在Tsuji-Trost结合中的反直觉动力学:离子对分割和对不对称催化物的影响
Louise A Evans1, Natalie Fey, Jeremy N Harvey
1University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
Journal of the American Chemical Society
|October 9, 2008
概括
电子捐赠的素连接体加速了催化合反应. 添加四 ((bis-3,5-trifluoromethyl) phenylborate 增强了反应速率和Tsuji-Trost 合并中的不对称诱导.
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.
- 有机合成 有机合成
背景情况:
- 帕拉催化Tsuji-Trost化是有机合成中的一个关键反应.
- 反应机制涉及电友-基中间体.
- 配体选择显著影响催化活性和选择性.
研究的目的:
- 为了研究催化Tsuji-Trost结合的动力学与不同的素配体.
- 阐明联体电子特性对反应速率的作用.
- 探索对应效应对催化周转和不对称感应的影响.
主要方法:
- 催化合并反应的动力学研究.
- 素联体的电子性质的系统变化.
- 包括催化四 ((bis-3,5-trifluoromethyl) phenylborate (NaBAr'F) 在其中.
- 使用奇拉色谱学分析异构选择性.
主要成果:
- 素配体的电子捐赠能力增加提高了反应速度,与最初的假设相反.
- NaBAr'F减弱了离子对回归,导致了显著的速率加速.
- 在NaBAr'F的存在下,BINAP联体的不对称诱导从28%提高到78% ee.
结论:
- 联体电子效应和对子相互作用在Tsuji-Trost异位化动力学中起着至关重要的作用.
- 使用[M]n+([BAr'F]-) n共催化为优化过渡金属催化反应提供了一个有希望的策略.
- 这种方法在涉及离子中间体的其他催化过程中具有广泛的应用.
相关概念视频
02:05SN1 Reaction: Kinetics
In an SN2 reaction, the reaction rate depends on both the type of nucleophile and the substrate. A hindered tertiary alkyl halide is practically inert to the SN2 mechanism despite using a strong nucleophile.
However, Sir Christopher Ingold and Edward D. Hughes, who studied the kinetics of various nucleophilic substitution reactions, noticed that a tertiary alkyl halide does undergo a nucleophilic substitution reaction in the presence of a weak nucleophile. While studying the substitution...
However, Sir Christopher Ingold and Edward D. Hughes, who studied the kinetics of various nucleophilic substitution reactions, noticed that a tertiary alkyl halide does undergo a nucleophilic substitution reaction in the presence of a weak nucleophile. While studying the substitution...
02:23SN2 Reaction: Stereochemistry
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
02:26SN2 Reaction: Transition State
An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
01:33Regioselective Formation of Enolates
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are more stable. But the energy required to form kinetic enolates is less.
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...
02:27Predicting Products: SN1 vs. SN2
Nucleophilic substitution reactions of alkyl halides can proceed via an SN1 or an SN2 mechanism. While in SN2 reactions, the nucleophile attacks the substrate simultaneously as the leaving group departs, in SN1 reactions, the substrate first dissociates to give the carbocation intermediate. Various factors such as the structure of the substrate, the strength of the nucleophile, and the nature of the solvent promote one mechanism over the other.
With increased substitution on the alkyl halide,...
With increased substitution on the alkyl halide,...