三座標鉄 (III) カーベンの複合体における正常から異常への再配置とNHC活性化
Benjamin M Day1, Thomas Pugh, Daniël Hendriks
1School of Chemistry, The University of Manchester , Manchester, M13 9PL, U.K.
Journal of the American Chemical Society
|August 28, 2013
まとめ
普通の鉄-N-ヘテロサイクリックカルベン (NHC) 複合体を加熱すると,希少な異常な鉄-aNHC構造が生じる. テートブチル置換複合体は,C-HとC-Nの活性化経路を通じて熱分解を経験する.
科学分野:
- 有機金属化学 有機金属化学
- 協調化化学について
- カタリシス カタリシス カタリシス
背景:
- N-ヘテロサイクリックカルベン (NHCs) は,有機金属化学における多用途リガンドである.
- NHCリガンドを含む鉄複合体は,鉄の豊富さと低毒性のために興味があります.
- "正常"と"異常"のNHC協調モードの区別は,反応性を理解するために重要である.
研究 の 目的:
- 普通の3座標の鉄-NHC複合体の熱的再配置を調査する.
- 希少な異常な鉄-aNHC複合体を合成し,特徴づけること.
- テート-ブチル置換鉄-NHC複合体の熱分解経路を探求する.
主な方法:
- 鉄-NHC複合体の合成と特徴付け.
- 複合物の熱処理 (加熱) について
- 構造を決定するために,光譜分析 (例えば,NMR) とX線結晶学.
主要な成果:
- 正常な鉄-NHC複合体[[IPr]Fe[N′′]2]は加熱すると,異常な同位体[aIPr]Fe[N′′]2に再構成される.
- この再配置は,3座標の異常な鉄-aNHC複合体の希少な例である.
- テルト-ブチル置換複合体 [(I(t) Bu) Fe((N′′) ]2は熱分解してbis(imidazole) 複合体 [((t) BuIm) 2Fe(N′′) ]2を形成する.
- 分解には,連続したC-HとC-N結合の活性化を含むメカニズムが提案されています.
結論:
- 熱的条件は,鉄複合体の正常なNHCリガンドの異常なNHCリガンドへの再配置を誘導することができます.
- 異常な鉄-aNHC複合体,特に3座標複合体はアクセス可能である.
- 特定の鉄-NHC複合体の熱分解は,新しいC-HとC-N活性化経路を経て進行し,予期せぬ製品につながる可能性があります.
関連する概念動画
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01:21[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
03:02Colors and Magnetism
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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...
02:57Coordination Number and Geometry
For transition metal complexes, the coordination number determines the geometry around the central metal ion. Table 1 compares coordination numbers to molecular geometry. The most common structures of the complexes in coordination compounds are octahedral, tetrahedral, and square planar.
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...