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Stefan M. Huber - One of the best experts on this subject based on the ideXlab platform.
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bidentate chiral bis imidazolium based Halogen Bond donors synthesis and applications in enantioselective recognition and catalysis
Angewandte Chemie, 2020Co-Authors: Revannath L Sutar, Elric Engelage, Raphael Stoll, Stefan M. HuberAbstract:Even though Halogen Bonding-the noncovalent interaction between electrophilic Halogen substituents and Lewis bases-has now been established in molecular recognition and catalysis, its use in enantioselective processes is still very rarely explored. Herein, we present the synthesis of chiral bidentate Halogen-Bond donors based on two iodoimidazolium units with rigidly attached chiral sidearms. With these Lewis acids, chiral recognition of a racemic diamine is achieved in NMR studies. DFT calculations support a 1:1 interaction of the Halogen-Bond donor with both enantiomers and indicate that the chiral recognition is based on a different spatial orientation of the Lewis bases in the Halogen-Bonded complexes. In addition, moderate enantioselectivity is achieved in a Mukaiyama aldol reaction with a preorganized variant of the chiral Halogen-Bond donor. This represents the first case in which asymmetric induction was realized with a pure Halogen-Bond donor lacking any additional active functional groups.
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hypervalent iodine iii compounds as biaxial Halogen Bond donors
Journal of the American Chemical Society, 2020Co-Authors: Flemming Heinen, Elric Engelage, Christopher J Cramer, Stefan M. HuberAbstract:"Hypervalent" iodine(III) derivatives have been established as powerful reagents in organic transformations, but so far only a handful of studies have addressed their potential use as Halogen-Bonding noncovalent Lewis acids. In contrast to "classical" Halogen-Bond donors based on iodine(I) compounds, iodine(III) salts feature two directional electrophilic axes perpendicular to each other. Herein we present the first systematic investigation on biaxial binding to such Lewis acids in solution. To this end, hindered and unhindered iodolium species were titrated with various substrates, including diesters and diamides, via 1H NMR spectroscopy and isothermal titration calorimetry. Clear evidence for biaxial binding was obtained in two model systems, and the association strengths increased by 2 orders of magnitude. These findings were corroborated by density functional theory calculations (which reproduced the trend well but underestimated the absolute binding constants) and a cocrystal featuring biaxial coordination of a diamide to the unhindered iodolium compound.
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Carbon-Halogen Bond Activation by Selenium-Based Chalcogen Bonding.
Angewandte Chemie, 2017Co-Authors: Patrick Wonner, Lukas Vogel, Maximilian Düser, Luís Gomes, Florian Kniep, Bert Mallick, Daniel B. Werz, Stefan M. HuberAbstract:Chalcogen Bonding is a little explored noncovalent interaction similar to Halogen Bonding. This manuscript describes the first application of selenium-based chalcogen Bond donors as Lewis acids in organic synthesis. To this end, the solvolysis of benzhydryl bromide served as a halide abstraction benchmark reaction. Chalcogen Bond donors based on a bis(benzimidazolium) core provided rate accelerations relative to the background reactivity by a factor of 20-30. Several comparative experiments provide clear indications that the observed activation is due to chalcogen Bonding. The performance of the chalcogen Bond donors is superior to that of a related brominated Halogen Bond donor.
