthesized and characterized by NMR and HRMS. Using i-PrOH as solvent and hydrogen source, asymmetric transfer hydrogenation of various ketones was investigated. The catalyst generated in situ from chiral multidentate aminophosphine ligand (R,R,R,R)-3 and IrCl(CO)(PPh3)2 exhibited highly catalytic activity and excellent enantioselectivity under mild conditions, achieving the corresponding chiral alcohols with up to 99% yield and 99% ee.

The hydrogenation of phenol to cyclohexanone is an important industrial reaction and supported palladium catalysts are the most popular catalysts applied nowadays. Hitherto, there has been no success in using ruthenium catalysts for this reaction because of their poor catalytic performance, in spite of the fact that ruthenium is a frequently used metallic component in hydrogenation catalysts. Herein, we report our effort in creating a meso-structured catalyst composed of ruthenium clusters enclosed in the super cages of X-zeolite, which is prepared by mixing precursors of ruthenium and X-zeolite at the beginning stage of preparation, i.e., before the crystallization of the zeolite. This well-defined Ru catalyst exhibits excellent catalytic performance for the selective hydrogenation of phenol, similar to palladium catalysts. The results demonstrate that the joint effects of the 3D negatively charged grid of X-zeolite and the enclosed electron-deficient ruthenium clusters enhance the activity of metallic ruthenium and suppress the further hydrogenation of the valuable product cyclohexanone, which is not possible with traditional Ru catalysts. This investigation reveals the fact that although catalytic reactions are always initiated on the active centers of the catalyst at dimensions on the atomic scale, the effect of the neighboring environment surrounding the active species might extend it to the meso-scale, which should not be ignored as it might induce electronic and structural changes in the active species as well as possibly dramatic changes in the performance of the catalyst. The meso-structured catalyst integrated active species and the neighboring environment as a whole should be considered in discussing the performance of catalysts.

An efficient asymmetric hydrogenation of 3-substituted 2,5-dihydropyrroles using an Ir catalyst with an axially flexible chiral phosphine-oxazoline ligand was developed and chiral 3-substituted pyrrolidines could be prepared with excellent ee. 3-Substituted 2,5-dihydrothiophene 1,1-dioxides could also be hydrogenated by our catalyst, giving the desired products with moderate to high enantioselectivities.

A high selectivity was achieved in the Ni2B-catalyzed hydrogenation of α,β-unsaturated ketones containing a hydroxyaryl (phenolic) substituent in the β-position. The developed hydrogenation procedure was used to synthesize natural compounds of the phenylpropane series and their structural analogs.

An enantioselective hydrogenation of cyclic iminium salts has been successfully realized by employing [Ir(COD)Cl]2 and chiral diphosphine ligands as catalyst, furnishing chiral N-alkyl tetrahydroisoquinolines and N-alkyl tetrahydro-β-carbolines with up to 96% ee and 88% ee, respectively. The hydrogenation provides a direct, simple and efficient protocol toward chiral tertiary amines. Meanwhile, asymmetric hydrogenation at the gram scale was also conducted smoothly without loss of reactivity and enantioselectivity.

Chemoselective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols is not only an important reaction in the chemical industry but also a good model system to understand the catalytic selectivity in heterogeneous catalysis. In the current work, the selectivity of partial hydrogenation of acrolein (C3H4O), the simplest α,β-unsaturated aldehyde, is investigated employing density functional theory (DFT) calculations. Two hydrogenation mechanisms, namely the Horiuti–Polanyi mechanism and the non-Horiuti–Polanyi mechanism, are employed to study the partial hydrogenation of acrolein over Ag(111), Ag(100), Ag(211) and Ag(111)-mono surfaces. It is found that the hydrogenation of C3H4O to C3H5O at the terminal carbon and oxygen atoms follows the non-Horiuti–Polanyi mechanism in which C3H4O reacts with hydrogen molecules directly over all the silver surfaces studied, whilst atomic hydrogen is the active hydrogen species for the hydrogenation of C3H5O to C3H6O. Subsequently, the selectivities between partial hydrogenation products, i.e. propenol, propanal and enol, over silver surfaces with different morphologies are compared by calculating the energy difference between the rate-determining transition states. We find that the selectivity of propenol formation increases with the coordination number of surface silver atoms, which is in good agreement with the trend of selectivities obtained experimentally. It is also interesting to find that the selectivity trend obtained based solely upon the Horiuti–Polanyi mechanism for the hydrogenation of C3H4O to C3H5O and C3H5O to C3H6O cannot explain the experimental results. In other words, the non-Horiuti–Polanyi mechanism is able to give a more reasonable explanation for the selectivity trend observed experimentally than the normally used Horiuti–Polanyi mechanism in heterogeneous catalysis. Our work highlights the significance of the non-Horiuti–Polanyi mechanism in understanding heterogeneous catalytic hydrogenation reactions.

