![[(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)
分子酸素とPd(II) -ヒドリドの反応によりPd(II) -ヒドロペロキシドが生成:HX-還元-除去経路の実験的証拠
Michael M Konnick1, Shannon S Stahl
1Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Journal of the American Chemical Society
|April 9, 2008
まとめ
この研究では,分子酸素とパラジウム ((II) -ヒドリド種との反応を調査しており,これはパラジウム触媒による有酸素酸化における重要なステップである. 研究者は,還元性除去と酸素挿入を含む提案されたメカニズムを検証し,触媒再酸化経路の洞察を提供しました.
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
- 反応メカニズム 反応メカニズム
背景:
- パラジウムによって触媒化された有酸素酸化反応は,有機合成において極めて重要です.
- パラジウム触媒の再酸化,特にPd(II) -ヒドリドからPd(II) -ヒドロペロキシドへの再酸化は提案されているが,しばしば確認されていない経路です.
- 最近の発見により,明確に定義されたPd (II) -ヒドリド種の研究が可能になりました.
研究 の 目的:
- 分子酸素が特定のPd(II) - 水素複合体,トランス- IMes) 2Pd(H) OBz) と反応するメカニズムを研究する.
- 対応するPd(II) -ヒドロペロキシド種の形成の経路を解明する.
- パラジアム触媒による有酸素酸化における提案された触媒再酸化機構の実験的検証を行う.
主な方法:
- ベンゼン-d6.6における1H NMRスペクトロスコーピーを用いて,トランス-{IMes) 2Pd{H}{OBz}とO2の反応を監視する.
- 速度法則を決定し,速度を制限するステップを特定するために運動学的研究を行う.
- デウテリウム運動同位体効果 (k(Pd-H) /k(Pd-D)) を測定し,反応機構を調査する.
主要な成果:
- この反応は,Pd(II) -ヒドロペロキシド複合体トランス- ((IMes) 2Pd ((OOH) ((OBz) を生成する.
- 動力学的研究は,2項の速度法則 (rate = k1[1] + k2[1][BzOH]) と小さなデウテリウム動力同位体効果 (1.3(1) を明らかにした.
- 酸素圧は反応速度とは無関係であることが判明し,ベンゾ酸のようなプロティック添加物は反応を触媒化する.
結論:
- このデータは,Pd (II) -ヒドリドからベンゾ酸 (BzOH) の速度を制限する還元性除去を含む段階的なメカニズムを支持しています.
- その後,分子酸素がPd(0) 種で素早く反応し,Pd-O結合がエタ(2) -ペロキソ複合体でプロト解離されます.
- この研究は,Pd-ヒドリド種の有酸素酸化の提案されたメカニズムの最初の実験的検証を提供し,パラジウム触媒の再酸化の理解を深める.
さらに関連する動画
10:21Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
Published on: October 5, 2019
![Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium Under Mild Reaction Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F51444.jpg&w=3840&q=50)
11:44Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium Under Mild Reaction Conditions
Published on: March 20, 2014
関連する概念動画
00:51Radical Formation: Elimination
Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions with respect to...
01:17Radical Anti-Markovnikov Addition to Alkenes: Mechanism
The reaction of hydrogen bromide with alkenes in the presence of hydroperoxides or peroxides proceeds via anti-Markovnikov addition. The radical chain reaction comprises initiation, propagation, and termination steps.
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...
02:04Oxidation 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.
02:35Regioselectivity of Electrophilic Additions-Peroxide Effect
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.
01:19Acid Halides to Alcohols: LiAlH4 Reduction
Acid halides are reduced to alcohols in the presence of a strong reducing agent like lithium aluminum hydride.
The mechanism proceeds in three steps. First, the nucleophilic hydride ion attacks the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs as a leaving group, generating an aldehyde. A second nucleophilic attack by the hydride yields an alkoxide ion, which, upon protonation, gives a primary alcohol as...
The mechanism proceeds in three steps. First, the nucleophilic hydride ion attacks the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs as a leaving group, generating an aldehyde. A second nucleophilic attack by the hydride yields an alkoxide ion, which, upon protonation, gives a primary alcohol as...
01:17Esters to Alcohols: Hydride Reductions
Esters are reduced to primary alcohols when treated with a strong reducing agent like lithium aluminum hydride. The reaction requires two equivalents of the reducing agent and proceeds via an aldehyde intermediate.
Lithium aluminum hydride is a source of hydride ions and functions as a nucleophile. The mechanism proceeds in three steps. Firstly, the nucleophilic hydride ion attacks the carbonyl carbon of the ester to form a tetrahedral intermediate. Subsequently, the carbonyl group re-forms,...
Lithium aluminum hydride is a source of hydride ions and functions as a nucleophile. The mechanism proceeds in three steps. Firstly, the nucleophilic hydride ion attacks the carbonyl carbon of the ester to form a tetrahedral intermediate. Subsequently, the carbonyl group re-forms,...