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1,3,2,5-Diazadiborinine featuring nucleophilic and electrophilic boron centres.

Wu D, Kong L, Li Y, Ganguly R, Kinjo R - Nat Commun (2015)

Bottom Line: In marked contrast to the reactivity of benzene, borazine, and even azaborinines previously reported, 1,3,2,5-diazadiborinine readily forms the adducts with methyl trifluoromethanesulfonate and phenylacetylene without any catalysts.Moreover, 1,3,2,5-diazadiborine activates carbon dioxide giving rise to a bicycle[2,2,2] product, and the binding process was found to be reversible.These results, thus, demonstrate that 1,3,2,5-diazadiborinine features both nucleophilic and electrophilic boron centres, with a formal B(+I)/B(+III) mixed valence system, in the aromatic six-membered B2C2N2 ring.

View Article: PubMed Central - PubMed

Affiliation: Division of Chemistry and Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore, Singapore.

ABSTRACT
The seminal discovery in 1865 by Kekulé that benzene nucleus exists with cyclic skeleton is considered to be the beginning of aromatic chemistry. Since then, a myriad of cyclic molecules displaying aromatic property have been synthesized. Meanwhile, borazine (B3N3H6), despite the isostructural and isoelectronic relationships with benzene, exhibits little aromaticity. Herein, we report the synthesis of a 1,3,2,5-diazadiborinine (B2C2N2R6) derivative, a hybrid inorganic/organic benzene, and we present experimental and computational evidence for its aromaticity. In marked contrast to the reactivity of benzene, borazine, and even azaborinines previously reported, 1,3,2,5-diazadiborinine readily forms the adducts with methyl trifluoromethanesulfonate and phenylacetylene without any catalysts. Moreover, 1,3,2,5-diazadiborine activates carbon dioxide giving rise to a bicycle[2,2,2] product, and the binding process was found to be reversible. These results, thus, demonstrate that 1,3,2,5-diazadiborinine features both nucleophilic and electrophilic boron centres, with a formal B(+I)/B(+III) mixed valence system, in the aromatic six-membered B2C2N2 ring.

No MeSH data available.


Preparation of 1,3,2,4-diazadiborinine 4.4a–c present the resonance forms.
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f1: Preparation of 1,3,2,4-diazadiborinine 4.4a–c present the resonance forms.

Mentions: Oxazolinyl groups were introduced into a boron atom by treatment of two equivalents of 2-lithio-4,4'-dimethyl-2-oxazolide 1 with dichlorophenylborane (Fig. 1). Without further purification of the crude product 2, a subsequent reaction with one equivalent of dichlorophenylborane in toluene afforded a 2,5-dichloro-1,3,2,5-diazadiborinine derivative 3 (29% yield), which was fully characterized by standard spectroscopic methods, including a single-crystal X-ray diffraction study. Treatment of 3 with excess amounts of potassium graphite (KC8) in toluene cleanly proceeded, and after workup 1,3,2,5-diazadiborinine derivative 4 was isolated as a white powder in 32% yield. In the 11B nuclear magnetic resonance (NMR) spectrum of 4, a sharp signal for the boron atom between two carbon atoms appeared at δ=7.3 parts per million (p.p.m.) and a broad peak for the boron atom between two nitrogen atoms was observed at δ=24.9 p.p.m. Both signals shifted downfield compared with those of the precursor 3 (δ=−11.4 and 3.5 p.p.m.). Compound 4 is thermally stable both in the solid state and in solutions, and it melts at 133 °C without decomposition.


1,3,2,5-Diazadiborinine featuring nucleophilic and electrophilic boron centres.

Wu D, Kong L, Li Y, Ganguly R, Kinjo R - Nat Commun (2015)

Preparation of 1,3,2,4-diazadiborinine 4.4a–c present the resonance forms.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4490389&req=5

f1: Preparation of 1,3,2,4-diazadiborinine 4.4a–c present the resonance forms.
Mentions: Oxazolinyl groups were introduced into a boron atom by treatment of two equivalents of 2-lithio-4,4'-dimethyl-2-oxazolide 1 with dichlorophenylborane (Fig. 1). Without further purification of the crude product 2, a subsequent reaction with one equivalent of dichlorophenylborane in toluene afforded a 2,5-dichloro-1,3,2,5-diazadiborinine derivative 3 (29% yield), which was fully characterized by standard spectroscopic methods, including a single-crystal X-ray diffraction study. Treatment of 3 with excess amounts of potassium graphite (KC8) in toluene cleanly proceeded, and after workup 1,3,2,5-diazadiborinine derivative 4 was isolated as a white powder in 32% yield. In the 11B nuclear magnetic resonance (NMR) spectrum of 4, a sharp signal for the boron atom between two carbon atoms appeared at δ=7.3 parts per million (p.p.m.) and a broad peak for the boron atom between two nitrogen atoms was observed at δ=24.9 p.p.m. Both signals shifted downfield compared with those of the precursor 3 (δ=−11.4 and 3.5 p.p.m.). Compound 4 is thermally stable both in the solid state and in solutions, and it melts at 133 °C without decomposition.

Bottom Line: In marked contrast to the reactivity of benzene, borazine, and even azaborinines previously reported, 1,3,2,5-diazadiborinine readily forms the adducts with methyl trifluoromethanesulfonate and phenylacetylene without any catalysts.Moreover, 1,3,2,5-diazadiborine activates carbon dioxide giving rise to a bicycle[2,2,2] product, and the binding process was found to be reversible.These results, thus, demonstrate that 1,3,2,5-diazadiborinine features both nucleophilic and electrophilic boron centres, with a formal B(+I)/B(+III) mixed valence system, in the aromatic six-membered B2C2N2 ring.

View Article: PubMed Central - PubMed

Affiliation: Division of Chemistry and Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, 637371 Singapore, Singapore.

ABSTRACT
The seminal discovery in 1865 by Kekulé that benzene nucleus exists with cyclic skeleton is considered to be the beginning of aromatic chemistry. Since then, a myriad of cyclic molecules displaying aromatic property have been synthesized. Meanwhile, borazine (B3N3H6), despite the isostructural and isoelectronic relationships with benzene, exhibits little aromaticity. Herein, we report the synthesis of a 1,3,2,5-diazadiborinine (B2C2N2R6) derivative, a hybrid inorganic/organic benzene, and we present experimental and computational evidence for its aromaticity. In marked contrast to the reactivity of benzene, borazine, and even azaborinines previously reported, 1,3,2,5-diazadiborinine readily forms the adducts with methyl trifluoromethanesulfonate and phenylacetylene without any catalysts. Moreover, 1,3,2,5-diazadiborine activates carbon dioxide giving rise to a bicycle[2,2,2] product, and the binding process was found to be reversible. These results, thus, demonstrate that 1,3,2,5-diazadiborinine features both nucleophilic and electrophilic boron centres, with a formal B(+I)/B(+III) mixed valence system, in the aromatic six-membered B2C2N2 ring.

No MeSH data available.