bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Novel Chiral Benzophospholanes and Their Application in Asymmetric Hydrogenation
Authors: Shimizu Hideo , Saito Takao , Kumobayashi Hidenori 
Published: January 2003

AbstractA new class of chiral ligands bearing one or two benzophospholanes was developed for the purpose of Ru‐catalyzed asymmetric hydrogenation. Although results of the Ru catalysis remain insufficient so far, 1,2‐bis(2‐isopropyl‐2,3‐dihydro‐1H‐phosphindol‐1‐yl)benzene (iPr‐BeePHOS: 2b) has been found to provide high enantioselectivity in the Rh‐catalyzed asymmetric hydrogenation of an enamide.
High Throughput Kinetic Investigations of Asymmetric Hydrogenations with Microdevices
Authors: de Bellefon C. , Pestre N. , Lamouille T. , Grenouillet P. , Hessel V. 
Published: January 2003

AbstractA high throughput test which is based on a micromachined mixer for molecular gas‐liquid reactions was evaluated for the kinetic investigation of the asymmetric hydrogenation of methyl Z‐(α)‐acetamidocinamate with a rhodium/(S,S‐BDPPTS) catalyst in an aqueous phase. Up to 214 tests were performed in a short time and with an average inventory of Rh/test as low as 14 μg. Comparisons with traditional batch experiments are provided.
Enantioselective Hydrogenation of Imines Using a Diverse Library of Ruthenium Dichloride(diphosphine)(diamine) Precatalysts
Authors: Cobley Christopher J. , Henschke Julian P. 
Published: January 2003

AbstractA range of aromatic and cyclic imines were subjected to asymmetric hydrogenation with catalysts derived from complexes of the type RuCl2(diphosphine)(diamine). Good to high enantioselectivities were observed. For each imine, a library of chiral complexes based on different diphosphine and diamine combinations was screened. A different combination of diphosphine and diamine was required each time to obtain the optimum enantioselectivity.
Catalyst Encapsulation and Substrate Solubilization in Polymer‐Surfactant Complexes and Their Use in a Membrane Reactor
Authors: Fuhrmann Hans , Dwars Torsten , Michalik Dirk , Holzhüter Gerd , Grüttner Cordula , Kragl Udo , Oehme Günther 
Published: January 2003

AbstractA chiral non‐racemic Rh complex was entrapped in a number of charged polymer‐surfactant complexes (PSCs) and used as micellar‐enlarged catalyst for the enantioselective hydrogenation of an α‐amino acid precursor in a membrane reactor. The retention behavior of different ultrafiltration membranes in dependence on the chemical nature and the molar mass of the PSCs as well as the loading behavior of the system were investigated. The chiral hydrogenation product was obtained with good enantioselectivity and space‐time yield. A lowering of the activity of the multiply used catalyst was caused mainly by a blockage of the PSC and not by the decomposition and leaching of the encapsulated catalyst. TEM images before and after the solubilization of the catalytic system support the view that a PSC with a loose, gel‐like structure and incorporated micelles yields the best results in the repetitive batch process.
Minor Modifications to the Ligands Surrounding a Ruthenium Complex Lead to Major Differences in the Way in which they Catalyse the Hydrogenation of Arenes
Authors: Dyson Paul J. , Ellis David J. , Laurenczy Gábor 
Published: January 2003

AbstractThe hydrogenation of benzene and other arenes under aqueous‐organic biphasic conditions is evaluated using the ruthenium complexes Ru(η6‐C10H14)(pta)Cl2 (pta=1,3,5‐triaza‐7‐phosphaadamantane), Ru(η6‐C10H14)(tppts)Cl2 (tppts=tris‐3‐sulfonatophenylphosphine trisodium salt) and [Ru(η6‐C10H14)(pta)2Cl]+. The active catalysts formed during the hydrogenations correspond to a trinuclear cluster, a colloid and a mononuclear complex, respectively.
A Comparison of Ruthenium‐Catalysed Arene Hydrogenation Reactions in Water and 1‐Alkyl‐3‐methylimidazolium Tetrafluoroborate Ionic Liquids
Authors: Dyson Paul J. , Ellis David J. , Henderson William , Laurenczy Gábor 
Published: January 2003

