Ahsan Faiza, Ansari Mursaleem, Klein Johannes E M N, Swart Marcel
IQCC and Dept. Chem., Universitat de Girona, 17003 Girona, Spain.
Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Science and Engineering, University of Groningen, Nijenborgh 3, 9747 AG Groningen, the Netherlands.
J Inorg Biochem. 2025 Nov;272:112989. doi: 10.1016/j.jinorgbio.2025.112989. Epub 2025 Jul 5.
C(sp)-H bond activation mechanisms typically involve σ- and π-channel pathways, as characterized by FeOH (or FeOC) angles of ca. 180° and 120°, respectively. It is well known that the preference for either the σ- or π-channel depends on the spin state, but doubts exist on what would be characteristic values for the FeOX (X = H or C) angles. Here we study the oxidation of methane and ethane mediated by an Fe(IV)oxo model complex through density functional theory. A systematic comparison of dispersion-corrected B3LYP (B3LYP-D2, B3LYP-D3, B3LYP-D3BJ, B3LYP-D4) and the uncorrected counterpart (B3LYP) was conducted to evaluate the role of dispersion interactions in both gas and solvent phases. Our results reveal that dispersion corrections significantly influence barriers at transition states (TSs), particularly in the solvent phase, where dispersion contributions enhance stabilization of TS structures. The σ-channel pathway dominates for high spin (S = 2), while intermediate spin (S = 1) states favor the π-channel. Dispersion effects were found to be more pronounced for ethane, where larger non-covalent interactions between the substrate and Fe(IV)oxo complex arise. The FeOX angles vary substantially depending on the choice of dispersion correction, and between gas phase and solution phase. Indeed, for the reaction with ethane the FeOX values of the σ-channel approach values that are typically associated with the π-channel. Fortunately, the Spin-Resolved Charge Displacement Function provides a clear visual tool to distinguish the two channels. These insights advance the understanding of hydrocarbon functionalization by high-valent iron-oxo species, with implications for synthetic catalyst design in homogeneous and enzymatic catalysis.
C(sp) - H键活化机制通常涉及σ-和π-通道途径，其特征分别为FeOH（或FeOC）角约为180°和120°。众所周知，对σ-或π-通道的偏好取决于自旋态，但对于FeOX（X = H或C）角的特征值存在疑问。在此，我们通过密度泛函理论研究了由Fe(IV)氧代模型配合物介导的甲烷和乙烷的氧化反应。对色散校正的B3LYP（B3LYP-D2、B3LYP-D3、B3LYP-D3BJ、B3LYP-D4）和未校正的对应物（B3LYP）进行了系统比较，以评估色散相互作用在气相和溶剂相中的作用。我们的结果表明，色散校正显著影响过渡态（TSs）的能垒，特别是在溶剂相中，色散贡献增强了TS结构的稳定性。对于高自旋（S = 2），σ-通道途径占主导，而中间自旋（S = 1）态有利于π-通道。发现乙烷的色散效应更明显，其中底物与Fe(IV)氧代配合物之间产生了更大的非共价相互作用。FeOX角根据色散校正的选择以及在气相和溶液相之间有很大变化。实际上，对于与乙烷的反应，σ-通道的FeOX值接近通常与π-通道相关的值。幸运的是，自旋分辨电荷位移函数提供了一个清晰的可视化工具来区分这两个通道。这些见解推进了对高价铁氧物种进行烃官能化的理解，对均相和酶催化中的合成催化剂设计具有重要意义。
