Intramolecular Iron-Mediated C鈥揌 Bond Heterolysis with an Assist of Pendant Base in a [FeFe]-Hydrogenase Model

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• 作者：Dehua Zheng ; Ning Wang ; Mei Wang ; Shengda Ding ; Chengbing Ma ; Marcetta Y. Darensbourg ; Michael B. Hall ; Licheng Sun
• 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：16817-16823
• 全文大小：442K
• ISSN：1520-5126

文摘

Although many metalloenzymes containing iron play a prominent role in biological C鈥揌 activation processes, to date iron-mediated C(sp³)鈥揌 heterolysis has not been reported for synthetic models of Fe/S-metalloenzymes. In contrast, ample precedent has established that nature鈥檚 design for reversible hydrogen activation by the diiron hydrogenase ([FeFe]-H₂ase) active site involves multiple irons, sulfur bridges, a redox switch, and a pendant amine base, in an intricate arrangement to perform H鈥揌 heterolytic cleavage. In response to whether this strategy might be extended to C鈥揌 activation, we report that a [FeFe]-H₂ase model demonstrates iron-mediated intramolecular C鈥揌 heterolytic cleavage via an agostic C鈥揌 interaction, with proton removal by a nearby pendant amine, affording Fe^II鈥揫Fe鈥?sup>II鈥揅H鈥?img src="/templates/jsp/_style2/_achs/images/tiebar-above-end.gif" class="tbAbove" alt="tiebar above end" />S] three-membered-ring products, which can be reduced back to 1 by Cp₂Co in the presence of HBF₄. The function of the pendant base as a proton shuttle was confirmed by the crystal structures of the N-protonated intermediate and the final deprotonated product in comparison with that of a similar but pendant-amine-free complex that does not show evidence of C鈥揌 activation. The mechanism of the process was backed up by DFT calculations.