AbstractThe hydrogenation of benzene and other arene substrates under biphasic conditions is evaluated using the catalyst precursor Ru(η6‐C10H14)(pta)Cl2 (pta=1,3,5‐triaza‐7‐phosphaadamantane) immobilised in water and 1‐alkyl‐3‐methylimidazolium tetrafluoroborate ionic liquids. The effect that contamination of the 1‐alkyl‐3‐methylimidazolium tetrafluoroborate ionic liquids with chloride has on the hydrogenation reaction has also been examined. Of the immobilisation solvents tested the optimum solvent was found to be chloride‐free 1‐butyl‐3‐methylimidazolium tetrafluoroborate. Catalytic turnovers in this solvent are highest, and in general, turnovers for the hydrogenation reactions follow the trend: chloride‐free 1‐butyl‐3‐methylimidazolium tetrafluoroborate > water > chloride‐contaminated 1‐butyl‐3‐methylimidazolium tetrafluoroborate.
Arene Hydrogenation with a Stabilised Aqueous Rhodium(0) Suspension: A Major Effect of the Surfactant Counter‐Anion
Authors: Roucoux Alain , Schulz Jürgen , Patin Henri 
Published: January 2003

AbstractA reduced aqueous colloidal suspension of rhodium shows an efficient activity in the catalytic hydrogenation of various benzene derivatives under biphasic conditions at room temperature and under atmospheric hydrogen pressure. The rhodium nanoparticles in the size range of 2–2.5 nm have been synthesised by reducing RhCl3⋅3 H2O with sodium borohydride and were stabilised by highly water‐soluble N,N‐dimethyl‐N‐cetyl‐N‐(2‐hydroxyethyl)ammonium salts (HEA16X, X=Br, Cl, I, CH3SO3, BF4). The major influence of the counter‐ion of these surfactants on catalytic activity and recycling is described. The best results have been obtained with chloride ammonium salts HEA16Cl.
Ruthenium‐Catalysed Enantioselective Hydrogenation of Trisubstituted Enamides Derived from 2‐Tetralone and 3‐Chromanone: Influence of Substitution on the Amide Arm and the Aromatic Ring
Authors: Renaud J. L. , Dupau P. , Hay A.‐E. , Guingouain M. , Dixneuf P. H. , Bruneau C. 
Published: January 2003

AbstractCyclic enamides were prepared in one step from tetralone and chromanone derivatives and primary amides under acidic conditions. The enantioselective hydrogenation of these enamides bearing an endocyclic trisubstituted carbon‐carbon double bond was performed at room temperature in the presence of ruthenium catalysts. On the one hand, the nature of the amide group had little influence on the enantioselectivity of the hydrogenation when mononuclear precatalysts were used. On the other hand, the presence of a coordinating atom at some specific position on the tetralone and chromanone skeleton led to a dramatic decrease of the enantiomeric excesses.
Asymmetric Cleavage of Racemic 1,3‐Oxazolidines – A New Dynamic Process in Homogeneous Rh(I)‐Catalyzed Hydrogenation
Authors: Tararov Vitali I. , Kadyrov Renat , Monsees Axel , Riermeier Thomas H. , Börner Armin 
Published: January 2003

AbstractThe mechanism of the homogeneously catalyzed hydrogenation of 1,3‐oxazolidines with a Rh(I) diphosphane catalyst affording tertiary hydroxyethyl‐substituted amines was investigated with the help of D2 labelling experiments. It was found that the reaction proceeds via prochiral intermediates with, preferentially, an iminium cation being in equilibrium with the 1,3‐oxazolidine. This observation opened up the opportunity to run the reaction stereoselectively by employment of a racemic 1,3‐oxazolidine and a chiral catalyst. By means of high‐throughput screening considering 144 catalysts a cationic Rh(NORPHOS)‐complex was identified as the most efficient catalyst, which afforded after optimization of solvent, temperature and H2 pressure the corresponding chiral hydroxyethylamine in 95% yield and 80% ee.
Asymmetric Activation/Deactivation of Racemic Ru Catalysts for Highly Enantioselective Hydrogenation Irrespective of Ketonic Substrates: Molecular Design of Dimethylbinaphthylamine for Enantiomeric Catalysts Discrimination
Authors: Mikami Koichi , Korenaga Toshinobu , Yusa Yukinori , Yamanaka Masahiro 
Published: January 2003

