Transfer Hydrogenation Of Various Ketones Research Articles

Preparation of catechol boronate esters enabled by N → B dative bond as efficient, stable, and green catalysts for the transfer hydrogenation of various ketones

A series of new structurally related catechol boronate esters enabled by N → B dative bond of general composition (B1-B4) and (B1N-B4N) were designed and synthesized for the transfer hydrogenation of various ketones, as catalysts. The structures of the synthesized trigonal-planar and tetrahedral catechol boronate esters forming dative bonds with neutral base were well-elucidated by NMR (1H, 13C, and 11B), FT-IR, UV–Vis, fluorescence, and LC-MS/MS spectroscopy, melting point and microanalysis. With the development of a more active and stable catalytic system for transfer hydrogenation of ketones in mind, all catechol boronate esters were tested as catalysts for the transfer hydrogenation of aromatic ketones, showing good activity in this reaction. Particularly, it was proved that the mononuclear molecules can afford an efficient catalytic conversion compared to the corresponding dinuclear boronate esters in transfer hydrogenation catalytic studies. Among the catalysts, (B4) and (B4N) are the most active catalysts and catalytic activity of (B4) was generally much higher in the studied hydrogen transfer reactions than that of (B4N) under mild conditions in isoPrOH. This clearly suggests that catechol boronate esters are also one of the propitious catalyst candidates and are worthy of further investigations.

Efficient transfer hydrogenation of ketones using molybdenum complexes by comprehensively verifying the auxiliary ligands.

Molybdenum complexes ligated with N1,N1-dialkyl-N2-(5,6,7,8-tetrahydroquinolin-8-yl)ethane-1,2-diamines and auxiliary ligands, providing various structural features, were developed: [NNH/NNHN]Mo(CO)4/3 (Mo1-Mo3), [NNHN]Mo(CO)2Br (Mo4-Mo5), [NNH]Mo(CO)(η3-C3H5)Br (Mo6) and [NNHN/S]Mo(CO)(PPh3)2 (Mo7-Mo8). All the complexes were highly active in the transfer hydrogenation (TH) of a model substrate (acetophenone), providing excellent yields of 1-phenylethanol. The structural variation in the ligand framework had a modest effect on the catalyst performance as compared to the changes in the auxiliary ligands Br, PPh3 and CO. This structural evolution provided the complex [Mo(NNH)(η3-C3H5)(CO)2Br] (Mo6) as the most effective catalyst not only for the transfer hydrogenation of acetophenone but also for a wide range of diverse ketones (up to 43 examples). Moreover, easy purification of the products by only removing the acetone byproduct is another noteworthy feature of this environmentally friendly route.

Chiral salen - Ni (II) based spherical porous silica as platform for asymmetric transfer hydrogenation reaction and synthesis of potent drug intermediate montekulast

Heterogeneous catalyst has an edge over homogeneous systems in terms of recyclability, activity, stability and recovery. Silica has evolved as a good support material in heterogeneous systems due to its stability and ability to get modified as per the end application. Herein, we report a novel chiral Ni-Schiff base derived catalyst and its immobilization into mesoporous silica which was synthesized by post-grafting process. The chiral catalyst demonstrated remarkably high catalytic activity, enantioselectivity (up to 99 % enantiomers excess) for heterogeneous asymmetric transfer hydrogenation of various ketones. The developed catalyst was characterized by Ultraviolet-visible spectroscopy (UV–vis), Fourier-Transform Infrared spectroscopy (FT-IR), X-ray Powder Diffraction (XRD), Brunauer-Emmett-Teller (BET isotherm), Scanning Electron Microscopy – Energy Dispersive X-ray Spectroscopy (SEM-EDX), High Resolution – Transmission Electron Microscopy (HR-TEM), Vibrating Sample Magnetometer (VSM), X-ray Photoelectron Spectroscopy (XPS) and elemental analysis. The catalyst could be recovered and reused for multiple consecutive runs without losing the enantioselectivity. The chiral catalyst was used in asymmetric transfer hydrogenation reaction for synthesizing enantiomerically pure drug intermediate Montekulast.

