O2と[(-) -スパルテイン]Pd(H) Clの反応:分子内 [H-L]+"還元性排除"経路の証拠
Nattawan Decharin1, Brian V Popp, Shannon S Stahl
1Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States.
Journal of the American Chemical Society
|July 28, 2011
まとめ
この研究は,エアロビック酸化触媒の以前のモデルに挑戦しています. 双分子H原子抽象化ではなく,新しい還元性除去機構が,パラジウム水化物の中間物質と酸素の反応を説明しています.
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
- 酸化反応は,酸化反応によるものです.
背景:
- (-) - スパルテイン (Sp) などのケラート性窒素リガンドを含むパラジウム (II) 複合体は,エアロビック酸化反応を触媒化する.
- 鍵となるステップは,O(2) とPd(II) -ヒドリド中間体, (Sp) Pd(H) Cl.の反応である.
- 以前のコンピューティング研究では,H原子抽象化によるO(2) 挿入が提案されていた.
研究 の 目的:
- (Sp) Pd (H) Cl中間物質の酸化メカニズムを調査する.
- 提案されている二分子H原子抽象経路に異議を唱えるため.
- パラジアム触媒による有酸素酸化におけるケラート性窒素リガンドの役割を解明するため.
主な方法:
- (Sp) Pd (H) Cl.Clのインサイト生成と酸素化.
- O(2) に関する反応の順序を決定するための運動学的研究.
- 密度関数理論 (DFT) による計算研究.
主要な成果:
- (Sp) Pd (((H)) Clの酸化は,O (((2) 濃度に対するゼロ順位の依存を示した.
- この運動データは,双分子H原子抽象化メカニズムと矛盾しています.
- DFTの計算により,リガンドデプロトネーションを含む新しい分子内還元性除去経路が特定されました.
結論:
- O(2) と (Sp) Pd(H) Clの反応は,H原子抽象ではなく,新しい還元性除去機構によって行われます.
- この発見は,塩化窒素リガンドを含むパラジウム触媒による有酸素酸化のための新しい機械的パラダイムを示唆しています.
- この研究は,関連する触媒システムの再評価を促しています.
関連する概念動画
Radical Formation: Elimination
Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions with respect to...
Nucleophilic Aromatic Substitution: Elimination–Addition
Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is confirmed through isotopic...
Elimination Reactions
A nucleophile can react with an alkyl halide to give the substitution product by displacing the halogen. Or it can function as a base to give the elimination product by deprotonation of the neighboring carbon to form an alkene. In an elimination reaction, the substrate loses two groups from adjacent carbons forming at least one π bond. The carbon attached to the halogen is called the α carbon, while the adjacent carbon is called the β carbon; hence, these reactions are called β elimination or...
E1 Reaction: Kinetics and Mechanism
Here, in contrast to the E2 reaction mechanism, we delve into the aspects of the E1 reaction mechanism, which has two steps: rate-limiting loss of the leaving group and abstraction of the beta hydrogen by a weak base. Typically, the experimental proof for the E1 mechanism is via kinetic studies or isotope studies. While the former demonstrates the first-order kinetics—the dependence of the reaction solely on substrate concentration—the latter proves the abstraction of hydrogen only in the...
Regioselectivity of Electrophilic Additions-Peroxide Effect
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.
Carboxylic Acids to Acid Chlorides
Carboxylic acids react with SOCl2 or PCl5 to form acid chlorides. Amongst the carboxylic acid derivatives, acid chlorides are the most reactive and synthetically important derivatives. They are useful reagents for Friedel–Crafts acylation of some aromatic compounds.
![[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F59739.jpg&w=3840&q=50)
