Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen
Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen
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DOI：
10.1021/jacs.0c01896
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发表时间：
2020-06-03
影响因子：
15
通讯作者：
Agapie, Theodor
中科院分区：
文献类型：
--
作者：
Arnett, Charles H.;Agapie, Theodor
固氮酶对N-2的结合需要FeMo-辅因子的还原活化，但FeMoco在其活化形式下的精确结构和原子组成尚不清楚。然而，最近的晶体学研究表明，N-2还原可能发生在FeMoco的碳桥连二铁亚基。为了模拟Fe-（mu-C）-Fe位点对N-2结合的活化，我们合成了一种新的双核六膦配体，其衍生自2，6-二取代的甲苯平台。配体的中心甲基的活化提供了二铁II -碳炔络合物（P6 ArC）Fe-2（μ-H），其特征在于生物学相关的Fe（β-碳炔）（μ-H）Fe基序。SQUID磁测量、穆斯堡尔谱和DFT计算表明，（P6 ArC）Fe-2（μ-H）具有良好隔离的S = 1基态，将其与所有其他抗磁性的二铁ii -碳炔配合物区分开来。在添加H+/e（-）（H-2、TEMPO-H或HCl）源时，（P6 ArC）Fe-2（μ-H）被活化朝向N-2结合，伴随着碳炔配体的质子化。虽然与H-2的反应最终导致碳炔部分的完全质子化，但机理研究表明，形成单个C-H键，伴随着一个Fe-C键的裂解，产生能够配位N-2的铁-卡宾中间体。
Binding of N-2 by nitrogenase requires a reductive activation of the FeMo-cofactor, but the precise structure and atomic composition of FeMoco in its activated form is not well understood. However, recent crystallographic studies suggest that N-2 reduction may occur at a carbon-bridged diiron subunit of FeMoco. Toward modeling the activation of a Fe-(mu-C)-Fe site toward N-2 binding, we synthesized a new dinucleating, hexaphosphine ligand derived from a 2,6-disubstituted toluene platform. Activation of the central methyl group of the ligand affords the diiron ii -carbyne complex (P6ArC) Fe-2(mu-H) featuring a biologically relevant Fe(p-carbyne)(mu-H)Fe motif. SQUID magnetometry, MOssbauer spectroscopy, and DFT calculations reveal that (P6ArC)Fe-2(mu-H) has a well-isolated S = 1 ground state, distinguishing it from all other diiron ii -carbyne complexes which are diamagnetic. Upon the addition of sources of H+/e(-) (H-2, TEMPO-H or HCI), (P6ArC)Fe-2(mu-H) is activated toward N-2 binding, with concomitant protonation of the carbyne ligand. Although reaction with H-2 ultimately leads to complete protonation of the carbyne moiety, mechanistic investigations indicate that formation of a single C-H bond, with concomitant cleavage of one Fe-C bond, generates an iron-carbene intermediate capable of coordinating N-2.