Transfer Hydrogenation Of Ketones Research Articles

Polarizability matters in enantio-selection

The prevalence of chirality, or, handedness in biological world is a fundamental phenomenon and a characteristic hallmark of life. Thus, understanding the origin of enantio-selection, i.e., the sense and magnitude of asymmetric induction, has been a long-pursued goal in asymmetric catalysis. Herein, we demonstrated a polarizability-derived electronic effect that was shown to be capable of rationalizing a broad range of stereochemical observations made in the field of asymmetric catalysis. This effect provided a consistent enantio-control model for the prediction of major enantiomers formed in a ruthenium-catalyzed asymmetric transfer hydrogenations of ketones. Direct and quantitative linear free energy relationships between substrates’ local polarizabilities and observed enantio-selectivity were also revealed in three widely known asymmetric catalytic systems covering both reductions and oxidations. This broadly applicable polarizability-based electronic effect, in conjunction with conventional wisdom mainly leveraging on steric effect considerations, should aid rational design of enantio-selective processes for better production of chiral substances.

Catalytic performance of Noyori–Ikariya-type ruthenium complex with tethered syn-ULTAM ligand for the asymmetric transfer hydrogenation of ketones

The ruthenium complex of the tethered syn-ULTAM ligand, i.e. syn-3-(α-aminobenzyl)-benzo-γ-sultam, has been evaluated for the asymmetric transfer hydrogenation (ATH) of a variety of ketones in formic acid/triethylamine mixture. Its performance was similar to the established Noyori–Ikariya-type catalysts for the reduction of benzo-fused cyclic ketones, but the enantioselectivity for the reduction of acetophenone was only moderate. The syn-ULTAM-based catalyst was particularly efficient and enantioselective for ATH of the sterically demanding α,α-disubstituted ketones. Moreover, we report a divergent ATH of 2-phenyl-1,3-indandione to either cis-2-phenyl-1-indanol, or cis,trans-2-phenyl-1,3-indandiol.

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.

Air-Stable Coordinatively Unsaturated Ruthenium(II) Complex for Ligand Binding and Catalytic Transfer Hydrogenation of Ketones from Ethanol.

Coordinatively unsaturated complexes are interesting from a fundamental level for their formally empty coordination site and, in particular, from a catalytic perspective as they provide opportunities for substrate binding and transformation. Here, we describe the synthesis of a novel underligated ruthenium complex [Ru(cym)(N,N')]+, 3, featuring an amide-functionalized pyridylidene amide (PYA) as the N,N'-bidentate coordinating ligand. In contrast to previously investigated underligated complexes, complex 3 offers potential for dynamic modifications, thanks to the flexible donor properties of the PYA ligand. Specifically, they allow both for stabilizing the formally underligated metal center in complex 3 through nitrogen π-donation and for facilitating through π-acidic bonding properties the coordination of a further ligand L to the ruthenium center to yield the formal 18 e- complexes [Ru(cym)(N,N')(L)]+ (4: L = P(OMe)3; 5: L = PPh3; 6: L = N-methylimidazole; 7: L = pyridine) and neutral complex [RuCl(cym)(N,N')] 8. Analysis by 1H NMR and UV-vis spectroscopies reveals an increasing Ru-L bond strength along the sequence pyridine <1-methylimidazole < PPh3 < P(OMe)3 with binding constants varying over 3 orders of magnitude with log(Keq) values between 2.8 and 5.7. The flexibility of the Ru(PYA) unit and the ensuing accessibility of saturated and unsaturated species with one and the same ligand are attractive from a fundamental point of view and also for catalytic applications, as catalytic transformations rely on the availability of transiently vacant coordination sites. Thus, while complex 3 does not form stable adducts with O-donors such as ketones or alcohols, it transiently binds these species, as evidenced by the considerable catalytic activity in the transfer hydrogenation of ketones. Notably, and as one of only a few catalysts, complex 3 is compatible with EtOH as a hydrogen source. Complex 3 shows excellent performance in the transfer hydrogenation of pyridyl-containing substrates, in agreement with the poor coordination strength of this functional group to the ruthenium center in 3.

