Showing papers on "Transfer hydrogenation published in 2005"
549 citations
TL;DR: The first enantioselective Brønsted acid catalyzed reduction of imines has been developed and this new organocatalytic transfer hydrogenation of ketimines with Hantzsch dihydropyridine as the hydrogen source offers a mild method to various chiral amines with high enantiOSElectivity.
428 citations
288 citations
TL;DR: Catalyst 3 is a significantly more active catalyst for this application than the untethered derivative, exhibits higher enantioselectivities across a range of substrates, and appears to be highly stable to the reaction conditions.
Abstract: Ruthenium dimer 6 (readily available in two steps from TsDPEN) is converted directly to monomeric asymmetric transfer hydrogenation catalyst 3 in situ under the conditions employed for ketone reduction. Catalyst 3 is a significantly more active catalyst for this application than the untethered derivative, exhibits higher enantioselectivities across a range of substrates, and appears to be highly stable to the reaction conditions. It is active at loadings of as low as 0.01 mol %, and reductions at the 0.1 mol % level are complete within 20 min at 80 °C without significant loss of enantioselectivity.
250 citations
TL;DR: Water is an ideal solvent for chemical reactions and asymmetric transfer hydrogenation of aromatic ketones with the Ru– (R,R)-Ts-dpen catalyst or its polymer-supported analogue is reported.
Abstract: Catalysis in water represents a major area of intense research in modern chemistry. Water is inexpensive, readily available, and environmentally benign, and is thus an ideal solvent for chemical reactions. We recently reported that asymmetric transfer hydrogenation of aromatic ketones with the Ru– (R,R)-Ts-dpen catalyst (Ts-dpen = N-(p-toluenesulfonyl)-1,2diphenylethylenediamine) or its polymer-supported analogue
195 citations
TL;DR: A combined chemo-genetic procedure allows us to optimize the activity and selectivity of these hybrid catalysts: up to 94% enantiomeric excess for the reduction of p-methylacetophenone.
Abstract: Most physiological and biotechnological processes rely on molecular recognition between chiral (handed) molecules. Manmade homogeneous catalysts and enzymes offer complementary means for producing enantiopure (single-handed) compounds. As the subtle details that govern chiral discrimination are difficult to predict, improving the performance of such catalysts often relies on trial-and-error procedures. Homogeneous catalysts are optimized by chemical modification of the chiral environment around the metal center. Enzymes can be improved by modification of gene encoding the protein. Incorporation of a biotinylated organometallic catalyst into a host protein (avidin or streptavidin) affords versatile artificial metalloenzymes for the reduction of ketones by transfer hydrogenation. The boric acid·formate mixture was identified as a hydrogen source compatible with these artificial metalloenzymes. A combined chemo-genetic procedure allows us to optimize the activity and selectivity of these hybrid catalysts: up to 94% (R) enantiomeric excess for the reduction of p-methylacetophenone. These artificial metalloenzymes display features reminiscent of both homogeneous catalysts and enzymes.
164 citations
TL;DR: Asymmetric transfer hydrogenation ofketones, especially alpha-bromomethyl aromatic ketones, catalyzed by unmodified, hydrophobic transition metal-amido complexes (TsDPEN-M), was performed successfully with significant enhancement of activity, chemoselectivity, and enantioselectivities in aqueous media containing micelles and vesicles.
Abstract: Asymmetric transfer hydrogenation of ketones, especially α-bromomethyl aromatic ketones, catalyzed by unmodified, hydrophobic transition metal−amido complexes (TsDPEN−M), was performed successfully with significant enhancement of activity, chemoselectivity, and enantioselectivity (up to 99% ee) in aqueous media containing micelles and vesicles. The hydrophobic catalyst, embedded in micelles constructed from the surfactant cetyltrimethylammonium bromide (CTAB), could be separated from the organic phase along with the products and was recycled for at least six times.
150 citations
TL;DR: A rhodium(III) catalyst for asymmetric transfer hydrogenation of ketones has been designed with the incorporation of a tethering group between the diamino group and the cyclopentadienyl unit to provide extra stereochemical rigidity.
147 citations
TL;DR: The utility of the reaction has been demonstrated through an efficient two-step procedure for the attachment of unfunctionalized poly(ethylene glycol) to protein targets.