Catalytic experiments were performed for the hydrogenation of o-cresol in n-dodecane over a platinum catalyst. Batch reactions analyzed with an in-situ ATR IR probe suggest that the hydrogenation results in the formation of the final product, 2-methyl-cyclohexanol, with 2-methyl-cyclohexanone as the intermediate product. Ab initio density-functional theory was employed to investigate the atomic-scale mechanism of o-cresol hydrogenation on the Pt(111) surface. The formation of 2-methyl-cyclohexanone was found to involve two steps. The first step is a hydrogen abstraction, that is, the H atom in the hydroxyl group migrates to the Pt surface. The second step is hydrogenation, that is, the pre-existing H atoms on Pt react with the carbon atoms in the aromatic ring. On the other hand, 2-methyl-cyclohexanonol may be produced through two paths, with activation energies slightly greater than that for the formation of 2-methyl-cyclohexanone. One path involves direct hydrogenation of the aromatic ring. Another path involves three steps, with the partial hydrogenation of the ring as the first step, hydrogen abstraction of the OH group as the second, and hydrogenation of remaining C atoms and the O atom the last.

An efficient access to optically active sulfahydantoins, 4-aryl-1,2,5-thiadiazolidin-3-one 1,1-dioxides, was developed through palladium-catalyzed asymmetric hydrogenation of the corresponding cyclic N-sulfonylketimines with up to 98% ee.

A highly efficient enantioselective hydrogenation of 1,2-dicyanoalkenes catalyzed by the complex of rhodium and f-spiroPhos has been developed. A series of 1,2-dicyanoalkenes were successfully hydrogenated to the corresponding chiral 1,2-dicyanoalkanes under mild conditions with excellent enantioselectivities (up to 98% ee). This methodology provides efficient access to the asymmetric synthesis of chiral diamines.

Catalytic transfer hydrogenation of the C═O bond has been considered to be one of the most important processes for the synthesis of fuels and chemicals. In this study, we have developed a metal-free transfer hydrogenation of furfural into furfuryl alcohol and some other valuable carbonyl compounds into alcohols as the hydrogen donors. Hydroxyapatite-encapsulated magnetic γ-Fe2O3 (γ-Fe2O3@HAP) acted as a magnetic base to promote this transfer hydrogenation with iso-propanol as the hydrogen donor. The catalytic performance of the γ-Fe2O3@HAP catalyst was greatly affected by the structure of alcohol. iso-Propanol was the best hydrogen donor for the transfer hydrogenation. In addition, the reaction temperature and the catalyst loading also affected this reaction. The highest yield of furfuryl alcohol reached 91.7% at a furfural conversion of 96.2%. Furthermore, this method was also useful for the transfer hydrogenation of other important carbonyl compounds into value-added chemicals and fuels. After the react...

Our group previously reported the development of iron carbonyl catalysts bearing chiral tridentate P–N–P′ ligands for the asymmetric hydrogenation of prochiral ketones in THF. An NMR study into the activation process identified the amine hydride alkoxide complexes Fe(P-NH-P′)(CO)(H)(OR1) with R1 = Me, tBu, or tAmyl and P-NH-P′ = PPh2CH2CH2NHCH2CH2PiPr2 or (S,S)-PPh2CHPhCHMeNHCH2CH2PCy2. These still required treatment with excess KOtBu and H2(g) to be catalytically active in THF. Both experimental methods and density functional theory (DFT) calculations were used to show that this treatment leads to the formation of a hydride amide complex Fe(P–N–P′)(CO)(H), which reacts with dihydrogen to form cis and trans dihydride complexes Fe(P-NH-P′)(CO)(H)2, identified by NMR spectroscopy. In the presence of KOtBu, NaOtBu, or KOtBu/2,2,2-cryptand and H2(g), these species are active for the catalytic hydrogenation of acetophenone, whereas in the absence of H2(g), inactive Fe(0) complexes are formed. Ketone hydrogenat...

