分子 σ-アルカンの複合体からの室温無受容体アルカンの脱水
Alasdair I McKay1, Alexander J Bukvic1, Bengt E Tegner2
1Chemistry Research Laboratories, University of Oxford , Oxford OX1 3TA , United Kingdom.
Journal of the American Chemical Society
|June 28, 2019
まとめ
この研究では,固体分子の有機金属化学を用いて,室温でアルカンのC−H結合を活性化し,非酸化脱水化を可能にします. この突破は,触媒アルカンの機能化のための新しい経路を提供します.
科学分野:
- 有機金属化学
- カタリシス
- 固体化学
背景:
- C-H活性化による軽アルカンの非酸化的触媒脱水は,高い内熱性および不利な熱力学により困難である.
- アルカンは弱いリガンドであるため,C−H活性化前の金属中心への結合が困難である.
- 熱力学的障壁を克服するために,通常,高温または犠牲の水素受容器が必要です.
研究 の 目的:
- 固体分子有機金属化学 (SMOM-chem) を用いて軽度な条件下でアルカンC-H結合を活性化するための新しい方法を示す.
- よく定義されたアルカンシグマ複合体を準備し,特徴づける.
- これらの複合体の脱水メカニズムと運動を調査する.
主な方法:
- ロジウム-アルケンのシグマ複合体の合成 ([Rh ((Cy2PCH2CH2PCy2) ((アルケーン)) ]) [BArF4]) は,前体アルケンの複合体の固体/ガス単結晶から単結晶への変換を経由する.
- 固体ガスH/D交換実験で,C−H結合の反応性を探求する.
- 変動温度固体核磁共振 (NMR) スペクトロスコーピーと周期的密度関数理論 (DFT) の計算により,流動的プロセスと反応機構を研究する.
- 運動イソトープ効果 (KIEs) を含む運動学研究と,古典的化学運動学またはジョンソン・メル・アヴラミ・コルモゴロフ (JMAK) モデルを用いたモデリング.
主要な成果:
- よく定義されたイソブタンとサイクロヘキサンシグマ複合体は,成功裏に準備され,特徴づけられました.
- アルケンのシグマ複合体からアルケンの複合体への自発的な無受容体脱水は,真空またはAr-フロー下で298Kで発生した.
- サイクロヘクサンの脱水化のための動的同位体効果 (kH/kD = 3.6 ((5) と10.8 ((6)) は,速度決定のステップとしてC-H活性化を示した.
- 定期的な DFT 計算は,活性化バリアを予測し,C-H 結合の延長とβ-H 転送を含むメカニズムを明らかにする実験的発見を裏付けました.
結論:
- 固体分子有機金属化学 (SMOM-chem) は,アルケンのシグマ複合体を製造し,その後の脱水化を軽度な条件下で可能にします.
- この研究は,アルカン脱水化におけるC-H活性化の直接的な実験的証拠を提供し,運動データと計算データによって支持されています.
- このアプローチは,熱力学的限界を克服し,アルカンの触媒的機能化のための有望な新しい道を提供します.
さらに関連する動画
関連する概念動画
Structure of Alkanes
32.7K
The formation of carbon-carbon bonds leading to the creation of the carbon chain is the basis of organic chemistry. August Kekulé and Archibald Scott Couper independently developed this idea of carbon chain formation.
Hydrocarbons are the simplest organic compounds composed of carbons and hydrogens. Based on the bond order between carbons, the hydrocarbons are further classified into alkanes, alkenes, and alkynes.
Alkanes are the simplest hydrocarbons with sp3 hybrid carbon atoms....
Hydrocarbons are the simplest organic compounds composed of carbons and hydrogens. Based on the bond order between carbons, the hydrocarbons are further classified into alkanes, alkenes, and alkynes.
Alkanes are the simplest hydrocarbons with sp3 hybrid carbon atoms....
32.7K
Nomenclature of Alkanes
26.2K
In the late 19th-century, the number of new chemical compounds discovered increased tremendously. Hence, the necessity arose to develop a naming system for the systematic nomenclature of these newly discovered compounds. IUPAC (International Union for Pure and Applied Chemistry), established in 1919, sets rules for the nomenclature.
The alkane nomenclature considers the length of the carbon chain, the number, and the location of the substituent to arrive at its systematic name. The IUPAC...
The alkane nomenclature considers the length of the carbon chain, the number, and the location of the substituent to arrive at its systematic name. The IUPAC...
26.2K
Mass Spectrometry: Long-Chain Alkane Fragmentation
2.4K
The molecular ions of linear alkanes prefer to fragment at the carbon-carbon bond away from the end of the chain since the cleavage of an inner bond creates a stable carbocation and a stable radical. Consequently, the mass signals of linear alkanes feature intense peaks in the middle of the mass-to-charge ratio plot with weaker peaks on either end. The fragmentation of each carbon-carbon bond with the release of a methyl group in each splitting leads to prominent peaks in the mass spectra...
2.4K
Constitutional Isomers of Alkanes
21.9K
Organic compounds of the same molecular formula can have different structural formulas called constitutional isomers, and the phenomenon is known as constitutional isomerism. Alkanes with four or more carbons showing multiple structures with the same molecular formula thereby exhibit constitutional isomerism.
The linear isomer of an alkane is prefixed by the term “n”; hence a linear isomer of pentane is known as n-pentane. Based on the type of branching, some of the...
The linear isomer of an alkane is prefixed by the term “n”; hence a linear isomer of pentane is known as n-pentane. Based on the type of branching, some of the...
21.9K
Physical Properties of Alkanes
14.1K
Alkanes are nonpolar molecules due to the presence of only carbon and hydrogen atoms. The electronegativity difference between carbon and hydrogen is minimal, and hence alkanes have a zero dipole moment. This leads to the presence of only dispersion forces between the molecules. The strength of dispersion forces is dependent on the surface area of the molecules on which they act. Since the surface area increases with the molecular length for straight-chain alkanes, the dispersion forces also...
14.1K
Radical Substitution: Halogenation of Alkanes and Alkyl Substituents
9.8K
In the presence of heat or light, alkanes react with molecular halogens to form alkyl halides by a substitution reaction called radical halogenation. This reaction has three steps: initiation, propagation, and termination, as seen in the radical chlorination of methane to produce methyl chloride.
In the initiation step of the reaction, the chlorine molecule undergoes homolytic cleavage in the presence of light or heat, forming two highly reactive chlorine radicals. Propagation occurs in two...
In the initiation step of the reaction, the chlorine molecule undergoes homolytic cleavage in the presence of light or heat, forming two highly reactive chlorine radicals. Propagation occurs in two...
9.8K


