This study was aimed at investigating the substitution behaviour of mononuclear trans-platinum(II) complexes with mixed amine ligands. The rate of substitution of the chloride moieties from the complexes trans-Pt(NH 3 )(NH 2 C 2 H 5 )Cl 2 (tPt2), trans-Pt(NH 3 )(NH 2 C 3 H 7 )Cl 2 (tPt3), trans-Pt(NH 3 )(NH 2 C 4 H 9 )Cl 2 (tPt4) and trans-Pt(NH 3 )(NH 2 C 5 H 11 )Cl 2 (tPt5), by three nucleophiles, viz. thiourea (TU), 1-methyl-2-thiourea (MTU) and 1,3-dimethyl-2-thiourea (DMTU), was studied by stopped-flow spectrophotometry using a large excess of nucleophile. Pseudo-first-order rate constants ( k obs ) were measured as a function of nucleophile concentration and temperature. Reactions were first order in both [complex] and [nucleophile] and therefore second-order overall (rate = k obs [complex] where k obs = k 2 [nucleophile]). The kinetics are consistent with a stepwise mechanism involving rate determining substitution of the first chloride followed by a fast second substitution step, with no intermediates being detected. The reactivity of the complexes was largely dependent on the length of the alkyl chain of the alkylamine moiety of the complexes. Computational modelling using density functional theory calculations showed that an increase in chain length by a methylene unit has no direct electronic consequence on the metal centre but did, however, pose significant steric hindrance on the substitution sites due to the flexibility of the alkyl chains and thus governed the overall reaction pattern. 195 Pt NMR kinetic studies established that the mixed amine ligands remain coordinated to the metal centre in the final kinetic product. This implies that mononuclear trans-platinum(II) complexes are resistant to complete substitution of ligands by the incoming thiourea nucleophiles at the reaction sites. The reactions follow an associative mechanism of substitution.

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具有混合胺配体的单核反式铂 (II) 配合物的动力学研究

本研究旨在研究单核反式铂 (II) 配合物与混合胺配体的取代行为。来自复合物反式 Pt(NH 3 )(NH 2 C 2 H 5 )Cl 2 (tPt2)、反式 Pt(NH 3 )(NH 2 C 3 H 7 )Cl 2 ( tPt3)、反式 Pt(NH 3 )(NH 2 C 4 H 9 )Cl 2 (tPt4) 和反式 Pt(NH 3 )(NH 2 C 5 H 11 )Cl 2 (tPt5)，通过三个亲核试剂，即. 硫脲 (TU)、1-甲基-2-硫脲 (MTU) 和 1,3-二甲基-2-硫脲 (DMTU)，使用大量过量的亲核试剂通过停流分光光度法进行研究。伪一级速率常数 (k obs) 作为亲核试剂浓度和温度的函数进行测量。[复合物]和[亲核试剂]中的反应都是一级反应，因此总体上是二级反应（速率= k obs [复合物]，其中k obs = k 2 [亲核试剂]）。动力学与逐步机制一致，包括确定第一个氯化物的取代速率，然后是快速的第二个取代步骤，没有检测到中间体。配合物的反应性很大程度上取决于配合物的烷基胺部分的烷基链的长度。使用密度泛函理论计算的计算模型表明，通过亚甲基单元增加链长对金属中心没有直接的电子影响，但由于烷基链的灵活性，确实对取代位点造成了显着的空间位阻，因此控制了整体反应模式。195 Pt NMR 动力学研究表明，混合胺配体与最终动力学产物中的金属中心保持配位。这意味着单核反式铂 (II) 复合物可以抵抗反应位点处进入的硫脲亲核试剂对配体的完全取代。反应遵循取代的缔合机制。