AbstractAsymmetric activation and deactivation of racemic catalysts are two extremes in asymmetric catalysis. In a combination of these two protocols, higher enantioselectivity can be achieved by maximizing the difference in catalytic activity between the enantiomers of racemic catalysts through selective activation and deactivation of enantiomeric catalysts. 3,3′‐Dimethyl‐2,2′‐diamino‐1,1′‐binaphthyl (DM‐DABN) is thus designed as a chiral poison (deactivator) for complete enantiomer resolution of racemic BINAP‐Ru(II) catalysts. The catalyst system of DM‐DABN, 1,2‐diphenylethylenediamine (DPEN), and racemic BINAP‐Ru(II) led to great success in highly enantioselective hydrogenation irrespective of the ketonic substrates. The lower catalytic activity of the BINAP‐Ru(II)/DM‐DABN complex stems from the electron delocalization from the Ru center to the diamine moiety in contrast to the BINAP‐Ru(II)/DPEN complex where the highest electron densities are localized on the Ru‐N region. The present ‘asymmetric activation/deactivation protocol' can provide a guiding principle for the rational design of a molecule for enantiomeric discrimination between racemic catalysts.
Non‐Linear Effect of Modifier Composition on Enantioselectivity in Asymmetric Hydrogenation over Platinum Metals
Authors: Huck Wolf‐Rüdiger , Mallat Tamas , Baiker Alfons 
Published: January 2003

AbstractProminent non‐linear behavior was observed when mixtures of cinchona alkaloids were applied as chiral modifiers in enantioselective hydrogenations over Pt/Al2O3 and Pd/TiO2. The phenomenon is traced to differences in the strength and geometry of alkaloid adsorption on the metal surface. In ethyl pyruvate hydrogenation under close to ambient conditions the weaker adsorbing quinidine (QD) outperformed the generally preferred modifier cinchonidine (CD) and afforded the highest ee (96–98%) at 1–5 bar. In the partial hydrogenation of 4‐methoxy‐6‐methyl‐2‐pyrone to the dihydro derivative 4 CD gave 73% ee to (S)‐4 and QD provided 72% ee to (R)‐4, and still the alkaloid mixture containing less than 5 mol % CD afforded 15% ee to (S)‐4. This non‐linear behavior may be advantageous in asymmetric synthesis as low purity chiral compounds can be applied as efficient modifiers for Pt or Pd.
Enantioselective Hydrogenation of β‐Keto Esters using Chiral Diphosphine‐Ruthenium Complexes: Optimization for Academic and Industrial Purposes and Synthetic Applications
Authors: Ratovelomanana‐Vidal V. , Girard C. , Touati R. , Tranchier J. P. , Hassine B. Ben , Genêt J. P. 
Published: January 2003

AbstractEnantioselective hydrogenation using chiral complexes between atropisomeric diphosphines and ruthenium is a powerful tool for producing chiral compounds. Using a simple and straightforward in situ catalyst preparation, the conditions were optimized using molecular hydrogen for both academic and industrial purposes. This led to the best conditions and the lowest catalytic ratio required for the pressure used. Hydrogenation of various β‐keto esters was efficiently performed at atmospheric and higher pressures, leading to the use of very low catalyst‐substrate ratios up to 1/20,000. Asymmetric hydrogenations were used in key‐steps towards the total synthesis of corynomycolic acid, Duloxetine and Fluoxetine.
The NiCl2‐Li‐Arene (cat.) Combination as Reducing System, Part 9: Catalytic Hydrogenation of Organic Compounds using the NiCl2‐Li‐(Naphthalene or Polymer‐Supported Naphthalene) (cat.) Combination
Authors: Alonso Francisco , Candela Pablo , Gómez Cecilia , Yus Miguel 
Published: January 2003

