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. 2015 Jun 26;54(27):7819-22.
doi: 10.1002/anie.201502967. Epub 2015 Jun 11.

1,2-Azaborine: The Boron-Nitrogen Derivative of ortho-Benzyne

Klara Edel  1 , Sarah A Brough  1 , Ashley N Lamm  2 , Shih-Yuan Liu  2   3 , Holger F Bettinger  4
Affiliations

1,2-Azaborine: The Boron-Nitrogen Derivative of ortho-Benzyne

Klara Edel et al. Angew Chem Int Ed Engl. .

Abstract

The BN analogue of ortho-benzyne, 1,2-azaborine, is generated by flash vacuum pyrolysis, trapped under cryogenic conditions, and studied by direct spectroscopic techniques. The parent BN aryne spontaneously binds N2 and CO2, thus demonstrating its highly reactive nature. The interaction with N2 is photochemically reversible. The CO2 adduct of 1,2-azaborine is a cyclic carbamate which undergoes photocleavage, thus resulting in overall CO2 splitting.

Keywords: ab initio calculations; arynes; boron; matrix isolation; nitrogen heterocycles.

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Figures

Figure 1
Figure 1
Generation of 1,2-azaborine through irradiation of 3 in Ar/N2 (70:30). (a) IR difference spectrum obtained from the pyrolysis products of 2 frozen at 6 K after two hours of irradiation with visible light (λ > 395 nm, 4 K). The decreasing signals (pointing downwards) belong to dinitrogen adduct 3, increasing signals belong to 1 (blue stars) and 2. (b) Difference spectrum after subsequent annealing for 30 minutes at 12 K (starting from 4 K), showing reversibility of the reaction 3 ⇌ 1 + N2. (c) Computed IR spectrum of 1 at the CCSD(T)/TZ2P level of theory.
Figure 2
Figure 2
Difference spectra obtained upon irradiation (λ > 305 nm, 4 K) of 4 that was generated by trapping of 1 with neat carbon dioxide at a deposition temperature of 52 K after FVP of 2 at 740 °C. Carbonyl stretching of 4 disappears (bands pointing downwards) upon irradiation with UV light, while new bands for 8 are appearing (bands pointing upwards) for natural (top), C(18O)2 (center), and 13CO2 (bottom) isotopomers.
Figure 3
Figure 3
a) Natural bond orbitals (NBOs) and their occupation numbers that describe the in-plane part of the BN linkage as computed at the B3LYP/6-311+G** level of theory; b) Resonance forms of 1,2-azaborine; c) Structures and selected bond lengths in Å of molecules 1, 3, and 4 as computed at the CCSD(T)/TZ2P level of theory.
Scheme 1
Scheme 1
Generation and trapping of 1,2-azaborine (1) with N2 and CO2 by flash vacuum pyrolysis (FVP) of 2 at 850 °C.
See this image and copyright information in PMC

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