イミダゾ[1,5-a]ピリジン:安定したN-ヘテロサイクリックカルベンの汎用的な構造
Manuel Alcarazo1, Stephen J Roseblade, Andrew R Cowley
1Instituto de Investigaciones Químicas (CSIC-US), Américo Vespucio 49, E-41092 Seville, Spain.
Journal of the American Chemical Society
|March 10, 2005
まとめ
研究者は,イミダゾ[1,5-a]ピリジンフレームワークを使用して,新しいN-ヘテロサイクリックカルベンを開発しました. これらの安定したカルベンは,Rh (I) モノカルベンとバイカルベンを含め,触媒と材料科学において新しい可能性を秘めています.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 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
背景:
- イミダゾ[1,5-a]ピリジン基架は,新型カルベンのリガンドを開発する可能性を認識されています.
- N-ヘテロサイクリックカルベン (NHCs) は,そのユニークな電子およびステリック特性により,触媒および材料科学において極めて重要です.
研究 の 目的:
- イミダゾ[1,5-a]ピリジンの骨格から派生した新しい安定したN-ヘテロサイクリックカルベンを合成し,特徴づけること.
- オーガノメタリック化学におけるリガンドとしてのこれらの新型カルベンの有用性を探求する.
主な方法:
- イミダゾ[1,5-a]ピリジン-3-イリデン (ImPy) およびその誘導体の合成.
- Rh ((I) モノおよびビスカルベンの複合体の製造と特徴付け.
- 特徴づけのテクニックには,おそらくNMRスペクトロスコピー,質量スペクトロメトリー,そして潜在的にX線結晶学が含まれていた.
主要な成果:
- 安定したイミダゾ[1,5-a]ピリジンベースのN-ヘテロサイクリックカルベンの合成が成功しました.
- Rh(I) モノカルベンおよびビカルベン複合体 (6および7) とメソイオンカルベンの誘導体 (13) の形成.
- 特徴づけられたカルベン複合体は,イミダゾ[1,5-a]ピリジンプラットフォームの汎用性を示しています.
結論:
- イミダゾ[1,5-a]ピリジンの骨格は,新しい安定したN-ヘテロサイクリックカルベンを生成するための実行可能で汎用的なプラットフォームです.
- 合成されたカルベンとそのRh (I) 複合体は,触媒と調整化学における応用が有望であることを示している.
関連する概念動画
02:34Structural Isomerism
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
02:10Carbocations
Carbocations are one of the reaction intermediates formed during several nucleophilic substitutions or elimination reactions. A carbocation is an electron-deficient species with the central carbon atom having six electrons and three bonded atoms. The central carbon in a carbocation is sp2 hybridized with trigonal planar geometry. It has an empty p orbital perpendicular to the plane of the structure that can accept electrons. Thus, carbocations act as strong electrophiles and may react with any...
01:28Structures of Carboxylic Acid Derivatives
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...
01:19Structure of Amines
The hybridized nitrogen atom in amines possesses a lone pair of electrons and is bound to three substituents with a bond angle of around 108°, which is less than the tetrahedral angle of 109.5°. However, the C–N–H bond angle is slightly larger at 112°, with a carbon–nitrogen bond length of 147 pm. This carbon–nitrogen bond length of of amines is longer than the carbon–oxygen bond of alcohols (143 pm) but shorter than alkanes’ carbon–carbon bond (154 pm). These aspects are illustrated in Figure...
01:25Basicity of Heterocyclic Aromatic Amines
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).
01:11Nomenclature of Carboxylic Acid Derivatives: Amides and Nitriles
Naming Amides
The IUPAC and common names of amides are derived from the parent carboxylic acid, by replacing the suffix “oic acid” and “ic acid,” respectively, with “amide.” In the following example, the IUPAC name ethanamide is derived from ethanoic acid, and the common name, acetamide, is obtained from acetic acid.
The IUPAC and common names of amides are derived from the parent carboxylic acid, by replacing the suffix “oic acid” and “ic acid,” respectively, with “amide.” In the following example, the IUPAC name ethanamide is derived from ethanoic acid, and the common name, acetamide, is obtained from acetic acid.