Neal P. Mankad*, Sylvain Roland, Matthieu Sollogoub* and Jeremiah E. Stevens,
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引用次数: 0
摘要
虽然二级配位层对催化活性位点的影响已得到广泛重视,但这种相互作用对(异)双核活性位点的影响尚未得到全面研究。在此,我们详细分析了环糊精封装对(NHC)Cu-FeCp(CO)2分子的影响,众所周知,(NHC)Cu-FeCp(CO)2分子在多种转化过程中具有催化活性。与游离的 (NHC)CuFp 复合物(Fp = FeCp(CO)2)相比,根据摩斯鲍尔光谱和红外光谱,封装的 (NHC)CuFp 复合物从类似于 Fe(0)转变为具有 Fe(II)特征。根据 DFT 建模,电子结构的这种变化与 Fp 片段从平面取向的金字塔化以及 (NHC)CuFp 复合物中常见的半桥式 CO 相互作用的破坏有关。后一种变化可部分归因于反静电 C-H--Cu负电相互作用的存在,由于几何限制,这种作用超过了半桥式 Cu---CO相互作用。这些综合因素导致其中一个 CO 配体只有在超分子结构中才能发生类似于 Fe(II) 的取代反应。本文提供的数据让我们了解了(异)双核反应中心,尤其是涉及 CO 配体的反应中心,是如何受到来自主配位层以外的部分共价相互作用的影响的。
Supramolecular Perturbation of Metal–Metal Bonding in Cyclodextrin-Encapsulated (NHC)Cu-FeCp(CO)2 Complexes
Although secondary coordination sphere effects on catalytic active sites are widely appreciated, the influence of such interactions on (hetero)binuclear active sites has not been examined comprehensively. Here, the influence of cyclodextrin encapsulation on the (NHC)Cu-FeCp(CO)2 moiety, which is known to be catalytically active in several transformations, is analyzed in detail. Compared to free (NHC)CuFp complexes (Fp = FeCp(CO)2), encapsulated (NHC)CuFp complexes were found to shift from resembling Fe(0) toward having Fe(II) character according to Mössbauer and IR spectroscopies. According to DFT modeling, this change in electronic structure is correlated to the pyramidalization of the Fp fragment away from a planar orientation and to the disruption of semibridging CO interactions typically found in (NHC)CuFp complexes. The latter change can be attributed, in part, to the presence of contra-electrostatic C–H···Cu anagostic interactions that outcompete semibridging Cu···CO interactions due to geometric constraints. These combined factors result in Fe(II)-like substitution reactivity of one of the CO ligands that is enabled only within the supramolecular architecture. The data presented herein provide understanding of how (hetero)binuclear reaction centers, especially those involving CO ligands, are influenced by partially covalent interactions from beyond the primary coordination sphere.
期刊介绍:
Organometallics is the flagship journal of organometallic chemistry and records progress in one of the most active fields of science, bridging organic and inorganic chemistry. The journal publishes Articles, Communications, Reviews, and Tutorials (instructional overviews) that depict research on the synthesis, structure, bonding, chemical reactivity, and reaction mechanisms for a variety of applications, including catalyst design and catalytic processes; main-group, transition-metal, and lanthanide and actinide metal chemistry; synthetic aspects of polymer science and materials science; and bioorganometallic chemistry.