Abstract The chemical reactivity of 4,4‘-dichloro-2,2‘-bipyridine (bipy-Cl2) changes profoundly upon coordination to a [Ru]2+ center. When not coordinated to [Ru]2+, bipy-Cl2 is relatively unreactive toward nucleophiles; but when coordinated to [Ru]2+, the chlorine atoms become susceptible to nucleophilic displacement. The X-ray structures of bipy-Cl2, cis-dichlorobis (4,4‘-dichloro-2,2‘-bipyridine)rhodium (III) hexafluorophosphate [Rh](PF6), and tris(4,4‘-dichloro-2,2‘-bipyridine)ruthenium (II) hexafluorophosphate [Ru](PF6)2 reveal that the carbon-chlorine bond lengths do not change substantially upon coordination to the rhodium or ruthenium centers – implying that the carbon-chlorine bond strengths also do not change substantially. B3LYP calculations reveal that the standard enthalpy of activation (ΔH°≠) for the nucleophilic substitution of the chlorine atom in [Ru (bipy)2{bipy-Cl}]2+(bipy = 2,2‘-bipyridine; bipy-Cl = 4-chloro-2,2‘-bipyridine) by OCH3− is 46.7 kJ mol−1, while the calculated ΔH°≠ value for the nucleophilic substitution of the chlorine atom in free bipy-Cl by OCH3− is 72.8 kJ mol−1. However, the B3LYP calculations of the ΔH°≠ values for the nucleophilic displacement of the chlorine atom in the cis and trans isomers of [Ru (bipy) (2,2‘-biphenyl){bipy-Cl}], which are neutral complexes, are 76.0 and 73.8 kJ mol−1 respectively – comparable to that for the reaction involving free bipy-Cl. Hence, the calculations suggest that the overall positive charge of the complex is primarily responsible for lowering the activation barrier to nucleophilic substitution in coordinated chloro-bipyridines.

中文翻译：

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使用配位的 4,4'-二氯-2,2'-联吡啶增强亲核取代：4,4'-二氯-2,2'-联吡啶 (Bipy-Cl2)、顺式二氯双 (4,4) 的 X 射线结构'-二氯-2,2'-联吡啶)铑(III)六氟磷酸[Rh](PF6)和三(4,4'-二氯-2,2'-联吡啶)六氟磷酸钌(II)[Ru](PF6) )2

摘要 4,4'-二氯-2,2'-联吡啶 (bipy-Cl2) 的化学反应性在与 [Ru]2+ 中心配位后发生深刻变化。当不与 [Ru]2+ 配位时，bipy-Cl2 对亲核试剂相对不反应；但是当与 [Ru]2+ 配位时，氯原子变得易于亲核置换。bipy-Cl2、顺式二氯双 (4,4'-二氯-2,2'-联吡啶)铑 (III) 六氟磷酸 [Rh](PF6) 和三 (4,4'-二氯-) 的 X 射线结构2,2'-联吡啶)钌 (II) 六氟磷酸 [Ru](PF6)2 表明碳 - 氯键长度在与铑或钌中心配位时不会发生实质性变化 - 这意味着碳 - 氯键强度也会发生变化不会发生实质性的变化。B3LYP 计算表明 [Ru (bipy)2{bipy-Cl}]2+(bipy = 2,2'-bipyridine; bipy-Cl) 中氯原子亲核取代的标准活化焓 (ΔH°≠) = 4-chloro-2,2'-bipyridine) 通过 OCH3− 为 46.7 kJ mol−1，而计算的 ΔH°≠ 游离 bipy-Cl 中氯原子被 OCH3− 亲核取代的值为 72.8 kJ mol− 1. 然而，B3LYP 计算 [Ru (bipy) (2,2'-联苯){bipy-Cl}] 的顺式和反式异构体中氯原子亲核置换的 ΔH°≠ 值，它们是中性配合物，分别为 76.0 和 73.8 kJ mol-1 - 与涉及游离 bipy-Cl 的反应相当。因此，