AbstractThe reaction of lithium powder, a catalytic amount of naphthalene or polymer‐supported naphthalene, and anhydrous nickel(II) chloride, in THF at room temperature, generates a finely divided and very reactive nickel(0) which has been efficiently applied to the catalytic hydrogenation of different organic compounds such as alkenes, alkynes, carbonyl compounds, imines, organic halides, aromatic compounds, hydrazines, azoxy compounds, and N‐oxides.
Unusual 1‐Alkyne Dimerization/Hydrogenation Sequences Catalyzed by [Ir(H)2(NCCH3)3(P‐i‐Pr3)]BF4: Evidence for Homogeneous‐Like Mechanism in Imidazolium Salts
Authors: Navarro Janeth , Sági Mária , Sola Eduardo , Lahoz Fernando J. , Dobrinovitch Isabel T. , Kathó Ágnes , Joó Ferenc , Oro Luis A. 
Published: January 2003

AbstractThe reaction of complex [Ir(H)2(NCCH3)3(P‐i‐Pr3)]BF4 (1) with excess of 1‐alkynes such as t‐BuC≡CH and PhC≡CH gave the butadiene compounds Ir[η4‐(R)2C4H4](NCCH3)2(P‐i‐Pr3)}BF4 (R=t‐Bu, 5; R=Ph, 6). Compound 5 was obtained as a single isomer containing a 1,3‐disubstituted butadiene ligand, whereas 6 was formed as a 7:1 mixture of isomers containing 1,3‐ and 1,4‐disubstituted butadienes, respectively. Spectroscopic observations showed alkenyl hydride reaction intermediates, consistent with a double insertion/C‐C coupling sequence. Complexes 5 and 6 were found to react with dihydrogen to give 1 and alkenes resulting from the partial hydrogenation of the butadiene moieties. This dimerization/hydrogenation sequence has been found to be the major reaction of t‐BuC≡CH under conditions of homogeneous hydrogenation whereas that of PhC≡CH produced styrene and ethylbenzene as major products. Similar selectivity was observed for these hydrogenations using organic/ionic liquid biphasic conditions with toluene/BMIM⋅BF4, suggesting reaction mechanisms similar to those operating under homogeneous conditions. This conclusion is also supported by the spectroscopic observation of alkenyl hydride intermediates during the formation of 6 in BMIM⋅BF4 as solvent.
Hydrogenation of Glucose to Sorbitol over Nickel and Ruthenium Catalysts
Authors: Kusserow Burkhard , Schimpf Sabine , Claus Peter 
Published: January 2003

AbstractHydrogenation of aqueous glucose solution was performed in batch and continuous reactors using supported nickel and ruthenium catalysts. Preparation methods were precipitation, impregnation, sol‐gel and template syntheses, and SiO2, TiO2, Al2O3 and carbon were used as support materials. A procedure for the one‐step synthesis of templated metal on support catalysts was established. The influence of support material and preparation methods was studied and the results were compared with those of an industrial nickel catalyst. In a detailed study taking more than 1100 h time on stream we investigated the deactivation of the industrial catalyst and a supported ruthenium catalyst, and evaluated the deactivation mechanisms. As yet unpublished side products of the glucose hydrogenation were identified and a scheme of the reaction network was set up.
Synthesis and Applications of HexaPHEMP, a Novel Biaryl Diphosphine Ligand
Authors: Henschke Julian P. , Burk Mark J. , Malan Christophe G. , Herzberg Daniela , Peterson Justine A. , Wildsmith Andrew J. , Cobley Christopher J. , Casy Guy 
Published: January 2003

