Catalysts For Hydrogenation Of Ketones Research Articles

Enhancing enantioselectivity of manganese catalyst for asymmetric transfer hydrogenation of ketones through P,N,N-chelation of a cyclooctyl pyridine

A new ferrocene-based chiral PNN pincer ligand (L1) was successfully applied in Mn-catalyzed asymmetric transfer hydrogenation (ATH) of ketones (37 examples), leading to high activities (up to 4000 TON with 48 h) and excellent enantioselectivities (up to >99 % ee) for their product alcohols. The combined coordination and catalytic studies led to the conclusion that PNN pincer ligand L1 proved higher enantioselectivity in ATH than that observed by PN bidentate analogue L0. Furthermore, DFT calculations and control experiments highlighted the significance of the cyclooctyl group among these cycloalkyl motifs in the Mn-catalysts, resulting in enhanced enantioselectivity (up to 99 % ee), and disclosed the stereocontrol with the assistance of an attractive aromatic π-π stacking interaction between substrate and catalyst in the catalytic process.

Bidentate Ru(II)‐NC Complexes as Catalysts for Transfer Hydrogenation of Ketones with Ethanol

AbstractIn this study, we developed a bidentate Ru(II)‐NC‐catalyzed transfer hydrogen reaction of ketones using ethanol (EtOH) as the hydrogen source under weak base conditions. The control experiments suggested that the reaction proceeded via a Ru‐H mechanism, yielding ethyl acetate as the only byproduct. The deuterium‐labeling experiments showed that hydrogen evolved from the CH2 and OH groups. These results provide a new weak base system for the transfer hydrogen reaction of ketones using EtOH as the hydrogen donor.

Cover Feature: Novel Metallomacrocyclic Carboxamide Mn(II) Complexes as Efficient Catalysts for the Transfer Hydrogenation of Ketones (ChemCatChem 23/2023)

Cover Feature: Novel Metallomacrocyclic Carboxamide Mn(II) Complexes as Efficient Catalysts for the Transfer Hydrogenation of Ketones (ChemCatChem 23/2023)

Novel Metallomacrocyclic Carboxamide Mn(II) Complexes as Efficient Catalysts for the Transfer Hydrogenation of Ketones

AbstractHerein, we present the first metallomacrocyclic Mn(II) complexes as efficient catalysts for the transfer hydrogenation of ketones. The dinuclear Mn(II) complexes [Mn2(L1–L4)2Cl2] (Mn1–Mn4), were synthesised in good yields by reacting MnCl2 ⋅ 4H2O with the ligands N,N′‐(1,4‐phenylene)dipicolinamide (L1), N,N′‐(1,2‐phenylene)dipicolinamide (L2), N,N′‐(4‐methoxy‐1,2‐phenylene)dipicolinamide (L3) and N,N′‐(4,5‐dimethyl‐1,2‐phenylene)dipicolinamide (L4). Structural characterization of the resulting Mn(II) complexes was achieved using FT‐IR spectroscopy, mass spectrometry, magnetic moment measurements, elemental analysis, and single‐crystal X‐ray diffraction for Mn2. The solid‐state structure of complex Mn2 reveals a dinuclear Mn(II) core, in which the metal coordination sphere consists of two bidentate, K2(N−O) bridging L2 units and two chlorido ligands to give a distorted octahedral geometry. The Mn(II) complexes (Mn1–Mn4) were quite active catalysts for the transfer hydrogenation of ketones displaying turnover numbers (TON) of up to 2633, which is comparable to those of well‐established Mn(I) catalysts. The new Mn(II) complexes also efficiently hydrogenated a number of aromatic, heterocyclic, functionalized and aliphatic ketones. More significantly, cheaper, and readily available hydrogen sources like ethanol also gave decent catalytic activities in the transfer hydrogenation reactions.

Polymeric Micelles with Chiral Diamine-Ru(II) Catalysts for Asymmetric Transfer Hydrogenation of Ketones in Water

Polymeric Micelles with Chiral Diamine-Ru(II) Catalysts for Asymmetric Transfer Hydrogenation of Ketones in Water

Assembled Porphyrin‐Based Multinuclear Ruthenium(II)‐NNNN Complex Catalysts for Transfer Hydrogenation of Ketones

AbstractMultinuclear porphyrin‐based ruthenium(II)‐NNNN complexes were efficiently assembled by means of coordinatively unsaturated 16‐electron mononuclear ruthenium(II)‐pyrazolyl‐imidazolyl‐pyridine complex, zinc(II) meso‐tetra(4‐pyridyl)‐porphyrin (ZnTPyP), and 4,4′‐linked bipyridines. The resultant multinuclear (Ru4 and Ru8) porphyrin‐based ruthenium(II)‐NNNN complexes exhibited exceptionally high catalytic activity at as low as 0.008 mol % Ru loading for the transfer hydrogenation reaction of ketones in refluxing 2‐propanol, reaching up to 99 % yields and 5.7×106 h−1 TOFs.

