Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, USA.
Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Nat Commun. 2014;5:3046. doi: 10.1038/ncomms4046.
Synthetically useful hydrocarbon oxidations are catalysed by bio-inspired non-heme iron complexes using hydrogen peroxide as oxidant, and carboxylic acid addition enhances their selectivity and catalytic efficiency. Talsi has identified a low-intensity g=2.7 electron paramagnetic resonance signal in such catalytic systems and attributed it to an oxoiron(V)-carboxylate oxidant. Herein we report the use of Fe(II)(TPA*) (TPA*=tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine) to generate this intermediate in 50% yield, and have characterized it by ultraviolet-visible, resonance Raman, Mössbauer and electrospray ionization mass spectrometric methods as a low-spin acylperoxoiron(III) species. Kinetic studies show that this intermediate is not itself the oxidant but decays via a unimolecular rate-determining step to unmask a powerful oxidant. The latter is shown by density functional theory calculations to be an oxoiron(V) species that oxidises substrate without a barrier. This study provides a mechanistic scenario for understanding catalyst reactivity and selectivity as well as a basis for improving catalyst design.
仿生非血红素铁配合物使用过氧化氢作为氧化剂，催化具有合成应用价值的碳氢化合物氧化反应，添加羧酸可以提高其选择性和催化效率。Talsi 在这类催化体系中发现了一个低强度 g=2.7 的电子顺磁共振信号，并将其归因于一个氧代铁(V)-羧酸氧化剂。在此，我们报告了使用 Fe(II)(TPA*)（TPA*=三（3,5-二甲基-4-甲氧基-2-吡啶基）甲胺）以 50%的产率生成这种中间体，并通过紫外-可见、共振拉曼、穆斯堡尔和电喷雾电离质谱法对其进行了表征，结果表明它是一种低自旋酰基过氧铁(III)物种。动力学研究表明，这种中间体本身并不是氧化剂，而是通过单分子速率决定步骤衰减，从而暴露出一种强大的氧化剂。密度泛函理论计算表明，后者是一种氧化态为 V 的铁氧物种，它可以在没有势垒的情况下氧化底物。这项研究为理解催化剂的反应性和选择性提供了一个机制方案，也为改进催化剂设计提供了一个基础。
