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In-Depth Theoretical Investigations of Borazine's Aromaticity: Tailoring Electron Delocalization through Substituent
Alex-Cristian Tomut1, Ionut-Tudor Moraru1, Gabriela Nemes1
1Faculty of Chemistry and Chemical Engineering, Department of Chemistry, Babeș-Bolyai University, 1 M. Kogalniceanu Street, 400084 Cluj-Napoca, Romania.
Molecules (Basel, Switzerland)
|October 26, 2024
Summary
Substituents on borazine, or "inorganic benzene", influence its aromaticity. Electron-donating groups on nitrogen atoms enhance aromatic character, while those on boron atoms decrease it, offering tunable aromaticity in these compounds.
Area of Science:
- Computational Chemistry
- Inorganic Chemistry
- Quantum Chemistry
Background:
- Borazine, known as "inorganic benzene", exhibits aromatic properties.
- Understanding factors influencing borazine's aromaticity is crucial for designing novel inorganic materials.
- The electronic and steric effects of substituents can significantly alter molecular properties.
Purpose of the Study:
- To investigate the impact of various R substituents on the aromaticity of borazine derivatives.
- To elucidate the electronic interactions governing the aromatic character of substituted borazines.
- To establish structure-aromaticity relationships for B- and N-substituted borazines.
Main Methods:
- Employed hybrid Density Functional Theory (DFT) methods.
- Utilized computational techniques including Natural Bond Orbital (NBO), Quantum Theory of Atoms in Molecules (QTAIM), Gauge-Including Magnetically Induced Current (GIMIC), and Nucleus-Independent Chemical Shift (NICS).
- Evaluated four distinct aromaticity indices: para-delocalization index (PDI), multi-centre bond order (MCBO), ring current strength (RCS), and NICS parameters.
Main Results:
- Aromatic character of borazine derivatives can be tuned by modulating electronic effects of R groups at B or N positions.
- The position of R substituents is critical in determining the extent of aromaticity.
- Key interactions include lone pair (LP) donations from substituents to π*(B=N) orbitals and Pauli repulsions between LP and π(B=N) bonds.
Conclusions:
- Electron-donating substituents (e.g., F, OH, NH2) on nitrogen atoms enhance borazine's aromaticity, though stabilization is moderate.
- Replacing hydrogen with R groups on boron atoms decreases aromaticity due to strong exocyclic LP(R)→π*(B=N) donations.
- This study provides quantitative insights into substituent effects on borazine aromaticity, aiding in the design of functional inorganic compounds.
Keywords:
DFT methodsNBO analysesPauli repulsionsaromaticityaromaticity indiceshyperconjugations“inorganic” benzeneMore Related Videos
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