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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Experimental and Theoretical Studies of MCF↑(+)↓(3) (M = Fe and Co): Reactivities, Structures and Potential Energy Surface for C-F Activation
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Experimental and Theoretical Studies of MCF↑(+)↓(3) (M = Fe and Co): Reactivities, Structures and Potential Energy Surface for C-F Activation

机译：MCF↑（+）↓（3）（M = Fe和Co）的实验和理论研究：C-F活化的反应性，结构和势能面

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摘要

The gas-phase reactions of FeCF↑(+)↓(3) and CoCF↑(+)↓(3) with a series of small alkanes and alkenes were studied by Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. These ions, which are generated from the reactions of the bare metal ions with CF↓(3)I, both react with alkanes larger than ethane and with small alkenes primarily by CF2 displacement reactions. Hydride abstraction is also observed in some cases. Collision-induced dissociation and ion-molecule reactions indicate that the structure of MCF↑(+)↓(3)( M = Fe, Co) is an ion-dipole complex, FM+…F↓(2)C, involving C-F activation. A good fit of pseudo-first-order kinetics is obtained for the reactions of FeCF3↑(+)and CoCF3↑(+) with the above selected hydrocarbons. The reaction rates of FeCF3↑(+) and CoCF3↑(+) with the alkanes increase dramatically with the length of the alkane chain. The C-F activation mechanism of Fe↑(+) or Co↑(+) with the CF↑(3) ligand was also investigated theoretically. The potential energy surface (PES) of the [Fe, C, F3] ↑(+) system and the local minima of the [Co, C, F3] ↑(+) system are examined by density functional calculations. For the iron system, three local minima are detected including the intact trifluoromethyl isomer, Fe↑(+)-CF↓(3), the inserted fluoro-difluorocarbene isomer, F↓(2)C-Fe↑(+)-F, and the ion-dipole complex, FCF…Fe↑(+)-F. Two transition-state structures connecting the above minima are also found. The PES of [Fe, C, F3]↑(+) indicates a unique mechanism in which C-F insertion takes place first with a large activation barrier of 6.4 kcal/mol, followed by rotation of the CF↓(2) unit to the final FCF…Fe↑(+)-F structure with an activation barrier of 2.4 kcal/mol. Three similar minima are also detected for CoCF3↑(+).
机译：通过傅立叶变换离子回旋共振（FTICR）质谱研究了FeCF↑（+）↓（3）和CoCF↑（+）↓（3）与一系列小链烷烃的气相反应。这些由裸金属离子与CF↓（3）I反应生成的离子，主要通过CF2置换反应与大于乙烷的烷烃和与较小的烯烃反应。在某些情况下，还会观察到氢化物抽象。碰撞诱导的离解和离子分子反应表明，MCF↑（+）↓（3）（M = Fe，Co）的结构是离子偶极复合物FM +…F↓（2）C，涉及C-F活化。 FeCF3↑（+）和CoCF3↑（+）与上述选定的烃类反应获得了良好的拟一级动力学拟合。 FeCF3↑（+）和CoCF3↑（+）与烷烃的反应速率随烷烃链长度的增加而急剧增加。理论上研究了Fe↑（+）或Co↑（+）与CF↑（3）配体的C-F活化机理。 [Fe，C，F3]↑（+）系统的势能面（PES）和[Co，C，F3]↑（+）系统的局部最小值通过密度泛函计算进行了检验。对于铁系统，检测到三个局部最小值，包括完整的三氟甲基异构体Fe↑（+）-CF↓（3），插入的氟-二氟卡宾异构体F↓（2）C-Fe↑（+）-F，离子-偶极复合物FCF…Fe↑（+）-F。还发现了两个连接上述极小值的过渡状态结构。 [Fe，C，F3]↑（+）的PES表示一种独特的机制，其中CF插入首先以6.4 kcal / mol的大激活势垒发生，然后旋转CF↓（2）单元直至最终FCF…Fe↑（+）-F结构，活化势垒为2.4 kcal / mol。 CoCF3↑（+）也检测到三个相似的最小值。

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