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Ortho-Carborane-Derived Halogen Bonding Organocatalysts
Christoph J Vonnemann1, Elric Engelage1, Jas S Ward2
1Fakultät für Biochemie und Chemie, Ruhr-Universität Bochum, Universitätsstraße 150, 44801, Bochum, Germany.
Angewandte Chemie (International Ed. in English)
|February 14, 2025
Summary
New iodinated ortho-carborane catalysts exhibit strong halogen bonding and superior Lewis acidity. These novel catalysts effectively perform halide abstraction and catalyze challenging nitro-Michael additions, expanding the scope of organocatalysis.
Area of Science:
- Organometallic Chemistry
- Supramolecular Chemistry
- Catalysis
Background:
- Halogen bonding (XB) is a non-covalent interaction crucial in various chemical processes.
- Traditional halogen bond donors often face limitations in Lewis acidity and scope.
- Icosahedral carboranes offer a unique scaffold for designing novel XB catalysts.
Purpose of the Study:
- To introduce and characterize novel multidentate neutral halogen bonding catalysts based on iodinated icosahedral ortho-carborane moieties.
- To evaluate the Lewis acidity and binding capabilities of these new catalysts.
- To demonstrate the catalytic activity of these carborane-based catalysts in challenging organic transformations.
Main Methods:
- Co-crystallization studies to determine structural interactions.
- Calorimetric measurements to quantify binding enthalpies.
- Proton Nuclear Magnetic Resonance (¹H NMR) titrations for binding analysis.
- Quantum-chemical calculations to understand electronic properties and Lewis acidity.
- Testing in halide abstraction and nitro-Michael addition reactions.
Main Results:
- The iodocarborane catalysts demonstrated strong binding affinities towards halides and neutral compounds.
- Superior Lewis acidity was observed compared to traditional perfluorinated halogen-bond donors.
- The catalysts successfully outperformed existing donors in a halide abstraction reaction.
- Catalytic activity was achieved in a nitro-Michael addition reaction, a transformation previously inaccessible for neutral XB organocatalysts.
Conclusions:
- Multidentate neutral iodinated ortho-carborane moieties represent a powerful new class of halogen bonding catalysts.
- These catalysts exhibit enhanced Lewis acidity and binding strength, surpassing conventional XB donors.
- The developed catalysts enable challenging organic reactions, broadening the applications of neutral halogen bonding in organocatalysis.
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