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Sı́pos, É.; Tungler, Antal; Bitter, István

doi:10.1023/a:1024163818818

Cited by 28 publications

(29 citation statements)

References 23 publications

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“…69 Attempts to anchor the 318 proline moiety to the metal surface by incorporating quinoline or indole units into the chiral modifier 319 have also been investigated. 70 However this method would suffer from exactly the same problem of 320 hydrogenation of the aromatic anchoring functionalities during reaction, as discussed immediately above 321 for similarly anchored aromatic chiral modifiers on Pd catalysts. In contrast, as will be shown later, 322 chiral organic sulfides that tether covalently to the Pd surface do offer a promising way forward in this 323 respect.…”

Section: Asymmetric Hydrogenation Of C=c Bonds 280 13mentioning

confidence: 99%

Aspects of Heterogeneous Enantioselective Catalysis by Metals

2011

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Publisher's copyright statement:This document is the Accepted Manuscript version of a Published Work that appeared in nal form in Langmuir, copyright c American Chemical Society after peer review and technical editing by the publisher. To access the nal edited and published work see http://pubs.acs.org/doi/abs/10.1021/la200009w. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Some aspects of metal-catalyzed heterogeneous enantioselective reactions are reviewed with specific 23 reference to four different systems where the phenomena that control enantioselection appear to be very 24 different. In the case of glucose electro-oxidation it is clear that any intrinsic chirality present at the 25 metal surface plays a vital role. With -keto hydrogenation, achiral surfaces modified by the adsorption 26 of chiral agents become effective enantioselective catalysts and formation of extended arrays of chiral 27 species appears not to be of importance: instead a 1:1 docking interaction controlled by hydrogen 28 bonding between the adsorbed chiral modifier and the prochiral reactant determines the outcome. 29Hydrogen bonding also plays a central role in -ketoester hydrogenation, but here fundamental studies 30indicate that the formation of ordered arrays involving the reactant and chiral ligand is of importance. 31Asymmetric C=C hydrogenation, though relatively little studied, has the potential for major impact in 32 synthetic organic chemistry both at the laboratory scale and in the manufacture of fine chemicals and 33 pharmaceuticals. The structural attributes that determine whether or not a given chiral ligand is effective 34 have been identified; the ability to form strong covalent bonds with the metal surface while also 35 resisting hydrogenation and displacement by the strongly-adsorbing reactant under reaction conditions 36 are essential necessary conditions. Beyond these, ligand rigidity in the vicinity of the chirality center 37 coupled with resistance to SAM formation are critically important factors whose absence results in 38 racemic chemistry.

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Section: Asymmetric Hydrogenation Of C=c Bonds 280 13mentioning

confidence: 99%

Aspects of Heterogeneous Enantioselective Catalysis by Metals

2011

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“…A thoroughly investigated catalyst system is cinchonidine (CD)-modified Pt that provides higher than 90% enantiomeric excess (ee) in the hydrogenation of various activated ketones [14]. Any effort to surpass the performance of cinchona alkaloids or their simple derivatives by using synthetic organic compounds has failed [15][16][17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

An efficient synthetic chiral modifier for platinum

et al. 2005

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A new chiral modifier pantoyl-naphthylethylamine (PNEA) was synthesized by reductive alkylation of 1-(1-naphthyl)ethylamine with ketopantolactone. Platinum-on-alumina modified by PNEA afforded 93% ee and 100% chemoselectivity in the hydrogenation of the activated carbonyl group of 1,1,1-trifluoro-2,4-pentanedione. Reductive heat treatment and ultrasonication of the catalyst, and the use of chlorinated solvents under mild conditions (10 bar, 10°C) enhanced the enantioselectivity. This is the first case in heterogeneous catalysis that a synthetic modifier gives more than 90% ee, better than the commonly used modifier of natural origin (cinchonidine or O-methyl-cinchonidine).

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“…This strategy has been applied extensively for the hydrogenation of pyruvate esters on Pt, including some cinchona alkaloid derivatives, [21 -26] other alkaloids, [27 -30] various amines, [31,32] amino alcohols, [33 -37] amino acids, [38] and amino acid derivatives. [39,40] The most important conclusions emerging from these studies are that CD and many other effective modifiers adsorb via the extended aromatic ring lying close to parallel to the Pt surface, and the basic N-atom is responsible for interacting with the substrate in the enantiodifferentiating step. A somewhat disappointing conclusion from all these studies is that none of the new synthetic modifiers could surpass the performance of CD or its O-methyl derivative.…”

Section: Introductionmentioning

confidence: 99%

Synthetic Modifiers for Platinum in the Enantioselective Hydrogenation of Ketopantolactone: A Test for the Mechanistic Models of Ketone Hydrogenation

Orglmeister

Mallát

Baiker

2005

Advanced Synthesis & Catalysis

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Various derivatives of (R)-1-(1-naphthyl)-ethylamine have been synthesized and tested as chiral modifiers of Pt/alumina in the enantioselective hydrogenation of ketopantolactone. The best modifiers (ee up to 79%) possess an ester function in the a-position to the amino group. The modifiers performed far better in AcOH than in toluene, indicating that protonation of the N atom is important in enantioselection. The striking non-linear behaviour of modifier mixtures with cinchonine indicates that the alkaloid adsorbs much stronger on Pt than the naphthylethylamine derivatives. Two mechanistic models are proposed for interpretation of the results, involving anbetween the amine-type modifier and the keto carbonyl O atom of ketopantolactone, in apolar and protic media, respectively. In both cases the H atom originates from the modifier and not from the substrate ("half-hydrogenatedstate"). The higher ee achieved in acidic medium is attributed to the better proton donor ability of the protonated amine modifiers. The models are applicable also to the hydrogenation of ethyl pyruvate.

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Cited by 28 publications

References 23 publications

Aspects of Heterogeneous Enantioselective Catalysis by Metals

Aspects of Heterogeneous Enantioselective Catalysis by Metals

An efficient synthetic chiral modifier for platinum

Synthetic Modifiers for Platinum in the Enantioselective Hydrogenation of Ketopantolactone: A Test for the Mechanistic Models of Ketone Hydrogenation

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