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Homolytic, Heterolytic, Mesolytic - As You Like It: Steering the Cleavage of a HC(sp(3))-C(sp(3))H Bond in Bis(1H-2,1-benzazaborole)Derivatives
Authors: Hejda Martin | Lyčka Antonín | Mikysek Tomáš | Jambor Roman | Růžička Aleš | Vinklárek Jaromír | Wilfer Claudia | Hoffmann Alexander | Herres-Pawlis Sonja | Dostál Libor
Year: 2016
Type of publication: článek v odborném periodiku
Name of source: Chemistry - A European Journal
Publisher name: Wiley-VCH
Place: Weinheim
Page from-to: 15340-15349
Titles:
Language Name Abstract Keywords
cze Štěpení vazby HC(sp(3))-C(sp(3))H v Bis(1H-2,1-benzazaborolu) Bylo studováno možné štěpení vazby HC(sp(3))-C(sp(3))H v Bis(1H-2,1-benzazaborolu) pomocí NMR spektroskopie.
eng Homolytic, Heterolytic, Mesolytic - As You Like It: Steering the Cleavage of a HC(sp(3))-C(sp(3))H Bond in Bis(1H-2,1-benzazaborole)Derivatives A set of (3,3')-bis(1-Ph-2-R-1H-2,1-benzazaborole) compounds, in which R= tBu (Bab-tBu)(2), R= Dipp (BabDipp)2 or R= tBu and Dipp (Bab-Dipp)(Bab-tBu), was synthesized and fully characterized using H-1, B-11, C-13, and N-15 NMR spectroscopy as well as single-crystal X-ray diffraction analysis. The central HC(sp(3))-C(sp(3)) 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(sp(3))-C(sp(3)) 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 (BabtBu)(.) 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(sp(3))-C(sp(3))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 Et2O) and lithium methyl-substituted borate complex Li+(SOL)(n)(Bab-tBu-Me)(-) in a diastereoselective fashion. atropisomerism; boron; C-C bond cleavage; heterocycles; hindered rotation; radicals

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