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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
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Cationic Multidentate Halogen-Bond Donors in Halide Abstraction Organocatalysis: Catalyst Optimization by
Stefan H Jungbauer1, Stefan M Huber1
1Fakultät für Chemie und Biochemie, Organische Chemie I, Ruhr-Universität Bochum , Universitätsstrasse 150, 44801 Bochum, Germany.
Journal of the American Chemical Society
|September 3, 2015
Summary
This study introduces cationic halogen-bond donors for halide abstraction catalysis, demonstrating superior performance with rigid bis(halobenzimidazolium) compounds. These catalysts show high efficiency in organocatalysis, paving the way for new synthetic methodologies.
Area of Science:
- Organocatalysis
- Supramolecular Chemistry
- Halogen Bonding
Background:
- Hydrogen bonding is well-established in organocatalysis, but halogen bonding applications are limited.
- Cationic halogen-bond donors offer a promising, yet underexplored, avenue for catalytic activation.
Purpose of the Study:
- To investigate the catalytic application of cationic halogen-bond donors in halide abstraction reactions.
- To develop novel organocatalysts based on halobenzimidazolium scaffolds for enhanced reactivity.
Main Methods:
- Systematic screening of various cationic halogen-bond donors (halopyridinium, haloimidazolium, halotriazolium).
- Synthesis and structural characterization of rigid bis(halobenzimidazolium) compounds.
- Catalytic testing in a benchmark halide abstraction reaction (1-chloroisochroman with silyl enol ether).
- Computational studies (calculations) and kinetic investigations.
- Calorimetric titrations to determine binding affinities.
Main Results:
- Haloimidazolium and halotriazolium salts showed significant catalytic activity.
- Rigid bis(halobenzimidazolium) compounds, particularly the syn isomer, exhibited unprecedented catalytic potency, enabling reactions at 0.5 mol % loading.
- The syn isomer demonstrated bidentate binding to chloride, leading to a 20-fold rate acceleration compared to a neutral donor.
- Calorimetric titrations confirmed strong halogen-bond donor strength (K ≈ 4 × 10^6 M^-1).
Conclusions:
- Cationic halogen-bond donors, especially rigid bis(halobenzimidazolium) structures, are highly effective in halide abstraction catalysis.
- The developed catalysts represent a significant advancement in organocatalysis, offering high efficiency and strong halide binding.
- Further exploration of these potent halogen-bond donors could unlock new synthetic transformations.
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