Methane hydroxylation by metal-oxo oxidants is one of the Holy Grails in biomimetic and biotechnological chemistry. The only enzymes known to perform this reaction in Nature are iron-containing soluble methane monooxygenase and copper-containing particulate methane monooxygenase. Furthermore, few biomimetic iron-containing oxidants have been designed that can hydroxylate methane efficiently. Recent studies reported that μ-nitrido-bridged diiron(IV)-oxo porphyrin and phthalocyanine complexes hydroxylate methane to methanol efficiently. To find out whether the reaction rates are enhanced by replacing iron by ruthenium, we performed a detailed computational study. Our work shows that the μ-nitrido-bridged diruthenium(IV)-oxo reacts with methane via hydrogen atom abstraction barriers that are considerably lower in energy (by about 5 kcal mol‒1) as compared to the analogous diiron(IV)-oxo complex. An analysis of the electronic structure implicates similar spin and charge distributions for the diiron(IV)-oxo and diruthenium(IV)-oxo complexes, but the strength of the O‒H bond formed during the reaction is much stronger for the latter. As such a larger hydrogen atom abstraction driving force for the Ru complex than for the Fe complex is found, which should result in higher reactivity in the oxidation of methane.

中文翻译：

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μ-nitrido桥联双金属卟啉类配合物的性质和反应性：钌与铁相比如何？

金属氧合氧化剂使甲烷羟基化是仿生和生物技术化学中的圣杯。在自然界中已知进行此反应的唯一酶是含铁的可溶性甲烷单加氧酶和含铜的颗粒状甲烷单加氧酶。此外，几乎没有设计出能够将甲烷有效羟基化的仿生含铁氧化剂。最近的研究报道，μ-氮化桥联的二铁（IV）-羰基卟啉和酞菁可有效地将甲烷羟基化为甲醇。为了确定是否通过用钌代替铁来提高反应速率，我们进行了详细的计算研究。我们的工作表明，与类似的二铁（IV）-氧代相比，μ-氮杂桥联的二钌（IV）-氧代与甲烷通过氢原子夺取势垒反应，甲烷的能量要低得多（约5 kcal mol‒1）。复杂。对电子结构的分析表明，二铁（IV）-氧代和二钌（IV）-氧代配合物具有相似的自旋和电荷分布，但反应过程中形成的O‒H键的强度要强得多。因此，发现Ru络合物的氢原子抽象驱动力比Fe络合物的更大，这将导致甲烷氧化反应的活性更高。但是反应过程中形成的O‒H键的强度要强得多。因此，发现Ru络合物的氢原子抽象驱动力比Fe络合物的更大，这将导致甲烷氧化反应的活性更高。但是反应过程中形成的O‒H键的强度要强得多。因此，发现Ru络合物的氢原子抽象驱动力比Fe络合物的更大，这将导致甲烷氧化反应的活性更高。