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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.


Structural characterization and fluorescence property.(a) Solid state structure of 4. Thermal ellipsoids are set at the 30% probability level. Hydrogen atoms are omitted for clarity. (b) Plot of the HOMO of 4. (c) Plots of the HOMO-4 (left) and HOMO-5 (right) of 4. Calculated at the B3LYP/6-311+G(d,p) level of theory. Hydrogen atoms are omitted for clarity. (d) Photographic image of fluorescence emission in the solid state of 4 under irradiation of a ultraviolet lamp.
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f2: Structural characterization and fluorescence property.(a) Solid state structure of 4. Thermal ellipsoids are set at the 30% probability level. Hydrogen atoms are omitted for clarity. (b) Plot of the HOMO of 4. (c) Plots of the HOMO-4 (left) and HOMO-5 (right) of 4. Calculated at the B3LYP/6-311+G(d,p) level of theory. Hydrogen atoms are omitted for clarity. (d) Photographic image of fluorescence emission in the solid state of 4 under irradiation of a ultraviolet lamp.

Mentions: Single crystals of 4 suitable for X-ray diffractometry were obtained by recrystallization from a benzene solution at room temperature, and crystallographic analysis revealed that the six-membered B2C2N2 ring of 4 is nearly planar (Fig. 2a). Two boron atoms display trigonal-planar geometry (the sum of bond angles: B1=359.96° and B2=359.93°), which are characteristic for sp2 hybridization. Phenyl ring at B2 and the B2C2N2 six-membered ring are nearly perpendicular to each other with the twist angle of 89.1°, whereas phenyl group at B1 and the B2C2N2 skeleton are slightly twisted by 11.9°. The B1–C5 (1.483(3) Å) and B2–N1 (1.443(3) Å) distances are significantly shorter than those (1.575(5)–1.589(5) Å and 1.573(4)–1.563(4) Å) in 3, and lie between typical single and double-bond distances of boron–carbon and boron–nitrogen bonds, respectively. In contrast, the N1–C5 distance of 1.374(3) Å is longer than that (1.287(4)–1.292(4) Å) in 3. These structural features suggest the delocalization of 6π-electrons over the six-membered B2C2N2 ring in 4, which can be represented by the average of the several canonical forms including 4a–c.


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

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

Structural characterization and fluorescence property.(a) Solid state structure of 4. Thermal ellipsoids are set at the 30% probability level. Hydrogen atoms are omitted for clarity. (b) Plot of the HOMO of 4. (c) Plots of the HOMO-4 (left) and HOMO-5 (right) of 4. Calculated at the B3LYP/6-311+G(d,p) level of theory. Hydrogen atoms are omitted for clarity. (d) Photographic image of fluorescence emission in the solid state of 4 under irradiation of a ultraviolet lamp.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Structural characterization and fluorescence property.(a) Solid state structure of 4. Thermal ellipsoids are set at the 30% probability level. Hydrogen atoms are omitted for clarity. (b) Plot of the HOMO of 4. (c) Plots of the HOMO-4 (left) and HOMO-5 (right) of 4. Calculated at the B3LYP/6-311+G(d,p) level of theory. Hydrogen atoms are omitted for clarity. (d) Photographic image of fluorescence emission in the solid state of 4 under irradiation of a ultraviolet lamp.
Mentions: Single crystals of 4 suitable for X-ray diffractometry were obtained by recrystallization from a benzene solution at room temperature, and crystallographic analysis revealed that the six-membered B2C2N2 ring of 4 is nearly planar (Fig. 2a). Two boron atoms display trigonal-planar geometry (the sum of bond angles: B1=359.96° and B2=359.93°), which are characteristic for sp2 hybridization. Phenyl ring at B2 and the B2C2N2 six-membered ring are nearly perpendicular to each other with the twist angle of 89.1°, whereas phenyl group at B1 and the B2C2N2 skeleton are slightly twisted by 11.9°. The B1–C5 (1.483(3) Å) and B2–N1 (1.443(3) Å) distances are significantly shorter than those (1.575(5)–1.589(5) Å and 1.573(4)–1.563(4) Å) in 3, and lie between typical single and double-bond distances of boron–carbon and boron–nitrogen bonds, respectively. In contrast, the N1–C5 distance of 1.374(3) Å is longer than that (1.287(4)–1.292(4) Å) in 3. These structural features suggest the delocalization of 6π-electrons over the six-membered B2C2N2 ring in 4, which can be represented by the average of the several canonical forms including 4a–c.

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.