Formation of molecular complexes and subsequent heterolytic halogen-halogen bond splitting upon reactions of molecular Cl₂ with nitrogen-containing Lewis bases (LB) are computationally studied at M06-2X/def2-TZVPD and for selected compounds at CCSD(T)/aug-cc-pvtz//CCSD/aug-cc-pvtz levels of theory. Obtained results are compared with data for ICl and I₂ molecules. Reaction pathways indicate, that in case of Cl₂∙LB complexes the activation energies for the heterolytic Cl-Cl bond splitting are lower than the activation energies of the homolytic splitting of Cl₂ molecule into chlorine radicals. The heterolytic halogen splitting of molecular complexes of X₂∙Py with formation of [XPy₂]⁺…${\mathrm{X}}_3^{-}$ contact ion pairs in the gas phase is slightly endothermic in case of Cl₂ and I₂, but slightly exothermic in the case of ICl. Formation of {[ClPy₂]⁺…${\mathrm{Cl}}_3^{-}$}₂ dimers makes the overall process exothermic. Taking into account that polar solvents favor ionic species, generation of donor-stabilized Cl⁺ in the presence of the Lewis bases is expected to be favorable. Thus, in polar solvents the oxidation pathway via donor-stabilized Cl⁺ species is viable alternative to the homolytic Cl-Cl bond breaking.

中文翻译：

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与 Lewis 碱反应时分子氯的易异解键分裂：与 ICl 和 I2 的比较


在 M06-2X/def2-TZVPD 和在 CCSD（T）/aug-cc-pvtz//CCSD/aug-cc-pvtz 理论水平上对选定化合物反应时分子复合物的形成和随后的异解卤素-卤素键分裂进行了计算研究。将获得的结果与 ICl 和 I₂ 分子的数据进行比较。反应途径表明，在 Cl₂∙LB 络合物的情况下，异质溶解 Cl-Cl 键分裂的活化能低于 Cl₂ 分子均解分裂成氯自由基的活化能。X₂∙Py 分子复合物的异质溶解卤素分裂，形成 [XPy₂]⁺...气相中的 ${\mathrm{X}}_3^{-}$ 接触离子对在 Cl 2 和 I 2 的情况下略微吸热，但在 ICl 的情况下略微放热。{[ClPy₂]⁺... 的形成${\mathrm{Cl}}_3^{-}$}₂ 个二聚体使整个过程放热。考虑到极性溶剂有利于离子物质，在 Lewis 碱存在下产生供体稳定的 Cl⁺ 预计是有利的。因此，在极性溶剂中，通过供体稳定的 Cl⁺ 物质的氧化途径是均溶 Cl-Cl 键断裂的可行替代方案。