シリリウムカルボラン触媒を用いたパーフルオロアルキル基の水素化
Christos Douvris1, Oleg V Ozerov
1Department of Chemistry, Brandeis University, MS 015, 415 South Street, Waltham, MA 02454, USA.
Science (New York, N.Y.)
|August 30, 2008
まとめ
研究者らは,炭素-フッ素結合を効率的に分解する,カルボランによるシリリウム触媒を開発した. これらの触媒は,軽度な条件下でパーフルオロアルキル基の選択的水素化を可能にし,化学的改変のための新しい経路を提供します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- カタリシス カタリシス カタリシス
- 環境化学 環境化学
背景:
- 炭素-フッ素結合は極めて安定しており,活性化が困難である.
- 人為的なポリフルオルガニック化合物は,地球温暖化の可能性が高い.
- パルフオロアルキル基の効率的な触媒性水素化は,依然として大きな課題です.
研究 の 目的:
- パルフオロアルキル基の水素化のための効率的な触媒を開発する.
- カーボランを添加したシリリウム化合物の触媒活性を調査する.
- アリファティックな炭素-フッ素結合の選択的な割れ目を達成するために.
主な方法:
- カーボランを支える,高度に電離性のシリリウム化合物の合成.
- アクセシブルなシランを用いた触媒性水素化反応.
- 軽度の反応条件.
- 選択的なC-Fボンド活性化研究.
主要な成果:
- 寿命の長い新種の触媒が特定されました.
- トリフローロメチルおよびノンフローロブチル基の効率的な水素化が達成されました.
- 反応は,広く利用可能なシラネスで穏やかな条件下で進行した.
- アリファティック・オーバー・アロマティック・炭素・フッ素結合の完全な選択性が観察されました.
結論:
- カーボランを添加したシリリウム化合物は,水素化のための効果的な触媒である.
- この方法論は, perfluoroalkylの機能性を修正するための有望な経路を提供します.
- 観察された選択性は,標的化された化学変換のための貴重なツールを提供します.
関連する概念動画
01:13Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene
Bromination and chlorination of aromatic rings by electrophilic aromatic substitution reactions are easily achieved, but fluorination and iodination are difficult to achieve. Fluorine is so reactive that its reaction with benzene is difficult to control, resulting in poor yields of monofluoroaromatic products. To address this, Selectfluor reagent is used as a fluorine source in which a fluorine atom is bonded to a positively charged nitrogen.
02:26Preparation and Reactions of Sulfides
Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.
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.
01:01Acid Halides to Carboxylic Acids: Hydrolysis
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
01:28Multiple Halogenation of Methyl Ketones: Haloform Reaction
A method involving the transformation of methyl ketones to carboxylic acids using excess base and halogen is called the haloform reaction. It begins with the deprotonation of α hydrogen to form an enolate ion which reacts with the electrophilic halogen to give an α-halo ketone. The step continues until all the α protons are substituted to form a trihalomethyl ketone. The resulting molecule is unstable, and in the presence of a hydroxide base, it readily undergoes nucleophilic acyl substitution.
02:46Halogenation of Alkenes
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.