Electrophilic, Ambiphilic, and Nucleophilic C-H Bond Activation: Understanding the Electronic Continuum of C-H Bond Activation Through Transition-State and Reaction Pathway Interaction Energy Decompositions
Electrophilic, Ambiphilic, and Nucleophilic C-H Bond Activation: Understanding the Electronic Continuum of C-H Bond Activation Through Transition-State and Reaction Pathway Interaction Energy Decompositions
复制标题
DOI：
10.1021/om100879y
复制
发表时间：
2010-12-13
期刊：
影响因子：
2.8
通讯作者：
Periana, Roy A.
中科院分区：
文献类型：
--
作者：
Ess, Daniel H.;Goddard, William A., III;Periana, Roy A.
使用 B3LYP 密度泛函理论 (DFT) 和绝对定域分子轨道能量分解分析 (ALMO-EDA) 探索了金属和金属配体介导的烷烃 C-H 键活化的势能和相互作用能分布。探索的这组配合物范围从后过渡金属 10 族（Pt 和 Pd）和 11 族（Au）金属中心到 7-9 族（Ir、Rh、Ru 和 W）金属中心以及 3 Sc 配合物。配位几何、电子金属数（d(8)、d(6)、d(4) 和 d(0)）和配体（N-杂环、O-供体、膦和 Cp*）也各不相同。使用 ALMO-EDA 对金属配体片段和用于 C-H 键断裂的过渡态中的配位 C-H 键之间的两个方向的电荷转移稳定（占据到未占据轨道稳定）能量进行定量分析，可以根据电荷转移能量稳定的净方向将 C-H 活化反应分类为亲电子、双亲或亲核反应。这种键合模式超越了任何特定的机械或键合范例，例如氧化加成、西格玛键复分解或取代。后过渡金属，例如具有 N-杂环、卤化物或 O-供体配体的 Au(III)、Pt(II)、Pd(II) 和 Rh(III) 金属中心，显示出亲电子主导的反应曲线，电荷从 C-H 键正向转移到金属，比从金属到 C-H 键的反向电荷转移更稳定。 d6 Ru(II) 和 Ir(III) 金属与 Tp 和 acac 配体的过渡态和反应曲线被发现具有几乎相同的正向和反向电荷转移能量稳定性。该双亲区域还包括经典标记的亲电阳离子物种 Cp*(PMe3)Ir(Me)。亲核特性，其中金属与 C-H 键的电荷转移相互作用最为稳定，在反应中与 W(II) 和 Sc(III) 金属中心配合物以及进行 C-H 键插入的后过渡金属 Ir(I) 和 Rh(I) 钳配合物的复分解反应中发现。钳配体的比较表明，PCP 配体比去质子化的 PNP 配体赋予 Ir 金属中心更多的亲核特性。 PCP 和 POCOP 配体在 C-H 激活电子方面没有表现出实质性差异。研究还发现，Rh(T) 的亲核性明显高于 Ir(I)。最后，作为定性近似，对过渡态碎片轨道能量的研究表明，相对前沿轨道能隙正确反映了亲电、两亲或亲核电荷转移稳定模式。
The potential energy and interaction energy profiles for metal- and metal ligand-mediated alkane C-H bond activation were explored using B3LYP density functional theory (DFT) and the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA). The set of complexes explored range from late transition metal group 10 (Pt and Pd) and group 11 (Au) metal centers to group 7-9 (Ir, Rh, Ru, and W) metal centers as well as a group 3 Sc complex. The coordination geometries, electron metal count (d(8), d(6), d(4), and d(0)), and ligands (N-heterocycles, O-donor, phosphine, and Cp*) are also diverse. Quantitative analysis using ALMO-EDA of both directions of charge-transfer stabilization (occupied to unoccupied orbital stabilization) energies between the metal ligand fragment and the coordinated C-H bond in the transition state for cleavage of the C-H bond allows classification of C-H activation reactions as electrophilic, ambiphilic, or nucleophilic on the basis of the net direction of charge-transfer energy stabilization. This bonding pattern transcends any specific mechanistic or bonding paradigm, such as oxidative addition, sigma-bond metathesis, or substitution. Late transition metals such as Au(III), Pt(II), Pd(II), and Rh(III) metal centers with N-heterocycle, halide, or O-donor ligands show electrophilically dominated reaction profiles with forward charge-transfer from the C-H bond to the metal, leading to more stabilization than reverse charge transfer from the metal to the C-H bond. Transition states and reaction profiles for d6 Ru(II) and Ir(III) metals with Tp and acac ligands were found to have nearly equal forward and reverse charge-transfer energy stabilization. This ambiphilic region also includes the classically labeled electrophilic cationic species Cp*(PMe3)Ir(Me). Nucleophilic character, where the metal to C-H bond charge-transfer interaction is most stabilizing, was found in metathesis reactions with W(II) and Sc(III) metal center complexes in reactions as well as late transition metal Ir(I) and Rh(I) pincer complexes that undergo C-H bond insertion. Comparison of pincer ligands shows that the PCP ligand imparts more nucleophilic character to an Ir metal center than a deprotonated PNP ligand. The PCP and POCOP ligands do not show a substantial difference in the electronics of C-H activation. It was also found that Rh(T) is substantially more nucleophilic than Ir(I). Lastly, as a qualitative approximation, investigation of transition-state fragment orbital energies showed that relative frontier orbital energy gaps correctly reflect electrophilic, ambiphilic, or nucleophilic charge-transfer stabilization patterns.