Ketone transfer hydrogenation reactions catalyzed by catalysts based on a phosphinite ligand

Reaction of (±)-1-(2-furyl) ethanol with an equivalent Ph2PCl in the presence of Et3N proceeds in dry toluene under an argon atmosphere to give 1-(furan-2-yl)ethyl diphenylphosphinite (1) in good yield. Mononuclear complexes [dichloro(η6-p-cymene)(1-furan-2-ylethyl diphenylphosphinite)ruthenium(II)] (2), [dichloro(η6-benzene)(1-furan-2-ylethyl diphenylphosphinite)ruthenium(II)] (3), [chloro(η4-1,5-cyclooctadiene)(1-furan-2-ylethyl diphenylphosphinite)rhodium(I)] (4) and [dichloro(η5-pentamethylcyclopentadienyl)(1-furan-2-ylethyl diphenylphosphinite)iridium(III)] (5) were synthesized and characterized by microanalysis, infrared, MS, and NMR spectroscopies. The complexes are employed as catalysts in transfer hydrogenation of aromatic ketones. The complexes catalyzed reduction of a variety of aromatic ketone substrates bearing electron-withdrawing or donating substituents with very high conversion rates (up to 99%); 5 was the most efficient catalyst for the transfer hydrogenation of ketones.

Synthesis and Reactivity of Ampy-Based Ruthenium(II) Catalysts for Transfer Hydrogenation of Ketones

Synthesis and Reactivity of Ampy-Based Ruthenium(II) Catalysts for Transfer Hydrogenation of Ketones

Novel ruthenium complexes bearing bipyridine-based and N-heterocyclic carbene-supported pyridine (NCN) ligands: the influence of ligands on catalytic transfer hydrogenation of ketones.

Transfer hydrogenation (TH) is a powerful synthetic tool in the production of secondary alcohols from ketones by using a non-H2 hydrogen source along with metal catalysts. Among homogeneous catalysts, Ru(II) complexes are the most efficient catalysts. In our research, six novel ruthenium(II) complexes bearing bipyridine-based ligands [Ru(L1)Cl2] (1), [Ru(L1)(PPh3)Cl]Cl (2) and [Ru(L2)Cl2] (3) and N-heterocyclic carbene-supported pyridine (NCN) ligands [RuCp(L3)]PF6 (4), [RuCp*(L3)]PF6 (5), and [Ru(p-cymene)(L3)Cl]PF6 (6) (where L1 = 6,6'-bis(aminomethyl)-2,2'-bipyridine, L2 = 6,6'-bis(dimethylaminomethyl)-2,2'-bipyridine and L3 = 1,3-bis(2-methylpyridyl)imidazolium bromide) were synthesised and characterised by NMR spectroscopy, HRMS, and X-ray crystallography. The catalytic transfer hydrogenation of 28 ketones in 2-propanol at 80 °C in the presence of KOtBu (5 mol%) was demonstrated and the effect of ligands is highlighted. The results show that catalyst 1 exhibits improved TH efficiency compared to the commercially available Milstein catalyst and displays higher catalytic activity than 2 due to the steric effect from PPh3. From a combination of kinetic data and Eyring analysis, a zero-order dependence on the acetophenone substrate is observed, implying a rate-limiting hydride transfer step, leading to the proposed inner-sphere hydride transfer mechanism.

Structural characterization of a square planar Ni(II) complex and its application as a catalyst for the transfer hydrogenation of ketones

A new 2-hydroxy-1-naphthaldehyde Schiff base derived nickel(II) complex (4) was synthesized and fully characterized. Analysis of the structure of 4 by single-crystal X-ray diffraction shows two chelating Schiff base ligands bound to nickel in a trans [O∧N(Ni2+)N∧O] fashion. Hence, in a molecule of 4, two ligands are four coordinate to a Ni(II) center through the imine nitrogen and naphthyloxyl oxygen atoms. This coordination mode resulted in a square planar complex that is stabilized in the solid-state by a network of intermolecular O-H···N hydrogen bonds between neighboring molecules. The 1H NMR data showed the loss of the hydroxyl (OH) proton signal and an upfield shift of the metal-bound imine (-NH) proton signal, while the IR data also showed a lower energy shift in the absorption frequency of the imine (C = N) bond due to back donation from the coordinated Ni(II) center. As a catalyst for the transfer hydrogenation of a range of ketones, 4 showed good catalytic activity at a very low concentration of 0.1 mol% with 2-propanol as the model substrate. The catalyst is also effective for various related ketone substrates bearing a range of steric and electronic regulating groups.

