1613019-97-8Relevant articles and documents
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
Hejda, Martin,Ly?ka, Antonín,Mikysek, Tomá?,Jambor, Roman,R??i?ka, Ale?,Vinklárek, Jaromír,Wilfer, Claudia,Hoffmann, Alexander,Herres-Pawlis, Sonja,Dostál, Libor
, p. 15340 - 15349 (2016)
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)2or R=tBu and Dipp (Bab-Dipp)(Bab-tBu), was synthesized and fully characterized using1H,11B,13C, and15N 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)2is 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.