Synthesis of cis‐1,2‐diol‐type chiral ligands and their dioxaborinane derivatives: Application for the asymmetric transfer hydrogenation of various ketones and biological evaluation

Two cis‐1,2‐diol‐type chiral ligands (T1 and T2) and their tri‐coordinated chiral dioxaborinane (T(1–2)B(1–2)) and four‐coordinated chiral dioxaborinane adducts with 4‐tert‐butyl pyridine sustained by N → B dative bonds (T(1–2)B(1–2)‐N) were synthesized and characterized by various spectroscopic techniques such as NMR (1H, 13C, and 11B), FT‐IR and UV–Vis spectroscopy, LC–MS/MS, and elemental analysis. It was suggested that both ferrocene and trifluoromethyl groups played key roles in the catalytic and biological studies because they could tune the solubility of the chiral dioxaborinane complexes and adjust the strength of intermolecular interactions. To assess the biological activities of newly synthesized chiral dioxaborinane compounds, DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) radical scavenging, reducing power, antibacterial, DNA binding, and DNA cleavage activities were tested. Then, all chiral dioxaborinane complexes were investigated as catalysts for the asymmetric transfer hydrogenation of various ketones under suitable conditions. The results indicated that the chiral dioxaborinane catalysts performed well with high yields.

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.

Catalysts for the asymmetric transfer hydrogenation of various ketones from [3-[(2S)-2-[(diphenylphosphanyl)oxy]-3-phenoxypropyl]-1-methyl-1H-imidazol-3-ium chloride] and [Ru(η6-arene)(μ-Cl)Cl]2, Ir(η5-C5Me5)(μ-Cl)Cl]2 or [Rh(μ-Cl)(cod)

The combination of [3-[(2S)-2-[(diphenylphosphanyl)oxy]-3-phenoxypropyl]-1-methyl-1H-imidazol-3-ium chloride] with [Ru(η6-arene)(μ-Cl)Cl]2, Ir(η5-C5Me5)(μ-Cl)Cl]2 or [Rh(μ-Cl)(cod)]2, in the presence of KOH/isoPrOH, has been found to generate catalysts that are capable of enantioselectively reducing alkyl, aryl ketones to the corresponding (R)-alcohols. Under optimized conditions, when the catalysts were applied to the asymmetric transfer hydrogenation, we obtained the secondary alcohol products in high conversions and enantioselectivities using only 0.5 mol% catalyst loading. In addition, [3-[(2S)-2-{[(chloro(ɳ4-1,5-cyclooctadiene)rhodium)diphenyl phosphanyl] oxy}-3-phenoxypropyl]-1-methyl-1H-imidazol-3-ium chloride], (6) complex is much more active than the other analogous complexes in the transfer hydrogenation. Catalyst 6 acts as excellent catalysts, giving the corresponding (R)-1-phenyl ethanol in 99% conversion in 30 min (TOF ≤ 396 h−1) and in high enantioselectivity (92% ee).

Half‒Sandwich (η6‒p‒Cymene) Ruthenium(II) complexes bearing 5‒Amino‒1‒Methyl‒3‒Phenylpyrazole Schiff base ligands: Synthesis, structure and catalytic transfer hydrogenation of ketones

New (η6‒p‒cymene) ruthenium(II) complexes containing Schiff base ligands of the general composition [RuCl(η6‒p‒cymene)(L1‒3)] have been synthesized. The complexes were characterized by analytical and spectral (FT‒IR, UV–Vis, 1H NMR and 13C NMR) methods. The molecular structure of the representative complex [RuCl(η6‒p‒cymene)(L3)] 6 was determined by single crystal X−ray diffraction studies, revealing a pseudo-octahedral piano stool geometry around ruthenium(II) ion. Further, one of the complexes 6 was screened for their efficiency as a catalyst in the transfer hydrogenation of various ketones to alcohols in the presence of KOH and 2‒propanol showed an excellent conversion up to 99%. Under the optimized conditions, the influence of base, reaction temperature and substrate scope was also reported.

