DFT Studies on the Reduction of Dinitrogen to Ammonia by a Thiolate-Bridged Diiron Complex as a Nitrogenase Mimic

详细信息    查看全文

• 作者：Yi Luo ; Yang Li ; Hang Yu ; Jinfeng Zhao ; Yanhui Chen ; Zhaomin Hou ; Jingping Qu
• 刊名：Organometallics
• 出版年：2012
• 出版时间：January 9, 2012
• 年：2012
• 卷：31
• 期：1
• 页码：335-344
• 全文大小：613K
• 年卷期：v.31,no.1(January 9, 2012)
• ISSN：1520-6041

文摘

We have recently reported that the binuclear iron complexes Cp*Fe(渭-SR¹)₂(渭,畏²-R²N鈺怤H)FeCp* (R¹ = Me, Et; R² = Me, Ph; Cp* = 畏⁵-C₅Me₅) as novel models of nitrogenase could effectively catalyze the N鈥揘 bond cleavage of hydrazines, including NH₂NH₂ ( J. Am. Chem. Soc. 2008, 130, 15250鈭?5251). However, the mechanistic aspects involved in the catalytic cycle and the possibility of reducing N₂ by these complexes have remained unexplored. In the present study, DFT has been applied for modeling the binding of Cp*Fe(渭-SEt)₂FeCp* with N₂ and the reduction of the N₂ to two NH₃ molecules at the diiron centers. The calculations of model system indicate that the hydrogenation (H⁺ + e^{鈥?/sup>) energetically prefers to occur at the N atoms rather than the Fe or S atoms. The rate-determining step of the reduction of HN鈺怤H could be the isomerization of a 渭,畏2-HN鈥揘H₂ moiety to a 渭-HN鈥揘H₂ form with a NH-bridging feature, which occurred at the diiron centers. Such a transformation of the binding mode of HN鈥揘H₂ might be driven by unequal charge populations on the two Fe atoms. The results show an event of net electron transfer from the ancillary ligands to the Fe atoms and the NHNH₂ moiety during the rate-determining step. In view of the experimental observations reported previously, the current computations suggest that the diiron complex Cp*Fe(渭-SEt)₂FeCp* is possible to bind N₂ and reduce it to NH₃ via protonation/reduction. Such a reduction of N₂ to NH₃ at the diiron centers favorably occurs through the HNNH and HNNH₂ forms rather than via the H₂NNH₂ unit.}