ツジ・トロスト結合における反直感的な動力学:イオン対分割と非対称な触媒への影響
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
まとめ
電子を寄贈するフォスフィンリガンドは,パラジアム触媒によるアリレーション反応を加速する. ナトリウムテトラ (((bis-3,5-トリフルオロメチル) フェニルボラートの添加は,Tsuji-Trost アリレーションにおける反応速度と非対称な誘導を高めます.
科学分野:
- 有機金属化学 有機金属化学
- カタリシス カタリシス カタリシス
- オーガニック・シンセシス オーガニック・シンセシス
背景:
- パラジウムで触媒化されたツジ・トロスト・アリレーションは,有機合成における重要な反応である.
- 反応のメカニズムは,電性パラジウム-アリル中間物質を含む.
- リガンドの選択は,触媒活性と選択性に大きく影響する.
研究 の 目的:
- パラジウム触媒によるツジ・トロスト・アリレーションの動力学を,様々なフォスフィン・リガンドと研究する.
- 反応速度に対するリガンド電子特性の役割を解明する.
- 触媒回転と非対称誘導に対する対比効果の影響を調査する.
主な方法:
- パラジアムで触媒化されたアリレーション反応の運動学的研究.
- フォスフィンリガンドの電子特性の体系的な変化.
- 触媒性ナトリウムテトラ(bis-3,5-トリフルオロメチル) フェニルボラート (NaBAr'F) を含む.
- キラルクロマトグラフィを用いたエナンチオセレクティブ性の分析.
主要な成果:
- フォスフィンリガンドの電子提供能力の向上は,最初の仮説に反して反応速度を高めました.
- NaBAr'Fはイオンペアリターンを弱め,速度が著しく加速する.
- BINAPリガンドによる非対称誘導は,NaBAr'F.の存在下で28%から78%に改善されました.
結論:
- リンガンド電子効果とカウンテリオン相互作用は,Tsuji-Trostアライレーション運動学において重要な役割を果たします.
- [M]n+([BAr'F]-) nコカタリシスの使用は,移行金属触媒反応の最適化のための有望な戦略を提供します.
- このアプローチは,イオン中介物質を含む他の触媒プロセスでも広く適用できます.
関連する概念動画
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,...