ベンゾキノンによって促進されたO2の反応は,Pd(II) -ヒドリドと起こる
Nattawan Decharin1, Shannon S Stahl
1Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States.
Journal of the American Chemical Society
|March 29, 2011
まとめ
ベンゾキノン (BQ) と分子酸素 (O2) は,パラジウム水化物複合体との異なる反応性を示す. これらの違いを理解することは,パラジウム触媒による酸化反応を進めるための鍵です.
科学分野:
- 有機金属化学 有機金属化学
- カタリシス カタリシス カタリシス
- 酸化反応は,酸化反応によるものです.
背景:
- パラジウム触媒による酸化反応では,通常,ベンゾキノン (BQ) または分子酸素 (O2) を酸化剤として使用します.
- これらの反応におけるBQとO2の異なる役割に関する機械学的洞察は,依然として限られている.
- よく定義されたパラジウム-水素化合物,Pd(IMes) 2 ((H) ((O2CPh) (1) は,酸化物質の反応性を調査するためのモデルシステムとして機能します.
研究 の 目的:
- ベンゾキノン (BQ) と分子酸素 (O2) が特定のパラジアム・ヒドリド複合体との相互作用におけるメカニズム的な違いを解明する.
- Pd-ヒドリド複合体とのBQの反応性を調査する (1).
- 反応経路における有酸素条件とO2の影響を調べる.
主な方法:
- よく定義されたパラジウム-水化物複合体,Pd(IMes) 2 ((H) ((O2CPh) (1) を利用した.
- コンプレックス (1) とベンゾキノン (BQ) の反応を調査した.
- O2.2の効果を観察するために,エアロビック条件下で複合体 (1) の反応を研究した.
主要な成果:
- ベンゾキノン (BQ) は,複合体 (1) からベンゾ酸 (PhCO2H) の還元性除去を促進することが判明しました.
- エロビック条件下では,この反応により,パラジウム ((II) -ヒドロペロキソ (Pd-OOH) 複合体の形成が触媒化されました.
- パラジウム-ヒドリド複合体でBQとO2の明確なメカニズム的経路が観察されました.
結論:
- ベンゾキノン (BQ) と分子酸素 (O2) は,パラジアム-ヒドリド複合体との異なる反応性プロファイルを示します.
- この発見は,パラジウム触媒による酸化反応の最適化のための重要なメカニズム的理解を提供します.
- エアロビック条件下でのPd(II) -OOH中間物の形成は,酸素ベースの酸化における重要な経路を強調しています.
関連する概念動画
Oxidation of Phenols to Quinones
In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...
Hydrolysis of Chlorobenzene to Phenol: Dow Process
Simple aryl halides do not react with nucleophiles under normal conditions. However, the reaction can proceed under drastic conditions involving high temperatures and high pressure to give the substituted products. For example, chlorobenzene is converted to phenol using aqueous sodium hydroxide at 350 °C under high pressure by the Dow process. The reaction follows an elimination-addition mechanism involving a benzyne intermediate. Here, the chloride ion is eliminated to generate the benzyne...
Radical Chain-Growth Polymerization: Overview
Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
Nucleophilic Aromatic Substitution: Elimination–Addition
Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is confirmed through isotopic...
Reactions at the Benzylic Position: Oxidation and Reduction
The benzylic position describes the position of a carbon atom attached directly to a benzene ring. Benzene by itself does not undergo oxidation. In contrast, the benzylic carbon is quite reactive in the presence of strong oxidizing agents such as KMnO4 or H2CrO4. Therefore, alkylbenzenes are readily oxidized to benzoic acid, irrespective of the type of alkyl groups.
Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
![[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F59739.jpg&w=3840&q=50)

