Enantioselective Transfer Hydrogenation Of Acetophenone Research Articles

Cat‐in‐a‐Cup: Facile Separation of Large Homogeneous Catalysts

A cat with nine lives: Catalyst separation and recycling is the bane of homogeneous catalysis. This problem is addressed by a two-layered ceramic membrane cylinder that allows the diffusion of reactants and products in and out, but keeps the catalyst trapped. The concept is demonstrated for the enantioselective transfer hydrogenation of acetophenone to (S)-phenylethyl alcohol with large molecular catalysts anchored on Frechet-type dendrimers.

Homogeneous [lbond2]C [dbnd]O hydrogenation and transfer hydrogenation catalyzed by ruthenium(II) complexes containing optically active Ph 2PCH(Ph)CH(Me)NH 2 and 1,2-C 5H 8(PPh 2) 2 ligands

Combination of (1 S,2 S)-cyclopentanediylbis(diphenylphosphine) with [Ru(η 4-C 8H 12){η 3-(CH 2) 2CMe} 2] afforded the chelate complex [Ru{η 3-(CH 2) 2CMe} 2{(1 S,2 S)-C 5H 8(PPh 2) 2}] ( 1), which gave ( OC-6-13)-[RuCl 2{(1 S,2 S)-C 5H 8(PPh 2) 2}{(1 S,2 S)-Ph 2PCH(Ph)CH(Me)NH 2}] ( 2) upon reaction with methanolic HCl in acetone, followed by the addition of the β-aminophosphine in DMF. The ( P ∩ N) 2-chelated complexes ( OC-6-13)-[RuCl 2{(1 S,2 S)-Ph 2PCH(Ph)CH(Me)NH 2} 2] ( 3) and ( OC-6-13)-[RuCl 2{(1 R,2 S)-Ph 2PCH(Ph)CH(Me)NH 2} 2] ( 4) resulted from RuCl 3 · 3H 2O and the P, N ligands under reducing conditions. The crystal structures of 3 and 4 were determined by single-crystal X-ray diffraction. Following activation by KOBu- t in isopropanol, compounds 2– 4 catalyzed the enantioselective transfer hydrogenation of acetophenone with i-PrOH as the hydrogen source as well as the direct hydrogenation of the ketone by H 2 in low to moderate e.e. (up to 67%).

Water‐Soluble Arene Ruthenium Complexes Containing a trans‐1,2‐Diaminocyclohexane Ligand as Enantioselective Transfer Hydrogenation Catalysts in Aqueous Solution (Eur. J. Inorg. Chem. 22/2005)

AbstractThe cover picture shows the postulated catalytic cycle for the pH‐dependent, enantioselective transfer hydrogenation of acetophenone to give phenylethanol in water, using formate as hydrogen donor and (arene)ruthenium(trans‐diaminocyclohexane) as chiral catalyst. This work illustrates the increasing interest for water‐soluble enantioselective catalysts operating in aqueous solution. Details are discussed in the article by G. Süss‐Fink et al. on p. 4493 ff.

Ruthenium–benzocrownether complexes: Synthesis, structures, catalysis and immobilisation in ionic liquids

A facile pathway to [RuCl 2(η 6-benzocrownether)] 2 complexes is described and crystal structures of the complexes [RuCl 2(η 6-benzo-15-crown-5)] 2 and [RuCl 2(η 6-dibenzo-18-crown-6)] 2 are reported. The complexes were derivatised with (1 S,2 R)-2-amino-1,2-diphenylethanol and evaluated in the enantioselective transfer-hydrogenation of acetophenone. The effect of complexation of different alkaline metals (Na, K, Cs) within the crown on the selectivity and reaction rate was studied. Interaction of a sulfonated phosphine ligand with the crown was probed by NOESY-NMR and utilisation of the crownether to serve as an anchor for catalyst immobilisation was investigated.

Enantioselective Catalysis;150:Chiral-at-Metal (η6-p-Cymene)Ruthe­nium(II) Complexesof Binaphthyl Ligands - Synthesis, Characterization, andEnantioselective Catalysis

Neutral and cationic half-sandwich (η 6 -p-cymene)ruthe-nium complexes 9-12 with chiral Schiff base ligands derived from binaphthylamino derivatives and salicylaldehyde, diphenyl(2-formylphenyl)phosphane, and 2-pyridinealdehyde form two diastereomers which only differ in the metal configuration. From the diastereomeric mixtures of compounds 10 and 12 the major diastereomers crystallize, whereas for compound 9 both diastereomers co-crystallize in a 1:1 ratio in the same single crystal. In compounds 13 and 14 containing the reduced Schiff base ligands, the nitrogen atom of the secondary amine functionality becomes another chiral center. In solution at room temperature the various diastereomers interconvert rapidly. The new compounds were used as catalysts in the enantioselective transfer hydrogenation of acetophenone with 2-propanol and in the Diels-Alder reaction of cyclopentadiene with methacrolein.

ChemInform Abstract: Enantioselective Catalysis. Part 141. Tridentate Ligands with 1‐(Pyridin‐2‐yl)ethylamine as Chiral Building Block in the Enantioselective Transfer Hydrogenation of Acetophenone.