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cationic multidentate Halogen Bond donors in halide abstraction organocatalysis catalyst optimization by preorganization
Journal of the American Chemical Society, 2015Co-Authors: Stefan H Jungbauer, Stefan M. HuberAbstract:In contrast to hydrogen Bonding, which is firmly established in organocatalysis, there are still very few applications of Halogen Bonding in this field. Herein, we present the first catalytic application of cationic Halogen-Bond donors in a halide abstraction reaction. First, halopyridinium-, haloimidazolium-, and halo-1,2,3-triazolium-based catalysts were systematically tested. In contrast to the pyridinium compounds, both the imidazolium and the triazolium salts showed promising potency. For the haloimidazolium-based organocatalysts, we could show that the catalytic activity is based on Halogen Bonding using, e.g., the chlorinated derivatives as reference compounds. On the basis of these studies, halobenzimidazolium organocatalysts were then investigated. Monodentate compounds featured the same trends as the corresponding imidazolium analogues but showed a stronger catalytic activity. In order to prepare bidentate versions which are preorganized for anion binding, a new class of rigid bis(halobenzimidazolium) compounds was synthesized and structurally characterized. The corresponding syn isomer showed unprecedented catalytic potency and could be used in as low as 0.5 mol % in the benchmark reaction of 1-chloroisochroman with a silyl enol ether. Calculations confirmed that the syn isomer may bind in a bidentate fashion to chloride. The respective anti isomer is less active and binds halides in a monodentate fashion. Kinetic investigations confirmed that the syn isomer led to a 20-fold rate acceleration compared to a neutral tridentate Halogen-Bond donor. The strength of the preorganized Halogen-Bond donor seems to approach the limit under the reaction conditions, as decomposition is observed in the presence of chloride in the same solvent at higher temperatures. Calorimetric titrations of the syn isomer with bromide confirmed the strong Halogen-Bond donor strength of the former (K ≈ 4 × 10(6) M(-1), ΔG ≈ 38 kJ/mol).
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Cationic Multidentate Halogen-Bond Donors in Halide Abstraction Organocatalysis: Catalyst Optimization by Preorganization
2015Co-Authors: Stefan H. Jungbauer, Stefan M. HuberAbstract:In contrast to hydrogen Bonding, which is firmly established in organocatalysis, there are still very few applications of Halogen Bonding in this field. Herein, we present the first catalytic application of cationic Halogen-Bond donors in a halide abstraction reaction. First, halopyridinium-, haloimidazolium-, and halo-1,2,3-triazolium-based catalysts were systematically tested. In contrast to the pyridinium compounds, both the imidazolium and the triazolium salts showed promising potency. For the haloimidazolium-based organocatalysts, we could show that the catalytic activity is based on Halogen Bonding using, e.g., the chlorinated derivatives as reference compounds. On the basis of these studies, halobenzimidazolium organocatalysts were then investigated. Monodentate compounds featured the same trends as the corresponding imidazolium analogues but showed a stronger catalytic activity. In order to prepare bidentate versions which are preorganized for anion binding, a new class of rigid bis(halobenzimidazolium) compounds was synthesized and structurally characterized. The corresponding syn isomer showed unprecedented catalytic potency and could be used in as low as 0.5 mol % in the benchmark reaction of 1-chloroisochroman with a silyl enol ether. Calculations confirmed that the syn isomer may bind in a bidentate fashion to chloride. The respective anti isomer is less active and binds halides in a monodentate fashion. Kinetic investigations confirmed that the syn isomer led to a 20-fold rate acceleration compared to a neutral tridentate Halogen-Bond donor. The strength of the preorganized Halogen-Bond donor seems to approach the limit under the reaction conditions, as decomposition is observed in the presence of chloride in the same solvent at higher temperatures. Calorimetric titrations of the syn isomer with bromide confirmed the strong Halogen-Bond donor strength of the former (K ≈ 4 × 106 M–1, ΔG ≈ 38 kJ/mol)
Ulrich S Schubert - One of the best experts on this subject based on the ideXlab platform.
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Halogen Bond based cooperative ion pair recognition by a crown ether embedded 5 iodo 1 2 3 triazole
Chemical Communications, 2017Co-Authors: Ronny Tepper, Michael Jager, Helmar Gorls, Benjamin Schulze, Peter Bellstedt, Jan Heidler, Ulrich S SchubertAbstract:A crown-ether containing the iodo-triazole moiety for simultaneous cation–anion binding through Lewis-basic nitrogen atoms and C–I⋯I Halogen-Bond-donating iodine atoms was prepared. The complexation of the heteroditopic receptor was illustrated by X-ray and DFT analysis. The cooperative effect boosting the anion affinity was quantified by 1H/13C NMR titration experiments.