Abstract: An efficient transition metal catalyzed procedure for the reductive alkylation of proteins has been developed. Imines formed from the condensation of aldehydes (1 mM) with lysine residues and the N-terminus can be reduced efficiently by a [Cp*Ir(4,4‘-dimethoxy-2,2‘-bipyridine)(H2O)]SO4 catalyst in the presence of formate ions. The reaction proceeds readily at pH 7.4 in aqueous phosphate buffer at temperatures ranging from 22 to 37 °C, and reaches high levels of conversion for a number of aromatic aldehydes. UV experiments have confirmed that the catalyst does not bind to protein substrates. The utility of the reaction has been demonstrated through an efficient two-step procedure for the attachment of unfunctionalized poly(ethylene glycol) to protein targets.
144 citations
TL;DR: It was found that the chemoselectivity could be completely switched from C=O to C=C bonds in the transfer hydrogenation of activated alpha,beta-unsaturated ketones catalyzed by diamine-ruthenium complex.
Abstract: It was found that the chemoselectivity could be completely switched from CO to CC bonds in the transfer hydrogenation of activated α,β-unsaturated ketones catalyzed by diamine−ruthenium complex. Moreover, this addition via metal hydride had been applied to the reduction of various activated olefins. The electron-withdrawing ability of functional groups substituted on CC bonds at the α- or β-position had strong influence on the reactivity. In addition, a wide variety of chiral diamine−Ru(II)−(arene) systems was investigated to explore the asymmetric transfer hydrogenation of prochiral α,α-dicyanoolefins. Two parameters had been systematically studied, (i) the structure of the N-sulfonylated chiral diamine ligands, in which several chiral diamines substituted on the benzene ring of DPEN were first reported, and (ii) the structure of the metal precursors, and high enantioselectivitiy (up to 89% ee) at the β-carbon was obtained.
134 citations
TL;DR: A Rh(III) complex generated in situ from [Cp*RhCl2]2 and (1R,2R)-N-(p-toluenesulfonyl)-1,2-cyclohexanediamine (TsCYDN) serves as a remarkably effective, robust catalyst for the asymmetric transfer hydrogenation of aromatic ketones by HCOONa in water in air, affording alcohols in up to 99% ee.
TL;DR: Catalytic systems generated in situ from the chiral PNNP ligands with iridium or rhodium hydride complexes exhibited excellent catalytic activity and good enantioselectivity in the asymmetric transfer hydrogenation of aromatic ketones without added base.
TL;DR: The enantiopure complexes 1-9 have been employed as catalysts for the transfer hydrogenation of acetophenone in aqueous solution using sodium formate and water as a hydrogen source as discussed by the authors.
Abstract: The cationic chloro complexes [(arene)Ru(H 2 N∩NH 2 )Cl] + (1: arene = C 6 H 6 ; 2: arene = p-MeC 6 H 4 iPr; 3: arene = C 6 Me 6 ) have been synthesised from the corresponding arene ruthenium dichloride dimers and enantiopure (R,R or S,S) trans-1,2-diaminocyclohexane (H 2 N∩NH 2 ) and isolated as the chloride salts. The compounds are all water-soluble and, in the case of the hexamethylbenzene derivative 3, the aqua complex formed upon hydrolysis [(C 6 Me 6 )Ru(H 2 N∩NH 2 )-OH 2 ] 2 + (4) could be isolated as the tetrafluoroborate salt. The molecular structures of 3 and 4 have been determined by single-crystal X-ray diffraction analyses of [(C 6 Me 6 )Ru-(H 2 N∩NH 2 )Cl]Cl and [(C 6 Me 6 )Ru(H 2 N∩NH 2 )OH 2 ][BF 4 ] 2 . Treatment of [Ru 2 (arene) 2 Cl 4 ] with the monotosylated trans-1,2-diaminocyclohexane derivative (TsHN∩NH 2 ) does not yield the expected cationic complexes, analogous to 1-3 but the neutral deprotonated complexes [(arene)Ru(TsN∩NH 2 )-Cl] (5: arene = C 6 H 6 ; 6: arene = p-MeC 6 H 4 iPr; 7: arene = C 6 Me 6 ; 8: arene = C 6 H 5 COOMe). Hydrolysis of the chloro complex 7 in aqueous solution gave, upon precipitation of silver chloride, the corresponding monocationic aqua complex [(C 6 Me 6 )Ru)(TsHN∩NH 2 )(OH 2 )] 2 + (9) which was isolated and characterised as its tetrafluoroborate salt. The enantiopure complexes 1-9 have been employed as catalysts for the transfer hydrogenation of acetophenone in aqueous solution using sodium formate and water as a hydrogen source. The best results were obtained (60 °C) with 7, giving a catalytic turnover frequency of 43 h - 1 and an enantiomeric excess of 93 %.
