Grupo de Química Computacional y Teórica (QCT-UR), Facultad de Ciencias Naturales, Universidad del Rosario, Bogotá 111221, Colombia.
Grupo de Química Computacional y Teórica (QCT-USFQ), Departamento de Ingeniería Química, Universidad San Francisco de Quito, Diego de Robles y Vía Interoceánica, Quito 17-1200-841, Ecuador.
Molecules. 2022 Oct 26;27(21):7283. doi: 10.3390/molecules27217283.
The C-X bond cleavage in different methyl halides (CHX; X = Cl, Br, I) mediated by 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(II) (CoCbx) was theoretically investigated in the present work. An S2-like mechanism was considered to simulate the chemical process where the cobalt atom acts as the nucleophile and the halogen as the leaving group. The reaction path was computed by means of the intrinsic reaction coordinate method and analyzed in detail through the reaction force formalism, the quantum theory of atoms in molecules (QTAIM), and the calculation of one-electron density derived quantities, such as the source function (SF) and the spin density. A thorough comparison of the results with those obtained in the same reaction occurring in presence of 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(I) (CoCbx) was conducted to reveal the main differences between the two cases. The reactions mediated by CoCbx were observed to be endothermic and possess higher activation energies in contrast to the reactions where the CoCbx complex is present. The latter was supported by the reaction force results, which suggest a relationship between the activation energy and the ionization potentials of the different nucleophiles present in the cleavage reaction. Moreover, the SF results indicates that the lower axial ligand (i.e., 5,6-dimethylbenzimidazole) exclusively participates on the first stage of the reaction mediated by the CoCbx complex, while for the CoCbx case, it appears to have an important role along the whole process. Finally, the QTAIM charge analysis indicates that oxidation of the cobalt atom occurs in both cases; at the same time, it suggests the formation of an uncommon two-center one-electron bond in the CoCbx case. The latter was confirmed by means of electron localization calculations, which resulted in a larger electron count at the Co-C interatomic region for the CoCbx case upon comparison with its CoCbx counterpart.
本工作理论研究了 5,6-二甲基苯并咪唑-双（二甲基乙二肟）钴（II）（CoCbx）介导的不同甲基卤化物（CHX；X = Cl、Br、I）中的 C-X 键断裂。考虑了 S2 类似机制来模拟化学过程，其中钴原子作为亲核试剂，卤素作为离去基团。通过内禀反应坐标方法计算了反应路径，并通过反应力形式、原子分子量子理论（QTAIM）和单电子密度衍生量（如源函数（SF）和自旋密度）的计算进行了详细分析。将结果与在存在 5,6-二甲基苯并咪唑-双（二甲基乙二肟）钴（I）（CoCbx）的相同反应中获得的结果进行了彻底比较，以揭示两种情况下的主要区别。与 CoCbx 存在时的反应相比，由 CoCbx 介导的反应是吸热的，并且具有更高的活化能。反应力结果支持了这一点，这表明活化能与裂解反应中存在的不同亲核试剂的电离势之间存在关系。此外，SF 结果表明，较低的轴向配体（即 5,6-二甲基苯并咪唑）仅在 CoCbx 配合物介导的反应的第一阶段参与，而对于 CoCbx 情况，它似乎在整个过程中都起着重要作用。最后，QTAIM 电荷分析表明，在两种情况下钴原子都发生了氧化；同时，它表明在 CoCbx 情况下形成了一种不常见的双中心单电子键。通过电子定域化计算证实了这一点，与 CoCbx 相比，CoCbx 情况下 Co-C 原子间区域的电子计数更大。