Catalytic utility of PNN-based MnI pincer complexes in the synthesis of quinolines and transfer hydrogenation of carbonyl derivatives.

This manuscript describes the synthesis of a triazolyl-pyridine-based phosphine, N-((diphenylphosphaneyl)methyl)-N-methyl-6-(1-phenyl-1H-1,2,3-triazol-4-yl)pyridin-2-amine, [2,6-{(PPh2)CH2N(Me)(C5H3N)(C2HN3C6H5)}] (1) (here onwards referred to as PNN) and its cationic and neutral MnI complexes and catalytic applications. The reaction of 1 with Mn(CO)5Br afforded a cationic complex [Mn(CO)3(PNN)]Br (2), which is highly stable in solid state, but in solution it gradually loses one of the CO groups to form a neutral complex [Mn(CO)2(PNN)Br] (3). Complex 2 on treatment with AgBF4 also yielded a cationic complex [Mn(CO)3(PNN)]BF4 (4). These complexes efficiently promoted the synthesis of quinoline derivatives via acceptor-less dehydrogenative coupling of 2-aminobenzyl alcohol and ketones, with complex 3 showing the highest activity with a very low catalyst loading (0.03 mol%) at 110 °C. Complex 3 (0.5 mol%) also showed excellent catalytic activity in the transfer hydrogenation of ketones and aldehydes to form respective secondary and primary alcohols.

Mononuclear and dinuclear (pyridyl) dicarboxamide Ru(II) hydrido complexes: Ligand controlled coordination diversity and catalytic transfer hydrogenation of ketones

Reactions of ligand N,N-(1,4-phenylene)-dipicolinamide (H2L1), with [Ru(PPh3)3(CO)HCl] produced the dinuclear complex [Ru2(H2L1)(PPh3)4(CO)2H2]2+[2Cl−]− (Ru1). On the other hand, treatments of ligand N,N-(1,2-phenylene)-dipicolinamide (H2L2), with two and one molar equivalents of [Ru(PPh3)3(CO)HCl] afforded the dinuclear and mononuclear complexes [Ru2(HL2)(PPh3)3(CO)3HCl2] (Ru2) and [Ru(HL2)(PPh3)2(CO)H] (Ru3) respectively. The identities and structures of complexes Ru1-Ru3 were established using NMR, FT-IR spectroscopic techniques, mass spectrometry, and elemental analyses. The complexes Ru1-Ru3 displayed high catalytic activities in the transfer hydrogenation of a wide range of ketones. The hydride complex Ru1 was the most active, while the dinuclear complex Ru2 was more active than the analogous mononuclear complex Ru3. 31P NMR spectroscopic analyses of the reaction intermediates was used to propose a monohydride pathway in the transfer hydrogenation reactions involving dissociation of one PPh3 ligand.

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)

Ruthenium Complexes with N-Bound 2-Pyridonato Ligand as O-Donors: A New Synthetic Approach and the Effect on Reactivity.

In this study, Ru complexes [(η6-p-cymene)RuX(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O))] (3: X=Cl; 4: X=I) were prepared with N-bound 2-pyridonato ligand by thermal base-free MeX elimination from ionic N,N-chelated Ru complexes [(η6-p-cymene)RuX(κ2-L1)](X) (1: X=Cl; 2: X=I; L1={2-[(2,6-iPr2-C6H3)N=CH]-6-(OMe)C5H3N}). The Ru complex 3 was used as O-donor for Lewis (LA) or Brönsted acids. The reactions of 3 with SnCl2, Ph3SnCl, ZnCl2 or HCl provided [(η6-p-cymene)Ru(SnCl3)(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O→SnCl2)] (6), [(η6-p-cymene)RuCl(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O→SnPh3Cl)] (7), and [(η6-p-cymene)RuCl(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O→)]2(μ-ZnCl2) (8) and [(η6-p-cymene)RuCl(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(OH)}](Cl) (9). The easy conversion of the 2-pyridonato ligand in 3 to its 2-hydroxypyridine in 9 evoked testing of 3 and 4 as potential catalysts in base-free transfer-hydrogenation of ketones.

