Alkali Metal Control over N鈥揘 Cleavage in Iron Complexes

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• 作者：Katarzyna Grubel ; William W. Brennessel ; Brandon Q. Mercado ; Patrick L. Holland
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：December 3, 2014
• 年：2014
• 卷：136
• 期：48
• 页码：16807-16816
• 全文大小：445K
• ISSN：1520-5126

文摘

Though N₂ cleavage on K-promoted Fe surfaces is important in the large-scale Haber鈥揃osch process, there is still ambiguity about the number of Fe atoms involved during the N鈥揘 cleaving step and the interactions responsible for the promoting ability of K. This work explores a molecular Fe system for N₂ reduction, particularly focusing on the differences in the results obtained using different alkali metals as reductants (Na, K, Rb, Cs). The products of these reactions feature new types of Fe鈥揘₂ and Fe-nitride cores. Surprisingly, adding more equivalents of reductant to the system gives a product in which the N鈥揘 bond is not cleaved, indicating that the reducing power is not the most important factor that determines the extent of N₂ activation. On the other hand, the results suggest that the size of the alkali metal cation can control the number of Fe atoms that can approach N₂, which in turn controls the ability to achieve N₂ cleavage. The accumulated results indicate that cleaving the triple N鈥揘 bond to nitrides is facilitated by simultaneous approach of least three low-valent Fe atoms to a single molecule of N₂.