Manganese catalyzed asymmetric transfer hydrogenation of ketones

The asymmetric transfer hydrogenation (ATH) of a wide range of ketones catalyzed by manganese complex as well as chiral P_xN_y-type ligand under mild conditions was investigated. Using 2-propanol as hydrogen source, various ketones could be enantioselectively hydrogenated by combining cheap, readily available [MnBr(CO)₅] with chiral, 22-membered macrocyclic ligand (R,R,R',R')-CyP₂N₄ (L5) with 2 mol% of catalyst loading, affording highly valuable chiral alcohols with up to 95% ee.     

Asymmetric transfer hydrogenation of aromatic ketones catalyzed by the iridium hydride complex under ambient conditions

The chiral Ir catalytic system generated in situ from iridium hydride complex and chiral diaminodiphosphine ligand was employed in asymmetric transfer hydrogenation of aromatic ketones to give the corresponding optically active alcohols, with up to 99% ee in high yield were obtained even when the substrate-to-catalyst molar ratio reached 10000:1.     

Synthesis of novel chiral tetraaza ligands and their application in enantioselective transfer hydrogenation of ketones

Novel chiral tetraaza ligands(R)-N,N′-bis[2-(piperidin-1-yl)benzylidene]propane-l,2-diamine 6 and(S)-N-[2-(piperidin-l- yl)benzylidene]-3-{[2-(piperidin-1-yl)benzylidene]amino}-alanine sodium salt 7 have been synthesized and fully characterized by NMR,IR,MS and CD spectra.The catalytic property of the ligands was investigated in Ir-catalyzed enantioselective transfer hydrogenation of ketones.The corresponding optical active alcohols were obtained with high yields and moderate ees under mild reaction conditions.     

Highly efficient chiral PNNP ligand for asymmetric transfer hydrogenation of aromatic ketones in water

Chiral PNNP ligand II and [IrHCl₂(COD)]₂ were applied for the first time in the asymmetric transfer hydrogenation of aromatic ketones with HCOONa in water, giving the corresponding optical alcohols in high yield and excellent enantioselectivity (up to 99% ee). Particularly, the reduction of propiophenone proceeded smoothly at a substrate to catalyst molar ratio of 8000, without compromising the ee values obtained.     

Enantioselective transfer hydrogenation of ketones with planar chiral ruthenocene-based phosphinooxazoline ligands

1,2-Disubstituted planar chiral ruthenocene-based phosphinooxazoline ligands (Rc-PHOX, 3 and 4) were synthesized easily and applied in the transfer hydrogenation of ketones to chiral alcohols using 2-propanol as a source of hydrogen with excellent enantioselectivity and high catalytic activity.     

Synthesis of novel chiral N, P-containing multidentate ligands and their applications in asymmetric transfer hydrogenation

Novel chiral PN₄-type multidentate aminophosphine ligands have been successfully synthesized by Schiff-base condensation of bis（o-formylphenyl）phenylphosphane and various chiral amino-sulfonamides.Their structures were fully characterized by IR,EI-MS and NMR.The catalytic systems,prepared in situ from the multidentate ligands and iridium（I） complexes,showed high activity in asymmetric transfer hydrogenation of propiophenone in 2-propanol solution,leading to corresponding optical alcohol with up to 75%ee.     

Water-soluble chiral monosulfonamide-cyclohexane-1,2-diamine-RhCp complex and its application in the asymmetric transfer hydrogenation (ATH) of ketones

Monosulfonamide ligands with heteroatom/heterocyclic systems were derived from trans-(1R,2R)-cyclohexane-1,2-diamine and complexed with [Ru(benzene)Cl₂]₂, [Cp^∗RhCl₂]₂ in situ and used in the ATH of aromatic ketones with aqueous sodium formate as the hydrogen source. The chiral secondary alcohols were obtained with >93% enantioselectivity and >89% yield. Reduction in water was faster than in isopropanol/KOH. Addition of surfactants showed little or no effects.     

