Department of Chemistry, Central University of Haryana, India, 123031.
Dalton Trans. 2022 Apr 12;51(15):5878-5889. doi: 10.1039/d2dt00491g.
Metal-superoxo species play a very important role in many metal-mediated catalytic transformation reactions. Their catalytic reactivity is affected by many factors such as the nature of metal ions and ring size of ligands. Herein, for the first time, we report DFT calculations on the electronic structures of a series of metal-superoxo species (M = V, Cr, Mn, Fe, and Co) with two ring size ligands, , 13-TMC/14-TMC, and a detailed mechanistic study on the C-H bond activation of cyclohexa-1,4-diene followed by the effect of the ring size of ligands. Our DFT results showed that the electron density at the distal oxygen plays an important role in C-H bond activation. By computing the energetics of C-H bond activation and mapping the potential energy surface, it was found that the initial hydrogen abstraction is the rate-determining step with both TMC rings and all the studied metal-superoxo species. The significant electron density at the cyclohex-1,4-diene carbon indicates that the reaction proceeds the proton-coupled electron transfer mechanism. By mapping the potential energy surfaces, we found that the 13-TMC ligated superoxo with the anti-isomer are more reactive than the 14-TMC superoxo species except for the iron-superoxo species where the 14-TMC ligated superoxo species is more reactive smaller ring size TMC is more reactive towards C-H bond activation. This is also supported by the structural correlation, , the greater contraction in the smaller ring results in the metal being pushed out of plane along the -axis, which reduces the steric hindrance. Thus, the ring size can help in designing catalysts with better efficiency for catalytic reactions.
过渡金属-过氧物种在许多金属介导的催化转化反应中起着非常重要的作用。它们的催化反应活性受到许多因素的影响，如金属离子的性质和配体的环大小。在此，我们首次报道了一系列具有两种环大小配体（ ， 13-TMC/14-TMC）的过渡金属-过氧物种（M = V、Cr、Mn、Fe 和 Co）的电子结构的 DFT 计算，并对环己-1,4-二烯的 C-H 键活化及其配体环大小的影响进行了详细的机理研究。我们的 DFT 结果表明，远端氧的电子密度在 C-H 键活化中起着重要作用。通过计算 C-H 键活化的能垒并绘制势能面，发现初始氢抽提是决速步骤，同时涉及 TMC 环和所有研究的过渡金属-过氧物种。环己-1,4-二烯碳上的显著电子密度表明，反应遵循质子耦合电子转移机制。通过绘制势能面，我们发现反式 13-TMC 配位的过氧物种比 14-TMC 过氧物种更具反应活性，除了铁-过氧物种，其中 14-TMC 配位的过氧物种更具反应活性。较小的 TMC 环对 C-H 键活化更具反应活性。这也得到了结构相关性的支持，较小的环的更大收缩导致金属沿 - 轴被推出平面，从而减少了空间位阻。因此，环大小可以帮助设计催化反应效率更高的催化剂。