Amino Acid Derived Chiral Aminobenzimidazole Manganese Catalysts for Asymmetric Transfer Hydrogenation of Ketones

Amino Acid Derived Chiral Aminobenzimidazole Manganese Catalysts for Asymmetric Transfer Hydrogenation of Ketones

Manganese-Catalyzed Hydrogenation of Ketones under Mild and Base-free Conditions.

In this paper, several Mn(I) complexes were applied as catalysts for the homogeneous hydrogenation of ketones. The most active precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe) (CO)3(CH2CH2CH3)]. The reaction proceeds at room temperature under base-free conditions with a catalyst loading of 3 mol % and a hydrogen pressure of 10 bar. A temperature-dependent selectivity for the reduction of α,β-unsaturated carbonyls was observed. At room temperature, the carbonyl group was selectively hydrogenated, while the C=C bond stayed intact. At 60 °C, fully saturated systems were obtained. A plausible mechanism based on DFT calculations which involves an inner-sphere hydride transfer is proposed.

The catalytic activity of new iridium(I) N-heterocyclic carbene complexes for hydrogen transfer reaction of ketones

In this paper, the reaction of [Ir(COD)Cl]2 with in situ prepared Ag–N-heterocyclic carbene (NHC) complexes yields a series of [IrCl(COD)(NHC)] complexes. All compounds were fully characterized by 1H NMR, 13C NMR, and FT–IR spectroscopy. The manuscript focused on the preparation of new Ir–NHC complexes, characterization and catalytic behavior. A series of hydrogenation transfer reactions were performed to reveal the effects of the Ir–NHC complexes. The new Ir–NHC complexes of benzimidazole-2-ylidene are effective catalysts for the transfer of hydrogenation of different ketones, using i-PrOH as the source of hydrogen in the presence of KOH. The reactions were conducted at a substrate/catalyst/base (S/C/base) molar ratio of 1:0.001:2. Although all of the complexes are active catalysts for the transfer hydrogenation of ketones, moderate yields were obtained with acetylnaphthalene and conversion was not observed with very substituted ketones such as 2′,3′,4′,5′,6′-pentamethylacetophenone. It was observed that for transfer hydrogenation reactions Ir–NHC catalysts were more active, compared to Ru–NHC catalyzed studies performed by our team.

Acetate Acetylacetonate Ampy Ruthenium(II) Complexes as Efficient Catalysts for Ketone Transfer Hydrogenation

AbstractThe mixed acetate acetylacetonate (acac) ruthenium(II) phosphine complexes Ru(OAc)(acac)P2 [P2=(PPh3)2, Ph2P(CH2)4PPh2 (dppb)] were prepared by protonation of Ru(OAc)2(PPh3)2 with acetylacetone in dichloromethane. Reaction of the dppb derivative with 2‐(aminomethyl)pyridine (ampy) affords the complex Ru(OAc)(acac)(ampy)(dppb), which converts to [Ru(acac)(ampy)(dppb)](OAc) in toluene at 90 °C. In the former derivative the ampy ligand is monodentate and coordinates through the NH2‐moiety. The isolated acac complexes are active catalysts for the transfer hydrogenation of ketones with loadings as low as 0.01 mol%, the ampy having a strong accelerating effect. Several aromatic and aliphatic ketone substrates are converted to their corresponding alcohols, and different electronic influences through substituents on acetophenone are tolerated.

Reduced graphene oxide/iron oxide hybrid composite material as an efficient magnetically separable heterogeneous catalyst for transfer hydrogenation of ketones

Reduced graphene oxide was synthesized and functionalized with FeSO4⋅7H2O to form a reduced graphene oxide/iron oxide hybrid composite. The hybrid composite was extensively characterized using various techniques. Its application for transfer hydrogenation of various ketones was studied. The investigation showed that it serves as a good catalyst for transfer hydrogenation of aromatic and some aliphatic ketones resulting in excellent isolated yields (97–99%) of products. It is magnetically separable showing good reusability. The products were characterized and compared with authentic ones.

Stepwise Construction of Ru(II)Center Containing Chiral Thiourea Ligand on Graphene Oxide: First Efficient, Reusable, and Stable Catalyst for Asymmetric Transfer Hydrogenation of Ketones