Asymmetric hydrogenation of imines catalyzed by iridium complexes with phosphine-phosphite ligands: importance of backbone flexibility

Chiral phosphine-phosphites provide an alternative class of ligands for the iridium catalyzed enantioselective hydrogenation of imines. Optimization of ligand structure has afforded enantioselectivities up to 84% ee in the reduction of N-aryl imines. A significant influence of backbone nature on enantioselectivity has also been observed.     

Highly efficient catalysts derived from planar chiral ferrocenes for asymmetric transfer hydrogenation of ketones

Planar chiral ferrocenes 1 and its diastereoisomer 2 were found to be good lig-ands for the ruthenium catalyzed asymmetric transfer hydrogenation of ketones with i-PrOH as hydrogen source under refluxing in the presence of sodium hydroxide. The results showed that the absolute configuration of alcohol seemed to be governed by the central chirality in the oxazoline ring instead of the planar chirality. At a ratio of 1:2 for Ru:ligand, 3000:1 S/C and >100,000/h-1 TOF were observed for acetophenone. For propiophenone 99% yield and 85% e.e. were obtained     

Cobalt-catalyzed asymmetric hydrogenation of ketones: A remarkable additive effect on enantioselectivity

A chiral cobalt pincer complex, when combined with an achiral electron-rich mono-phosphine ligand, catalyzes efficient asymmetric hydrogenation of a wide range of aryl ketones, affording chiral alcohols with high yields and moderate to excellent enantioselectivities (29 examples, up to 93% ee). Notably, the achiral mono-phosphine ligand shows a remarkable effect on the enantioselectivity of the reaction.     

Transfer hydrogenation of ketones catalyzed by nickel complexes bearing an NHC [CNN] pincer ligand

Four NHC [CNN] pincer nickel (II) complexes, [^iPrCNN (CH₂)₄‐Ni‐Br] ( 5a ), [^nBuCNN (CH₂)₄‐Ni‐Br] ( 5b ), [^iPrCNN (Me)₂‐Ni‐Br] ( 6a ) and [^nBuCNN (Me)₂‐Ni‐Br] ( 6b ), bearing unsymmetrical [C (carbene)N (amino)N (amine)] ligands were synthesized by the reactions of [CNN] pincer ligand precursors 4 with Ni (DME)Cl₂ in the presence of Et₃N. Complexes 5a and 5b are new and were completely characterized. The transfer hydrogenation of ketones catalyzed by the four pincer nickel complexes were explored. Complexes 5a and 6a have better catalytic activity than 5b and 6b . With a combination of NaO^tBu/ⁱPrOH/80 °C and 2% catalyst loading of 5a , 77–98% yields of aromatic alcohols could be obtained.     

Binuclear ruthenium(II) pyridazine complex catalyzed transfer hydrogenation of ketones

A convenient and general method of synthesis of binuclear ruthenium(II) pyridazine complex was reported. The synthesized complex was characterized by analytical and spectral methods. The structure of the complex was confirmed by X-ray diffraction technique and was found to be an efficient catalyst for the transfer hydrogenation of ketones with excellent conversions in the presence of isopropanol/KOH at 82 °C. The effect of solvents, bases, and different catalyst/substrate ratio for the reaction was also investigated.     

Recent topics in catalytic asymmetric hydrogenation of ketones

Asymmetric hydrogenation of ketones (AHK) was revolutionized in 1987 and again in 1995 when Ru(CH₃COO)₂(binap)/HCl and RuCl₂(binap)/diamine, respectively, were developed. Since then, the number of reports on Ru-catalyzed AHK has increased exponentially, and the utility of other precious metals (Os, Rh, Ir, and Pd) has also been shown. The utilization of inexpensive base metals (Fe, Co, Ni, and Cu) has been a recent trend. This digest summarizes the key advances in AHK in the past decade by categorizing the chiral ligands into six types: (i) diphosphines, (ii) diphosphines/diamines, (iii) tridentate or tetradentate phosphine amines, (iv) diamines, (v) tetradentate amines, and (vi) tetradentate thioether amines.     

