B-ヘテロサイクルのπ-ラジカルと,ボリルラジカルとしてのその反応性の合成と特徴付け
Yoshitaka Aramaki1, Hideki Omiya, Makoto Yamashita
1Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Journal of the American Chemical Society
|December 5, 2012
まとめ
研究者らは,最初の安定したダイアザボラサイクルの中性基を報告した. ESRとDFTによって特徴づけられるこの赤色のラジカルは,位置外電子を発現し,ボリルラジカルとして反応する.
科学分野:
- 無機化学 無機化学とは
- 有機化学 オーガニック・ケミストリー
- コンピューティング・ケミストリー
背景:
- 安定した中性ラジカルは希少であり,化学において非常に求められている.
- ディアザボラサイクルの化合物は,ユニークな電子的および構造的性質を備えています.
研究 の 目的:
- 安定した,持続的なダイアザボラサイクルの中性基の最初の分離と完全な特徴を報告する.
- この新しい急性種の電子構造,特性,および反応性を調査する.
主な方法:
- ディフルオロボラン前駆物の化学還元.
- 電子スピン共振 (ESR) スペクトロスコーピーは,根幹の特徴を決定する.
- 電子構造分析のための密度関数理論 (DFT) 計算.
- 光学特性を決定するためのUV-VISスペクトロスコピー.
主要な成果:
- 安定したダイアザボラサイクルの中性基 (3) の分離と特徴づけに成功した.
- ラジカルには,1つのフッ素原子と2つの窒素原子に結合した平面的なsp(2) ハイブリッド化ボロン原子が特徴です.
- ESRとDFTの計算により,ペア化されていない電子が6つ環の上で異動していることが確認されました.
- UV-VISスペクトロスコピーは,電子トランジションによる最大吸収498nmで特徴的な赤い色を明らかにしました.
- ボロンのスピン密度が低いにもかかわらず,ボリル基は,電極性を持つ塩基安定化ボリル基として反応した.
結論:
- この研究は,材料科学と触媒処理における潜在的な応用を持つ,新しい種類の安定した中性基を提示しています.
- 分離された電子構造とユニークな反応性は,ダイアザボラサイクルのシステムの汎用性を強調しています.
- この研究は,既知の安定ラジカルの範囲を拡大し,将来の化学調査のための基礎を提供します.
関連する概念動画
Radical Reactivity: Overview
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three...
Radical Reactivity: Nucleophilic Radicals
Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For instance, consider...
Radical Reactivity: Steric Effects
The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic factors, steric factors also account...
Along with electronic factors, steric factors also account...
Radical Formation: Addition
Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...
Radical Reactivity: Electrophilic Radicals
Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a low‐energy SOMO, which interacts...
Radical Reactivity: Intramolecular vs Intermolecular
Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...


