A density functional theory (DFT) study (BMK/6-31+G(d)) was initiated to investigate the activation of benzylic carbon–hydrogen bonds by a molybdenum-oxo complex with a potentially redox noninnocent supporting ligand—a simple mimic of the active species of the enzyme ethylbenzene dehydrogenase (EBDH)—through deprotonation (C–H bond heterolysis) or hydrogen atom abstraction (C–H bond homolysis) routes. Activation free-energy barriers for neutral and anionic Mo-oxo complexes were high, but lower for anionic complexes than neutral complexes. Interesting trends as a function of substituents were observed that indicated significant H^δ+ character in the transition states (TS), which was further supported by the preference for [2 + 2] addition over HAA for most complexes. Hence, it was hypothesized that C–H activation by these EBDH mimics is controlled more by the pK_a than by the bond dissociation free energy of the C–H bond being activated. Therefore, the results suggest promising pathways for designing more efficient and selective catalysts for hydrocarbon oxidation based on EBDH active-site mimics.

中文翻译：

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通过Mo-Oxo配合物控制C–H键激活：p K _a或键离解自由能（BDFE）？

发起了密度泛函理论（DFT）研究（BMK / 6-31 + G（d）），以研究具有潜在氧化还原非无毒配体的钼-氧代复合物对苄基碳氢键的活化作用。乙苯脱氢酶（EBDH）的活性种类-通过去质子化（C–H键杂解）或氢原子抽象（CH–H键均解）途径。中性和阴离子型Mo-oxo配合物的活化自由能势垒较高，但阴离子性配合物的活化自由能势垒比中性配合物低。观察到作为取代基函数的有趣趋势，表明显着的^Hδ+过渡态（TS）中的“ H”字符，大多数复合物相对于HAA更倾向于[2 + 2]加法。因此，据推测，由这些EBDH模拟物引起的C–H活化更多地受p K _a的控制，而不是C–H键被活化的键解离自由能。因此，结果表明，基于EBDH活性位点模拟物设计更有效和更具选择性的烃氧化催化剂的途径很有希望。