ブロンステッド酸触媒 - イミン/リン酸複合体の構造的好みと移動性
Julian Greindl1, Johnny Hioe1, Nils Sorgenfrei1
1Institut für Organische Chemie, Universität Regensburg , D-93053 Regensburg, Germany.
Journal of the American Chemical Society
|December 15, 2016
まとめ
研究者は,NMRと計算を使用してイミン/ブロンステッド酸触媒複合体の動的構造を明らかにした. これらの発見は,触媒の移動性とコア構造の保存が,触媒化における高いエナチオ選択性をどのように可能にするかを説明する.
科学分野:
- 有機化学
- キャタリシス
- 構造化学
背景:
- エナチオセレクティブ・ブロンステッド酸触媒は非常に成功しています.
- 溶液中の基板/触媒の複合構造に関する実験データは少ない.
研究 の 目的:
- イミン/ブロンステッド酸触媒複合体の溶液構造と活性化モードに関する詳細な洞察を提供すること.
- エナチオ選択的触媒における触媒構造とダイナミクスの役割を調査する.
主な方法:
- 核磁共振 (NMR) スペクトロスコーピー
- 理論的な計算だ
- 6つのアロマティックイミンを使ったキラルブレンステッド酸触媒R-TRIPの調査.
主要な成果:
- 観察されたE-イミン/R-TRIPとZ-イミン/R-TRIP複合体,それぞれが2つの急速な相互変換構造として存在する (合計4つ).
- E と Z イミンの複合体の構造的特徴と交換経路 (傾き,回転) を特定した.
- 様々なイミンの4つのコアイミン/R-TRIP複合構造の保存が実証された.
結論:
- この研究は,コア構造の小さな変化を持つバイナリイミン/TRIP複合体の大きな構造空間を明らかにしています.
- 高い運動性と保存されたコア構造は,π-πとCH-πの相互作用とともに,高いエナチオ選択性および基板耐性にとって不可欠です.
関連する概念動画
01:23Aldehydes and Ketones with Amines: Imine Formation Mechanism
8.8K
Imine formation involves the addition of carbonyl compounds to a primary amine. It begins with the generation of carbinolamine through a series of steps involving an initial nucleophilic attack and then several proton transfer reactions. The second part includes the elimination of water, as a leaving group, to give the imine.
Imines are formed under mildly acidic conditions. A pH of 4.5 is ideal for the reaction.
If the pH is low or the solution is too acidic, the reaction slows down in the...
Imines are formed under mildly acidic conditions. A pH of 4.5 is ideal for the reaction.
If the pH is low or the solution is too acidic, the reaction slows down in the...
8.8K
01:25Basicity of Heterocyclic Aromatic Amines
7.1K
Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
7.1K
01:28Structures of Carboxylic Acid Derivatives
4.0K
Structure of Carboxylic Acid Derivatives
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
4.0K
01:28Amides to Carboxylic Acids: Hydrolysis
4.6K
Amides can undergo either acid-catalyzed hydrolysis or base-promoted hydrolysis through a typical nucleophilic acyl substitution. Each hydrolysis requires severe conditions.
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more...
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more...
4.6K
01:19Amines to Amides: Acylation of Amines
3.7K
Various carboxylic acid derivatives (such as acid chlorides, esters, and anhydrides) can be used for the acylation of amines to yield amides. The reaction requires two equivalents of amines. The first amine molecule functions as a nucleophile and attacks the carbonyl carbon to produce a tetrahedral intermediate. This is followed by the loss of the leaving group and restoration of the C=O bond.
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary...
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary...
3.7K
02:42Acidity of 1-Alkynes
11.4K
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
11.4K