AbstractThe novel biaryldiphosphine ligand 1 (HexaPHEMP) has been prepared in five steps from commercially available 3,4,5‐trimethylphenol using a concise synthetic route. This approach also allows fine tuning of the ligand's stereoelectronic properties through the variation of the aromatic groups on the ligating phosphorus atoms. In certain asymmetric hydrogenation processes, catalysts containing this ligand were found to have enhanced activity and selectivity over other biaryldiphosphine‐containing catalysts.
Monodentate Phosphoramidites: A Breakthrough in Rhodium‐Catalysed Asymmetric Hydrogenation of Olefins
Authors: van den Berg Michel , Minnaard Adriaan J. , Haak Robert M. , Leeman Michel , Schudde Ebe P. , Meetsma Auke , Feringa Ben L. , de Vries André H. M. , Maljaars C. Elizabeth P. , Willans Charlotte E. , Hyett David , Boogers Jeroen A. F. , Henderickx Hubertus J. W. , de Vries Johannes G. 
Published: January 2003

AbstractMonodentate phosphoramidites based on BINOL or substituted BINOL are excellent ligands for the rhodium‐catalysed asymmetric hydrogenation of olefins. Very high enantioselectivities were obtained with MonoPhos (7a) the simplest member of this class, a ligand that is prepared in a single step from BINOL and HMPT. Turnover numbers up to 6000 have been obtained in the hydrogenation of dehydroamino acid derivatives. Enantioselectivities in the hydrogenation of dehydroamino acids are solvent dependent; in non‐protic solvents they range from 95–99%. Itaconic acid and its dimethyl ester could be hydrogenated with 96 and 94% e.e., respectively. Hydrogenation of aromatic enamides gave the corresponding acylated amines in 86–94% e.e. Several analogous phosphoramidite ligands have been prepared. Surprisingly, bidentate ligands gave poorer results, both in terms of rate as well as enantioselectivity. Taddol‐based phosphoramidites led to poor e.e. and slow rates. Methyl substituents at the 3,3′‐position of BINOL led to a sharply reduced rate and a somewhat lower enantioselectivity. Bromo substituents at the 6,6′‐position led to a slightly reduced rate but little effect was seen on enantioselectivity. Use of octahydro‐MonoPhos (11) gave results that were very similar to those obtained with 7a. The rate of the reaction is dependent on the hydrogen pressure, however, the enantioselectivity is not affected. The rate of the dehydroamino acid hydrogenation also increases if the ligand to rhodium ratio is reduced from 2.2 to 1.5 or even to 1.0; yet, there is no deleterious effect on the enantioselectivity. Catalytic activity ceases with L/Rh=3 when dehydroamino acid derivatives were used as substrate. The reaction shows a positive non‐linear effect, which confirms the presence of Rh‐complexes with more than one ligand. Following the hydrogenation of methyl 2‐acetamidocinnnamate with Rh(nbd)2BF4/7a by electrospray mass spectrometry showed the presence of several rhodium species. Notable are the presence of [Rh(7a)]3+ and [Rh(7a)]4+. There is at present insufficient evidence to conclude if the active catalytic species carries one or two ligands. In view of the low cost of MonoPhos this invention might well lead to a broader application of asymmetric olefin hydrogenation for the production of enantiopure amino acids and amines.
Iridium‐Catalyzed Enantioselective Hydrogenation of Olefins
Authors: Pfaltz Andreas , Blankenstein Jörg , Hilgraf Robert , Hörmann Esther , McIntyre Steven , Menges Frederik , Schönleber Marc , Smidt Sebastian P. , Wüstenberg Bettina , Zimmermann Nicole 
Published: January 2003

AbstractCationic iridium complexes with chiral P,N‐ligands and tetrakis[3,5‐(trifluoromethyl)phenyl]borate (BArF) as the counterion are efficient homogeneous catalysts for the enantioselective hydrogenation of olefins. The complexes are readily prepared, air‐stable, and easy to handle. In contrast to chiral rhodium‐ and ruthenium‐phosphine catalysts, they do not require the presence of a polar coordinating group near the CC bond. In the hydrogenation of unfunctionalized arylolefins, high enantioselectivities of >95% ee with turnover numbers of up to 5000 and turnover frequencies of >5000 h−1 have been achieved.
Asymmetric Hydrogenations (Nobel Lecture 2001)
Authors: Knowles William S. 
Published: January 2003