Heterogenization of homogenous catalysts on solid support has attracted tremendous attention in organic synthesis due to the key benefits of heterogenized catalysts such as easy recovery and reusability. Although a considerable number of heterogenized catalysts are available, to the best of our knowledge, there is no efficient and reusable heterogenized catalyst reported for asymmetric reactions to date. Herein, we prepared a [RuCl2(η6-p-cymene)]/chiralthiourea ligand covalently bonded to graphene nanosheets (G-CLRu(II), where G represents graphene oxide (GO), CL denotes chiral N-((1-phenylethyl)carbamothioyl)acetamide and Ru(II) symbolizes [RuCl2(η6-p-cymene)]), for the asymmetric transfer hydrogenation of ketones. Five simple steps were involved in the preparation of the G-CLRu(II) catalyst. The structure of G-CLRu(II) was investigated by means of various spectroscopic and microscopic techniques. Coordination mode and covalent bonding involved in the G-CLRu(II) structure we reconfirmed. G-CLRu(II) demonstrated good catalytic performance towards the asymmetric transfer hydrogenation of ketones (conversion of up to 95%, enantiomeric excesses (ee) of up to 99%, and turnover number (TON) and turnover frequency (TOF) values of 535.9 and 22.3 h−1, respectively). A possible mechanism is proposed for the G-CLRu(II)-catalyzed asymmetric transfer hydrogenation of ketones. Recovery (~95%), reusability (fifth cycle, yield of 89% and ee of 81%), and stability of G-CLRu(II) were found to be good. We believe that the present stepwise preparation of G-CLRu(II) opens a new door for designing various metal-centered heterogenized chiral catalysts for asymmetric synthesis.

Transfer Hydrogenation of Ketones and Imines with Methanol under Base-Free Conditions Catalyzed by an Anionic Metal-Ligand Bifunctional Iridium Catalyst.

An anionic iridium complex [Cp*Ir(2,2'-bpyO)(OH)][Na] was found to be a general and highly efficient catalyst for transfer hydrogenation of ketones and imines with methanol under base-free conditions. Readily reducible or labile substituents, such as nitro, cyano, and ester groups, were tolerated under present reaction conditions. Notably, this study exhibits the unique potential of anionic metal-ligand bifunctional iridium catalysts for transfer hydrogenation with methanol as a hydrogen source.

An iron variant of the Noyori hydrogenation catalyst for the asymmetric transfer hydrogenation of ketones.

We report the design of a new iron catalyst for the asymmetric transfer hydrogenation of ketones. This type of iron catalyst combines the structural characteristics of the Noyori hydrogenation catalyst (an axially chiral 2,2'-bis(phosphino)-1,1'-binaphthyl fragment and the metal-ligand bifunctional motif) and an ene(amido) group that can activate the iron center. After activation by 8 equivalents of potassium tert-butoxide, (SA,RP,SS)-7a and (SA,RP,SS)-7b are active but nonenantioselective catalysts for the transfer hydrogenation of acetophenone and α,β-unsaturated aldehydes at room temperature in isopropanol. A maximum turnover number of 14480 was observed for (SA,RP,SS)-7a in the reduction of acetophenone. The right combination of the stereochemistry of the axially chiral 2,2'-bis(phosphino)-1,1'-binaphthyl group and the carbon-centered chiral amine-imine moiety in (SA,RP,RR)-7b' afforded an enantioselective catalyst for the preparation of chiral alcohols with moderate to good yields and a broad functional group tolerance.

Computational Prediction of Ammonia-Borane Dehydrocoupling and Transfer Hydrogenation of Ketones and Imines Catalyzed by SCS Nickel Pincer Complexes.

Inspired by the catalytic mechanism and active site structure of lactate racemase, three scorpion-like SCS nickel pincer complexes were proposed as potential catalysts for transfer hydrogenation of ketones and imines with ammonia-borane (AB) as the hydrogen source. Density functional theory calculations reveal a stepwise hydride and proton transfer mechanism for the dehydrocoupling of AB and hydrogenation of N-methylacetonimine, and a concerted proton-coupled hydride transfer process for hydrogenation of acetone, acetophenone, and 3-methyl-2-butanone. Among all proposed Ni complexes, the one with symmetric NH2 group on both arms of the SCS pincer ligand has the lowest free energy barrier of 15.0 kcal/mol for dehydrogenation of AB, as well as total free energy barriers of 17.8, 18.2, 18.0, and 18.6 kcal/mol for hydrogenation of acetone, N-methylacetonimine, acetophenone, and 3-methyl-2-butanone, respectively.

Mont-K10 Supported Fe(II) Schiff-Base Complex as an Efficient Catalyst for Hydrogenation of Ketones

A new Fe(II) Schiff base complex anchored on mont-K10 (Fe@imine-mont-K10) was synthesized and extensively characterized by FTIR, powder X-ray diffraction, SEM–EDX, TEM, ESR, X-ray photoelectron spectroscopy (XPS), BET surface area measurement, solid state 29Si NMR and ICP-AES analysis. The catalytic activity of the complex was investigated for hydrogenation of ketones. The results indicated that it exhibited good catalytic activity for hydrogenation of aromatic as well as aliphatic ketones in i-PrOH/CH3CN (1:1) using Na-i-OPr as base at 80 °C resulting in moderate to excellent isolated yields (51–99%) of their corresponding products. The catalyst shows good reusability.