Synthesis, X-ray crystal structure, and solution behavior of Fe(NO)2(1-MeIm)2:: Implications for nitrosyl non-heme-iron complexes with g=2.03
Synthesis, X-ray crystal structure, and solution behavior of Fe(NO)2(1-MeIm)2:: Implications for nitrosyl non-heme-iron complexes with g=2.03
复制标题
DOI：
10.1021/ja982491h
复制
发表时间：
1999-11-03
影响因子：
15
通讯作者：
Li, LJ
中科院分区：
文献类型：
--
作者：
Reginato, N;McCrory, CTC;Li, LJ
在过去的十年中，一氧化氮（NO）的生物学重要性引起了人们的广泛关注。1，2广泛的EPR研究已经确定了亚硝酰基非血红素铁复合物作为体外NO生物合成进化后的产物，3-6和从NO添加到铁中心蛋白质。Muller等9和其他研究小组10、11也报道了一氧化氮作为亚硝酰非血红素铁络合物储存的证据。最近，一个光敏腈水合酶从红球菌属物种N771被发现有一个NO分子结合到非血红素铁中心。12这种酶在辐射时被激活，随后从铁中心释放NO。这些亚硝酰基非血红素-铁络合物是“Fe（NO）2”类型的顺磁性络合物，由于其特征性的各向同性g因子，更通常称为“g）2.03”络合物。然而，这些化合物的分离和结构测定的手段以外的IR和EPR都是非常繁琐和困难的，据我们所知，没有已知的。为了了解这些亚硝酰基非血红素铁络合物的结构，我们最近分离出了第一个非血红素铁络合物，它包含咪唑部分以及亚硝酰基配体，属于g）2.03家族。本文报道了Fe（NO）_2（1-甲基咪唑）_2（1）的合成、X-射线晶体结构、NMR和EPR研究。使用手套袋和干燥箱技术在干燥氮气气氛下进行合成。Fe（NO）_2（CO）_2（1.82× 10 ~（-3）mol）和过量的1-甲基咪唑（3.77× 10 ~（-3）mol）在乙醚中于带有磨口玻璃接头的试管中进行反应，试管用聚四氟乙烯阀塞住。反应非常迅速，颜色立即从红色变为绿色，并伴有气体逸出。1小时后，形成具有X射线晶体学质量的绿色晶体。13将这些晶体置于预先脱气并经钠干燥的石蜡油下。图1所示的1的X射线晶体结构14提供了关于非血红素铁亚硝酰基“2.03”家族的第一个直接结构见解。化合物1是单斜晶系，以C2/c空间群结晶，每个晶胞有8个分子。该配合物是一个具有d10铁中心的假四面体。亚硝酰基为线性（167.5（3），170.1（3））。亚硝基化合物的Fe-N（1）和Fe-N（2）键长分别为1.648（3）和1.650（3）<$. Fe-NO基团对称弯曲，O-Fe-O角为107.3，而N（NO）-Fe-N（NO）角为116.6。这被认为是“吸引”构象，因为NMN键角小于130，并且两个氧原子朝向彼此弯曲。15“吸引”构象通常有利于第一行过渡金属二亚硝基含有配体，是良好的π受体。[16]两个1-甲基咪唑配体平面之间的二面角为106.7。1-甲基咪唑的Fe-N（3）和Fe-N（5）键长分别为2.048（3）和2.044-（3）π。晶体包装揭示了亚硝酰基配体和咪唑配体之间的分层，都向下的bc平面。该晶体结构可与四面体化合物[（DAD）Fe（NO）2]（DAD）diazadiene）进行比较，其中Fe-NO距离和Fe-N（DAD）距离分别为1.642、1.641和2.037、2.043 nm。[17]将该结构与3，5-二甲基吡唑基铁二亚硝酰基二聚体[（N2 C5 H7）Fe（NO）2] 2进行比较也是有意义的，其中平均Fe-NO距离为1.696（2）nm，平均Fe-N（吡唑基）距离为2.009（5）nm。18 …
The biological importance of nitric oxide (NO) has attracted much attention in the past decade. 1, 2 Extensive EPR studies have identified nitrosyl non-heme-iron complexes as products after biosynthetic evolution of NO in vitro, 3-6 and from the addition of NO to iron-centered proteins. 7, 8 Muller et al. 9 and other groups10, 11 have also reported evidence for nitric oxide storage as nitrosyl non-heme-iron complexes. Recently, a light-sensitive nitrile hydratase from Rhodococuss sp. N771 was found to have an NO molecule bound to the non-heme-iron center. 12 This enzyme is activated upon irradiation, followed by the release of NO from the iron center. These nitrosyl non-heme-iron complexes are paramagnetic complexes of the type “Fe (NO) 2”, more commonly referred to as “g) 2.03” complexes because of their characteristic isotropic g-factor. However, the isolation and structural determination of these compounds by means other than IR and EPR are both extremely tedious and difficult, and to our knowledge