2-(Pyridin-2-yl)pyrrolide 配合物的降维家族中的顺式二空位八面体 Fe(II),Inorganic Chemistry

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2-(Pyridin-2-yl)pyrrolide 配合物的降维家族中的顺式二空位八面体 Fe(II)
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2021-09-30 , DOI: 10.1021/acs.inorgchem.1c02240
Sung-Min Hyun ₁ , Kaleb A Reid ₁ , Shaik Waseem Vali ₁ , Paul A Lindahl ₁ , David C Powers ₁

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四配位过渡金属配合物可以采用多种配位几何形状，其中方形平面和四面体配位最为普遍。以前，我们报道了三核 Fe(II) 配合物Fe ₃ TPM ₂的合成，由 3 倍对称 2-pyridylpyrrolide 配体 [即 tris(5-(pyridin-2-yl)-1 H - pyrrol-2-yl)methane]，在每个 Fe(II) 中心具有罕见的顺式二空八面体 (CDO) 几何形状。在这里，描述了一系列截断的 2-pyridylpyrrolide 配体，它们支持单核和双核 Fe(II) 配合物，这些配合物也表现出 CDO 几何形状。四齿配体双[5-(吡啶-2-基)-1 H-吡咯-2-基]甲烷( H ₂ BPM )的金属化) 在四氢呋喃 (THF) 中生成双核络合物Fe ₂ (BPM) ₂ (THF) ₂，其中两个 Fe(II) 离子均八面体配位。配位的 THF 溶剂配体是不稳定的：THF 解离导致Fe ₂ (BPM) ₂，其具有五配位 Fe(II) 离子。这些双核配合物中的 Fe-Fe 距离可以通过配体甲基化来延长。双[5-(6-甲基吡啶-2-基)-1 H-吡咯-2-基]甲烷 ( H ₂ BPM ^Me ) 在 THF 中的金属化导致四配位 CDO Fe(II) 中心的形成Fe(BPM ^Me ) ₂. 进一步的配体截短得到二齿配体 2-(1 H -pyrrol-2-yl)pyridine ( PyrPyrrH ) 和 2-methyl-6-(1 H -pyrrol-2-yl)pyridine ( Pyr ^Me PyrrH )。这些配体在 THF 中的金属化得到六配位络合物Fe(PyrPyrr) ₂ (THF) ₂和Fe(Pyr ^Me Pyrr) ₂ (THF) ₂。不稳定溶剂配体的解离提供了获得四配位 Fe(II) 配合物的途径。Fe(PyrPyrr) ₂的配体歧化导致形成Fe(PyrPyrr) ₃和铁（0）。配体甲基化抑制了这种歧化作用并能够分离出严格意义上的 CDO的Fe(Pyr ^Me Pyrr) _{2 。}完全配体截断，通过将 2-吡啶基吡咯配体分离成组成单齿吡啶基和吡咯化物供体，得到Fe(Pyr) ₂ (Pyrr) ₂，其中 Fe(II) 是四面体配位的。计算分析表明，在这个四配位配合物家族中，决定配位几何的势能面在 CDO 配位附近相当平坦。这些综合研究为探索 CDO 几何结构对 Fe 催化反应的影响提供了结构基础。

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Cis-Divacant Octahedral Fe(II) in a Dimensionally Reduced Family of 2-(Pyridin-2-yl)pyrrolide Complexes

Four-coordinate transition-metal complexes can adopt a diverse array of coordination geometries, with square planar and tetrahedral coordination being the most prevalent. Previously, we reported the synthesis of a trinuclear Fe(II) complex, Fe₃TPM₂, supported by a 3-fold-symmetric 2-pyridylpyrrolide ligand [i.e., tris(5-(pyridin-2-yl)-1H-pyrrol-2-yl)methane] that featured a rare cis-divacant octahedral (CDO) geometry at each Fe(II) center. Here, a series of truncated 2-pyridylpyrrolide ligands are described that support mono- and binuclear Fe(II) complexes that also exhibit CDO geometries. Metalation of the tetradentate ligand bis[5-(pyridin-2-yl)-1H-pyrrol-2-yl]methane (H₂BPM) in tetrahydrofuran (THF) results in the binuclear complex Fe₂(BPM)₂(THF)₂ in which both Fe(II) ions are octahedrally coordinated. The coordinated THF solvent ligands are labile: THF dissociation leads to Fe₂(BPM)₂, which features five-coordinate Fe(II) ions. The Fe–Fe distance in these binuclear complexes can be elongated by ligand methylation. Metalation of bis[5-(6-methylpyridin-2-yl)-1H-pyrrol-2-yl]methane (H₂BPM^Me) in THF leads to the formation of four-coordinate, CDO Fe(II) centers in Fe(BPM^Me)₂. Further ligand truncation affords bidentate ligands 2-(1H-pyrrol-2-yl)pyridine (PyrPyrrH) and 2-methyl-6-(1H-pyrrol-2-yl)pyridine (Pyr^MePyrrH). Metalation of these ligands in THF affords six-coordinate complexes Fe(PyrPyrr)₂(THF)₂ and Fe(Pyr^MePyrr)₂(THF)₂. Dissociation of labile solvent ligands provides access to four-coordinate Fe(II) complexes. Ligand disproportionation at Fe(PyrPyrr)₂ results in the formation of Fe(PyrPyrr)₃ and Fe(0). Ligand methylation suppresses this disproportionation and enables isolation of Fe(Pyr^MePyrr)₂, which is rigorously CDO. Complete ligand truncation, by separating the 2-pyridylpyrrolide ligands into the constituent monodentate pyridyl and pyrrolide donors, affords Fe(Pyr)₂(Pyrr)₂ in which Fe(II) is tetrahedrally coordinated. Computational analysis indicates that the potential energy surface that dictates the coordination geometry in this family of four-coordinate complexes is fairly flat in the vicinity of CDO coordination. These synthetic studies provide the structural basis to explore the implications of CDO geometry on Fe-catalyzed reactions.

更新日期：2021-10-18

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