AbstractThe start of the development of catalysts for asymmetric hydrogenation was the concept of replacing the triphenylphosphane ligand of the Wilkinson catalyst with a chiral ligand. With the new catalysts, it should be possible to hydrogenate prochiral olefins. Knowles and his co‐workers were convinced that the phosphorus atom played a central role in this selectivity, as only chiral phosphorus ligands such as (R,R)‐DIPAMP, whose stereogenic center lies directly on the phosphorus atom, lead to high enantiomeric excesses when used as catalysts in asymmetric hydrogenation reactions. This hypothesis was disproven by the development of ligands with chiral carbon backbones. Although the exact mechanism of action of the phosphane ligands is not incontrovertibly determined to this day, they provide a simple entry to a large number of chiral compounds.
Enantioselective Hydrogenation Using Heterogeneous Modified Catalysts: An Update
Authors: Studer Martin , Blaser Hans‐Ulrich , Exner Christian 
Published: January 2003

AbstractThe state of the art for the enantioselective hydrogenation applying chirally modified heterogeneous catalysts is reviewed with emphasis on new developments between 1997 and 2002. Discussed are various combinations of metal–modifier–substrate which give enantioselectivities useful for synthetic applications. The three most important asymmetric catalysts types are nickel catalysts modified with tartaric acid, useful for β‐functionalized ketones with ees up to 98.6%, platinum catalysts modified with cinchona alkaloids and related modifiers, successful for α‐functionalized ketones with ees up to 98% and palladium catalysts modified with cinchona alkaloids which achieve ees up to 94% for selected activated CC bonds. Mechanistic investigations comprising surface science and spectroscopic studies often combined with computational modeling as well as kinetic studies are summarized and the various mechanistic models are discussed.
Ruthenium(II)‐Catalyzed Asymmetric Transfer Hydrogenation of Carbonyl Compounds with 2‐Propanol and Ephedrine‐Type Ligands
Authors: Everaere Kathelyne , Mortreux André , Carpentier Jean‐François 
Published: January 2003

AbstractThis account describes the development and application of Noyori's type catalysts based on ruthenium‐arene complexes and simple chiral β‐amino alcohols derived from ephedrine, for the asymmetric transfer hydrogenation of 2‐propanol to carbonyl substrates. The influence of key parameters of the catalyst system has been studied systematically, resulting in particular in the design of the novel ligand (4‐biphenylmethyl)norephedrine. Thanks to the latter, the catalytic precursors and true active species could be isolated for the first time, enabling a complete structural description of the catalytic cycle and of probable deactivation pathways. Highly effective applications of those catalysts systems, i.e., the asymmetric reductions of simple aryl ketones and aryl β‐keto esters, the synthesis of chiral phthalides and syn‐β,δ‐dihydroxy esters, are described.
Recent Developments in Catalytic Asymmetric Hydrogenation Employing P‐Chirogenic Diphosphine Ligands
Authors: Crépy Karen V. L. , Imamoto Tsuneo 
Published: January 2003

AbstractRhodium‐ and ruthenium‐catalyzed asymmetric hydrogenations reactions employing C2‐symmetric chiral diphosphine ligands have a long history, and exceedingly high enantioselectivities have been reported. On the other hand, metal complexes containing P‐chirogenic, electron‐rich diphosphine ligands such as 1,2‐bis(alkylmethylphosphino)ethane (BisP*) and bis(alkylmethylphosphino)methane (MiniPHOS) have been tested only recently, and proved greatly successful. These results prompted intensive research amongst organic chemists, and the scope and limitations of the use of ligands bearing the chiral center at phosphorus atoms is presented in this review. The most recent data have been collected and summarized. In terms of ligand design, it is necessary to address an important question: “which properties are responsible for very high enantioselectivity in hydrogenation reactions?”. To this extent, a full discussion of new aspects on the mechanism, in particular the demonstration of a dihydride mechanism for enantioselective hydrogenation as opposed to the unsaturated mechanism widely accepted so far, also constitutes an important part of this review.