Density functional theory calculation is used to investigate the oxidation of cyclo-olefin (cyclobutene, cyclopentene, cyclohexene, cycloheptene, and cyclo-octene) by the complex [Fe^IV(O)(TQA)(NCMe)]²⁺, which has S = 2 ground state, and the effect of electronic factors and steric hindrance on reaction barriers. Our results suggest that the oxo–iron(IV) complex can oxidise C–H and C = C bonds via a single-state mechanism, and two different ways of electron transport exist. The energy barriers initially decrease with increasing substrate size, and the trend then reverses. Comparison of the energy barrier in different systems reveals that except for the reaction between [Fe^IV(O)(TQA)(NCMe)]²⁺ and cycloheptene, oxo–iron(IV) complexes prefer epoxidation to hydroxylation. However, the hydroxylated product is more stable than the corresponding epoxidated product. This result indicates that the products of epoxidation tend to decompose first. The energy barrier of hydroxylation and epoxidation originates from the balance of orbital interaction and Pauli repulsion from the equatorial ligand and protons on the approaching substrate. In this regard, we calculate the weak interaction between two fragments (oxo–iron complex and substrates) using the independent gradient model and drawn the corresponding 3D isosurface representations of reactants.

中文翻译：

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S = 2基态配合物[FeIV（O）（TQA）（NCMe）] 2氧化环烯烃。

密度泛函理论计算中，使用由复调查环烯烃（环丁烯，环戊烯，环己烯，环庚烯，和环辛烯）的氧化的[Fe ^IV（O）（TQA）（NCMe）] ²⁺，其为S = 2基态，以及电子因素和位阻对反应壁垒的影响。我们的结果表明，氧-铁（IV）络合物可以通过单态机制氧化C–H和C = C键，并且存在两种不同的电子传输方式。能量势垒最初随着衬底尺寸的增加而减小，然后趋势相反。比较不同系统中的能垒，发现除了[Fe ^IV（O）（TQA）（NCMe）] ²⁺之间的反应和环庚烯，氧-铁（IV）配合物更喜欢环氧化而不是羟基化。但是，羟基化产物比相应的环氧化产物更稳定。该结果表明环氧化产物倾向于首先分解。羟化和环氧化的能垒来自于轨道相互作用和来自赤道配体和接近底物上的质子的保利排斥的平衡。在这方面，我们使用独立的梯度模型计算了两个片段（氧-铁络合物和底物）之间的弱相互作用，并绘制了反应物的相应3D等值面表示。