Berlinguette Curtis P, Miyaji Taichi, Zhang Yugen, Holm R H
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Inorg Chem. 2006 Mar 6;45(5):1997-2007. doi: 10.1021/ic051770k.
Members of the cluster set [(Tp)2Mo2Fe6S8L4]z contain the core unit M2Fe6(mu3-S)6(mu4-S)2 in which two MoFe3S4 cubanes are coupled by two Fe-(mu4-S) interactions to form a centrosymmetric edge-bridged double cubane cluster. Some of these clusters are synthetic precursors to [(Tp)2Mo2Fe6S9L2]3-, which possess the same core topology as the P(N) cluster of nitrogenase. In this work, the existence of a three-member electron-transfer series of single cubanes (Tp)MoFe3S4L3 (z = 3-, 2-, 1-) and a four-member series of double cubanes [(Tp)2Mo2Fe6S8L4]z (z = 4-, 3-, 2-, 1-) with L = F-, Cl-, N3, PhS- is demonstrated by electrochemical methods, cluster synthesis, and X-ray structure determinations. The potential of the [4-/3-] couple is extremely low (<-1.5 V vs SCE in acetonitrile) such that the 4- state cannot be maintained in solution under normal anaerobic conditions. The chloride double cubane redox series was examined in detail. The members [(Tp)2Mo2Fe6S8Cl4]4-,3-,2- were isolated and structurally characterized. The redox series includes the reversible steps [4-/3-] and [3-/2-]. Under oxidizing conditions, [(Tp)2Mo2Fe6S8Cl4]2- cleaves with the formation of single cubane [(Tp)MoFe3S4Cl3]1-. The quasireversible [2-/1-] couple is observed at more positive potentials than those of the single cubane redox step. Structure comparison of nine double cubanes suggests that significant dimensional changes pursuant to redox reactions are mainly confined to the Fe2(mu4-S)2 bridge rhomb. The synthesis and structure of [(Tp)2Mo2Fe6S9F2.H2O]3-, a new topological analogue of the P(N) cluster of nitrogenase, is described. (Tp = hydrotris(pyrazolyl)borate(1-)).
簇合物[(Tp)₂Mo₂Fe₆S₈L₄]ᵇ的成员包含核心单元M₂Fe₆(μ₃ - S)₆(μ₄ - S)₂，其中两个MoFe₃S₄立方烷通过两个Fe-(μ₄ - S)相互作用耦合形成一个中心对称的边缘桥连双立方烷簇。这些簇合物中的一些是[(Tp)₂Mo₂Fe₆S₉L₂]³⁻的合成前体，[(Tp)₂Mo₂Fe₆S₉L₂]³⁻与固氮酶的P(N)簇具有相同的核心拓扑结构。在这项工作中，通过电化学方法、簇合物合成和X射线结构测定，证明了单立方烷(Tp)MoFe₃S₄L₃（b = 3⁻, 2⁻, 1⁻）的三成员电子转移系列以及双立方烷[(Tp)₂Mo₂Fe₆S₈L₄]ᵇ（b = 4⁻, 3⁻, 2⁻, 1⁻）的四成员系列的存在，其中L = F⁻、Cl⁻、N₃⁻、PhS⁻。[4⁻/3⁻]电对的电位极低（在乙腈中相对于饱和甘汞电极<-1.5 V），以至于在正常厌氧条件下4⁻态在溶液中无法维持。对氯化物双立方烷氧化还原系列进行了详细研究。分离并对[(Tp)₂Mo₂Fe₆S₈Cl₄]⁴⁻、³⁻、²⁻成员进行了结构表征。氧化还原系列包括可逆步骤[4⁻/3⁻]和[3⁻/2⁻]。在氧化条件下，[(Tp)₂Mo₂Fe₆S₈Cl₄]²⁻裂解形成单立方烷[(Tp)MoFe₃S₄Cl₃]¹⁻。在比单立方烷氧化还原步骤更正的电位下观察到准可逆的[2⁻/1⁻]电对。对九个双立方烷的结构比较表明，氧化还原反应引起的显著尺寸变化主要局限于Fe₂(μ₄ - S)₂桥连菱形。描述了[(Tp)₂Mo₂Fe₆S₉F₂·H₂O]³⁻的合成和结构，它是固氮酶P(N)簇的一种新的拓扑类似物。（Tp = 氢三(吡唑基)硼酸根(1⁻)）
