This study was undertaken to investigate the comparative substitution behavior of mononuclear trans‐platinum(II) complexes with symmetric and asymmetric amine ligands. The rate of substitution of the aqua moeities from the complexes trans‐[Pt(NH₃)₂(H₂O)₂](ClO₄)₂ (tPt), trans‐[Pt(NH₃)(NH₂C₂H₅)(H₂O)₂](ClO₄)₂ (tPt2H₂O), trans‐[Pt(NH₃)(NH₂C₃H₇)(H₂O)₂](ClO₄)₂ (tPt3H₂O), [trans‐Pt(OH₂)₂(NH₂CH₃)₂](ClO₄)₂ (tPtM), and [trans‐Pt(OH₂)₂{NH₂CH(CH₃)₂}₂](ClO₄)₂ (tPtR), by three nucleophiles, namely thiourea (TU), 1,3‐dimethylthiourea (DMTU), and 1,1,3,3‐tetramethylthiourea (TMTU) was studied under pseudo–first‐order conditions as a function of concentration and temperature by stopped‐flow spectrophotometry. All the substitution reactions of each of the trans‐platinum(II) complexes proceeds by a stepwise mechanism involving rate‐determining substitution of the first aqua ligand followed by a fast second substitution step, without any intermediates formed. The reactions were second order overall (rate = k_obs[complex] where k_obs = k₂[nucleophile]), first order in both [complex] and [nucleophile]. The reactivity of the complexes was essentially governed by both steric and electronic factors. Comparing the second‐order rate constants for the substitution reactions of the mononuclear diaqua trans‐platinum(II) complexes with the thiourea‐based nucleophiles, the observed trend follows: tPt > tPt2H₂O > tPtM > tPt3H₂O > tPtR. This reactivity trend is consistent with the pK_a values obtained for the first deprotonation step. The reactivity of the nucleophiles with the complexes decreases with an increase in steric demand in the following order: TU > DMTU > TMTU. The low positive values of activation enthalpy and large negative values of activation entropy indicate an associative mechanism of substitution in all the complexes. The computational modeling using density functional theory calculations was employed to provide theoretical interpretation of kinetic data.

中文翻译：

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带有对称和不对称烷基胺配体的双功能跨铂（II）配合物的比较取代行为研究

进行这项研究以研究具有对称和不对称胺配体的单核反式铂（II）配合物的比较取代行为。水色moeities的取代从复合物中的速率反式[PT（NH - ₃）₂（H ₂ O）₂ ]（CLO ₄）₂（TPT），反式- [铂（NH ₃）（NH ₂ C ^ ₂ ħ ₅）（H ₂ O）₂ ]（ClO ₄）₂（tPt2H ₂ O），反式[Pt（NH ₃）（NH ₂ C ₃ H ₇）（H ₂ O）₂ ]（ClO ₄）₂（tPt3H ₂ O），[反式-Pt（OH ₂）₂（NH ₂ CH ₃）₂ ]（ClO ₄）₂（ tPtM）和[反式-Pt（OH ₂）₂ {NH ₂ CH（CH ₃）₂ } ₂ ]（ClO ₄）₂（tPtR）由三种亲核试剂，即硫脲（TU），1,3-二甲基硫脲（DMTU）和1,1,3,3-四甲基硫脲（TMTU）在伪一级条件下研究，是浓度的函数停止流式分光光度法测定温度。每种反铂（II）配合物的所有取代反应均通过逐步机制进行，该机制涉及确定第一个水配体的速率确定的取代反应，然后进行快速的第二个取代步骤，而没有形成任何中间体。反应总体上是二阶的（速率=  k _obs [复杂]，其中k _obs  =  k ₂[亲核试剂]），在[复合物]和[亲核试剂]中都是一阶。配合物的反应性主要由空间和电子因素决定。比较单核diaqua反铂（II）配合物与基于硫脲的亲核试剂的取代反应的二级速率常数，观察到的趋势如下：tPt> tPt2H ₂ O> tPtM> tPt3H ₂ O> tPtR。该反应趋势与p K _a一致第一个去质子化步骤获得的值。亲核试剂与配合物的反应性随空间需求的增加而降低，顺序如下：TU> DMTU> TMTU。活化焓的低正值和活化熵的大负值表明在所有配合物中都有关联的取代机理。利用密度泛函理论计算的计算模型被用来提供动力学数据的理论解释。