Showing papers on "Transfer hydrogenation published in 1998"
TL;DR: In this article, it was shown that the formation of a metal-ligand bifunctional catalyst can greatly increase the substrate affinity to the catalyst active site and induce high enantioselectivity.
Abstract: Asymmetric catalytic transfer hydrogenation using 2-propanol as a hydrogen source offers an attractive route for reducing simple unfunctionalized ketones to chiral alcohols. 1 The reaction uses inexpensive reagents and is usually easy to perform. Notable among the recently developed efficient transition-metal-based chiral reduction catalysts 2 is the Ru(II)-TsDPEN (TsDPEN) N-(p-tolylsulfonyl)-1,2-diphenylethylenediamine) system reported by Noyori3 et al., who suggested that an NH moiety in the ligand may promote a cyclic transition state through hydrogen bonding to a ketone substrate. 1c It therefore appears that the formation of a metal -ligand bifunctional catalyst can greatly increase the substrate affinity to the catalyst active site and induce high enantioselectivity. Earlier results from Noyori and Lemaire with different ligands have also shown a similar “NH effect”. 4,5
166 citations
TL;DR: The rhodium and iridium (η5-C5Me5) MCl complexes were found to be catalyst precursors for asymmetric transfer hydrogenation of acetophenone, 2-acetonaphthone, 1-tetralone, and 1-indanone as discussed by the authors.
Abstract: The rhodium and iridium (η5-C5Me5)MCl complexes (3a: M = Rh; 3b: M = Ir) of (1S,2S)-N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine were found to be catalyst precursors for asymmetric transfer hydrogenation of acetophenone, 2-acetonaphthone, 1-tetralone, and 1-indanone to give (S)-1-phenylethanol (90% ee), (S)-1-(2-naphthyl)ethanol (85% ee), (S)-1-tetralol (97% ee), and (S)-indanol (99% ee), respectively
142 citations
TL;DR: (1S,3R,4R)-2-Azanorbornylmethanol, an Efficient Ligand for Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of Ketones is presented.
Abstract: (1S,3R,4R)-2-Azanorbornylmethanol, an Efficient Ligand for Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of Ketones
113 citations
TL;DR: In this article, the authors summarized recent reports on (i) hydrogenation (including transfer hydrogenation by HCO 2 Na) of olefins or aldehydes in water, and (ii) reduction of aromatic compounds with carbon monoxide and water by homogeneous transition metal catalysts.
Abstract: This paper summarizes recent reports on (i) hydrogenation (including transfer hydrogenation by HCO 2 Na) of olefins or aldehydes in water, and (ii) reduction of aromatic nitro compounds with carbon monoxide and water by homogeneous transition metal catalysts. The discussion will be focused on the hydrogenation of α , β -unsaturated aldehydes by ruthenium–sulfonated phosphine complexes that show remarkable chemoselectivity toward CO bonds. The author also introduces selective reduction of aromatic nitro-groups by ruthenium or rhodium catalysts under CO/H 2 O conditions. These catalytic reactions are very important from both synthetic and industrial viewpoints, not only because the after-treatment of by-products can be simplified from the conventional methods, but also because the reaction also proceeds with high selectivity affording the desired products.
101 citations
TL;DR: In this article, the half-sandwich hydride and 16-electron complexes of rhodium and iridium bearing an anion of (1S,2S)-N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine were synthesized.
Abstract: We prepared the half-sandwich hydride and 16-electron complexes of rhodium and iridium bearing an anion of (1S,2S)-N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine: for the iridium catalyst system, a 16-electron complex 2b and an 18-electron, hydride complex 3b were synthesized, while only a 16-electron complex 2a was detected for the rhodium catalyst.
75 citations
TL;DR: A polymer bound transfer hydrogenation catalyst has been developed based on Noyori's (1S,2S)- or (1R,2R)-N-(p-tolylsulfonyl)-1,2-diphenylethylenediamine as mentioned in this paper.
