Homolytic, Heterolytic, Mesolytic - As You Like It: Steering the Cleavage of a HC(sp3)−C(sp3)H Bond in Bis(1H-2,1-benzazaborole) Derivatives
| Autor: | Claudia Wilfer, Libor Dostál, Sonja Herres-Pawlis, Martin Hejda, Roman Jambor, Alexander Hoffmann, Antonín Lyčka, Tomáš Mikysek, Aleš Růžička, Jaromír Vinklárek |
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| Rok vydání: | 2016 |
| Předmět: |
Atropisomer
010405 organic chemistry Hydrogen bond Stereochemistry Chemistry Radical Organic Chemistry General Chemistry Nuclear magnetic resonance spectroscopy 010402 general chemistry 01 natural sciences Medicinal chemistry Heterolysis Catalysis 0104 chemical sciences Homolysis law.invention law Reactivity (chemistry) Electron paramagnetic resonance |
| Zdroj: | Chemistry - A European Journal. 22:15340-15349 |
| ISSN: | 0947-6539 |
| Popis: | A set of (3,3')-bis(1-Ph-2-R-1H-2,1-benzazaborole) compounds, in which R=tBu (Bab-tBu)2 , R=Dipp (Bab-Dipp)2 or R=tBu and Dipp (Bab-Dipp)(Bab-tBu), was synthesized and fully characterized using 1 H, 11 B, 13 C, and 15 N NMR spectroscopy as well as single-crystal X-ray diffraction analysis. The central HC(sp3 )-C(sp3 )H bond with restricted rotation at the junction of both 1H-2,1-benzazaborole rings displayed an intriguing reactivity. It was demonstrated that this bond is easily mesolytically cleaved using alkali metals to form the respective aromatic 1Ph-2R-1H-2,1-benzazaborolyl anions M+ (THF)n (Bab-tBu)- (M=Li, Na, K) and K+ (THF)n (Bab-Dipp)- . Furthermore, the central HC(sp3 )-C(sp3 )H bond of bis(1H-2,1-benzazaborole)s is also homolytically cleaved either by heating or photochemical means, giving corresponding 1Ph-2R-1H-2,1-benzazaborolyl radicals (Bab-tBu). and (Bab-Dipp). , which rapidly self-terminate. Nevertheless, their formation was unambiguously established by NMR analysis of the reaction mixtures containing products of the self-termination of the radicals after heating or irradiation. (Bab-Dipp). radical was also characterized using EPR spectroscopy. Importantly, it turned out that the essentially non-polarized HC(sp3 )-C(sp3 )H bond in (Bab-tBu)2 is also cleaved heterolytically with 2 equiv of MeLi, giving the mixture of Li+ (SOL)n (Bab-tBu)- (SOL=THF or Et2 O) and lithium methyl-substituted borate complex Li+ (SOL)n (Bab-tBu-Me)- in a diastereoselective fashion. |
| Databáze: | OpenAIRE |
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