Immobilization of chiral Rh catalyst on glass and application to asymmetric transfer hydrogenation of aryl ketones in aqueous media

A chiral catalyst, Cp＊RhTsDPEN （Cp＊ = pentamethyl cyclopentadiene, TsDPEN = substitutive phenylsulfonyl-l,2-diphenylethylenediamine）, was synthesized and immobilized at the surface of glass. The immobilized catalyst exhibited good catalytic efficiency for asymmetric transfer hydrogenation of aromatic ketones in water with HCOONa as hydrogen source.     

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.     

Design of novel polymer-supported chiral catalyst for asymmetric transfer hydrogenation in water

New polymer-supported chiral sulfonamides containing sulfonated pendant group have been synthesized. Chiral catalyst prepared from the new polymer-support is more effective for asymmetric transfer hydrogenation of aromatic ketones in water compared to that prepared from conventional polystyrene-support. Polymer-supported catalysts containing quaternary ammonium salt as a pendant increased not only the reactivity but also the enantioselectivity in asymmetric transfer hydrogenation in water. Moreover, this type of polymer can be reused without loss of the catalytic activity.     

A chiral [(dipyridylphosphine)RuCl2(1,3-diphenylpropanediamine)] catalyst for the hydrogenation of aromatic ketones

The use of chiral 1,3-diphenylpropanediamine in combination with Ru-Xyl-P-Phos, gave up to 95% ee in the hydrogenation of acetophenone.     

Transfer hydrogenation of activated ketones using novel chiral Ru(II)-N-arenesulfonyl-1,2-diphenylethylenediamine complexes

A series of α-keto esters and α,α,α-trifluoromethyl ketones were reduced in high yields and excellent enantioselectivities under Ru-catalysed transfer hydrogenation using novel chiral N-arenesulfonyl-1,2-diphenylethylenediamine ligands.     

Heterogeneous asymmetric reactions, 33. Novel interpretation of the enantioselective hydrogenation of a-ketoesters on Pt/alumina-cinchona alkaloid catalyst system

The enantioselective hydrogenation of ethyl pyruvate (EtPy) was studied in toluene and in acetic acid, under identical reaction conditions (H₂pressure 1 bar, Pt-alumina catalyst E 4759, dihydrocinchonidine (DHCD) concentration 0.001- 0.1 mmol/L). The DHCD concentration necessary for achieving maximal enantioselectivity (i.e. 80% ee in toluene and 90% ee in acetic acid) is higher by one order of magnitude in toluene than in acetic acid. This relatively high difference suggests a difference in reaction mechanism. This study calls attention to the formation of new chiral surface sites via chemisorption of DHCD on platinum atoms and the possible role of such sites in enantioselection.     

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.     

Asymmetric hydrogenation of aromatic ketones with MeO-PEG-supported BIPHEP/DPEN ruthenium catalysts

A soluble polymer (MeO-PEG) supported biphenylbisphosphine (BIPHEP)-Ru/chiral diamine (1,2-diphenylethylenediamine) complex, in which the polymer is attached to the two phenyl rings of BIPHEP ligand, has been prepared, and shown to be highly active with good enantioselectivity for the catalyzed asymmetric hydrogenation of unfunctionalized aromatic ketones. The derived chiral ruthenium complex 5 proved to be stable in air allowing facile catalyst recycling. Especially for 4′-tert-butyl-acetophenone and 1-acetonaphthone, excellent ee values up to 96.5% and 95.9% have been obtained which are comparable to or even higher than the enantioselectivity achieved with 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl-Ru-DPEN catalyst under similar conditions.     

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     

Palladium-catalyzed asymmetric hydrogenation of simple ketones activated by Brønsted acids

Homogeneous Pd(OCOCF₃)₂/(R)-C₄-TunePhos has been successfully applied in the asymmetric hydrogenation of simple ketones activated by catalytic amount of Brønsted acid with up to 88% ee.     

Ir-catalyzed asymmetric hydrogenation of simple ketones with chiral ferrocenyl P,N,N-ligands

The Ir-catalyzed asymmetric hydrogenation of simple aromatic ketones with chiral ferrocenyl P,N,N-ligands has been developed. Under the optimized conditions, a wide range of ketones were hydrogenated to afford the corresponding chiral alcohols in good to excellent enantioselectivities (up to 98%?ee).     

XPS study of the surface composition of modified nickel-cobalt powder catalysts for enantioselective ethyl acetoacetate hydrogenation

The surface cobalt concentration in the powder bimetallic Ni-Co catalysts (ratio Co/Ni ≈ 0.25) was shown by X-ray photoelectron spectroscopy to be 2–4 times that of the volume content. Both Ni and Co exist in mixed valent states, viz., M⁰ and M²⁺, even after catalyst reduction. After ethyl acetoacetate hydrogenation, the cobalt content on the surface increases 16 times compared to that in the bulk. In addition, the metals are partially oxidized, and the amount of Ni⁰ and Co⁰ in the surface layers of the catalyst decreases 2–3 times. It was assumed that the increase in the cobalt content indicates an increase in the amount of cobalt complexes that involve the modifier, substrate, and reaction product, and which shield the nickel active sites. As a result, the enantioface differentiating ability of the catalyst decreases. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2265–2268, November, 2007.     

Practical enantioselective reduction of ketones using oxazaborolidine catalyst generated in situ from chiral lactam alcohol and borane

Reduction intermediate prepared in situ from chiral lactam alcohol 3 and borane at room temperature was found to catalyze the borane reduction of various prochiral ketones with high enantioselectivity up to 98% ee.     

Further ‘tethered’ Ru(II) catalysts for asymmetric transfer hydrogenation (ATH) of ketones; the use of a benzylic linker and a cyclohexyldiamine ligand

The synthesis and characterisation of two new Ru(II) catalysts for the asymmetric transfer hydrogenation (ATH) of ketones is described. In the case of 4, the novelty lies in the use of a benzyl tethering group between the asymmetric ligand part (TsDPEN) and the η⁶-arene ring, which increases the complex rigidity. For 5, the use of a cyclohexyldiamine as a chiral ligand is described for the first time. In the ATH of ketones in formic acid/triethylamine, alcohols with ees of up to 97% were formed.     

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.     

Iron phthalocyanine as new efficient catalyst for catalytic transfer hydrogenation of simple aldehydes and ketones

Catalytic transfer hydrogenation (CTH) of various aldehydes and ketones was studied using iron phthalocyanine catalyst, in order to substitute the typically used rare transition metals (Ir, Rh, Ru) with an easily available and less expensive metal. Iron phthalocyanine was found to be an efficient hydrogenation catalyst and its immobilized version was successfully prepared. The immobilized iron phthalocyanine was also active in the CTH reaction of various carbonyl compounds, and it was easy to handle and possible to recycle. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

Synthesis and application of chiral N, N'-dialkylated cyclohexanedi- amine for asymmetric hydrogenation of aryl ketones

Chiral N, N'-dialkylated cyclohexanediamine derived ligands have been synthesized and used in the asymmetric hydrogenation of aryl ketones. Optically active alcohols with up to 90% enantiomeric excess were obtained in high yields.     

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.