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首页> 外文期刊>Chemistry: A European journal >A two-state reactivity rationale for counterintuitive axial ligand effects on the C-H activation reactivity of nonheme Fe-IV = O oxidants
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A two-state reactivity rationale for counterintuitive axial ligand effects on the C-H activation reactivity of nonheme Fe-IV = O oxidants

机译：违反直觉的轴向配体对非血红素Fe-IV = O氧化剂的C-H活化反应的影响的两态反应原理

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This paper addresses the observation of counterintuitive reactivity patterns of iron-oxo reagents, TMC(L)FeO2+.1+; L = CH3CN, CF3CO-, N-3(-), and SR-, in O-transfer to phosphines versus H-abstraction from; for example, 1,4-cyclohexadiene. Experiments show that O-transfer reactivity correlates with the electrophilicity of the oxidant, but H-abstraction reactivity follows an opposite trend. DFT/B3LYP calculations reveal that two-state reactivity (TSR) serves as a compelling rationale for these trends, whereby all reactions involve two adjacent spin-states of the iron(IV)-oxo species, triplet and quintet. The ground state triplet surface has high barriers, whereas the excited state quintet surface features lower ones. The barriers, on any single surface, are found to increase as the electrophilicity of TMC(L)FeO2+.1+ decreases. Thus, the counterintuitive behavior of the H-abstraction reactions cannot be explained by considering the reactivity of only a single spin state but can be rationalized by a TSR model in which the reactions proceed on the two surfaces. Two TSR models are outlined: one is traditional involving a variable transmission coefficient for crossover from triplet to quintet, followed by quintet-state reactions; the other considers the net barrier as a blend of the triplet and quintet barriers. The blending coefficient (x), which estimates the triplet participation, increases as the quintet-triplet energy gap of the TMC(L)FeO2+.1+ reagent increases, in the following order of L: CH3CN > CF3CO2- > N-3(-) > SR-. The calculated barriers predict the dichotomic experimental trends and the counterintuitive behavior of the H-abstraction series. The TSR approaches make a variety of testable predictions.
机译：本文讨论了铁-氧试剂TMC（L）FeO2 + .1 +违反直觉的反应模式的观察。 L = CH3CN，CF3CO-，N-3（-）和SR-，O转移到膦中，而H从中转移;例如1，4-环己二烯。实验表明，O-转移反应性与氧化剂的亲电性相关，但H-吸收反应性却相反。 DFT / B3LYP计算表明，二态反应性（TSR）可作为这些趋势的有说服力的依据，其中所有反应都涉及铁（IV）-氧代物种的两个相邻自旋态，即三重态和五重态。基态三重态表面具有较高的势垒，而激发态五重态表面具有较低的势垒。发现在任何单个表面上的势垒会随着TMC（L）FeO2 + .1 +的亲电子性的降低而增加。因此，不能通过仅考虑单个自旋态的反应性来解释H-吸引反应的反直觉行为，而是可以通过其中在两个表面上进行反应的TSR模型来合理化。概述了两种TSR模型：一种是传统的模型，涉及从三重态到五重态的转换的可变传递系数，然后是五重态反应。另一方则将净屏障视为三重和五重屏障的混合体。估计三重态参与度的混合系数（x）随着TMC（L）FeO2 + .1 +试剂的五重态-三重态能隙的增加而增加，按L的以下顺序排列：CH3CN> CF3CO2-> N-3（ -）> SR-。计算的势垒预测了H-抽象序列的二分法实验趋势和违反直觉的行为。 TSR方法可进行各种可测的预测。

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