Synthesis and Characterization of B-Heterocyclic π-Radical and Its Reactivity as a Boryl Radical

Aramaki, Yoshitaka; Omiya, Hideki; Yamashita, Makoto; Nakabayashi, Koji; Ohkoshi, Shin‐ichi; Nozaki, Kyoko

doi:10.1021/ja3094372

Cited by 106 publications

(56 citation statements)

References 33 publications

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“…In this case, however, the spin density localizeda tt he borona tom seems to be considerably lower. [29] Furthermore the theoretical study also showed close similarity of both SOMOso f(Bab-Dipp)C and (Bab-tBu)C ( Figure 6).…”

Section: Photo-induced Hc(sp 3 )àC(sp 3 )H Bondcleavage In Bis(1h-21supporting

confidence: 53%

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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

Lyčka

Mikýsek

et al. 2016

Chemistry A European J

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A set of (3,3')-bis(1-Ph-2-R-1H-2,1-benzazaborole) compounds, in which R=tBu (Bab-tBu) , R=Dipp (Bab-Dipp) or R=tBu and Dipp (Bab-Dipp)(Bab-tBu), was synthesized and fully characterized using H, B, C, and N NMR spectroscopy as well as single-crystal X-ray diffraction analysis. The central HC(sp )-C(sp )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) (Bab-tBu) (M=Li, Na, K) and K (THF) (Bab-Dipp) . Furthermore, the central HC(sp )-C(sp )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(sp )-C(sp )H bond in (Bab-tBu) is also cleaved heterolytically with 2 equiv of MeLi, giving the mixture of Li (SOL) (Bab-tBu) (SOL=THF or Et O) and lithium methyl-substituted borate complex Li (SOL) (Bab-tBu-Me) in a diastereoselective fashion.

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Section: Photo-induced Hc(sp 3 )àC(sp 3 )H Bondcleavage In Bis(1h-21supporting

confidence: 53%

“…is Nozaki's persistent N,N ‐stabilized neutral boron radical. In this case, however, the spin density localized at the boron atom seems to be considerably lower . Furthermore the theoretical study also showed close similarity of both SOMOs of (Bab‐Dipp) .…”

Section: Resultsmentioning

confidence: 60%

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

Lyčka

Mikýsek

et al. 2016

Chemistry A European J

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“…In 2013, Roesky and co‐workers found that silyl‐substituted CAACs yielded the radicals 32 a – c , which were stable under inert atmosphere . Utilizing steric bulk and nitrogen‐derived electronic effects, Yamashita, Nozaki, and co‐workers prepared the heterocyclic radical 33 with 7π electrons . This radical was best described as an allylic radical but reacted with benzoquinone and benzoyl peroxide at the boron atom.…”

Section: Radicals Based On Electron Push And/or Pull Systemsmentioning

confidence: 99%

Platforms for Stable Carbon‐Centered Radicals

Kato

Osuka

2019

Angewandte Chemie

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Organic radicals can potentially play important roles in functional materials owing to an unpaired electron, but they are usually highly reactive and difficult to use. Therefore, stabilization of organic radicals is important. Among organic radicals, carbon‐centered radicals are promising because of their trivalent nature, which enables structural diversity and elaborate designs, but they are also less stable because of the reactivities towards carbon–carbon bond formation and atmospheric oxygen. Recently, stable carbon‐centered radicals across diverse molecular platforms have been increasingly explored. This Minireview highlights these newly explored, stable carbon‐centered radicals, with a focus on porphyrinoid‐stabilized radicals because of their remarkable spin delocalization abilities.

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“…An X‐ray diffraction study revealed the dicationic property of 3 , in which two diazadiborinine units are bridged through the B−O bonds of the para ‐OC 6 H 4 O linker. Although similar B−O bond‐forming reactions between neutral and anionic boron radicals and benzoquinone or benzoyl peroxide have been described previously, to the best of our knowledge, this result is the first example of boron‐centered radical reactivity of cationic boron radicals.…”

Section: Figurementioning

confidence: 99%

A Crystalline Diazadiborinine Radical Cation and Its Boron‐Centered Radical Reactivity

Wang

Ganguly

et al. 2018

Angew Chem Int Ed

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One-electron oxidation of 1,4,2,5-diazadiborinine 1 has been studied. While the reaction of 1 a bearing phenyl groups on the B atoms with AgAl{OC(CF ) } afforded a complex mixture, the same oxidation reaction with 1 b featuring bulky mesityl substituents on the B atoms rendered the corresponding cation radical 2 b as an isolable species. X-ray diffraction analysis, EPR spectroscopy, and DFT calculations of 2 b revealed the delocalization of the unpaired electron over the entire π-system of 2 b, as well as a large spin density (0.76 in total) on the two equivalent boron atoms. The chemical trapping reaction of 2 b with p-benzoquinone and triphenyltin hydride afforded the dicationic species 3 containing two newly formed B-O bonds and the monocationic product 2b-H containing a B-H bond, respectively, thus confirming the boron-centered radical reactivity of 2 b.

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Synthesis and Characterization of B-Heterocyclic π-Radical and Its Reactivity as a Boryl Radical

Cited by 106 publications

References 33 publications

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

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

Platforms for Stable Carbon‐Centered Radicals

A Crystalline Diazadiborinine Radical Cation and Its Boron‐Centered Radical Reactivity

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Synthesis and Characterization of B-Heterocyclic π-Radical and Its Reactivity as a Boryl Radical

Cited by 106 publications

References 33 publications

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

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

Platforms for Stable Carbon‐Centered Radicals

A Crystalline Diazadiborinine Radical Cation and Its Boron‐Centered Radical Reactivity

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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

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