Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
Chem Rev. 2017 Jul 12;117(13):9140-9162. doi: 10.1021/acs.chemrev.7b00034. Epub 2017 May 10.
TAML activators of peroxides are iron(III) complexes. The ligation by four deprotonated amide nitrogens in macrocyclic motifs is the signature of TAMLs where the macrocyclic structures vary considerably. TAML activators are exceptional functional replicas of the peroxidases and cytochrome P450 oxidizing enzymes. In water, they catalyze peroxide oxidation of a broad spectrum of compounds, many of which are micropollutants, compounds that produce undesired effects at low concentrations-as with the enzymes, peroxide is typically activated with near-quantitative efficiency. In nonaqueous solvents such as organic nitriles, the prototype TAML activator gave the structurally authenticated reactive iron(V)oxo units (FeO), wherein the iron atom is two oxidation equivalents above the Fe resting state. The iron(V) state can be achieved through the intermediacy of iron(IV) species, which are usually μ-oxo-bridged dimers (FeFe), and this allows for the reactivity of this potent reactive intermediate to be studied in stoichiometric processes. The present review is primarily focused at the mechanistic features of the oxidation by FeO of hydrocarbons including cyclohexane. The main topic is preceded by a description of mechanisms of oxidation of thioanisoles by FeO, because the associated studies provide valuable insight into the ability of FeO to oxidize organic molecules. The review is opened by a summary of the interconversions between Fe, FeFe, and FeO species, since this information is crucial for interpreting the kinetic data. The highest reactivity in both reaction classes described belongs to FeO. The resting state Fe is unreactive oxidatively. Intermediate reactivity is typically found for FeFe; therefore, kinetic features for these species in interchange and oxidation processes are also reviewed. Examples of using TAML activators for C-H bond cleavage applied to fine organic synthesis conclude the review.
TAML 过氧化物酶激活剂是三价铁配合物。在大环结构中，四个去质子酰胺氮的配位是 TAML 的特征，大环结构变化很大。TAML 激活剂是过氧化物酶和细胞色素 P450 氧化酶的特殊功能副本。在水中，它们催化过氧化物氧化广泛的化合物，其中许多是微量污染物，这些化合物在低浓度下会产生不良影响——与酶一样，过氧化物通常以接近定量的效率被激活。在非水溶剂（如有机腈）中，原型 TAML 激活剂产生了结构确证的反应性铁（V）氧单位（FeO），其中铁原子的氧化态比 Fe 基态高出两个氧化当量。铁（V）态可以通过铁（IV）物种的中间体来实现，这些物种通常是μ-氧桥联二聚体（FeFe），这使得这种强反应性中间体的反应性可以在计量过程中进行研究。本综述主要集中在 FeO 氧化烃类化合物（包括环己烷）的反应机制方面。主要主题之前是 FeO 氧化硫醚的机制描述，因为相关研究为 FeO 氧化有机分子的能力提供了有价值的见解。综述以 Fe、FeFe 和 FeO 物种之间的转化摘要开始，因为这些信息对于解释动力学数据至关重要。在描述的两类反应中，最高的反应性属于 FeO。基态 Fe 不具有氧化性。中间反应性通常在 FeFe 中发现；因此，也综述了这些物种在相互转化和氧化过程中的动力学特征。综述以使用 TAML 激活剂进行 C-H 键断裂应用于精细有机合成为结尾。
