Trishomoaromatic (B3 N3 Ph6 ) Dianion: Characterization and Two-Electron Reduction.
1Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking University, Beijing, 100871, China.
Angewandte Chemie (International Ed. in English)
|March 6, 2020
Summary
Borazine undergoes a unique two-electron reduction to form stable homoaromatic compounds. This novel borazine dianion acts as an efficient reductant for various unsaturated molecules.
Area of Science:
- Inorganic Chemistry
- Organic Chemistry
- Theoretical Chemistry
Background:
- Benzene, a stable aromatic compound, forms an unstable antiaromatic intermediate upon two-electron reduction.
- Borazine, an isoelectronic analog of benzene, possesses weaker aromaticity.
- The electronic properties of borazine differ significantly from benzene upon reduction.
Purpose of the Study:
- To synthesize and characterize the two-electron reduced form of borazine, (B3N3Ph6)2-.
- To investigate the electronic structure and bonding in the reduced borazine species.
- To explore the potential of the reduced borazine as a reducing agent.
Main Methods:
- Synthesis of homoaromatic (B3N3Ph6)2- via reduction of B3N3Ph6 using potassium or rubidium with 18-crown-6 ether.
- Theoretical investigations using computational methods to analyze electron delocalization and bonding.
- Application of the reduced borazine as a reductant for unsaturated compounds like anthracene, chalcone, and tanshinones.
Main Results:
- Successful synthesis of the homoaromatic (B3N3Ph6)2- species.
- Theoretical studies revealed delocalization of two electrons over the three boron atoms, resulting in (π,σ)-mixed homoaromaticity.
- The (B3N3Ph6)2- dianion demonstrated robust and selective 2e reduction capabilities for various unsaturated substrates under mild conditions.
Conclusions:
- Borazine's two-electron reduction leads to stable homoaromatic compounds, unlike benzene's antiaromatic intermediate.
- The synthesized (B3N3Ph6)2- exhibits unique (π,σ)-mixed homoaromaticity.
- The reduced borazine is a versatile and efficient 2e reductant, regenerating neutral borazine after reaction.
Related Concept Videos
01:07Radicals: Electronic Structure and Geometry
4.9K
This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a lone pair, where the unpaired electron influences the geometry at the radical center.
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...
4.9K
01:18Aromatic Hydrocarbon Cations: Structural Overview
3.6K
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
Removing one hydrogen from the intervening CH2 group...
3.6K
01:11ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
7.2K
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
7.2K
01:18Aromatic Hydrocarbon Anions: Structural Overview
3.5K
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous...
Due to the absence of continuous...
3.5K
01:19Diazonium Group Substitution: –OH and –H
3.2K
Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.
3.2K
01:18Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism
2.5K
Birch reduction uses solvated electrons as reducing agents. The reaction converts benzene to 1,4-cyclohexadiene. The reaction proceeds by the transfer of a single electron to the ring to form a benzene radical anion. This anion is highly basic—it abstracts a proton from the alcohol to form a cyclohexadienyl radical. Another single electron transfer gives the cyclohexadienyl anion. A proton transfer from the alcohol forms 1,4-cyclohexadiene. Since this reduction occurs via radical anion...
2.5K