- Supramolecular fixation of NO2 with calix[4]arenes
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Reaction of NO2 with simple calix[4]arenes in chloroform in the presence of a Lewis acid rapidly results in intense coloration caused by the encapsulation of nitrosonium cation.
- Zyryanov, Grigory V.,Kang, Yanlong,Stampp, Stephen P.,Rudkevich, Dmitry M.
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- Sensing and fixation of NO2/N2O4 by calix[4]arenes
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An approach toward visual detection and chemical utilization of NO2/N2O4 is proposed, which employs simple calix[4]arenes. Exposure of tetra-O-alkylated calix[4]arenes 1 and 2, possessing either a cone or a 1,3-alternate conformation, to NO2/N2O4, both in chloroform solution and in the solid state, results in deeply colored calixarene-nitrosonium (NO+) complexes. In the presence of a Lewis acid, such as SnCl4, stable calixarene-NO+ complexes 7 and 8 were isolated in a quantitative yield and characterized by UV-vis, FTIR, high-resolution 1H NMR spectroscopy and elemental analysis. NO+ is found encapsulated within the calixarene cavity, and stable charge-transfer complexes result with Kass > 106 M-1 (CDCl3). The NO+ encapsulation was also demonstrated in titration experiments with calixarenes 1, 2, and 5 and commercially available NO+SbF6- salt in chloroform. The complexation process is reversible, and the complexes dissociate upon addition of water and alcohol, recovering the parent calixarenes. Attachment of functionalized calix[4]arenes to silica gel was demonstrated, which afforded a solid material 15 capable of visual detection and entrapment of NO2/N2O4. Calixarene-NO+ complexes can be utilized for the NO+ transfer processes and nitrosation reactions. The NO+ guest transfer between two calixarene containers 2 and 5 was achieved and studied by UV-vis and 1H NMR spectroscopy. Chemical fixation of NO2/N2O4 was demonstrated through their quantitative transformation into the calixarene-NO+ complex and its use as a nitrosonium transfer agent in the synthesis of N-nitrosoamides. These results may lead toward novel nitrogen oxides storing materials.
- Zyryanov, Grigory V.,Kang, Yanlong,Rudkevich, Dmitry M.
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- Polymer-supported calix[4]arenes for sensing and conversion of NO 2/N2O4
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The use of simple calix[4]arenes 1a,b for NO2/N 2O4 sensing and conversion is demonstrated, both in solution and in the solid state. Upon reacting with these gases, compounds 1a,b encapsulate reactive NO+ cation
- Kang, Yanlong,Rudkevich, Dmitry M.
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- Tert -Butyl nitrite promoted transamidation of secondary amides under metal and catalyst free conditions
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A mild and efficient method is demonstrated for the transamidation of secondary amides with various amines including primary, secondary, cyclic and acyclic amines in the presence of tert-butyl nitrite. The reaction proceeds through the N-nitrosamide intermediate and provides the transamidation products in good to excellent yields at room temperature. Moreover, the developed methodology does not require any catalyst or additives.
- Sureshbabu, Popuri,Azeez, Sadaf,Chaudhary, Priyanka,Kandasamy, Jeyakumar
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supporting information
p. 845 - 850
(2019/01/30)
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- Towards supramolecular fixation of NOx gases: Encapsulated reagents for nitrosation
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The use of simple calix[4]arenes for chemical conversion of NO2/ N2O4 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 5a-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/ N2O4 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 6d,e were obtained with ~30% yields, while bulkier amides were nitrosated with much lower yields (+ species, which can be generated by a number of NOx gases, these supramolecular reagents and materials may be useful for NOx entrapment and separation in the environment and biomedical areas.
- Kang, Yanlong,Zyryanov, Grigory V.,Rudkevich, Dmitry M.
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p. 1924 - 1932
(2007/10/03)
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- Toward Synthetic Tubes for NO2/N2O4: Design, Synthesis, and Host-Guest Chemistry
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Design of molecular nanotubes is proposed for entrapment and conversion of NO2/N2O4 gases. Synthesis of 1,3-alternate bis-calix[4]arene tube 3 of 5 × 11 A internal dimensions is presented, and its reversible reactions with
- Zyryanov, Grigory V.,Rudkevich, Dmitry M.
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p. 4264 - 4270
(2007/10/03)
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- Encapsulated reagents for nitrosation
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(Matrix presented) A novel class of stable, mild, and size-shape-selective nitrosating agents for secondary amides is introduced. These are based on reversible entrapment and release of reactive nitrosonium species by calix[4]arenes. The NO+ encapsulation controls the reaction selectivity.
- Zyryanov, Grigory V.,Rudkevich, Dmitry M.
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p. 1253 - 1256
(2007/10/03)
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