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. 2012 Jun 20;134(24):10279-85.
doi: 10.1021/ja303595z. Epub 2012 Jun 6.

UV-photoelectron spectroscopy of 1,2- and 1,3-azaborines: a combined experimental and computational electronic structure analysis

Anna Chrostowska  1 , Senmiao Xu, Ashley N Lamm, Audrey Mazière, Christopher D Weber, Alain Dargelos, Patrick Baylère, Alain Graciaa, Shih-Yuan Liu
Affiliations

UV-photoelectron spectroscopy of 1,2- and 1,3-azaborines: a combined experimental and computational electronic structure analysis

Anna Chrostowska et al. J Am Chem Soc. .

Abstract

We present a comprehensive electronic structure analysis of structurally simple BN heterocycles using a combined UV-photoelectron spectroscopy (UV-PES)/computational chemistry approach. Gas-phase He I photoelectron spectra of 1,2-dihydro-1,2-azaborine 1, N-Me-1,2-BN-toluene 2, and N-Me-1,3-BN-toluene 3 have been recorded, assessed by density functional theory calculations, and compared with their corresponding carbonaceous analogues benzene and toluene. The first ionization energies of these BN heterocycles are in the order N-Me-1,3-BN-toluene 3 (8.0 eV) < N-Me-1,2-BN-toluene 2 (8.45 eV) < 1,2-dihydro-1,2-azaborine 1 (8.6 eV) < toluene (8.83 eV) < benzene (9.25 eV). The computationally determined molecular dipole moments are in the order 3 (4.577 D) > 2 (2.209 D) > 1 (2.154 D) > toluene (0.349 D) > benzene (0 D) and are consistent with experimental observations. The λ(max) in the UV-vis absorption spectra are in the order 3 (297 nm) > 2 (278 nm) > 1 (269 nm) > toluene (262 nm) > benzene (255 nm). We also establish that the measured anodic peak potentials and electrophilic aromatic substitution (EAS) reactivity of BN heterocycles 1-3 are consistent with the electronic structure description determined by the combined UV-PES/computational chemistry approach.

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Figures

Figure 1
Figure 1
UV-PE spectra of (a) benzene and (b) 1,2-dihydro-1,2-azaborine 1, (c) toluene, (d) N-Me-1,2-BN-toluene 2, and (e) N-Me-1,3-BN-toluene 3. The y-axis is defined as the negative value of the experimentally determined ionization energy (-IE). The top seven occupied molecular orbitals associated with the corresponding energy levels for each of the molecules are also depicted
Figure 2
Figure 2
Limiting resonance structures for 3 highlighting the localization of formal charge.
Figure 3
Figure 3
Comparison of TD-DFT calculations (CAM-B3LYP/6-311++G(d,p)) and observed UV-Vis absorption spectra for benzene, 1,2-dihydro-1,2-azaborine 1, toluene, N-Me-1,2-BN-toluene 2, and N-Me-1,3-BN-toluene 3.
Figure 4
Figure 4
Cyclicvoltammograms of (a) benzene and (b) 1,2-dihydro-1,2-azaborine 1, (c) toluene, (d) N-Me-1,2-BN-toluene 2, and (e) N-Me-1,3-BN-toluene 3 (0.1M TBABF4 in CH3CN; scan rate, 50 mV/s).
Figure 5
Figure 5
(a) HOMO of A with corresponding p orbital coefficients. (b) Electrostatic potential surface of A at the 0.001 electron a.u.−3 density iso-contour level (+12.55 to −12.55 kcal mol−1).
Scheme 1
Scheme 1
BN isosteres of benzene.
Scheme 2
Scheme 2
Scheme 3
Scheme 3
Synthesis of N-Me-1,3-BN-Toluene 3 and N-Me-1,2-BN-Toluene 2.
See this image and copyright information in PMC

References

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