Asymmetric hydrogenations of ketones catalyzed by Ru–achiral phosphine-enantiopure diamine complexes

Five novel ruthenium complexes, RuCl₂(MOTPP)₂[(S,S)-DPEN] [MOTPP = tris(4-methoxyphenyl)phosphine] (1), RuCl₂(TFTPP)₂[(S,S)-DPEN] [TFTPP = tris(4-trifluoromethylphenyl)phosphine] (2), RuCl₂(PPh₃)₂[(S,S)-DPEN] (3), RuCl₂(BDPX)[(S,S)-DPEN] [BDPX = 1,2-bis(diphenylphosphinomethyl)benzene] (4), RuCl₂(BISBI)[(S,S)-DPEN][BISBI = 2,2′-bis((diphenylphosphino)methyl)-1,1′-biphenyl]] (5) were synthesized and used for the hydrogenation of aromatic ketones. The complexes showed high catalytic activities, especially that the catalytic activity of complex 5 containing the diphosphine with large bite angle and complex 1 containing triarylphosphine with electron-donating group were higher than the other three complexes. The enantioselectivities of products were almost not influenced by the electron factors of phosphine.     

Efficient asymmetric transfer hydrogenation of activated olefins catalyzed by ruthenium amido complexes

The asymmetric transfer hydrogenation of activated olefins with chiral ruthenium amido complexes (Noyori catalyst) using formic acid-triethylamine azeotrope as hydrogen source resulted in excellent yields and high enantioselectivities (up to 88.5%).     

钌(II)-吡啶基NNN配合物催化酮的室温(不对称)氢转移反应

合成了一种基于吡啶骨架含有苯并咪唑和手性咪唑啉基团的三齿NNN配体及其二价钌(II)配合物,通过核磁共振波谱学和X射线单晶晶体结构测定确认了钌(II)配合物的分子结构.这些配合物在室温下催化酮的氢转移反应,表现出了优异的催化活性,收率和ee值最高分别可达99%和97%.     

Alkoxy substituted MeO-BIPHEP-type diphosphines ligands for asymmetric hydrogenation of aryl ketones

<正>In this paper,a series of optically active MeO-BIPHEP-type ligands,(S)-6,6′-dimethoxy-2,2'-bis(di-p-alkoxyphenylphosphine)- 1,1′-biphenyl were synthesized and used to prepare the ruthenium complex.The effects of para-substituted were observed,the results showed that the ruthenium catalysts[diphosphine RuCl_2 diamine]containing both t-Bu and i-Pr substitutions have better activities and enantioselectivities than the non-substituted ruthenium catalysts in the asymmetric hydrogenation of acetophenone.     

Asymmetric transfer hydrogenation of ketones catalyzed by ruthenium(II) complexes bearing a chiral phosphinoferrocenyloxazoline ligand

The catalytic activity in asymmetric transfer hydrogenation of ketones using octahedral and half-sandwich (η⁵-indenyl and η⁶-arene) ruthenium(II) complexes containing the chiral ligand (4S)-2-[(S_p)-2-(diphenylphosphino)ferrocenyl]-4-(isopropyl)oxazoline (FcPN) has been explored. Catalytic studies with complex fac-[RuCl₂{η²(P,N)-FcPN}(PMe₃)₂] (1) show excellent TOF values (9600 h⁻¹). Experiments in the presence of free FcPN, which lead to an increase in conversion rates and ee values when the catalyst is complex [Ru(η⁵-C₉H₇){κ²(P,N)-FcPN}(PPh₃)][PF₆] (4) have been carried out. The characterization of the new complexes mer-trans-[RuCl₂{P(OMe)₃}₂{κ²(P,N)-FcPN}] and of the water-soluble complexes fac- and mer-trans-[RuCl₂(PTA)₂{κ²(P,N)-FcPN}] is also reported.     

Iridium complex bearing a chiral hydroxy-amide functionalized N-heterocyclic carbene: a catalyst precursor for asymmetric transfer hydrogenation

A new monodentate iridium(III) complex bearing a readily accessible and tunable chiral hydroxy-amide functionalized N-heterocyclic carbene ligand, Cp^∗Ir(NHC)Cl₂, has been synthesized and characterized by crystallographic methods. The monodentate Cp^∗Ir(NHC)Cl₂ complex was found to act as a catalyst precursor for the stereoselective transfer hydrogenation of acetophenone in the presence of KOH even at room temperature. Moderate enantioselectivity was observed in the initial screening of the chiral ligands.