Abstract: A polymer bound transfer hydrogenation catalyst has been developed based on Noyori's (1S,2S)- or (1R,2R)-N-(p-tolylsulfonyl)-1,2-diphenylethylenediamine. The ruthenium catalysed reduction of acetophenone was examined and the activity of the catalyst was found to be dependent on the type of polymer used. The catalyst was found to be reusable and retained high ee's when HCO2H:Et3N was used as the hydrogen donor.
70 citations
TL;DR: In this paper, the new C 2 -symmetrical ferrocenyl diamines 5 − 7 and 13 proved to be good ligands for the ruthenium catalyzed enantioselective transfer hydrogenation of unsymmetric ketones.
Abstract: The new C 2 -symmetrical ferrocenyl diamines 5 – 7 and 13 proved to be good ligands for the ruthenium catalyzed enantioselective transfer hydrogenation of unsymmetrical ketones. The stereocontrolled and highly flexible synthetic route to the new diamines made it possible to vary the ligand structure in an efficient manner. A short trial and error process led to a very active catalytic system with diamine 6a as the ligand, which is capable of reducing ketones even at −30°C using 2-propanol as a hydrogen source. Enantioselectivities up to 90% were reached in the reduction of 1′-acetonaphthone.
68 citations
Patent•
20 Mar 1998
TL;DR: In this article, a catalytic transfer hydrogenation process is described, where the catalyst is a metal cyclopentadienyl complex which is coordinated to defined bidentate ligands.
Abstract: A catalytic transfer hydrogenation process is provided. The catalyst employed in the process is a metal cyclopentadienyl complex which is coordinated to defined bidentate ligands. Preferred metals include rhodium, ruthenium and iridium. Preferred bidentate ligands are diamines and aminoalcohols, particularly those comprising chiral centres. The hydrogen donor is advantageously a secondary alcohol or a mixture of triethylamine and formic acid. The process can be employed to transfer hydrogenate ketones and imines, which are preferably prochiral. Catalysts for use in such a process are also provided.
63 citations
TL;DR: The historical development of asymmetric hydrogenation of N-acyl dehydroamino acids and their derivatives is reported in this paper, where both homogeneous and heterogeneous catalysis are illustrated by selected examples.
Abstract: The historical development of asymmetric hydrogenation of N-acyl dehydroamino acids and their derivatives is reported. Both homogeneous and heterogeneous catalysis are illustrated by selected examples. Catalysis by water soluble complexes and transfer hydrogenation are also treated in this review. The mechanism of catalytic hydrogenation, its elementary steps and the origin of enantioselection are discussed.
46 citations
41 citations
TL;DR: Several chiral 3-substituted benzosultams, synthesized through an enantioselective Ru(II)-catalyzed transfer hydrogenation of corresponding sulfonylimines, are evaluated as chiral auxiliaries in the asymmetric azidation reaction of their N-acyl derivatives.
TL;DR: Heterogenized dialdimine ligands complexed to iridium were tested in the asymmetric transfer hydrogenation of acetophenone as discussed by the authors, achieving an Ee of up to 70% but the recycling was unsatisfactory.
Abstract: Heterogenized dialdimine ligands complexed to iridium were tested in the asymmetric transfer hydrogenation of acetophenone Ees of up to 70% were achieved but the recycling was unsatisfactory When such ligands were used in asymmetric epoxidation of styrene, a modest ee of 15% was achieved
TL;DR: In this article, the reductive cleavage of azobenzenes, including the reduction of oximes to their corresponding amines, has been achieved with Pd0 using ammonium formate as hydrogen source.
Abstract: The reductive cleavage of azobenzenes, including the reduction of oximes to their corresponding amines, has been achieved with Pd0 using ammonium formate as hydrogen source.
Abstract: Ruthenium complexes, prepared by mixing potassium salt of α-amino acids and [RuCl2(arene)]2, acted as catalysts for asymmetric transfer hydrogenation of ketones from 2-propanol in the presence of KOH, and enantiomeric excesses of the products reached 92%.
