Homogeneous and heterogeneous catalytic asymmetric reactions

Wittmann, Gyula; Bartók, Gizella B.; Bartók, Mihály; Smith, Gerard V.

doi:10.1016/0304-5102(90)85061-l

Cited by 40 publications

(13 citation statements)

References 35 publications

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“…Although the results of the optimization of the parameters affecting the enantioselectivity (type of a modifier and co-modifier, modification pH, modification temperature, and modification time) have differed according to the researchers [26,60,64,[71][72][73][74][75][76], the following conditions are generally accepted for attaining a high enantioselectivity, that is, i) the use of tartaric acid and NaBr as a modifier and a comodifier, respectively, ii) the use of a weakly acidic modification solution, and iii) a high temperature modification. Under these conditions, modification is a corrosive procedure, and both the adsorption of the (co-) modifier and the conditioning of the Ni surface are simultaneously carried out.…”

Section: Pre-modification 31211 Modification In An Aqueous Mediamentioning

confidence: 99%

Asymmetrically Modified Nickel Catalyst for the Enantio-Differentiating Hydrogenation of Prochiral Ketones

Osawa

Harada

Takayasu

2006

COC

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The state of the art for the enantio-differentiating hydrogenation over an asymmetrically modified nickel catalyst is reviewed along with the background development of the catalyst. An enantioselectivity up to 98% was obtained for the hydrogenation of β-functionalized ketones. The durability of the enantioselectivity was significantly improved using an in-situ-modified nickel powder catalyst (80-90% enantioselectivity for over 20 runs). Recent mechanistic investigations based on surface science are also summarized for the discussion of the enantio-differentiating model.

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Section: Pre-modification 31211 Modification In An Aqueous Mediamentioning

confidence: 99%

Asymmetrically Modified Nickel Catalyst for the Enantio-Differentiating Hydrogenation of Prochiral Ketones

Osawa

Harada

Takayasu

2006

COC

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“…The reaction has been carried out over a variety of supported (3,4,(18)(19)(20)28,30,31,37,38) and unsupported (1-3, l l , 2 8 , 2 9 , 32, 36) nickel systems, principally in the liquid phase (3,4, 11, 19,20,27-32, 34, 35, 37, 38), but gas phase transformations have also been reported (23,26,30,36). In attempting to define the nature of the surface sites that promote enantiodifferentiation, the effects of varying the modification conditions have been considered (1,3,4,18,24,25,27,28,32,33) and the reaction variables have also been altered to optimize the enantioselectivity process (1,4,10,12,14,17,34). Regardless, there is still no consensus of opinion regarding the actual source of the enantiocontrol and, to date, the efforts made to relate optical yield to the coverage of the catalyst surface by the modifier have been largely unsuccessful (20,27,33,35,36).…”

Section: Introductionmentioning

confidence: 99%

“…It has, how-'present address: Department of and ever, been concluded in a number of instances (7,12,17 ing part of the active metal surface. In addition, several workers have noted a difficulty in obtaining reproducible product compositions (10,12,18,23,24,31). In this paper, accurate M A A hydrogenation rates and enantioselectivities are reported for a range of well characterized Ni-Si02 catalysts prepared by impregnation and homogeneous precipitation-deposition and modified with optically pure TA.…”

Section: Introductionmentioning

confidence: 99%

The role of catalyst activation in the enantioselective hydrogenation of methyl acetoacetate over silica-supported nickel catalysts

Keane¹

1994

Can. J. Chem.

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A range of Ni-Si02 catalysts have been prepared by homogeneous precipitation-deposition and impregnation techniques and modified with aqueous solutions of R-(+)-tartaric acid (TA) to induce enantioselectivity in the asymmetric hydrogenation of a prochiral P-ketoester (methyl acetoacetate) to a P-hydroxyester ((R)-(-)-methyl3-hydroxybutyrate). The effects of catalyst precursor preparation, nickel loading, and precalcination on the reduction of the precursor were examined and the nature of the resultant nickel particle size distribution is described. The influence of metal-support interactions on the uptake of TA was investigated and data on the corrosive metal leaching and the consequent changes in metal dispersion are presented. Modification of the catalysts with TA not only induced enantioselectivity, but also increased the turnover frequency by up to 15 times that observed for the unmodified surface. The amount of TA adsorbed and the fractional surface coverage by TA is related to the degree of enantiodifferentiation. The effects of variations in supported nickel metal particle sizes (in the overall range of 1.4-13.6 nm) on the reaction rate and enantioselectivity were examined; while the selectivity was independent of metal particle size, the rate of hydrogenation was found to be structure sensitive and a correlation between reaction rate sensitivity and particle size is presented.MARK A. KEANE. Can. J. Chem. 72,372 (1994). On a prCparC une sene de catalyseurs Ni-Si02 par des techniques de prCcipitation-dCp6t et d'imprkgnation homogbnes et on les a modifiCs avec des solutions aqueuses d'acide R-(+)-tartrique (AT) dans le but d'induire de I'CnantiosClectivitC dans l'hydrogCnation asymCtrique d'un ester P-cCtonique prochiral (acetoacetate de mCthyle) en ester P-hydroxylC, (R)-(-)-3-hydroxybutyrate de mCthyle. On a CvaluC les effets de la prCparation des prCcurseurs des catalyseurs, de la quantitC de nickel et de la prCcalcination sur la reduction du prCcurseur et on dCcrit la nature de la distribution des grosseurs des particules de nickel qui en rCsulte. On a CtudiC l'influence des interactions mCtal-support sur la quantitC d'AT adsorb6 et on prCsente des donnCes concernant le lixiviation par des mCtaux corrosifs et sur les changements qui en rCsultent sur la dispersion du mCtal. La modification des catalyseurs par I'AT n'induit pas seulement de l'CnantiosClectivitC, le frCquence dlCchange est 15 fois plus rapide que sur une surface non modifiCe. La quantitC d'AT adsorbke et la fraction de la surface qui est couverte sont relikes au degrC d'Cnantiodiffkrentiation. On a examink les effets des variations dans les grosseurs des particules du nickel support6 (grosseurs allant de 1,4 B 13,6 nm) sur la vitesse de rCaction et sur llCnantiosClectiviC; alors que l'on a trouvC que la sClectivitC est indCpendante de la grosseur des particules mktalliques, la vitesse d'hydrogknation est sensible ? I la structure et on prCsente une corrClation entre la sensibilitC de la vitesse rkactionnelle et la grosseur des particules.[...

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“…Studies on enantioselective catalytic hydrogenation at the University of Szeged started with the investigation of the MRNi catalyst [247][248][249][250]. These studies were also extended to the hydrogenation of steroids [251][252][253][254][255][256][257][258], an important family of compounds successfully researched at the University of Szeged [259][260][261][262].…”

Section: Other Heterogeneous Chiral Hydro-genationmentioning

confidence: 99%