TL;DR: A series of natural amino acid (alanine, valine, phenylalanine and isoleucine) amides have been synthesized and fully characterized in this article, and they have been used as supporting ligands in the Ru(II)-catalyzed asymmetric transfer hydrogenation (ath) of acetophenone in the presence of i-PrOH/KOH.
TL;DR: A new Bronsted acid catalysed hydrogenation of imines with Hantzsch dihydropyridine as the hydrogen source has been developed, making it the first metal-free hydrogen transfer to give various amines under mild reaction conditions.
Abstract: A new Bronsted acid catalysed hydrogenation of imines with Hantzsch dihydropyridine as the hydrogen source has been developed. Diphenyl phosphate (DPP) and various other acids catalyse this first metal-free hydrogen transfer to give various amines under mild reaction conditions.
TL;DR: The dihydride ruthenium N-heterocyclic carbene complex Ru(Imes)(PPh 3 ) 2 CO(H) 2 (1) (IMes = 1,3dimesityl-1,3-dihydro-2H-imidazol-2-ylidene) is an efficient catalyst for both direct hydrogenation and transfer hydrogenation of ketones and imines, in the absence of base as discussed by the authors.
Abstract: The dihydride ruthenium N-heterocyclic carbene complex Ru(Imes)(PPh 3 ) 2 CO(H) 2 (1) (IMes =1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene) is an efficient catalyst for both direct hydrogenation and transfer hydrogenationof ketones and imines, in the absence of base.
TL;DR: Ruthenacycles obtained by cyclometalation of enantiopure aromatic primary or secondary amines with [(eta6-benzene)RuCl2]2 or with)]2 are efficient catalysts for asymmetric transfer hydrogenation (TOF up to 190 h(-1) at room temperature).
TL;DR: A series of novel trans-ruthenium hydride borohydride complexes with chiral phosphinite and diamine ligands were synthesized and can be used in the asymmetric transfer hydrogenation of aryl ketones to give chiral alcohols in moderate to good enantioselectivities.
TL;DR: A novel task-specific ionic ligand with an imidazolium salt moiety was synthesized, and its catalytic ability and recyclability for asymmetric transfer hydrogenation of acetophenone derivatives with a formic acid-triethylamine azeotropic mixture in an ionic liquid was examined.
TL;DR: Dendritic catalysts demonstrated much better recyclability, which verified the stabilizing effects of the bulky polyether wedge on the catalytically active complex, and moderate to excellent enantioselectivitiy was achieved comparable to that of monomeric catalysts.
Abstract: Frechet-type core-functionalized chiral diamine-based dendritic ligands and hybrid dendritic ligands condensed from polyether wedge and Newkome-type poly(ether-amide) supported multiple ligands were designed and synthesized. The solubility of hybrid dendrimers was found to be finely controlled by the polyether dendron. The catalytic efficiency and recovery use of dendritic ruthenium complexes were compared in the transfer hydrogenation of acetophenone. The core-functionalized dendritic catalysts demonstrated much better recyclability, which verified the stabilizing effects of the bulky polyether wedge on the catalytically active complex. Moreover, the dendritic catalysts were applied in the asymmetric transfer hydrogenation of ketones, enones, imine, and activated olefin, and moderate to excellent enantioselectivitiy was achieved comparable to that of monomeric catalysts.
TL;DR: Stereochemically well-defined ruthenium(II) catalysts have been applied to the asymmetric transfer hydrogenation of a series of ketones and statistical experimental design was employed to optimize the enantiomeric excess.
Abstract: Stereochemically well-defined ruthenium(II) catalysts have been applied to the asymmetric transfer hydrogenation of a series of ketones. In one case, statistical experimental design was employed to optimize the enantiomeric excess of the product. In the case of the TsDPEN-based systems, the replacement of trans-1,2-diphenyl substitution with cis-, or deletion of one of the phenyl groups, results in significant deterioration of the enantiomeric excess. A new method is described for the synthesis of tethered amino alcohol-containing catalysts.
TL;DR: The free carbene 1,3,4triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene reacts with trans,cisRuHCl(PPh3)2(ampy) (ampy = 2-(aminomethyl)pyridine) affording an orthometalated N-heterocyclic carbene complex characterized by an X-ray diffraction study.