A modular ligand library of -amino acid hydroxyamides and thioamides was prepared from 10 different N-tert-butyloxycarbonyl-protected -amino acids and three different amino alcohols derived from 2, ...

Gas-phase hydrogenation of alkenes and their derivatives, catalyzed by nickel nanoparticles supported on zeolite or silica gel support occurs at 150–250°С and an atmospheric hydrogen pressure and results in a high conversion. The selectivity of the hydrogenation depends on the amount of hydrogen: at a low diene (triene)–hydrogen ratio, selective hydrogenation of one multiple bond in the substrate is possible.

A ferrocenyl-benzo-fused imidazolylidene complex of RuII was prepared and fully characterized. In the presence of acetylferrocenium tetrafluoroborate this complex can be oxidized to generate a complex with a cationic ligand. The neutral complex can be recovered by reducing the oxidized cationic compound with cobaltocene. The activity of the neutral and oxidized complexes was tested in the transfer hydrogenation of ketones and imines, using isopropyl alcohol as the hydrogen source. The neutral complex is very active in the reduction of all tested substrates, whereas the oxidized species shows low activity in the reduction of ketones. The rate of the reduction of hexaphenone could be modulated by addition of subsequent amounts of oxidant and reductant. The addition of acetylferrocenium tetrafluoroborate caused a decrease in the catalytic activity, whereas the addition of cobaltocene restored the activity. The catalytic activity shown by both catalysts in the reduction of N-benzylideneaniline was similar.

Catalytic hydrogenation is an important process used for the production of everything from foods to fuels. Current heterogeneous implementations of this process utilize metals as the active species. Until recently, catalytic heterogeneous hydrogenation over a metal-free solid was unknown; implementation of such a system would eliminate the health, environmental, and economic concerns associated with metal-based catalysts. Here, we report good hydrogenation rates and yields for a metal-free heterogeneous hydrogenation catalyst as well as its unique hydrogenation mechanism. Catalytic hydrogenation of olefins was achieved over defect-laden h-BN (dh-BN) in a reactor designed to maximize the defects in h-BN sheets. Good yields (>90%) and turnover frequencies (6 × 10–5–4 × 10–3) were obtained for the hydrogenation of propene, cyclohexene, 1,1-diphenylethene, (E)- and (Z)-1,2-diphenylethene, octadecene, and benzylideneacetophenone. Temperature-programmed desorption of ethene over processed h-BN indicates the formation of a highly defective structure. Solid-state NMR (SSNMR) measurements of dh-BN with high and low propene surface coverages show four different binding modes. The introduction of defects into h-BN creates regions of electronic deficiency and excess. Density functional theory calculations show that both the alkene and hydrogen-bond order are reduced over four specific defects: boron substitution for nitrogen (BN), vacancies (VB and VN), and Stone–Wales defects. SSNMR and binding-energy calculations show that VN are most likely the catalytically active sites. This work shows that catalytic sites can be introduced into a material previously thought to be catalytically inactive through the production of defects.

The methylenation/hydrogenation cascade reaction of aldehydes or ketones through a domino process involving two ensuing steps in a single pot is realized. The compatibility of Matsubara's reagent and Wilkinson's complex give a combination that allows, under dihydrogen, the transformation of a carbonyl function into a methyl group. This new method is suitable to introduce an ethyl motif from aromatic and aliphatic aldehydes with total chemoselectivity and total retention of α-stereochemical purity. The developed procedure is also extended to the introduction of methyl groups from ketones.

