Synthesis, Structures, and Electronic Properties of [8Fe-7S] Cluster Complexes Modeling the Nitrogenase P-Cluster
Synthesis, Structures, and Electronic Properties of [8Fe-7S] Cluster Complexes Modeling the Nitrogenase P-Cluster
复制标题
DOI：
10.1021/ja9055036
复制
发表时间：
2009-09-16
影响因子：
15
通讯作者：
Tatsumi, Kazuyuki
中科院分区：
文献类型：
--
作者：
Ohki, Yasuhiro;Imada, Motosuke;Tatsumi, Kazuyuki
铁硫簇[{N（SiMe 3）（2）}{SC（NMe 2）（2））Fe 4S 3]（2）（mu（6）-S）{mu-N（SiMe 3）（2））（2）（1）的高产率合成，其再现固氮酶P-N-簇的[8 Fe-7S]核心结构，已经通过两种途径实现：（1）Fe-3 {N（SiMe 3）（2）}（2）+ HSTip（Tip = 2，4，6-（Pr 3C 6 H2）-Pr 1）+四甲基硫脲（SC（NMe 2）（2））+元素硫（S-8）;和（2）Fe-3{N（SiMe 3）（2）}（2）（μ-STip）（4）（2）+ HSTip + SC（NMe 2）（2）+ S-8。在-40 ℃下，化合物1的硫脲和末端酰胺配体分别被硫醇根离子和硫醇取代，合成了一系列含有2 ~ 4个硫醇根配体的[8 Fe-7S]簇合物，并通过X射线衍射分析确定了它们的结构.这些模型[8 Fe-7S]团簇的结构都非常类似于具有8 Fe（II）中心的还原形式的P-团簇（P-N），而它们的6 Fe（II）-2Fe（III）氧化态对应于氧化形式的P-团簇（P-OX）。[8 Fe-7S]团簇的循环伏安图揭示了两个准可逆的单电子还原过程，导致与P-N-团簇相同的8 Fe（II）状态，并且合成模型表明天然P-团簇的两个主要氧化态之间的氧化还原行为。取代SC（NMe 2）2配体在1与硫醇阴离子导致更负的还原电位，而轻微的正移发生后，取代的终端酰胺配体与硫醇盐。簇1，（NEt 4）（2）[{N（SiMe 3）（2）}[（SC6H4-4-Me）Fe4S3]（2）（mu（6）-S）{mu-N（SiMe3）（2）}（2）（3a）和[（SBtp）{SC（NMe2）（2）}Fe4S3]（2）（mu（6）-S）{mu-N（SiMe3）（2）}（2）（5; Btp = 2;6-（SiMe 3）（2）C6 H3）在4-100 K下是EPR沉默的，它们的磁矩随温度的变化表明铁中心之间存在反铁磁耦合的单重基态。这些团簇的Fe-57穆斯堡尔谱与6 Fe（II）-2Fe（III）氧化态相一致，每个团簇都有两个强度比约为0.001的双峰。1：3，分别归属于Fe（III）和Fe（II）。通过比较1、3a和5的四极分裂，得出了两个Fe（III）位置是团簇外围铁原子的结论。
High-yield synthesis of the iron-sulfur cluster [{N(SiMe3)(2)}{SC(NMe2)(2))Fe4S3](2)(mu(6)-S) {mu-N(SiMe3)(2))(2) (1), which reproduces the [8Fe-7S] core structure of the nitrogenase P-N-cluster, has been achieved via two pathways: (1) Fe{N(SiMe3)(2)}(2) + HSTip (Tip = 2,4,6-(Pr3C6H2)-Pr-i) + tetramethylthiourea (SC(NMe2)(2)) + elemental sulfur (S-8); and (2) Fe-3{N(SiMe3)(2)}(2)(mu-STip)(4) (2) + HSTip + SC(NMe2)(2) + S-8. The thiourea and terminal amide ligands of 1 were found to be replaceable by thiolate ligands upon treatment with thiolate anions and thiols at -40 degrees C, respectively, and a series of [8Fe-7S] clusters bearing two to four thiolate ligands have been synthesized and their structures were determined by X-ray analysis. The structures of these model [8Fe-7S] clusters all closely resemble that of the reduced form of P-cluster (P-N) having 8Fe(II) centers, while their 6Fe(II)-2Fe(III) oxidation states correspond to the oxidized form of P-cluster (P-OX). The cyclic voltammograms of the [8Fe-7S] clusters reveal two quasi-reversible one-electron reduction processes, leading to the 8Fe(II) state that is the same as the P-N-cluster, and the synthetic models demonstrate the redox behavior between the two major oxidation states of the native P-cluster. Replacement of the SC(NMe2)2 ligands in 1 with thiolate anions led to more negative reduction potentials, while a slight positive shift occurred upon replacement of the terminal amide ligands with thiolates. The clusters 1, (NEt4)(2)[{N(SiMe3)(2)}(SC6H4-4-Me)Fe4S3](2)(mu(6)-S){mu-N(SiMe3)(2)}(2) (3a), and [(SBtp){SC(NMe2)(2)}Fe4S3](2)(mu(6)-S){mu-N(SiMe3)(2)}(2) (5; Btp = 2;6-(SiMe3)(2)C6H3) are EPR silent at 4-100 K, and their temperature-dependent magnetic moments indicate a singlet ground state with antiferromagnetic couplings among the iron centers. The Fe-57 Mossbauer spectra of these clusters are consistent with the 6Fe(II)-2Fe(III) oxidation state, each exhibiting two doublets with an intensity ratio of ca. 1:3, which are assignable to Fe(III) and Fe(II), respectively. Comparison of the quadrupole splittings for 1, 3a, and 5 has led to the conclusion that two Fe(III) sites of the clusters are the peripheral iron atoms.