Pyridyl based ruthenium(II) catalyst precursors and their dihydride analogues as the catalytically active species for the transfer hydrogenation of ketones

In this study we describe the one-pot and high yield synthesis of the ruthenium(II) complex cis-dichloride [RuCl2(PPh3)2(L1)] (L1 = 4-methyl-2-(2′-pyridyl)quinoline) (1). The solid state structure of L1 is described. The catalytic activity of 1 in the transfer hydrogenation of various ketones by 2-propanol at 82 °C, has been studied and compared with the activity of the known catalyst precursors cis-[RuCl2(PPh3)2(L2)] (L2 = 2-(2'-pyridyl)quinoline) (2), cis-[RuCl2(PPh3)2(L3)] (L3 = 2-(2′-pyridyl)quinoxaline) (3) and cis-[RuCl2(PPh3)2(bipy)] (bipy = 2,2′-bipyridine) (4). The ruthenium monohydride complex [RuHCl(PPh3)2(L3)] 3-H (Cl cis to H) was prepared from the reaction of 3 with 2.5 equivalents of a KOiPr solution. Reaction of 3 with 10 equivalents of KOiPr yields the cis-[RuH2(PPh3)2(L3)] (3-H2). Treatment of 1, 2 and 4 with KOiPr (in excess) affords the ruthenium cis-dihydride complexes [RuH2(PPh3)2(L1)] (1-H2), [RuH2(PPh3)2(L2)] (2-H2) and [RuH2(PPh3)2(bipy)] (4-H2). The formation of 1-H2, 2-H2, 3-H2 and 4-H2 is supported by NMR spectroscopic data. The cis-dihydrides 1-H2 to 4-H2 catalyze successfully the transfer hydrogenation of benzophenone to benzhydrol in the absence of a base, suggesting that presumably the active catalyst is a ruthenium dihydride complex (RuH2). Catalyst 1 has been potentially recovered and reused at least four times.

A new class of well-defined ruthenium catalysts for enantioselective transfer hydrogenation of various ketones

A pair of novel optically pure phosphinite ligands were synthesized by ring opening reaction of chiral amines with (R)-styrene oxide or (S)-glycidyl phenyl ether oxide using a straightforward method in high yields and their ruthenium complexes were described in detail. The ruthenium complexes proved to be highly efficient catalysts for the enantioselective hydrogenation of ketones, affording products up to 99% ee. The results showed that the corresponding chiral alcohols could be obtained with high activity and excellent enantioselectivities at the desired temperature. (2S)-1-{benzyl[(1S)-1-(naphthalen-1-yl)ethyl]amino}-3-phenoxypropan-2-yl diphenylphosphinito[dichloro(η6-benzene)ruthenium (II)] acts an excellent catalyst in the reduction of ketones, giving the corresponding alcohol up to 99% ee.

Catechol-type ligand containing new modular design dioxaborinane compounds: Use in the transfer hydrogenation of various ketones

A novel class of tricoordinate dioxaborinane compounds, which have the general formula [B1(L1–5)] and [B2(L1–5)], were designed and synthesized by the corresponding catechol-type ligands (L1–L5) at ambient temperature. All the new compounds were fully characterized by NMR (1H, 13C, and 11B), FT-IR, UV–vis, LC-MS spectroscopy, and melting point analysis and microanalysis. The dioxaborinane [B1(L1–5)] and [B2(L1–5)] compounds were investigated as catalyst for the transfer hydrogenation of various ketones under suitable conditions. Particularly, it was proved that the ferrocene-based dioxaborinane [B1(L1–5)] molecules can afford an efficient catalytic conversion compared to corresponding 3,5-bis(trifluoromethyl)phenyl-based [B2(L1–5)] dioxaborinanes in transfer hydrogenation catalytic studies.

