ダイアルキルビアリルフォスフィンの分子酸素による酸化に対する抵抗の裏付け
Timothy E Barder1, Stephen L Buchwald
1Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
Journal of the American Chemical Society
|March 29, 2007
まとめ
電子が豊富なダイアルキルビアリルホスフィンは,その構造により酸化に抵抗する. アルキル基と特定のビアリル基幹の位置は,パラジアム触媒によるクロスカップリング反応において極めて重要なこれらのリガンドを保護する.
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
- リガンドデザインはリガンドデザインです.
背景:
- 電子に富んだダイアルキルビアリルフォスフィンは,パラジアム触媒によるクロスカップリング反応における不可欠なリガンドである.
- これらのリンガンドは,分子酸素による酸化に対する顕著な耐性を発揮し,これは触媒の共通の課題である.
- この酸化安定性を理解することは,より堅牢な触媒システムの開発の鍵です.
研究 の 目的:
- 電子が豊富なダイアルキルビアリルフォスフィンの高酸化抵抗に寄与する構造的要因を調査する.
- これらのリガンドが分子酸素から保護されるメカニズムを解明する.
主な方法:
- フォスフィンリガンドの合成と特徴づけに関する実験研究.
- 電子効果とステリック効果をモデル化するための理論的計算 (例えば,密度関数理論)
- 酸化測定は,様々な条件下でリガンドの安定性を評価するために行われます.
主要な成果:
- リン原子に2つのアルキル置換物質が存在することは,酸化安定性を著しく高めます.
- ビアリル骨幹の2'および6'位置の置換剤によって提供されるステリック阻害は,酸化を防止する上で重要な役割を果たします.
- 計算データは,電子とステリック要因の相互作用を強調して,実験的発見を支持します.
結論:
- 電子が豊富なダイアルキルビアリルフォスフィン,特にアルキル群とビアリル骨幹置換のユニークな構造特性は,酸化に対する例外的な耐性を授与します.
- この理解は,要求の高い触媒応用のための次世代フォスフィンリガンドの合理的な設計を容易にする.
- この発見は,有機金属触媒におけるリガンドの安定性に関するより広範な知識に寄与する.
関連する概念動画
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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.
Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
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.
Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
Aldehydes and Ketones to Alkenes: Wittig Reaction Mechanism
The Wittig reaction, which converts aldehydes or ketones to alkenes using phosphorus ylides, proceeds through a nucleophilic addition‒elimination process.
The reaction begins with the nucleophilic addition between a phosphorus ylide and the carbonyl compound. Due to its carbanionic character, phosphorus ylide acts as a strong nucleophile and attacks the electrophilic carbonyl group. This generates a charge-separated dipolar intermediate called betaine. The negatively charged oxygen atom and...
The reaction begins with the nucleophilic addition between a phosphorus ylide and the carbonyl compound. Due to its carbanionic character, phosphorus ylide acts as a strong nucleophile and attacks the electrophilic carbonyl group. This generates a charge-separated dipolar intermediate called betaine. The negatively charged oxygen atom and...
Diels–Alder Reaction: Characteristics of Dienophiles
In a Diels–Alder reaction, the diene is usually an electron-rich system and acts as a nucleophile, whereas the dienophile is electron-deficient and functions as an electrophile. Much like the diene, the nature of the dienophile significantly impacts the outcome of the reaction.
Characteristics of Dienophiles
Generally, the best dienophiles are alkenes containing electron-withdrawing substituents such as carbonyl, nitrile, and nitro groups. The feasibility of a Diels–Alder reaction depends on...
Characteristics of Dienophiles
Generally, the best dienophiles are alkenes containing electron-withdrawing substituents such as carbonyl, nitrile, and nitro groups. The feasibility of a Diels–Alder reaction depends on...
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