A series of M/Mo2C (M = Cu, Pd, Co and Fe) were synthesized and evaluated for CO2 hydrogenation at 135–200 °C in liquid 1,4-dioxane solvent. The Mo2C served as both a support and a co-catalyst for CO2 hydrogenation, exhibiting turnover frequencies of 0.6 × 10−4 and 20 × 10−4 s−1 at 135 and 200 °C, respectively. Methanol was the major product at 135 °C, while CH3OH, C2H5OH, and C2+ hydrocarbons were produced at 200 °C. The addition of Cu and Pd onto the high surface area Mo2C enhanced the production of CH3OH, while Co and Fe enhanced the production of C2+ hydrocarbons. Results for CO2, CO, and CH3OH hydrogenation experiments suggested that CO2 was the primary source for CH3OH while CO was the intermediate to hydrocarbons during CO2 hydrogenation. Characterization of the spent M/Mo2C catalysts revealed very little change in the surface and bulk chemistries and structures, indicating their stability in the liquid environment.

International audience; The first efficient and general rhenium-catalyzed hydrogenation of carbonyl derivatives was developed. The key to the success of the reaction was the use of a well-defined rhenium complex bearing a tridentate diphosphinoamino ligand as the catalyst (0.5 mol %) at 70 °C in the presence of H2 (30 bar). The mechanism of the reaction was investigated by DFT(PBE0-D3) calculations.

For the first time an easily accessible and well-defined manganese N,N,N-pincer complex catalyzes the transfer hydrogenation of a broad range of ketones with good to excellent yields. This cheap earth abundant-metal based catalyst provides access to useful secondary alcohols without the need of hydrogen gas. Preliminary investigations to explore the mechanism of this transformation are also reported.

The catalytic properties of a novel Raney-Nickel mold were investigated in the liquid-phase hydrogenation of benzene and compared to commercially available Raney-Nickel. The novel Raney-Nickel catalyst showed similar activity as the commercial catalyst but facile product/catalyst separation. Furthermore, the novel Raney-Nickel catalyst is recyclable without loss in activity unlike the commercial nickel sponge.

Asymmetric transfer hydrogenation of α,β-unsaturated esters is realized by using a nickel/bisphosphine catalyst and N,N-dimethylformamide (DMF) as the hydride source.

Six quinazoline ligands (i.e., 3–8) were synthesized by starting from vasicine and vasicinone, and their applications towards ruthenium-catalyzed transfer hydrogenation reactions were evaluated. The 3/[RuCl2(p-cymene)]2 catalytic system was assessed for its use in the ruthenium-catalyzed transfer hydrogenation reaction of aldehydes, ketones, and imines to give the corresponding alcohols and amines and also assessed for its use in the direct reductive amination of carbonyl compounds with anilines. The 3/[RuCl2(p-cymene)]2 catalytic system demonstrated good to excellent activity in water with sodium formate as the hydrogen source. Current studies have revealed that among all of the synthesized ligands, those that have secondary amine groups and a rigid backbone are more active towards transfer hydrogenation reactions of unsaturated compounds.

Over the last few decades, the development of new and highly efficient synthetic methods to obtain chiral compounds has become an increasingly important and challenging research area in modern synthetic organic chemistry. In this account, we review recent work from our laboratory toward the synthesis of valuable chiral building blocks through transition-metal-catalyzed asymmetric hydrogenation and transfer hydrogenation of C=O, C=N and C=C bonds. Application to the synthesis of biologically relevant products is also described.

A new catalyst containing metallic ruthenium nanoparticles intercalated in hectorite (nanoRu′@hectorite) was found to catalyze the reduction of quinoline and quinoline derivatives by NaBH4 in aqueous solution to give selectively the corresponding 1,2,3,4-tetrahydroquinolines (N-cycle hydrogenation). In most cases the reaction can be done under mild conditions (25–60 °C) without pressure equipment, conversion and selectivity being superior to 99%. In the case of sterically hindered derivatives, the reaction can be done in a pressure vessel under self-generated pressure (up to 9 bar). Isoquinoline and quinoxalines also undergo selective N-cycle hydrogenation, but 2-phenyl-quinoline is hydrogenated to give 2-phenyl-5,6,7,8-tetrahydroquinoline (C-cycle hydrogenation). Isotope labeling experiments combined with semi-empirical calculations of the electrostatic potentials support a heterolytic hydrogenation mechanism involving a hydride from NaBH4 and a proton from H2O. The catalyst nanoRu′@hectorite can be recycled and reused.