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

Piano‐stool dinuclear ruthenium (II) complexes of pyrazine‐carboxylate/carboxamide ligands: Structural studies and catalytic transfer hydrogenation of ketones

Reactions of ligand pyrazine‐2‐carboxylic acid (HL1) with [Ru(η6‐p‐cymene)Cl2]2 precursor gave the dinuclear piano‐stool ruthenium (II) complex [{Ru(η6‐p‐cymene)Cl2}‐μ‐(L1)‐{Ru(p‐cymene)Cl}] (Ru1). Separately, reactions of N‐(quinolin‐8‐yl) pyrazine‐2‐carboxamide (HL2), 5‐methyl‐N‐(−(quinolin‐8‐yl) pyridine‐2‐carboxamide (HL3) and 5‐chloro‐N‐(quinolin‐8‐yl) pyridine‐2‐carboxamide (HL4) with [Ru(η6‐p‐cymene)Cl2]2 dimer in the presence of KPF6 afforded the cationic dinuclear complexes [{Ru(η6‐p‐cymene)Cl}2‐μ‐(L2)][PF6] (Ru2), [{Ru(η6‐p‐cymene)Cl}2‐μ‐(L3)][Ru(L3)Cl3] (Ru3) and [{Ru(η6‐p‐cymene)Cl}2‐μ‐(L4)][PF6] (Ru4). The Ru (II) complexes were analysed using FT‐IR, 1H, 13C{1H}, 31P{1H} (Ru2 and Ru4) and 19F (Ru2 and Ru4) NMR spectroscopic techniques, micro‐analyses and mass spectrometry. Molecular structures of complexes Ru1 and Ru3 were confirmed to display piano‐stool coordination nature using single‐crystal X‐ray crystallography analyses. All the complexes (Ru1–Ru4) mediated the transfer hydrogenation (TH) of a broad spectrum of ketones in isopropanol in the presence of a base and demonstrated high catalytic activities (TON of 24,000) at catalyst concentrations of 0.002 mol%. In general, the catalytic performance of these Ru (II) complexes depended on the identity of the ligands, coordination chemistry and ketone substrates.

Pincer Ru with a single stereogenic identity for highly efficient asymmetric transfer hydrogenation of ketones

Pincer Ru with a single stereogenic identity for highly efficient asymmetric transfer hydrogenation of ketones

Ru(II) complexes containing NOO donors of tridentate Schiff base ligands: Synthesis, characterization, crystal structure and catalytic activity in transfer hydrogenation of ketones

A new series of pincer type ruthenium(II) Schiff base complexes namely [Ru(CO)(PPh3)2(L1‒6)] (1–6) (where, L1‒6 ​= ​NOO ‒ donors of tri-dentate ligands) have been synthesized from ruthenium precursor such as [RuHCl(CO)(PPh3)3] containing tri-dentate Schiff bases ligands (H2L1‒H2L6). These ruthenium complexes were analyzed by elemental analysis and diverse characterizations such as FT‒IR, UV–Vis and NMR (1H and 31P) spectroscopy studies. The crystal structure of one of the complexes 5 ([Ru(CO)(PPh3)2L5]) was determined by single crystal X‒ray crystallography that revealed pincer type of coordination mode of complexes. Furthermore, complexes 1–6 have been utilized for transfer hydrogenation of aromatic ketones to secondary alcohols in the presence of i‒PrOH/KOH. The catalytic efficiency of complexes showed an efficient for transfer hydrogenation of ketones with alcohol as moderate to high conversions.

Synthesis and catalytic applications of metal complexes supported by indole‐functionalized mesoionic 1,2,3‐triazolylidenes

We report the synthesis and full characterization of a novel series of indole-derived triazolium salts and their corresponding triazolylidene gold, palladium, rhodium and iridium complexes. All new compounds were fully characterized by means of 1H and 13C NMR spectroscopy, elemental analyses and in the case of triazoliums 1 and 2 and complexes 3, 4 and 9, by single crystal X-ray diffraction. Gold complexes demonstrated a good catalytic performance in the hydrohydrazination of terminal alkynes producing a series of substituted hydrazones in good yields under mild reaction conditions. Additionally, the iridium complex (9) performed well in the catalytic transfer hydrogenation of ketones and aldehydes using isopropanol as hydrogen source.

