Electronic Structure and Bonding in Iron(II) and Iron(I) Complexes Bearing Bisphosphine Ligands of Relevance to Iron-Catalyzed C-C Cross-Coupling.
Electronic Structure and Bonding in Iron(II) and Iron(I) Complexes Bearing Bisphosphine Ligands of Relevance to Iron-Catalyzed C-C Cross-Coupling.
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DOI：
10.1021/acs.inorgchem.5b02263
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发表时间：
2016-01-04
影响因子：
4.6
通讯作者：
Neidig ML
中科院分区：
文献类型：
--
作者：
Kneebone JL;Fleischauer VE;Daifuku SL;Shaps AA;Bailey JM;Iannuzzi TE;Neidig ML
螯合膦是一种有效的添加剂和支持配体，用于广泛的铁催化交叉偶联反应。虽然最近的研究已经开始解开原位形成的铁物种在这些反应中的几个，包括活性铁物种的识别，洞察到的起源的差异有效性的双膦配体在催化作为其骨架和外围空间结构的功能仍然难以捉摸。在此，我们报告了一个光谱和计算调查定义良好的FeCl 2（双膦）配合物（双膦= Sciphos，dpbz，tBudppe，或Xantphos）和已知的铁（I）的变种系统地辨别双膦骨架的字符和空间取代的整体电子结构和键合的相对影响，其铁复合物内跨氧化态暗示相关的催化。磁性圆二色性（MCD）和密度泛函理论（DFT）的研究表明，常见的邻亚苯基和饱和乙基骨架图案的结果在小，但不可忽略的扰动10 Dq（Td）和铁-双膦键合字符在铁（II）水平内的同构四面体，以及在五坐标铁（I）配合物FeCl（dpbz）2和FeCl（dppe）2。值得注意的是，Xantphos与FeCl 2的配位导致配体场相对于其铁（II）伙伴的配体场显著降低，其中大的咬合角和随之而来的铁-磷迈耶键级（MBO）的降低可能在促进Xantphos成为Kumada和Suzuki-Miyaura烷基-烷基交叉偶联中有效添加剂的独特能力中发挥作用。此外，它已被发现，外围立体散装的SciCl 2配体并没有扰动FeCl 2（SciCl 2）的电子结构相对于类似的FeCl 2（dpbz）复杂，潜在地表明，这些配体的空间特性的差异可能是更重要的，在确定原位铁的形态和反应性。在铁催化的C-C交叉偶联中使用双膦作为支持配体已经导致了许多成功的反应方法;在此，光谱和密度泛函理论研究提供了对双膦配体结构对铁（II）和铁（I）承载催化相关配体支架内的电子结构和键合的影响的基本见解。在此基础上，讨论了铁催化交叉偶联反应中电子效应和周边空间效应的潜在贡献。
Chelating phosphines are effective additives and supporting ligands for a wide array of iron-catalyzed cross-coupling reactions. While recent studies have begun to unravel the nature of the in situ-formed iron species in several of these reactions, including the identification of the active iron species, insight into the origin of the differential effectiveness of bisphosphine ligands in catalysis as a function of their backbone and peripheral steric structures remains elusive. Herein, we report a spectroscopic and computational investigation of well-defined FeCl2(bisphosphine) complexes (bisphosphine = SciOPP, dpbz, tBudppe, or Xantphos) and known iron(I) variants to systematically discern the relative effects of bisphosphine backbone character and steric substitution on the overall electronic structure and bonding within their iron complexes across oxidation states implicated to be relevant in catalysis. Magnetic circular dichroism (MCD) and density functional theory (DFT) studies demonstrate that common o-phenylene and saturated ethyl backbone motifs result in small but non-negligible perturbations to 10Dq(Td) and iron–bisphosphine bonding character at the iron(II) level within isostructural tetrahedra as well as in five-coordinate iron(I) complexes FeCl(dpbz)2 and FeCl(dppe)2. Notably, coordination of Xantphos to FeCl2 results in a ligand field significantly reduced relative to those of its iron(II) partners, where a large bite angle and consequent reduced iron–phosphorus Mayer bond orders (MBOs) could play a role in fostering the unique ability of Xantphos to be an effective additive in Kumada and Suzuki–Miyaura alkyl–alkyl cross-couplings. Furthermore, it has been found that the peripheral steric bulk of the SciOPP ligand does little to perturb the electronic structure of FeCl2(SciOPP) relative to that of the analogous FeCl2(dpbz) complex, potentially suggesting that differences in the steric properties of these ligands might be more important in determining in situ iron speciation and reactivity. Use of bisphosphines as supporting ligands in iron-catalyzed C−C cross-coupling has led to numerous successful reaction methodologies; herein, spectroscopic and density functional theory investigations provide fundamental insight into consequences of bisphosphine ligand structure on electronic structure and bonding within iron(II) and iron(I) bearing catalytically relevant ligand scaffolds. On the basis of these studies, potential contributions of electronic effects and peripheral steric effects in iron-catalyzed cross-coupling reactions are discussed.