Novel chiral cobalt complexes containing a PNNP-type ligand were synthesized using a straightforward method. The structures of the cobalt complexes have been fully characterized by X-ray crystallography, high resolution mass spectrometry (HRMS), and electron paramagnetic resonance (EPR). Using H2 as the hydrogen source, the cobalt-catalyzed asymmetric hydrogenation of various ketones was investigated, and the corresponding chiral alcohols were afforded with up to 99 % yield and 95 % ee. To the best of our knowledge, this is the first example of a cobalt-catalyzed enantioselective hydrogenation of ketones with molecular hydrogen.

The new chiral aminomethyl quinazoline (amq) type ligand derived from L-phenylalanine was synthesized and coordinated with [RuCl2(PPh3) dppb] to obtain ruthenium(II) complex. This catalyst displayed considerable reactivity (up to 97% ee and 99% conversion) in the asymmetric transfer hydrogenation of ketones using 2-propanol as a hydrogen source in the presence of NaOiPr. (C) 2016 Elsevier B.V. All rights reserved.

The asymmetric reduction of prochiral ketones is a pivotal reaction for the preparation of chiral alcohols which form an extremely important class of intermediates for fine chemicals and pharmaceuticals. Especially, iridium-based asymmetric reduction of ketones to enantiomerically enriched alcohols has recently attracted important attention by a number of research groups and interest in this area is growing. Therefore, a series of novel neutral mononuclear iridium(III) ferrocenyl-phosphinite complexes have been prepared and applied in the iridium(III)-catalyzed asymmetric transfer hydrogenation (ATH) of ketones to give corresponding secondary alcohols with outstanding enantioselectivities and reactivities using 2-propanol as the hydrogen source (up to 99% ee and 99% conversion). It was seen that the substituents on the backbone of the ligands resulted in a significant effect on both the activity and % enantioselectivity. Furthermore, the structural elucidation of the complexes was carried out by elemental analysis, IR and multi-nuclear NMR spectroscopic data.

In this study we report the catalytic hydrogenation of biomass-derived condensation product of furfural and cyclopentanone (F2C) with molecular hydrogen and formic acid as a source of hydrogen. Supported palladium catalysts have been used for hydrogenation and decomposition of formic acid. Complete conversion of F2C and higher than 90% yield of C15 bis-cyclic ether were achieved over 5% Pd/C catalyst at mild reaction conditions and short reaction time by catalytic hydrogenation with molecular hydrogen. Despite high activity of palladium catalysts in F2C hydrogenation with molecular hydrogen and also decomposition of formic acid to hydrogen these catalysts exhibited significantly lower activity in transfer hydrogenation. A dramatic activity loss in transfer hydrogenation may be caused by a strong adsorption of formic acid on Pd sites which hinders the competitive adsorption of F2C molecules solvated with formic acid.

Palladium catalysts supported on a carbon–silica material were synthesized. Hydrogenation by molecular hydrogen was studied in the presence of straight-chain and cyclic olefins. As distinct from what is observed for olefins having a phenyl substituent, for aliphatic alkenes the reaction rate decreases with an increasing conversion due to the accumulation of hydrogenation products. The synthesized palladium catalysts show a higher hydrogenation activity than Pd/C.

Chiral ruthenium half-sandwich complexes were prepared using a chelating diamine made from proline with a phenyl, ethyl, or benzyl group, instead of hydrogen on one of the coordinating arms. Three of these complexes were obtained as single diastereoisomers and their configuration identified by X-ray crystallography. The complexes are recyclable catalysts for the reduction of ketones to chiral alcohols in water. A ruthenium hydride species is identified as the active species by NMR spectroscopy and isotopic labelling experiments. Maximum enantio-selectivity was attained when a phenyl group was directly attached to the primary amine on the diamine ligand derived from proline.