none are known. To gain understanding of the structures of these nitrosyl non-heme-iron complexes, we have recently isolated the first non-heme-iron complex that incorporates an imidazole moiety as well as nitrosyl ligands and is of the g) 2.03 family. Here we report the synthesis, X-ray crystal structure, and NMR and EPR studies of Fe (NO) 2 (1-methylimidazole) 2 (1). Syntheses were carried out under dry nitrogen atmosphere using glovebag and drybox techniques. Reactions of Fe (NO) 2 (CO) 2 (1.82× 10-3 mol) and excess of 1-methylimidazole (3.77× 10-3 mol) were carried out in diethyl ether in test tubes with ground glass joints which were stoppered with Teflon valve stopcocks. The reactions were very rapid, changing color from red to green immediately and with gas evolution. After 1 h, green crystals formed that were of X-ray crystallographic quality. 13 These crystals were placed under paraffin oil which had been previously degassed and dried over sodium. One was selected and sealed in a capillary tube under nitrogen.The X-ray crystal structure14 of 1, shown in Figure 1, provides the first direct structural insight concerning the “2.03” family of non-heme-iron nitrosyls. Compound 1 is monoclinic and crystallizes in a C2/c space group, with eight molecules per unit cell. The complex is pseudo-tetrahedral with a d10 iron center. The nitrosyl groups are linear (167.5 (3), 170.1 (3)). The Fe-N (1) and Fe-N (2) bond distances of the nitrosyls are 1.648 (3) and 1.650 (3) Å, respectively. The Fe-NO groups are bent symmetrically, with a O-Fe-O angle of 107.3, as compared with the N (NO)-Fe-N (NO) angle of 116.6. This is considered an “attracto” conformation because the NMN bond angle is less than 130 and the two oxygen atoms bend toward each other. 15 “Attracto” conformations are generally favored for first-row transition-metal dinitrosyls containing ligands that are good π-acceptors. 16 The dihedral angel between the planes of the two 1-methylimidazole ligands is 106.7. The Fe-N (3) and Fe-N (5) bond distances of the 1-methylimidazole are 2.048 (3) and 2.044-(3) Å, respectively. Crystal packing reveals a layering of nitrosyl ligands and a layering between imidazole ligands, both down the bc plane. This crystal structure can be compared with the tetrahedral compound [(DAD) Fe (NO) 2](DAD) diazadiene), in which the Fe-NO distances and the Fe-N (DAD) distances are 1.642, 1.641 and 2.037, 2.043 Å, respectively. 17 It is also of interest to compare this structure with the 3, 5-dimethylpyrazolyl iron dinitrosyl dimer,[(N2C5H7) Fe (NO) 2] 2, in which the mean Fe-NO distance is 1.696 (2) Å and the mean Fe-N (pyrazolyl) distance is 2.009 (5) Å. 18 …