New rhodium complexes anchored on modified USY zeolites. A remarkable effect of the support on the enantioselectivity of catalytic hydrogenation of prochiral alkenes

Corma, Avelino; Iglesias, Marta; Pino, C. Del; Sánchez, Félix

doi:10.1039/c39910001253

Cited by 139 publications

(59 citation statements)

References 9 publications

(2 reference statements)

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“…However this effect was not ascribed to a surface effect, but to 15 a change in the coordinating ability of the anion. It was observed that the substitution of triflate by a less coordinating anion, SbF 6 − or ClO 4 − , produces the same reversal in solution due to a change in the geometry, from octahedral with the coordinating anion to tetrahedral with the non-coordinating 20 one. The hydrogen bonds between silanols and triflates might be responsible for this change in coordinating character on the solid support.…”

mentioning

confidence: 98%

“…In spite of the non-crystalline character of clays, probably the most documented confinement effect on enantioselectivity is the surface effect of clay-supported chiral catalysts. In this case we can consider the surface around the catalytic complex 20 as a bidimensional nanoreactor, able to condition the approach of the reagents and thus the relative energies of the transition states. Why surface and not interlamellar space?…”

Section: Hydrogen Bondsmentioning

confidence: 99%

“…1 In principle, the applicability of these systems would be improved if they 20 were heterogeneous in nature, due to the advantages from a practical point of view of heterogeneous catalysts as compared to homogeneous ones. 2 The main strategy used to prepare chiral heterogeneous catalysts is the immobilization of catalytically active chiral metal complexes.…”

Section: Introductionmentioning

confidence: 99%

“…Confinement effects due to the situation of the complex inside the micro-or mesopores of crystalline materials were invoked in some preliminary publications, 20 and in more recent ones, 21 although no systematic studies were carried out regarding pore size effect or role of spacer. In all cases, chiral Rh or Ru 60 complexes covalently bonded to USY zeolite or mesoporous MCM-41 were used in hydrogenation reactions with slight to significant enhancement of enantioselectivity from the results obtained in solution.…”

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confidence: 99%

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Enantioselective catalysis with chiral complexes immobilized on nanostructured supports

et al. 2009

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5In spite of the inherent advantages of reuse and stability of immobilized chiral catalysts, they are frequently not enough to justify the effort necessary to immobilize the chiral complexes, unless additional advantages are found. When chiral catalysts are immobilized on solids with surface and pores of well controlled size, shape and dimensionality, the solid may act as a nano-reactor reducing the free movement of reagents, intermediates and, mainly, transition states. In this way 10 relative energies of the transition states leading to the different stereoisomers may be modified and, as a consequence, the stereochemical result of the reaction is modified when compared with the obtained in solution. The use of support effects to improve and/or change the stereochemical result of enantioselective reactions is currently emerging as an area of interest, but still with a limited number of examples. A better comprehension of the support influence will be needed in 15 order to allow, in the near future, the design of chiral ligands better adapted to this strategy.

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confidence: 98%

Section: Hydrogen Bondsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Enantioselective catalysis with chiral complexes immobilized on nanostructured supports

et al. 2009

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“…Despite the abundance of chirality in nature, the discovery of a zeolite or zeolite-like microporous material with enantioselective properties has remained elusive. Enantioenriched, chiral zeolitic materials are of particular interest for their potential to provide robust, new, enantiospecific, shape-selective catalytic pathways and separation processes (6)(7)(8)(9)(10)(11)(12)(13).…”

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confidence: 99%

Enantiomerically enriched, polycrystalline molecular sieves

Brand

Schmidt

Deem

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

116

140

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Zeolite and zeolite-like molecular sieves are being used in a large number of applications such as adsorption and catalysis. Achievement of the long-standing goal of creating a chiral, polycrystalline molecular sieve with bulk enantioenrichment would enable these materials to perform enantioselective functions. Here, we report the synthesis of enantiomerically enriched samples of a molecular sieve. Enantiopure organic structure directing agents are designed with the assistance of computational methods and used to synthesize enantioenriched, polycrystalline molecular sieve samples of either enantiomer. Computational results correctly predicted which enantiomer is obtained, and enantiomeric enrichment is proven by high-resolution transmission electron microscopy. The enantioenriched and racemic samples of the molecular sieves are tested as adsorbents and heterogeneous catalysts. The enantioenriched molecular sieves show enantioselectivity for the ring opening reaction of epoxides and enantioselective adsorption of 2-butanol (the R enantiomer of the molecular sieve shows opposite and approximately equal enantioselectivity compared with the S enantiomer of the molecular sieve, whereas the racemic sample of the molecular sieve shows no enantioselectivity). chirality | zeolite | asymmetric catalysis | chiral adsorption

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Shape‐Selective Catalysis – Heterogeneous

Csicsery

Kiricsi

2002

Encyclopedia of Catalysis

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Molecular sieves have uniform pores. If the pores are small, the fate of the reactants and the probability of forming products are determined by molecular dimensions and configurations as well as by the types of catalytically active sites present. Reactant shape selectivity occurs when some of the molecules in a reactant mixture are too large to enter the pores. Product selectivity occurs when, among all the product molecules formed within the pores, only those with the proper dimensions can diffuse out and appear as products. In restricted transition state type selectivity certain reactions are prevented because the corresponding transition state requires more space than is available inside the pores. Shape selective processes include acid‐ or base‐catalyzed reactions, oxidations, and reductions. Commercial applications of shape selectivity ( 1 ) form desirable isomers instead of undesirable ones, ( 2 ) crack undesirable molecules to smaller, easily removable fragments, or ( 3 ) avoid undesirable competing reactions such as coking and transalkylation. Ordered mesoporous materials, pillared layer structures, heteropolyacids, and carbon molecular sieves and nanotubes extend shape‐selective application to reactions of molecules too large to fit in the pores of aluminosilicate zeolites. Designing new molecular sieves and modifying existing ones can amplify shape selective effects and thus help to meet future challenges: diminishing raw material supplies, more stringent environmental regulations, changing fuel requirements, and the desire for more flexible, more economical, and environmentally more friendly processes.

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New rhodium complexes anchored on modified USY zeolites. A remarkable effect of the support on the enantioselectivity of catalytic hydrogenation of prochiral alkenes

Cited by 139 publications

References 9 publications

Enantioselective catalysis with chiral complexes immobilized on nanostructured supports

Enantioselective catalysis with chiral complexes immobilized on nanostructured supports

Enantiomerically enriched, polycrystalline molecular sieves

Shape‐Selective Catalysis – Heterogeneous

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