TL;DR: In this paper, the authors showed that β-ketoesters can be hydrogenated in the presence of catalytic combinations of [RuCl2(η6-arene)]2 and ephedrine or diamino type chiral ligands with activities up to 190 h−1 at 20°C and moderate to good enantiomeric excesses ranging from 36 to 94%.
Abstract: Chemoselective transfer hydrogenation of β-ketoesters to the corresponding alcohols is achieved in the presence of catalytic combinations of [RuCl2(η6-arene)]2 and ephedrine or diamino type chiral ligands with activities up to 190 h−1 at 20°C and moderate to good enantiomeric excesses ranging from 36 to 94%.
TL;DR: Ni[P(OPh)3]4 was found to catalyze the transfer hydrogenation of various organic functional groups using HCOONH4 in this article, which was considered a breakthrough.
TL;DR: In this article, differentially deuterium labelled formic acid is shown to deliver a pair of hydrogen atoms either from the formyl or the carboxy position, which suggests that palladium diformate is a key intermediate in heterogeneous transfer hydrogenation.
TL;DR: Platinum catalysts supported on gamma-alumina and on a variety of zeolites have been characterized and evaluated for activity in the transfer hydrogenation of propylene using butanes as the hydrogen source as discussed by the authors.
TL;DR: In this paper, a number of chiral 1,2 1,3 and 1,4-diphosphines have been investigated as ligands for the rhodium catalyzed hydrogen transfer from formic acid and its salts to acrylic substrates.
TL;DR: In this paper, 2,6-dimethoxy-(4a), 2, 6-bis(dimethylamino)-(4b), 2.6-dichloro-(4c) and 2.9, 10-dihydroanthracene (4d) were used as hydrogen transfer donors to α-methylstyrene (5) between 290-350 °C.
Abstract: 2,6-Dimethoxy-(4a), 2,6-bis(dimethylamino)-(4b), 2,6-dichloro- (4c) and 2,6-dimethoxycarbonyl-9,10-dihydroanthracene (4d) were prepared by conventional methods and used as hydrogen transfer donors to α-methylstyrene (5) between 290-350 °C. The mechanism followed second order kinetics and the rate constants were only slightly influenced by the solvent polarity and the type of substituents introduced. The activation parameters are also closely similar in the series with ΔS≠ values between −21 and −28 cal/mol K. These results, together with the observation of a large isotope effect (kH/kD = 1.4–2.0 at 310–350 °C), suggest that the mechanism involves a primary kinetic H-atom-transfer from the donors to α-methylstyrene (5) in the rate determining step. The compounds 4a–4d constitute a new probe for investigating polar effects on H-transfer reactions.
TL;DR: The effect of APO/Ru ratio indicates the homogeneous nature of the catalytic process, proved by the absence of the inhibiting effect of added mercury (Hg) as mentioned in this paper.
Abstract: Catalytic hydrogen transfer in the acetophenone/propan-2-ol system by complexes formedin situ of RuCl3 and the ligands ofo-phenylene diamine (PDA);o-aminophenol (APO);o-aminobenzoic acid (ABA); 2,2′-dipyridyl (BIPY), has been studied The effect of APO/Ru ratio indicates the homogeneous nature of the catalytic process, proved by the absence of the inhibiting effect of added mercury (Hg) The experimental results show that RuCl3/APO exhibits fairly high catalytic activity even if under the air
TL;DR: In this article, the ruthenium complex was shown to be an asymmetric catalyst for transfer hydrogenation reactions in high chemical yield and modest enantioselectivity, and the relationship between the structure and catalytic reactivity was discussed.
TL;DR: In this article, a series of new hydridocarbonyl osmium(Ⅱ) complexes, OsHCl(CO)(PPh3),L-L, Ph2P(CH2)nPPh2 (n=1 (1), 2 (2), 3 (3), cis-Ph2PCH=CHPPh 2 (4), and Fe(η5-C5H4pPh2)2 (5)] has been synthesized from OsHCL(CO) and chelating diphosphines.