TL;DR: In this article, N-(p-tolylsulfonyl)-1,2-diphenylethylenediamine-(TsDPEN-) derived organic-inorganic hybrid ligands were prepared and applied to the heterogeneous asymmetric transfer hydrogenation in traditional HCO2H/NEt3 and in water with HCO 2Na as the hydrogen source and sodium dodecyl sulfate (SDS) as the phase-transfer catalyst.
TL;DR: In this article, a ruthenium(II) complex bearing the ligand 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine (Me(4)BPFy) was used for transfer hydrogenation of ketones.
TL;DR: In this article, the authors summarized the synthesis, modification and application of NOBIN derivatives as chiral ligands in asymmetric catalysis, and showed that NONB has become one type of privileged scaffold for the construction of various chiral chirality ligands for asymmetric reactions.
Abstract: 2-Amino-2'-hydroxy-1,1'-binaphthyl (NOBIN, 3) can be considered as the analogue of 1,1'-bi-2naphthol (BINOL, 1) and 1,1'-bi-2-naphthylamine (BINAM, 2) in terms of its functionality and scaffold Since the first report on the synthesis of NOBIN by Kocovsky, the chemistry of NOWN has been developed rapidly in the last decade This article summarizes its synthesis, modification and application of its derivatives as the chiral ligands in asymmetric catalysis The methods for the preparation of enantiopure NOBIN included asymmetric cross-coupling reaction of 2-naphthol and 2-naphthylamine, optical resolution of its racemic form and transformation from enantiopure BINOL A variety of chiral ligands could be easily obtained by simple transformation from NOBIN Their application in various asymmetric reactions, such as diethyl zinc addition to aldehydes, allylation of aldehydes, allylic substitutions, 1,4-addition to alpha,beta-unsaturated ketones, aldol-type reaction, Diels-Alder and hetero-Diels-Alder reactions, transfer hydrogenation of ketones, cyclopropanation, phase-transfer catalysis of alkylations, ring-opening/cross metathesis, alpha-vinylation/arylation of ketones and Suzuki coupling reactions, clearly demonstrated that NOBIN has become one type of privileged scaffold for construction of various chiral ligands for asymmetric catalysis
TL;DR: The low-cost and commercially available (−)-ephedrine hydrochloride was firstly employed in the [RuCl 2 (p -cymene)] 2 -catalyzed asymmetric transfer hydrogenation of prochiral ketones in water as mentioned in this paper.
TL;DR: Polymer-supported chiral ligands 9 and 17 were prepared based on Noyori's (1S,2S)- or (1R,2R)-N-(p-tolylsulfonyl)-1,2-diphenylethylenediamine to exhibit high activities and enantioselectivities for heterogeneous asymmetric transfer hydrogenation of aromatic ketones.
Abstract: Polymer-supported chiral ligands 9 and 17 were prepared based on Noyori's (1S,2S)- or (1R,2R)-N-(p-tolylsulfonyl)-1,2-diphenylethylenediamine. The combination with [RuCl2(p-cymene)]2 has been shown to exhibit high activities and enantioselectivities for heterogeneous asymmetric transfer hydrogenation of aromatic ketones (19a–c) with formic acid–triethylamine azeotrope as the hydrogen donor, whereby affording the respective optically active alcohols 20a–c, the key precursors of chiral fluoxetine. As exemplified by ligand 17 for substrate 19c, the catalysts can be recovered and reused in three consecutive runs with no significant decline in enantioselectivity. The procedure avoids the plausible contamination of fluoxetine by the toxic transition metal species.
TL;DR: The asymmetric transfer hydrogenation of 1-aryl-2-imidazol-1-yl-ethanones with formic acid using [(R,R)-TsDPEN]Ru(Cymene)Cl as precatalyst was shown to be effective in this transformation.
TL;DR: In this paper, the reduction of ketones to alcohols via transfer hydrogenation was achieved with catalytic amounts of ruthenium-N-heterocyclic carbene complexes (2−7) in the presence of t-BuOK.
Abstract: Six ruthenium-N-heterocyclic carbene complexes (2–7) have been prepared and the new compounds characterized by C, H, N analyses, 1H-n.m.r. and 13C-n.m.r. The reduction of ketones to alcohols via transfer hydrogenation was achieved with catalytic amounts of complexes (2–7) in the presence of t-BuOK.