Ru(II) mediated C[sbnd]H activation of 1-(biphenylazo)naphthol: Synthesis and catalytic evaluation for transfer hydrogenation of ketones

New cyclometalated ruthenium(II) complexes of the type [Ru(L)(CO)(EPh3)2] (L=di-anionic CNO- donor of 1-(biphenylazo)naphthol; E=P, As) have been synthesized by the reaction using [RuHCl(CO)(EPh3)3] (E=P, As) with 1-(biphenylazo)naphthol ligand (H2L). The 1-(biphenylazo)naphthol ligand and ruthenium complexes are characterized by analytical, spectral (FT–IR, UV–Vis, 1H NMR and 31P NMR) methods. The molecular structure of ruthenium complex 1 was further confirmed by single crystal X-ray diffraction method. The catalytic efficiency of ruthenium complex 1 was evaluated for the transfer hydrogenation of various ketones to alcohols with excellent conversion up to 99% in the presence of i-PrOH/KOH at 82°C.

Comparative transfer hydrogenation performance of homogeneous and heterogeneous ruthenium (II) catalysts derived from a Schiff base ligand

A new Schiff base ligand (E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol (L1H) 1 was synthesized and grafted to solid support successfully. Mononuclear Ru(II) complex 2, its solid supported analogue 4 and heterogeneous complex 5 were synthesized with [RuCl2(p-cymene)]2 and RuCl2(PPh3)dppb.According to the UV–visible, IR and NMR data, the Ru (II) complexes are formed by the coordination of both nitrogen atoms of the ligand. Molecular structures of the L1H 1 was determined by single crystal X-ray diffraction study. The Ruthenium (II) complexes 2, 4 and 5 were used as catalysts for the transfer hydrogenation of various ketones in 2-propanol. Following the comparison of complexes 2, 4 and 5 between each other, it was observed that immobilized complexes have higher catalytic activity against the homogeneous structure. The results showed that the diphosphine incorporated complex 5 is more efficient than the other Ru (II) complexes.

ChemInform Abstract: Synthesis and Catalytic Evaluation of Ruthenium(II) Benzhydrazone Complex in Transfer Hydrogenation of Ketones.

AbstractThe new Ru‐catalyst shows excellent activity in the transfer hydrogenation of various ketones.

Enantioselective transfer hydrogenation of various ketones with novel efficient iridium(III) ferrocenyl-phosphinite catalysts

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.

Novel chiral multidentate P3N4-type ligand for asymmetric transfer hydrogenation of aromatic ketones

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.

A 2-(2’-pyridyl)quinoline ruthenium(II) complex as an active catalyst for the transfer hydrogenation of ketones

AbstractThe ruthenium(II) complex cis-[RuCl2(PPh3)2(L1)] (1) where L1 = 2-(2’-pyridyl)quinoline was obtained in high yield from the reaction of [RuCl2(PPh3)3] with L1. The new compound was characterized by different spectroscopic methods including FT-IR, UV-Vis, NMR (1H, 31P) spectroscopy along with a mass spectrometric analysis (ESI-MS) and conductivity measurements. 31P NMR spectroscopy provided evidence that the two PPh3 ligands are orientated trans to each other in an octahedral environment. Complex (1) was tested in the transfer hydrogenation of various ketones in 2-propanol at 82 oC. The catalytic activity of (1) displayed quantitative conversions for benzophenone and 4-chloroacetophenone.

Synthesis and structures of ruthenium-NHC complexes and their catalysis in hydrogen transfer reaction.