Abstract: A series of new hydridocarbonyl osmium(Ⅱ) complexes, OsHCl(CO)(PPh3)(L-L)[L-L=Ph2P(CH2)nPPh2 (n=1 (1), 2 (2), 3 (3), cis-Ph2PCH=CHPPh2 (4), and Fe(η5-C5H4PPh2)2 (5)] has been synthesized from OsHCl(CO)(PPh3)3 and chelating diphosphines These complexes have been characterized by IR, 1H NMR and elemental analysis The catalytic activities of these complexes both for the transfer hydrogenation of trans-cinnamaldehyde with 2-propanol as the hydrogen donor, and for the selective hydrogenation of trans-cinnamaldehyde with H2, have been examined Complexes (1)-(5) were shown to have higher selectivities for the transfer hydrogenation of the C=O bond of aldehyde than for the transfer hydrogenation of the C=C bond of aldehyde The selectivities for the transfer hydrogenation with 2-propanol as well as for the hydrogenation with H2 have been found to decrease in the order 3 > 5 > 2 > 4 > 1 Complex (3) has shown to possess almost 90% of the selectivity to cinnamyl alcohol for transfer hydrogenation It is also found that there is a correlation between the ν(CO) of each complex and the hydrogenation, of the C=O bond of trans-cinnamaldehyde Overall, the selectivities with the complexes (1)-(5) are greater for the transfer hydrogenation with 2-propanol than for the hydrogenation with H2
TL;DR: In this paper, the influence of hydrogen on the yield of phenanthrene reactions was discussed with respect to the mechanism of hydrogen transfer, and it was shown that hydrogen can influence the hydrogen transfer mechanism.
Abstract: Transfer hydrogenation of phenanthrene was performed in the presence of superbases or strong acids and gaseous hydrogen. The influence of hydrogen on the yield of these reactions was discussed with respect to the mechanism of hydrogen transfer.
TL;DR: Chiral transfer hydrogenation of 16 methyl-substituted steroid 17-ketones in the presence of rhodium(I) complexes by hydrosilylation is described in this article.
Abstract: Chiral transfer hydrogenation of 16 methyl-substituted steroid 17-ketones in the presence of rhodium(I) complexes by hydrosilylation is described. During the preparation of the complex catalysts a wide variety of bidentate phosphines were used including chiral ligands, as well. The diastereoselectivity of the reduction depends strongly on the structure of the ligands. The method applied produces the hydroxy steroid products with excellent yield under very mild reaction conditions. Additionally, the procedure makes possible the preparation of 17α-OH isomers beside the easily synthesizable 17β-OH products.
TL;DR: (1S,3R,4R)-2-Azanorbornylmethanol, an Efficient Ligand for Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of Ketones.
Abstract: (1S,3R,4R)-2-Azanorbornylmethanol, an Efficient Ligand for Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of Ketones
TL;DR: In this paper, the metal complex structures formed on the carrier surface were examined by IR and electronic spectroscopy, and the preparation procedure (solvent, time of the complex deposition, size of chitosan corpuscles) strongly influenced the activity of the prepared catalysts.
Abstract: Novel catalysts of reduction reactions were prepared by immobilization of binuclear Rh(II) and Ru(II, III) teraaacetate complexes with metal-metal bond on original chitosan and succinamide chitosan derivative. Obtained metal complex systems catalyzed transfer hydrogenation of carbonyl group of cyclohexanone and acetophenone in the liquid phase under mild conditions (82.4 °C, Ar). 2-Propanol was a hydrogen donor and reaction promoted by KOH in 2-propanol solution. The preparation procedure (solvent, time of the complex deposition, size of chitosan corpuscles) strongly influenced the activity of the prepared catalysts. The metal complex structures formed on the carrier surface were examined by IR- and electronic spectroscopy.