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Enantioselective Catalysis CXLI [1]. Tridentate Ligands with 1-(Pyridin-2-yl)ethylamine as Chiral Building Block in the Enantioselective Transfer Hydrogenation of Acetophenone

A series of novel tridentate ligands with nitrogen and oxygen donor sites was synthesized starting from enantiomerically pure (S)- and (R)-1-(pyridin-2-yl)ethylamine, the preparation and resolution of which was developed. The new optically active ligands were tested as in situ catalysts together with Ru(PPh3)3Cl2 in the enantioselective transfer hydrogenation of acetophenone with isopropanol. The secondary amine ligand (S)-2,4-di-tert-butyl-6-(1-(pyridin-2-yl)ethylamino)methylphenol gave the best results with almost quantitative conversion and 47%ee.

Enantioselective catalysis. Part 143: Astonishingly high enantioselectivity in the transfer hydrogenation of acetophenone with 2-propanol using Ru complexes of the Schiff base derived from ( S)-2-amino-2′-hydroxy-1,1′-binaphthyl (NOBIN) and 2-pyridinecarbaldehyde

A series of bidentate and tridentate ( S)-NOBIN derivatives was synthesised and tested as chiral ligands in the Ru-catalysed enantioselective transfer hydrogenation of acetophenone with 2-propanol. Despite the similarities in chemical structure, only the imine derived from ( S)-NOBIN and 2-pyridinecarbaldehyde and the corresponding amine (obtained by NaBH 4 reduction of the imine) afforded ( S)-1-phenylethanol in nearly quantitative yields and outstanding enantioselectivities of up to 97% e.e.

Cationic rhodium complexes with chiral tetradentate ligands as catalysts for enantioselective reduction of simple ketones

The interaction of [Rh(COD)Cl] 2 with two equivalents of ( S)-N,N′-bis[ o-(diphenylphosphino)benzylidene]propane-1,2-diamine [( S)- 1] or ( S)-N,N′-bis[ o-(diphenylphosphino)benzyl]propane-1,2-diamine [( S)- 2] in benzene/methanol mixture and then precipitation by the addition of a solution of NH 4PF 6 in water afforded cationic rhodium(I) complexes [Rh( S)-MeP 2N 2][PF 6] and [Rh( S)-MeP 2(NH) 2][PF 6] in good yield, respectively. Complexes [Rh( R, R)-C 6P 2N 2][PF 6] and [Rh( R, R)-C 6P 2(NH) 2][PF 6] were also prepared by an analogous manner. All these rhodium complexes have been characterized by analytical and spectroscopic methods and their asymmetric catalytic properties for enantioselective transfer hydrogenation of acetophenone have been tested. [Rh( R, R)-C 6P 2(NH) 2][PF 6] was used as an excellent catalyst precursor for enantioselective transfer reduction of acetophenone in 2-propanol, leading to 2-phenylathanol in 97% yield and in 91% ee after 7 h at 83°C.

Probing subtle ligand effects in the enantioselective transfer hydrogenation of ketones

The rational modification of an established amino-alcohol scaffold has revealed new, highly effective ligands for the enantioselective transfer hydrogenation of acetophenone that affords the product in up to 95% ee.

ChemInform Abstract: Optically Active Phenanthrolines in Asymmetric Catalysis. Part 3. Highly Efficient Enantioselective Transfer Hydrogenation of Acetophenone by Chiral Rhodium/3‐Alkylphenanthroline Catalysts.

AbstractThe title phenanthrolines, e.g. (III) and (VI), are applied to the rhodium‐catalyzed transfer hydrogenation of the ketone (VII).

ChemInform Abstract: Optically Active Phenanthrolines in Asymmetric Catalysis. Part 2. Enantioselective Transfer Hydrogenation of Acetophenone by Rhodium/Alkylphenanthroline Catalysts.

AbstractSome phenanthroline derivatives bearing chiral alkyl substituents are prepared as shown in the reaction scheme.

Optically active phenanthrolines in asymmetric catalysis. III. Highly efficient enantioselective transfer hydrogenation of acetophenone by chiral rhodium/3-alkyl phenanthroline catalysts.

The in situ catalysts prepared from [Rh(Diol)Cl] 2 (Diol = 1,5-Hexadiene or 1,5-Cyclooctadiene) and 3-alkylphenanthrolines display an extremely high catalytic activity in the transfer hydrogenation of acetophenone. Turn over rates up to 10,000 cycles-per-hour (c/h) have been recorded in 2-propanol solution at 83°C in the presence of KOH as a promoter. Asymmetric inductions up to 655 e.e. are obtained with the ligand 3c bearing a chiral trimethylpropyl substituent. This is an extraordinarily high value in view of the long distance existing between the chiral carbon atom and the reactive site of the catalyst. Experimental evidences suggest that in the asymmetric process the most active and stereoselective catalytic species might be a rhodium hydride complex containing two phenanthroline ligands in a chiral C 2 array.

Optically active phenanthrolines in asymmetric catalysis: II. Enantioselective transfer hydrogenation of acetophenone by rhodium/alkyl phenanthroline catalysts

Three new alkyl phenanthrolines containing a norpinanyl substituent as the common chiral target, have been synthesized and tested as ligands in the rhodium-catalyzed asymmetric transfer hydrogenation of acetophenone. A marked catalytic activity was observed, but the highest optical yield was 24% e.e.