Ruthenium complexes [Ru(L1)2(CH3CN)2](PF6)2 (1), [RuL1(CH3CN)4](PF6)2 (2) and [RuL2(CH3CN)3](PF6)2 (3) (L1= 3-methyl-1-(pyrimidine-2-yl)imidazolylidene, L2 = 1,3-bis(pyridin-2-ylmethyl)benzimidazolylidene) were obtained through a transmetallation reaction of the corresponding nickel–NHC complexes with [Ru(p-cymene)2Cl2]2 in refluxing acetonitrile solution. The crystal structures of three complexes determined by X-ray analyses show that the central Ru(II) atoms are coordinated by pyrimidine- or pyridine-functionalized N-heterocyclic carbene and acetonitrile ligands displaying the typical octahedral geometry. The reaction of [RuL1(CH3CN)4](PF6)2 with triphenylphosphine and 1,10-phenanthroline resulted in the substitution of one and two coordinated acetonitrile ligands and afforded [RuL1(PPh3)(CH3CN)3](PF6)2 (4) and [RuL1(phen)(CH3CN)2](PF6)2 (5), respectively. The molecular structures of the complexes 4 and 5 were also studied by X-ray diffraction analysis. These ruthenium complexes have proven to be efficient catalysts for transfer hydrogenation of various ketones.

The first application of C2-symmetric ferrocenyl phosphinite ligands for rhodium-catalyzed asymmetric transfer hydrogenation of various ketones

Homogeneous catalysis has been responsible for many major recent developments in synthetic organic chemistry. The combined use of organometallic and coordination chemistry has produced a number of new and powerful synthetic methods for important classes of compounds in general and for optically active substances in particular. For this aim, a new class of chiral modular C2-symmetric ferrocenyl phosphinite ligands has been prepared in good yields by using the inexpensive 1,1′-ferrocenedicarboxyaldehyde and various ferrocene based-amino alcohols as starting materials, and applied in the rhodium(I)-catalyzed asymmetric transfer hydrogenation (ATH) of aromatic ketones to give corresponding secondary alcohols with excellent enantioselectivities and reactivities using isoPrOH as the hydrogen source (up to 99% conversion and 99%ee). The substituents on the backbone of the ligands are found to exhibit a remarkable effect on both the activity and % ee. The structures of these ligands and their complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis.

Asymmetric transfer hydrogenation of ketones catalyzed by thermoregulated ionic liquid-regulating ruthenium complexes

A sulfonated chiral diamine ligand anion-based functionalized ionic liquid has been synthesized. Then the new ionic liquid-regulating ruthenium complexes were prepared successfully and employed as efficient catalysts for the asymmetric transfer hydrogenation of various ketones. The catalysts were highly efficient for the hydrogenation of a wide range of substrates bearing different functional groups and could be separated easily from the reaction mixture by thermoregulated phase separation, which can be efficiently recycled five times without significant changes in catalytic activity and enantioselectivity.

A ruthenium(II) bipyridine complex containing a 4,5-diazafluorene moiety: Synthesis, characterization and its applications in transfer hydrogenation of ketones and dye sensitized solar cells

The ruthenium(II) complex [Ru(bpy)2L](PF6)2, where bpy is 2,2′-bipyridine and L is 1,5-dihydro-2-H-cyclopenta[1,2-b:5,4-b′]dipyridine-2-one, was synthesized from the reaction of cis-Ru(bpy)2Cl2·2H2O with L, and isolated as the hexafluorophosphate salt. The structure of L was unequivocally elucidated by single-crystal X-ray diffraction analysis. The new ruthenium(II) complex was thoroughly characterized by 1H and 13C NMR spectroscopy, along with FTIR, UV–Vis and LC MS/MS Triple Quadrupole Mass spectroscopy and elemental analysis. The catalytic activity of [Ru(bpy)2L](PF6)2 was tested in the transfer hydrogenation of various ketones in 2-propanol as both the solvent and hydrogen donor. The usage of [Ru(bpy)2L](PF6)2 for the formation of a dye sensitized solar cell is also presented.