Inducing Axial Chirality in a Supramolecular Catalyst

Wenz, Katharina Marie; Leonhardt-Lutterbeck, Günter; Breit, Bernhard

doi:10.1002/anie.201801048

Cited by 32 publications

(8 citation statements)

References 63 publications

(104 reference statements)

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“…Recently, the library of chiral 6-DPPon building blocks was extended to analogues with a chiral functional group at the 5 position of the pyridine ring, as illustrated in Scheme 33. 332 These self-assembled bidentate ligands are not planar but twisted around the HB motif, leading to atropisomeric structures, and the presence of additional chiral groups results in the formation of diastereotopic species. These diastereoisomers interconvert rapidly at room temperature but can be spectroscopically resolved at low temperature (−40 °C), showing the presence of a dominant species.…”

Section: -Ddpon Ligandsmentioning

confidence: 99%

Transition Metal Catalysis Controlled by Hydrogen Bonding in the Second Coordination Sphere

et al. 2022

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Transition metal catalysis is of utmost importance for the development of sustainable processes in academia and industry. The activity and selectivity of metal complexes are typically the result of the interplay between ligand and metal properties. As the ligand can be chemically altered, a large research focus has been on ligand development. More recently, it has been recognized that further control over activity and selectivity can be achieved by using the “second coordination sphere”, which can be seen as the region beyond the direct coordination sphere of the metal center. Hydrogen bonds appear to be very useful interactions in this context as they typically have sufficient strength and directionality to exert control of the second coordination sphere, yet hydrogen bonds are typically very dynamic, allowing fast turnover. In this review we have highlighted several key features of hydrogen bonding interactions and have summarized the use of hydrogen bonding to program the second coordination sphere. Such control can be achieved by bridging two ligands that are coordinated to a metal center to effectively lead to supramolecular bidentate ligands. In addition, hydrogen bonding can be used to preorganize a substrate that is coordinated to the metal center. Both strategies lead to catalysts with superior properties in a variety of metal catalyzed transformations, including (asymmetric) hydrogenation, hydroformylation, C–H activation, oxidation, radical-type transformations, and photochemical reactions.

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Section: -Ddpon Ligandsmentioning

confidence: 99%

Transition Metal Catalysis Controlled by Hydrogen Bonding in the Second Coordination Sphere

et al. 2022

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“…The auxiliary naproxen applied here was also successfully used in an interesting pyridone-based supramolecular catalyst developed by Breit and co-workers. 70 This catalyst showed high ee's of up to 91% in asymmetric Rh-catalyzed hydrogenations.…”

Section: ■ Stereodynamically Flexible Ligandsmentioning

confidence: 94%

Nonlinear Effects in Asymmetric Catalysis by Design: Concept, Synthesis, and Applications

2022

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Conspectus Asymmetric synthesis constitutes a key technology for the preparation of enantiomerically pure compounds as well as for the selective control of individual stereocenters in the synthesis of complex compounds. It is thus of extraordinary importance for the synthesis of chiral drugs, dietary supplements, flavors, and fragrances, as well as novel materials with tunable and reconfigurable chiroptical properties or the assembly of complex natural products. Typically, enantiomerically pure catalysts are used for this purpose. To prepare enantiomerically pure ligands or organocatalysts, one can make use of the natural chiral pool. Ligands and organocatalysts with an atropisomeric biphenyl and binaphthyl system have become popular, as they are configurationally stable and contain a C2-symmetric skeleton, which has been found to be particularly privileged. For catalysts with opposite configurations, both product enantiomers can be obtained. Configurationally flexible biphenyl systems initially appeared to be unsuitable for this purpose, as they racemize after successful enantiomer separation and thus are neither storable nor afford a reproducible enantioselectivity. However, there are strategies that exploit the dynamics of such ligands to stereoconvergently enrich one of the catalyst enantiomers. This can be achieved, for example, by coordinating an enantiomerically pure additive to a ligand–metal complex, which results in deracemization of the configurationally flexible biphenyl system, thereby enriching the thermodynamically preferred diastereomer. In this Account, we present our strategy to design stereochemically flexible catalysts that combine the properties of supramolecular recognition, stereoconvergent alignment, and catalysis. Such systems are capable to recognize the chirality of the target product, leading to an increase in enantioselectivity during asymmetric catalysis. We have systematically developed and investigated these smart catalyst systems and have found ways to specifically design and synthesize them for various applications. In addition to (i) reaction product-induced chiral amplification, we have developed systems with (ii) intermolecular and (iii) intramolecular recognition, and successfully applied them in asymmetric catalysis. Our results pave the way for new applications such as temperature-controlled enantioselectivity, controlled inversion of enantioselectivity with the same chirality of the recognition unit, generation of positive nonlinear effects, and targeted design of autocatalytic systems through dynamic formation of transient catalysts. Understanding such systems is of enormous importance for catalytic processes leading to symmetry breaking and amplification of small imbalances of enantiomers and offer a possible explanation of homochirality of biological systems. In addition, we are learning how to target supramolecular interactions to enhance enantioselectivities in asymmetric catalysis through secondary double stereocontrol. Configurationally flexible catalysts will enabl...

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“…21 The aim of this study was to investigate the product or product mimic induced chirality transfer 22 from a nonstereoselective interaction site in a stereodynamic ligand. 23 In particular, the here presented ligand are racemic, and because of the non-stereoselective nature of the product or product mimic interaction sites, there is also no preference or selectivity induced in favor for one of these enantiomers.…”

Section: Introductionmentioning

confidence: 94%

Supramolecular chirality transfer in a stereodynamic catalysts

Storch

Trapp

2018

Chirality

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We present rhodium catalysts that contain stereodynamic axially chiral biphenol-derived phosphinite ligands modified with non-stereoselective amides for non-covalent interactions. A chirality transfer was achieved with (R)- or (S)-acetylphenylalanine methyl amide, and the interaction mechanism was investigated by NMR measurements. These interactions at the non-stereoselective interaction sites and the formation of supramolecular complexes result in an enrichment of either the (R )- or (S ) enantiomer of the tropos catalysts, which in turn provide the (R)- or (S)-acetylphenylalanine methyl ester in the hydrogenation of (Z)-methyl-α-acetamidocinnamate.

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Inducing Axial Chirality in a Supramolecular Catalyst

Cited by 32 publications

References 63 publications

Transition Metal Catalysis Controlled by Hydrogen Bonding in the Second Coordination Sphere

Transition Metal Catalysis Controlled by Hydrogen Bonding in the Second Coordination Sphere

Nonlinear Effects in Asymmetric Catalysis by Design: Concept, Synthesis, and Applications

Supramolecular chirality transfer in a stereodynamic catalysts

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