Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen,Journal of the American Chemical Society

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Activation of an Open Shell, Carbyne-Bridged Diiron Complex Toward Binding of Dinitrogen
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2020-04-14 , DOI: 10.1021/jacs.0c01896
Charles H Arnett ₁ , Theodor Agapie ₁

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Binding of N2 by nitrogenase requires a reductive activation of the FeMo-cofactor, but the precise structure and atomic com-position of FeMoco in its activated form is not well understood. However, recent crystallographic studies suggest that N2 reduction may occur at a carbon-bridged diiron subunit of FeMoco. Toward modeling the activation of a Fe-(µ-C)-Fe site toward N2 binding, we synthesized a new dinucleating, hexaphosphine ligand derived from a 2,6-disubstituted toluene plat-form. Activation of the central methyl group of the ligand affords the diiron µ-carbyne complex (P6ArC)Fe2(µ-H) featuring a biologically relevant Fe(µ-carbyne)(µ-H)Fe motif. SQUID magnetometry, Mössbauer spectroscopy and DFT calculations reveal that (P6ArC)Fe2(µ-H) has a well-isolated S = 1 ground state, distinguishing it from all other diiron µ-carbyne com-plexes which are diamagnetic. Upon the addition of sources of H+/e- (H2, TEMPO-H or HCl), (P6ArC)Fe2(µ-H) is activated toward N2 binding, with concomitant protonation of the carbyne ligand. Although reaction with H2 ultimately leads to com-plete protonation of the carbyne moiety, mechanistic investigations indicate that formation of a single C-H bond, with con-comitant cleavage of one Fe-C bond, generates an iron-carbene intermediate capable of coordinating N2.

中文翻译：

活化开壳、卡宾桥的 Diiron 络合物以结合二氮

固氮酶与 N2 的结合需要 FeMo 辅因子的还原活化，但 FeMoco 以其活化形式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，N2 还原可能发生在 FeMoco 的碳桥二铁亚基上。为了模拟 Fe-(µ-C)-Fe 位点对 N2 结合的激活，我们合成了一种新的双核六膦配体，该配体源自 2,6-二取代甲苯平台。配体中心甲基的活化提供了具有生物学相关 Fe(μ-carbyne)(μ-H)Fe 基序的二铁 μ-carbyne 络合物 (P6ArC)Fe2(μ-H)。SQUID 磁力计、穆斯堡尔光谱和 DFT 计算表明 (P6ArC)Fe2(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 µ-碳炔配合物区分开来。添加 H+/e-（H2、TEMPO-H 或 HCl）源后，(P6ArC)Fe2(µ-H) 被激活以与 N2 结合，伴随着碳炔配体的质子化。尽管与 H2 的反应最终导致碳炔部分的完全质子化，但机理研究表明，单个 CH 键的形成，伴随着一个 Fe-C 键的断裂，产生了能够配位 N2 的铁-卡宾中间体。

更新日期：2020-04-14

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