A model for the enantioselective hydrogenation of pyruvate catalysed by alkaloid‐modified platinum

Simons, K.E.; Meheux, P.A.; Griffiths, S.P.; Sutherland, I. M.; Johnston, Peter; Wells, Peter B.; Carley, Albert Frederick; Rajumon, M.K.; Roberts, M.W.; Ibbotson, A.

doi:10.1002/recl.19941131011

Cited by 142 publications

(116 citation statements)

References 35 publications

Supporting

Mentioning

110

Contrasting

Order By: Relevance

“…To find a feasible explanation we have to consider the possible adsorption modes of substrate and modifier on the metal surface and their interaction during hydrogen uptake. According to the mechanistic models, developed for the hydrogenation of 1 over Pt by Wells et al [35] and our group, [31,36] the cinchona alkaloid adsorbs via the quinoline rings lying parallel to the Pt surface (p-bonded ™anchoring moiety∫). The substrate 1 adsorbs also flat via the C O bonds parallel to the Pt surface (Figure 3).…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Non‐Linear Effect of Modifier Composition on Enantioselectivity in Asymmetric Hydrogenation over Platinum Metals

2003

View full text Add to dashboard Cite

Prominent non-linear behavior was observed when mixtures of cinchona alkaloids were applied as chiral modifiers in enantioselective hydrogenations over Pt/Al 2 O 3 and Pd/TiO 2 . 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 nonlinear behavior may be advantageous in asymmetric synthesis as low purity chiral compounds can be applied as efficient modifiers for Pt or Pd.

show abstract

Section: Resultsmentioning

confidence: 99%

“…In AcOH this interaction corresponds to the 1-protonated CD interaction, [37] in apolar medium the complex resembles the half-hydrogenated state of 1. [35] At least three differently adsorbed species could be identified by in situ ATR-studies of CD adsorption on platinum:…”

Section: Resultsmentioning

confidence: 99%

Non‐Linear Effect of Modifier Composition on Enantioselectivity in Asymmetric Hydrogenation over Platinum Metals

2003

View full text Add to dashboard Cite

show abstract

“…It has been demonstrated that, using cinchonidine chiral alkaloid, it is possible to induce a preferential formation of (R)-lactate. [43][44] In the present study the enantioselective hydrogenation of ethyl pyruvate was carried out in liquid phase at 298 K and 40 bar overall pressure on colloidal platinum and on Pt-CD/SiO 2 catalysts obtained by impregnation of the colloids on the support. Experimental variables such as the weight of the catalysts and the concentration of CD added with the substrate during the reaction were also studied.…”

Section: Resultsmentioning

confidence: 99%

Enantioselective hydrogenation of ethyl pyruvate and 1-phenyl-1,2-propanedione on catalysts prepared by impregnation of colloidal platinum on SiO2

Ruiz¹,

Fierro²,

Reyes³

2010

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

A hidrogenação enantiosseletiva de piruvato de etila e de 1-fenil-1,2-propanodiona foi estudada a 298 K e sob 40 bar de H 2 sobre um catalisador de platina coloidal estabilizado com cinchonidina (CD) e suportado em sílica. O catalisador foi preparado por impregnação da platina coloidal em sílica, atingindo 1% em massa do metal no suporte. O colóide foi preparado a partir de uma solução aquosa de H 2 PtCl 6 estabilizada com diferentes quantidades de CD. O catalisador foi caracterizado por isotermas de adsorção-desorção de N 2 a 77 K e por XPS, XRD e TEM. As reações foram efetuadas em batelada em um reator de aço inoxidável, usando cicloexano como solvente e cinchonidina como modificador quiral. A adição de CD ao catalisador permite a estabilização e o controle do tamanho de partícula da platina, e também afeta o excesso enantiomérico (ee) do sistema, levando a um maior rendimento do produto com configuração R. A relação entre a concentração de CD adicionada in situ e a enantiosseletividade apresenta uma curva do tipo sino nas duas reações estudadas; este comportamento é um indicativo da importância da adsorção competitiva do modificador e do substrato na superfície do catalisador.The enantioselective hydrogenation of ethyl pyruvate and 1-phenyl-1,2-propanedione was studied at 298 K and 40 bar of H 2 over colloidal Pt stabilized with cinchonidine (CD) and supported on silica. The catalysts were prepared by impregnation of colloidal Pt on SiO 2 , leading to a metal load close to 1 wt.%. The colloid was prepared from an aqueous solution of H 2 PtCl 6 and stabilized with different quantities of CD. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, XPS, XRD and TEM techniques. The reactions were carried out in a stainless steel batch reactor using cyclohexane as solvent and cinchonidine as chiral modifier. The addition of CD to the catalysts allows the stabilization and control of the platinum particle size and also affects the enantiomeric excess (ee) of the system, affording a higher proportion of the (R)-product. The relationship between the enantioselectivity and the CD concentration (added in situ) exhibits a bell type curve for both reactions, this being indicative of the importance of a competitive adsorption of the modifier and substrate on the catalyst surface.Keywords: Pt colloids, enantioselectivity, ethyl pyruvate, 1-phenyl-1,2-propanedione, cinchonidine IntroductionEnantioselective hydrogenation reactions are important tools to obtain fine chemicals used in pharmaceutical and food products.1-4 Thus, the synthesis of chiral compounds is of growing interest; among them, the hydrogenation of a-ketoesters and ketones is the most widely studied. [5][6][7][8][9][10][11][12][13][14][15] Since Orito et al. reported the enantioselective hydrogenation of ethyl pyruvate to (R)-ethyl lactate over cinchonidine-modified Pt catalysts with ee's up to 95%, many other research teams have evaluated the performance of their catalytic systems in this reaction. [16][17][18] Indeed, this is n...

show abstract

“…The approach has the inherent advantage that the results are related to truly in situ conditions. 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.…”

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

View full text Add to dashboard Cite

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.

show abstract

A model for the enantioselective hydrogenation of pyruvate catalysed by alkaloid‐modified platinum

Cited by 142 publications

References 35 publications

Non‐Linear Effect of Modifier Composition on Enantioselectivity in Asymmetric Hydrogenation over Platinum Metals

Non‐Linear Effect of Modifier Composition on Enantioselectivity in Asymmetric Hydrogenation over Platinum Metals

Enantioselective hydrogenation of ethyl pyruvate and 1-phenyl-1,2-propanedione on catalysts prepared by impregnation of colloidal platinum on SiO2

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

Contact Info

Product

Resources

About