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preorganization in a cleft type anion receptor featuring iodo 1 2 3 triazoles as Halogen Bond donors
Organic Letters, 2015Co-Authors: Ronny Tepper, Michael Jager, Helmar Gorls, Benjamin Schulze, Peter Bellstedt, Ulrich S SchubertAbstract:Preorganization via intramolecular hydrogen Bonds was applied in a cleft-type receptor by exploiting the excellent Halogen Bond donor ability as well as hydrogen Bond acceptor function of iodo-1,2,3-triazoles. As investigated by isothermal calorimetric titrations, the restriction of conformational freedom causes an enhanced entropic contribution resulting in a strongly increased binding affinity. This efficient way to improve the binding strength of 5-halo-1,2,3-triazoles paves the way for applications of new charge-neutral Halogen Bond donors in solution.
Stefan H Jungbauer - One of the best experts on this subject based on the ideXlab platform.
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cationic multidentate Halogen Bond donors in halide abstraction organocatalysis catalyst optimization by preorganization
Journal of the American Chemical Society, 2015Co-Authors: Stefan H Jungbauer, Stefan M. HuberAbstract:In contrast to hydrogen Bonding, which is firmly established in organocatalysis, there are still very few applications of Halogen Bonding in this field. Herein, we present the first catalytic application of cationic Halogen-Bond donors in a halide abstraction reaction. First, halopyridinium-, haloimidazolium-, and halo-1,2,3-triazolium-based catalysts were systematically tested. In contrast to the pyridinium compounds, both the imidazolium and the triazolium salts showed promising potency. For the haloimidazolium-based organocatalysts, we could show that the catalytic activity is based on Halogen Bonding using, e.g., the chlorinated derivatives as reference compounds. On the basis of these studies, halobenzimidazolium organocatalysts were then investigated. Monodentate compounds featured the same trends as the corresponding imidazolium analogues but showed a stronger catalytic activity. In order to prepare bidentate versions which are preorganized for anion binding, a new class of rigid bis(halobenzimidazolium) compounds was synthesized and structurally characterized. The corresponding syn isomer showed unprecedented catalytic potency and could be used in as low as 0.5 mol % in the benchmark reaction of 1-chloroisochroman with a silyl enol ether. Calculations confirmed that the syn isomer may bind in a bidentate fashion to chloride. The respective anti isomer is less active and binds halides in a monodentate fashion. Kinetic investigations confirmed that the syn isomer led to a 20-fold rate acceleration compared to a neutral tridentate Halogen-Bond donor. The strength of the preorganized Halogen-Bond donor seems to approach the limit under the reaction conditions, as decomposition is observed in the presence of chloride in the same solvent at higher temperatures. Calorimetric titrations of the syn isomer with bromide confirmed the strong Halogen-Bond donor strength of the former (K ≈ 4 × 10(6) M(-1), ΔG ≈ 38 kJ/mol).
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5 iodo 1 2 3 triazolium based multidentate Halogen Bond donors as activating reagents
Chemical Communications, 2012Co-Authors: Florian Kniep, Stefan H Jungbauer, Laxmidhar Rout, Sebastian M Walter, Heide K V Bensch, Eberhardt Herdtweck, Stefan M. HuberAbstract:Bi- and tridentate polycationic Halogen Bond donors based on 5-iodo-1,2,3-triazolium groups have been synthesized by 1,3-dipolar cycloaddition reactions. These Halogen-based Lewis acids have been evaluated as activators in a halide-abstraction benchmark reaction.
Ronny Tepper - One of the best experts on this subject based on the ideXlab platform.
