通过与 Al-C 键的高合和化离子化离子的化协调,激活 C-H 键
Werner Uhl1, Andrej Vinogradov, Stefan Grimme
1Institut für Anorganische und Analytische Chemie der Universität Münster, Corrensstrasse 30, D-48149 Münster, Germany. uhlw@uni-muenster.de
Journal of the American Chemical Society
|August 21, 2007
概括
研究人员创造了新的有机元素化合物,具有稳定的阴离子碳原子. 这些化合物,一个乙烯基离子和一个亚利法性碳离子,通过与-碳键的过联结合表现出独特的稳定性.
科学领域:
- 有机金属化学 有机金属化学
- 碳化物化学 碳化物化学
- 有机合成 有机合成
背景情况:
- 二三) 丁丁是有机金属反应的基质.
- 甲基化是水合发光反应中的关键试剂.
- 稳定电离物种是化学中的一个重大挑战.
研究的目的:
- 为了合成和描述前所未有的有机元素化合物.
- 为了研究稳定的cationic碳物种的形成.
- 探索在稳定这些离子体中的作用.
主要方法:
- 在不同的条件下,二三丁与二甲基化的反应.
- 由此产生的化合物的光谱表征.
- 量子化学计算以支持实验发现.
主要成果:
- 获得了两种新的zwitterionic有机元素化合物.
- 合成了一种在室温稳定的乙烯基离子和一种在室温稳定的异质碳离子.
- 通过与Al-C键的高合,观察到C-H键激活和稳定的证据.
结论:
- 甲基化物可以从二三丁产生稳定的乙烯基和亚利法性碳酸.
- 带有合化对子的双基结构有助于离子稳定.
- 与Al-C键的过度结合在稳定阴离子中心中起着至关重要的作用.
相关概念视频
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...
01:21Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
01:10Aldehydes and Ketones with HCN: Cyanohydrin Formation Mechanism
Cyanohydrins are formed when cyanide nucleophiles and carbonyl compounds like aldehydes and ketones react. A strong base, the cyanide ion, catalyzes cyanohydrin formation. The ions are generated from HCN under aqueous conditions. Once the cyanide ions are generated, the first step involves the nucleophilic attack of the cyanide ions on the electrophilic carbonyl carbon. This attack shifts the π electrons from the C=O to the oxygen atom forming the alkoxide ion intermediate. The alkoxide anion...
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Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. The aldol condensation reaction presented in Figure 1 constitutes an aldol addition reaction followed by the dehydration process.
00:57C–C Bond Cleavage: Retro-Aldol Reaction
The reverse of the aldol addition reaction is called the retro-aldol reaction. Here, the carbon–carbon bond in the aldol product is cleaved under acidic or basic conditions to form two molecules of carbonyl compounds. The mechanism of the reaction consists of three steps.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.
01:33Aldol Condensation vs Claisen Condensation
Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A base-promoted condensation between ester molecules to produce a ꞵ-ketoester is known as the Claisen condensation. In the presence of a base, both reactions involve deprotonation of the acidic α hydrogen to produce the corresponding enolates. The nucleophilic enolates attack their respective nonenolized carbonyl compound forming a tetrahedral intermediate.