在固体状态下合成和表征 (I) σ-复合物
Sebastian D Pike1, Amber L Thompson, Andrés G Algarra
1Department of Chemistry, Chemical Research Laboratories, Oxford, UK.
Science (New York, N.Y.)
|August 28, 2012
概括
研究人员在固态中合成和表征了难以捉摸的过渡金属- σ-复合物. 这一突破允许使用X射线衍射在催化C-H激活中的这些关键中间体的结构确定.
科学领域:
- 有机金属化学 有机金属化学
- 催化剂是一种催化剂.
- 固态化学 固态化学
背景情况:
- 过渡金属- σ-复合物是催化C-H激活中的关键中间体.
- 通过X射线衍射对这些复合体进行固态表征一直是具有挑战性的.
- 阐明它们的结构对于理解C-H激活机制至关重要.
研究的目的:
- 开发一种方法来合成和表征固态的过渡金属- σ-复合物.
- 为了使这些难以捉摸的中间体的结构确定.
- 提供有关基 σ-复合物的结合和结构的见解.
主要方法:
- 用一个简单的气体-固体反应来直接合成基 σ-复合物.
- 单晶X射线衍射用于结构确定.
- 描述集中在一个d(8) - (I) 金属中心与一个norbornane连接体.
主要成果:
- 成功合成并对固态过渡金属-基 σ-复合物进行结构性表征.
- 确定了一个与 (I) 中心结合的norbornane σ-bound的X射线晶体结构.
- 观察到基联体通过两个σ-C-H键合金属中心.
结论:
- 开发的气体-固体反应策略对于合成固态过渡金属-基 σ-复合物是有效的.
- 这种方法克服了在这些关键催化中间体的表征上以前的局限性.
- 结构数据为CH激活和有机金属化学领域提供了宝贵的信息.
相关概念视频
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.
02:34Preparation of Alkynes: Dehydrohalogenation
Introduction
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
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.
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
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.