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polymeric Halogen Bond based donor systems showing self healing behavior in thin films
Angewandte Chemie, 2017Co-Authors: Ronny Tepper, Stefan Bode, Benjamin Dietzek, Robert Geitner, Michael Jager, Helmar Gorls, Jurgen Vitz, M Schmitt, Jürgen PoppAbstract:The synthesis and comprehensive characterization of a systematic series of cleft-type anion receptors imbedded into a polymeric architecture is presented. For the first time, isothermal calorimetric titrations on polymeric Halogen-Bond-based donors were exploited to evaluate the dependence of the anion affinity on different key parameters (i.e. monomeric versus polymeric receptor, Halogen versus hydrogen Bonding, charge assistance). The combination of these donor systems with a copolymer bearing accepting carboxylate groups led to supramolecular cross-linked polymer networks showing excellent intrinsic self-healing behavior. FT-Raman spectroscopy and nano-indentation measurements were utilized to clarify the thermally induced self-healing mechanism based on the formation of Halogen Bonds. These first self-healing materials based on Halogen Bonds pave the way for new applications of Halogen-Bond donors in polymer and material science.
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Halogen Bond based cooperative ion pair recognition by a crown ether embedded 5 iodo 1 2 3 triazole
Chemical Communications, 2017Co-Authors: Ronny Tepper, Michael Jager, Helmar Gorls, Benjamin Schulze, Peter Bellstedt, Jan Heidler, Ulrich S SchubertAbstract:A crown-ether containing the iodo-triazole moiety for simultaneous cation–anion binding through Lewis-basic nitrogen atoms and C–I⋯I Halogen-Bond-donating iodine atoms was prepared. The complexation of the heteroditopic receptor was illustrated by X-ray and DFT analysis. The cooperative effect boosting the anion affinity was quantified by 1H/13C NMR titration experiments.
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preorganization in a cleft type anion receptor featuring iodo 1 2 3 triazoles as Halogen Bond donors
Organic Letters, 2015Co-Authors: Ronny Tepper, Michael Jager, Helmar Gorls, Benjamin Schulze, Peter Bellstedt, Ulrich S SchubertAbstract:Preorganization via intramolecular hydrogen Bonds was applied in a cleft-type receptor by exploiting the excellent Halogen Bond donor ability as well as hydrogen Bond acceptor function of iodo-1,2,3-triazoles. As investigated by isothermal calorimetric titrations, the restriction of conformational freedom causes an enhanced entropic contribution resulting in a strongly increased binding affinity. This efficient way to improve the binding strength of 5-halo-1,2,3-triazoles paves the way for applications of new charge-neutral Halogen Bond donors in solution.
Benjamin Schulze - One of the best experts on this subject based on the ideXlab platform.
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Halogen Bond based cooperative ion pair recognition by a crown ether embedded 5 iodo 1 2 3 triazole
Chemical Communications, 2017Co-Authors: Ronny Tepper, Michael Jager, Helmar Gorls, Benjamin Schulze, Peter Bellstedt, Jan Heidler, Ulrich S SchubertAbstract:A crown-ether containing the iodo-triazole moiety for simultaneous cation–anion binding through Lewis-basic nitrogen atoms and C–I⋯I Halogen-Bond-donating iodine atoms was prepared. The complexation of the heteroditopic receptor was illustrated by X-ray and DFT analysis. The cooperative effect boosting the anion affinity was quantified by 1H/13C NMR titration experiments.
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preorganization in a cleft type anion receptor featuring iodo 1 2 3 triazoles as Halogen Bond donors
Organic Letters, 2015Co-Authors: Ronny Tepper, Michael Jager, Helmar Gorls, Benjamin Schulze, Peter Bellstedt, Ulrich S SchubertAbstract:Preorganization via intramolecular hydrogen Bonds was applied in a cleft-type receptor by exploiting the excellent Halogen Bond donor ability as well as hydrogen Bond acceptor function of iodo-1,2,3-triazoles. As investigated by isothermal calorimetric titrations, the restriction of conformational freedom causes an enhanced entropic contribution resulting in a strongly increased binding affinity. This efficient way to improve the binding strength of 5-halo-1,2,3-triazoles paves the way for applications of new charge-neutral Halogen Bond donors in solution.
