An Fe-N₂ Complex That Generates Hydrazine and Ammonia via Fe═NNH₂: Demonstrating a Hybrid Distal-to-Alternating Pathway for N₂ Reduction.
An Fe-N₂ Complex That Generates Hydrazine and Ammonia via Fe═NNH₂: Demonstrating a Hybrid Distal-to-Alternating Pathway for N₂ Reduction.
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DOI：
10.1021/jacs.6b01230
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发表时间：
2016-03-30
影响因子：
15
通讯作者：
Peters JC
中科院分区：
文献类型：
--
作者：
Rittle J;Peters JC
生物对NH3的N2固定可以在固氮酶活性位点辅助因子中的一个或多个铁位点进行。因此，在定义明确的合成体系中模拟铁连接N2的e - /H+转移步骤非常有趣，但仍然是一个重大挑战。虽然分子Fe物种最近被证明可以催化N2生成NH3，但这些过程的机制细节仍然难以捉摸。在本文中，我们报道了通过末端结合的Fe- n2 -配合物的直接质子化，合成和分离了由三（膦）硅基配体支持的抗磁性5配位铁（IV） Fe = NNH2+。Fe = NNH2+配合物具有氧化活性，低温光谱数据和DFT计算表明，在单电子还原到S = 1/2 Fe = NNH2时，在肼配体上积累了显著的自由基特征。在较热的温度下，Fe = NNH2通过溶液中质子和电子当量的额外转移迅速转化为铁络合物Fe- nh2nh2 +。Fe- nh2nh2 +可以释放氨，这里描述的反应序列表明，铁位点可以从远端中间体（Fe = NNH2+）穿梭到交替中间体（Fe = nh2nh2 +），从而从N2中释放NH3。有趣的是，考虑到类似的N2还原“杂交”机制可能在生物N2固定中起作用。
Biological N2 fixation to NH3 may proceed at one or more Fe sites in the active-site cofactors of nitrogenases. Modeling individual e−/H+ transfer steps of iron-ligated N2 in well-defined synthetic systems is hence of much interest but remains a significant challenge. While molecular Fe species have been recently demonstrated to catalyze the formation of NH3 from N2, mechanistic details of these processes remain elusive. Herein, we report the synthesis and isolation of a diamagnetic, 5-coordinate formally iron(IV) Fe═NNH2+ species supported by a tris(phosphino)silyl ligand via the direct protonation of a terminally bound Fe-N2− complex. The Fe═NNH2+ complex is redox-active, and low-temperature spectroscopic data and DFT calculations evidence an accumulation of significant radical character on the hydrazido ligand upon one-electron reduction to S = 1/2 Fe═ NNH2. At warmer temperatures, Fe═NNH2 rapidly converts to an iron hydrazine complex, Fe-NH2NH2+, via the additional transfer of proton and electron equivalents in solution. Fe-NH2NH2+ can liberate ammonia, and the sequence of reactions described here demonstrates that an iron site can shuttle from a distal intermediate (Fe═NNH2+) to an alternating intermediate (Fe-NH2NH2+) en route to NH3 liberation from N2. It is interesting to consider the possibility that similar “hybrid” mechanisms for N2 reduction may be operative in biological N2 fixation.
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影响因子：
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作者：
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通讯作者：
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