Da Silva C, Bonomo L, Solari E, Scopelliti R, Floriani C, Re N
Institut de Chimie Minérale et Analytique, Université de Lausanne, Switzerland.
Chemistry. 2000 Dec 15;6(24):4518-31. doi: 10.1002/1521-3765(20001215)6:24<4518::aid-chem4518>3.0.co;2-e.
The availability of the parent compound, meso-hexaethylporphodimetheneiron(II), [(Et6N4)Fe] (2), of this report results from a novel synthetic methodology that makes [Et6N4Li2] (1) easily available. The major focus is on how the axial positions, which are the key reactive sites in metalloporphyrins, and the electronic configuration of the metal can be affected by the breakdown of the aromaticity of the porphyrin skeleton and by the nonplanar conformation of the ligand. DFT calculations indicate a 3B1(dz2)1(dyz)1 ground state for 2 versus the 3A2(dxz)1(dyz)1 ground state in the porphyrin analogue. The intermediate-spin state (S = 1) of 2 changed drastically upon addition of one or two axial ligands, as hexacoordination is preferred by iron(II). The hexacoordinate complexes [(Et6N4)Fe(L)(L')] (L = L' = THF, 3; L = L' = Py, 4; L = PhNO, L' = Py, 14) have been isolated and structurally characterized. Strong-field ligands lead to a low-spin diamagnetic state for iron(II), namely for complexes 4-7, 9, and 14, whereas 3 is a typical d6 high-spin complex, as is the pentacoordinate [(Et6N4)Fe(CN)]Bu4N (8). The structural analysis showed common features for 6, 7, 9, and 14: i) a small displacement of the metal from the N4 plane, and ii) an N4 cavity, larger than that in the corresponding porphyrins, affecting the Fe-N bond lengths. The 1H NMR spectrum is quite diagnostic of the two-fold symmetry in the diamagnetic hexacoordinate complexes, revealing either a D2h or a C2v symmetry. The CO stretching frequency (1951 cm(-1)) in complex 6 probes the good electron density at the metal. The one-electron oxidation of 2 led to pentacoordinate iron(III) derivatives [(Et6N4)Fe(Cl)] (10), [(Et6N4)2Fe2(mu-O)] (11), and [(Et6N4)2Fe2(mu-p-OC6H4-O)] (12). Complex 10 is a typical high-spin iron(III) (5.85muB at 298 K), while 11 and 12 behave as antiferromagnetic coupled iron(III) (J = -9.4cm(-1), 12, and J = -115cm(-1), 11). In complexes 10, 11, and 12 iron is sitting in a quite distorted square pyramidal geometry, in which the ligand displays a very distorted roof conformation with different degrees of ruffling. Distinctive structural and magnetic features have been found for the nitrosyl derivative [(Et6N4)Fe-NO], which has a low-spin state (S = 1/2) and the following structural parameters: Fe-N-O, 147.3(2) degrees; Fe-N, 1.708(2) A; N-O, 1.172(3) A. A comparative structural, magnetic, and theoretical analysis of the compounds listed above has been made with the analogous porphyrin derivatives. The detailed structural investigation has been mapped through the X-ray analysis of 2, 7, 8, 9, 11, 13, and 14.
本报告中母体化合物内消旋 - 六乙基卟吩二甲烯铁（II），即[(Et6N4)Fe] (2) 的可得性源于一种新颖的合成方法，该方法使得[Et6N4Li2] (1) 易于获得。主要关注点在于金属卟啉中的关键反应位点——轴向位置，以及卟啉骨架芳香性的破坏和配体的非平面构象如何影响金属的电子构型。密度泛函理论（DFT）计算表明，2 的基态为 3B1(dz2)1(dyz)1，而卟啉类似物的基态为 3A2(dxz)1(dyz)1。2 的中间自旋态（S = 1）在添加一个或两个轴向配体后发生了显著变化，因为铁（II）更倾向于六配位。已分离并对六配位配合物[(Et6N4)Fe(L)(L')]（L = L' = 四氢呋喃，3；L = L' = 吡啶，4；L = 硝基苯，L' = 吡啶，14）进行了结构表征。强场配体导致铁（II）处于低自旋抗磁态，即配合物 4 - 7、9 和 14，而 3 是典型的 d6 高自旋配合物，五配位的[(Et6N4)Fe(CN)]Bu4N（8）也是如此。结构分析表明，6、7、9 和 14 具有共同特征：i）金属相对于 N4 平面有小的位移，ii）一个比相应卟啉中更大的 N4 空腔，影响 Fe - N 键长。1H NMR 谱对于抗磁六配位配合物中的二重对称性具有很好的诊断性，揭示了 D2h 或 C2v 对称性。配合物 6 中的 CO 伸缩频率（1951 cm(-1)）探测到金属处良好的电子密度。2 的单电子氧化产生了五配位铁（III）衍生物[(Et6N4)Fe(Cl)]（10）、[(Et6N4)2Fe2(μ - O)]（11）和[(Et6N4)2Fe2(μ - p - OC6H4 - O)]（12）。配合物 10 是典型的高自旋铁（III）（298 K 时为 5.85μB），而 11 和 12 表现为反铁磁耦合的铁（III）（J = -9.4cm(-1)，12，J = -115cm(-1)，11）。在配合物 10、11 和 12 中，铁处于相当扭曲的四方锥几何构型，其中配体呈现出不同程度褶皱的非常扭曲的屋顶构象。已发现亚硝酰基衍生物[(Et6N4)Fe - NO]具有独特的结构和磁性特征，其处于低自旋态（S = 1/2），具有以下结构参数：Fe - N - O，147.3(2)°；Fe - N，1.708(2) Å；N - O，1.172(3) Å。已对上述化合物与类似的卟啉衍生物进行了结构、磁性和理论的对比分析。通过对 2、7、8、9、11、13 和 14 的 X 射线分析绘制了详细的结构研究图谱。