The reactivity difference between the hydrogenation of CO2 catalyzed by various ruthenium bidentate phosphine complexes was explored by DFT. In addition to the ligand dmpe (Me2 PCH2 CH2 PMe2 ), which was studied experimentally previously, a more bulky diphosphine ligand, dmpp (Me2 PCH2 CH2 CH2 PMe2 ), together with a more electron-withdrawing diphosphine ligand, PN(Me) P (Me2 PCH2 N(Me) CH2 PMe2 ), have been studied theoretically to analyze the steric and electronic effects on these catalyzed reactions. Results show that all of the most favorable pathways for the hydrogenation of CO2 catalyzed by bidentate phosphine ruthenium dihydride complexes undergo three major steps: cis-trans isomerization of ruthenium dihydride complex, CO2 insertion into the Ru-H bond, and H2 insertion into the ruthenium formate ion. Of these steps, CO2 insertion into the Ru-H bond has the lowest barrier compared with the other two steps in each preferred pathway. For the hydrogenation of CO2 catalyzed by ruthenium complexes of dmpe and dmpp, cis-trans isomerization of ruthenium dihydride complex has a similar barrier to that of H2 insertion into the ruthenium formate ion. However, in the reaction catalyzed by the PN(Me) PRu complex, cis-trans isomerization of the ruthenium dihydride complex has a lower barrier than H2 insertion into the ruthenium formate ion. These results suggest that the steric effect caused by the change of the outer sphere of the diphosphine ligand on the reaction is not clear, although the electronic effect is significant to cis-trans isomerization and H2 insertion. This finding refreshes understanding of the mechanism and provides necessary insights for ligand design in transition-metal-catalyzed CO2 transformation.

Catalytic asymmetric hydrogenation of ketones through the "metal-ligand cooperative mechanism" has been improved in terms of the efficiency, stereoselectivity, and scope of substrates by varying the arrangement of the catalyst structure and reaction conditions. Imino compounds are also smoothly converted to the optically active amines with appropriate catalysts. This type of catalyst exhibits excellent performance on the asymmetric isomerization of primary allylic alcohols into the optically active aldehydes. This personal account describes recent progress on these topics.

This is an overview of the hydride-containing catalysts prepared in the Morris group for the efficient hydrogenation of simple ketones, imines, nitriles and esters and the asymmetric hydrogenation and transfer hydrogenation of prochiral ketones and imines. The work was inspired by and makes use of Noyori metal-ligand bifunctional concepts involving the hydride-ruthenium amine-hydrogen HRuNH design. It describes the synthesis and some catalytic properties of hydridochloro, dihydride and amide complexes of ruthenium and in one case, osmium, with monodentate, bidentate and tetradentate phosphorus and nitrogen donor ligands. The iron hydride that has been identified in a very effective asymmetric transfer hydrogenation process is also mentioned. The link between the HMNH structure and the sense of enantioinduction is demonstrated by use of simple transition state models.

N-heterocyclic carbene (NHC)-metal complexes have become known as efficient catalysts for numerous transition metal catalyzed processes. An important application of many NHC-metal complexes is in the field of asymmetric catalysis, and this is achieved through the introduction of chiral information on the NHC ligands. Among the asymmetric transformations catalyzed by NHC-metal complexes is asymmetric hydrogenation, which is an attractive process for the synthesis of optically active compounds due to its high atom economy. However, to date, few chiral NHC-metal catalysts have been reported to be highly stereoselective for asymmetric hydrogenation. Over the past few years our group has made some significant breakthroughs within the field of asymmetric hydrogenation using chiral NHC catalysts. We have reported the NHC-Ru catalyzed asymmetric hydrogenation of a wide range of heterocyclic compounds with high regio- and enantioselectivity. The field of chiral NHC-metal complex catalyzed asymmetric hydrogenation ...

The asymmetric hydrogenation of quinolines in oligo(ethylene glycol)s (OEGs) and poly(ethylene glycol)s (PEGs) with chiral cationic ruthenium diamine complexes has been investigated. Interestingly, in liquid PEGs or long-chain OEGs, the Ru catalysts lost their reactivity. Upon the addition of a little MeOH, the hydrogenation of quinoline was switched "ON". Evidence from mass spectrometry and control experiments revealed that encapsulation of the quinolinium salt by PEG or long-chain OEG molecules through supramolecular interactions is possibly the main reason for such a switchable hydrogenation reaction. Moreover, the asymmetric hydrogenation of 2-substituted quinoline derivatives was achieved in triethylene glycol (3-OEG), thereby affording 1,2,3,4-tetrahydroquinolines with excellent reactivities and enantioselectivities (up to 99 % ee). Furthermore, the Ru catalyst could be readily recycled for both pure 3-OEG and biphasic 3-OEG/n-hexane systems without a clear loss of reactivity and enantioselectivity.