New Ruthenium-p-Cymene Complexes Containing o-Vanillin and 4-Benzoxybenzaldehyde Schiff Base Ligands; Synthesis, Characterization and Catalytic Activity in the Transfer Hydrogenation of Ketones

New Ruthenium-p-Cymene Complexes Containing o-Vanillin and 4-Benzoxybenzaldehyde Schiff Base Ligands; Synthesis, Characterization and Catalytic Activity in the Transfer Hydrogenation of Ketones

Ir‐Catalyzed Transfer Hydrogenation and Alkylation of Aldehydes and Ketones Using Ethanol as the Hydrogen Source

AbstractBio‐derived ethanol is a promising green and sustainable hydrogen‐donor solvent. Herein, we have developed Ir‐catalyzed transfer hydrogenation of ketones and aldehydes using ethanol as a hydrogen source with amides as simple ligands. Furthermore, the alkylation of ketones and tandem alkylation/transfer hydrogenation of acetophenones is reported with ethanol.

Asymmetric transfer hydrogenation of ketones catalyzed by chiral macrocyclic cobalt(II) complexes

Using easily available CoBr2 and chiral cyclic PxNy-type ligands as starting materials, novel chiral cyclic cobalt(II) complexes could be conveniently prepared. Furthermore, we obtained the single crystals suitable for X-ray diffraction to confirm the structures of these cobalt(II) complexes. The asymmetric transfer hydrogenation (ATH) of ketones catalyzed by these well-designed cobalt(II) complexes was investigated. Among them, cobalt(II) complex containing chiral macrocyclic iminophosphine ligand CyP2N4 exhibited high catalytic activity and enantioselectivity (up to 99% ee). Density functional theory (DFT) calculations suggested that cobalt(II) complex (R,R,R',R')-CyP2N4-Co(II) (C1) is easier to form metal hydride, which is the key intermediate during the enantioselective transfer hydrogenation reaction. Study results also revealed that the unique macrocyclic structure of complex C1 could form a special microenvironment around cobalt ion. Therefrom the substrate coordinated with the central metal along this specific reaction channel during the asymmetric catalytic reaction, resulting high enantioselectivity.

Mechanistic insights and comparative analysis of Ru(ii)–NNC pincer complexes with anionic-, protic-, and classical-NHCs for transfer hydrogenation of ketones

A series of Ru(ii)–NNC pincer-type complexes bearing anionic-, protic- and classical-NHC ligands are reported. Comparative analysis of catalytic activity in transfer hydrogenation of ketones is investigated both experimentally and computationally.

Dipyrromethane-diphosphine: the effect of meso substituents on the formation of nickel complexes and on their performance in the transfer hydrogenation of ketones.

Three dipyrromethane-diphosphine ligands containing phenyl (L1H2), ethyl (L2H2) and cyclohexyl (L3H2) groups at their meso positions and their nickel complexes were synthesized and structurally characterized. Treatment of Ph2C(C4H3N)2-1,9-(CH2PPh2)2 (L1H2) with [NiCl2(DME)] gave complex [NiCl2(κ2-P,P-L1H2)] 2a. Conversely, the analogous reactions of L2H2 and L3H2 with [NiCl2(DME)] showed a mixture of products containing both a pyrrolide nitrogen coordinated complex of type [Ni(κ4-P,N,N,P-L)] 3 without an exogenous base and a chelated complex of type 2a. In addition, all three ligands react with [NiCl2(DME)] in the presence of a strong base to give a complex of type 3. Furthermore, a novel binuclear Ni(0) complex bearing L1H2 was characterized by X-ray crystallography. Both complexes 2a and 3 (0.5 mol% of loading) catalyze the transfer hydrogenation of a series of aromatic and aliphatic ketones (20 substrates) to their corresponding secondary alcohols using iPrOH as a hydrogen source in the presence of KOH at 100 °C in 6 h. The kinetic trace of the catalytic reaction shows that the meso-phenyl substituted diphosphine coordinated nickel complexes perform better than the other two ligand coordinated nickel complexes.

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.