ハイドリド-アルケニルカルビネからアルケニルカルベネへの変換は,ビスホスフィン-オスミウム複合体で起こる
Tamara Bolaño1, Ricardo Castarlenas, Miguel A Esteruelas
1Departamento de Química Inorgánica, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain.
Journal of the American Chemical Society
|August 4, 2005
まとめ
この研究は,新しいオスミウム複合体の合成を詳細に説明し,二水素複合体をヒドリド-アルケニルカルビネおよびアルケニルカルビネ誘導体に変換します. これらの反応は,有機金属化学とリガンドの行動に関する洞察を明らかにします.
科学分野:
- 有機金属化学 有機金属化学
- 協調化化学について
- カタリシス カタリシス カタリシス
背景:
- 延長型二水素複合体は,有機金属合成における多用途の起始材料である.
- オスミウム複合体と不飽和アルコールとの反応性は,新しい触媒変換の開発に重要な関心があります.
- オスミウム複合体のリガンドの振る舞いを理解することは,特定の性質を持つ新しい化合物の設計に不可欠です.
研究 の 目的:
- 二水素前駆体から派生した新しいオスミウム複合体を合成し,特徴づけること.
- ハイドリド-アルケニルカルビネ複合体のアルケニルカルビネ複合体への変換を調査する.
- ハイドリド-アルケニルカルビネからアルケニルカルビネへの変換における金属中心基本性の影響を調査する.
主な方法:
- 延長された二水素複合体の反応と置換プロピノール.
- 合成された複合体を酸と調整溶媒で処理する.
- 中間および最終オスミウム複合体の分離と特徴付け.
- 密度関数理論 (DFT) の計算と運動学的研究.
主要な成果:
- ヒドリド-ヒドロキシビニリデン-ピ-アルキノールオスミウム誘導体の合成.
- ディカチオンヒドリド-アルケニルカルビネオスミウム化合物の形成.
- 1,2-水素シフトによるアルケニルカルベンのオスミウム複合体への変換.
- キー複合体のX線構造決定と回転障壁の分析.
- DFTの計算では,金属の基本性と変換中のエネルギー差を相関させています.
結論:
- この研究では,一連の新しいオスミウム複合体を成功裏に合成し,特徴づけました.
- ハイドリドアルケニルカルビンがアルケニルカルベンに変換されるための協調的な1,2-水素シフトメカニズムが解明されました.
- 金属中心の基本性は,ヒドリド-アルケニルカルビネからアルケニルカルビネへの変換のエネルギー学において重要な役割を果たします.
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関連する概念動画
03:08Hydroboration-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.
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
02:47Alkynes 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.
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
01:14Aldehydes 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...