State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 116023 Dalian, People's Republic of China.
J Biol Inorg Chem. 2010 Mar;15(3):351-9. doi: 10.1007/s00775-009-0607-4.
The geometric structures and mechanisms for hydrogen abstraction from cyclohexane for four high-valent complexes, [Fe IV(O)(TMC)(NCMe)]2+ (where TMC is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; 1-NCMe), the inverted isomer [Fe IV(NCMe)(TMC)(O)]2+ (2-NCMe), [Ru IV(O)(TMC)(NCMe)]2+ (the ruthenium analogue of 1-NCMe; 3-NCMe), and the inverted isomer [Ru IV(NCMe)(TMC)(O)]2+ (4-NCMe), were investigated using density functional theory. The axial NCMe ligand was found to be sterically more hindered in 2-NCMe than in 1-NCMe, which is in accord with the calculated results that the Fe-L axial distance is longer in the former. Both 1-NCMe and 2-NCMe are capable of hydrogen abstraction from cyclohexane via two-state reactivity patterns. In contrast, 3-NCMe and 4-NCMe react with cyclohexane by a single-state mechanism. The reaction pathways computed reveal that 2-NCMe is more reactive than 1-NCMe, in agreement with experimental results, whereas the reactivity of 3-NCMe and 4-NCMe shows little dependence on whether the oxo unit is syn or anti to the four N-methyl groups. Our analysis shows that along the reaction pathway for 2-NCMe in the triplet spin state, the NCMe ligand moves away from the iron center, and therefore the energy of the sigma *2 z (alpha-spin) orbital decreases and an electron is transferred to this orbital. Finally, we calculated the kinetic isotope effect and investigated the relationship between this effect and reaction barriers.
使用密度泛函理论研究了四个高价配合物[Fe IV(O)(TMC)(NCMe)]2+（其中 TMC 是 1,4,8,11-四甲基-1,4,8,11-四氮杂环十四烷；1-NCMe）、反式异构体[Fe IV(NCMe)(TMC)(O)]2+（2-NCMe）、[Ru IV(O)(TMC)(NCMe)]2+（1-NCMe 的钌类似物；3-NCMe）和反式异构体[Ru IV(NCMe)(TMC)(O)]2+（4-NCMe）从环己烷中提取氢的几何结构和机制。轴向 NCMe 配体在 2-NCMe 中比在 1-NCMe 中受到更大的空间位阻，这与计算结果一致，即前者的 Fe-L 轴向距离更长。1-NCMe 和 2-NCMe 都能够通过两态反应模式从环己烷中提取氢。相比之下，3-NCMe 和 4-NCMe 通过单态机制与环己烷反应。计算出的反应途径表明，2-NCMe 比 1-NCMe 更具反应性，这与实验结果一致，而 3-NCMe 和 4-NCMe 的反应性几乎不取决于氧原子是与四个 N-甲基基团顺式还是反式。我们的分析表明，在三重态自旋状态下，2-NCMe 的反应途径中，NCMe 配体从铁中心移开，因此 sigma*2 z（alpha-自旋）轨道的能量降低，电子转移到该轨道。最后，我们计算了动力学同位素效应，并研究了这种效应与反应势垒之间的关系。
