Energetics of C−H Bond Activation of Fluorinated Aromatic Hydrocarbons Using a [Tp′Rh(CNneopentyl)] Complex

C−H bond activation of fluorinated aromatic hydrocarbons by [Tp′Rh(CNneopentyl)] resulted in the formation of products of the type Tp′Rh(CNneopentyl)(arylF)H. The stability of the Rh−Caryl product is shown to be strongly dependent on the number of ortho fluorines and only mildly dependent on the total number of fluorine substituents. Complexes with aryl groups containing two ortho fluorines have barriers to reductive elimination that are ∼5 kcal mol−1 higher than for those with a single ortho fluorine. Competition experiments along with ΔGre⧧ values allow for the determination of relative Rh−Caryl bond strengths and illustrate the large ortho fluorine effect on the strength of the Rh−Caryl bond. A large change in Rh−Caryl bond strength was measured for small changes in the respective calculated C−H bond strengths. Relating M−C to C−H bond strengths resulted in a line (slope = 2.14) that closely matches the theoretically calculated value (slope = 1.96). This is the first experimental quantization of an ortho fluorine effect as predicted by theory.

利用[Tp′Rh(CNneopentyl)]介导氟化芳烃的C−H键活化反应，可生成通式为Tp′Rh(CNneopentyl)(arylF)H的产物。研究发现，Rh−Caryl产物的稳定性强烈依赖于芳环邻位氟原子的数目，仅轻微受总氟取代基数目的影响。带有两个邻位氟原子的芳基配合物，其还原消除反应能垒比仅含单个邻位氟原子的对应配合物高出约5 kcal·mol⁻¹。结合竞争实验与标准吉布斯自由能活化能垒（ΔGre⧧）数据，可测定相对Rh−Caryl键强度，并阐明邻位氟原子对Rh−Caryl键强度具有显著调控作用。即便对应计算得到的C−H键强度仅发生微小变化，所测得的Rh−Caryl键强度亦会出现显著改变。将M−C键强度与C−H键强度进行线性关联时，得到的拟合直线斜率为2.14，与理论计算值（斜率=1.96）高度吻合。本研究首次通过实验量化了理论预测的邻位氟原子效应。