Towards Supramolecular Fixation of NOX Gases: Encapsulated Reagents for Nitrosation
✍ Scribed by Yanlong Kang; Grigory V. Zyryanov; Dmitry M. Rudkevich
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 207 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
The use of simple calix[4]arenes for chemical conversion of NO~2~/N~2~O~4~ gases is demonstrated in solution and in the solid state. Upon reacting with these gases, calixarenes 1 encapsulate nitrosonium (NO^+^) cations within their cavities with the formation of stable calixarene–NO^+^ complexes 2. These complexes act as encapsulated nitrosating reagents; cavity effects control their reactivity and selectivity. Complexes 2 were effectively used for nitrosation of secondary amides 5, including chiral derivatives. Unique size–shape selectivity was observed, allowing for exclusive nitrosation of less crowded N‐Me amides 5 a–e (up to 95 % yields). Bulkier N‐Alk (Alk>Me) substrates 5 did not react due to the hindered approach to the encapsulated NO^+^ reagents. Robust, silica gel based calixarene material 3 was prepared, which reversibly traps NO~2~/N~2~O~4~ with the formation of NO^+^‐storing silica gel 4. With material 4, similar size–shape selectivity was observed for nitrosation. The N‐Me–N‐nitroso derivatives 6 d,e were obtained with ∼30 % yields, while bulkier amides were nitrosated with much lower yields (<8 %). Enantiomerically pure encapsulating reagent 2 d was tested for nitrosation of racemic amide 5 t, showing modest but reproducible stereoselectivity and ∼15 % ee. Given high affinity to NO^+^ species, which can be generated by a number of NO~X~ gases, these supramolecular reagents and materials may be useful for NO~X~ entrapment and separation in the environment and biomedical areas.