The rate and mechanism of substitution in the Ru(II) complexes (C1–C6) by thiourea nucleophiles was studied at pH 2 and rate constants measured as a function of nucleophile concentrations and temperature using spectrometric methods. There is increased electron density at the Ru metal atom of C2 as a result of inductive donation by substituents on the arene ligand, making it less positive and therefore less reactive than C1. For the complexes C3–C6 bearing the 2,2′-bipyridyl ligand, the aqua ligands are located trans to the arene ligands, and hence, their reactivity increases in accordance to the number and type of alkyl substituents on the η6-arene ligands which donate inductively into the π-molecular orbitals, causing increased trans labialisation of the coordinated aquo co-ligand. Compared to the reactivity of triaquo complex (C1), the auxiliary bipyridyl ligand of (C3) complex lowers the rate of substitution for the later complex by a factor of about 100, possibly due to its steric hindrance at the Ru(II) metal centre. The significantly negative activation entropies and positive activation enthalpies suggest an associative mode of substitution. The reactivity of the nucleophiles follow the order DMTU > TU > TMTU.

中文翻译：

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η6-芳烃钌(II)配合物的取代率

在 pH 2 下研究了硫脲亲核试剂在 Ru(II) 配合物 (C1-C6) 中的取代速率和机制，并使用光谱方法测量速率常数作为亲核试剂浓度和温度的函数。由于芳烃配体上的取代基的感应捐赠，C2 的 Ru 金属原子处的电子密度增加，使其正性较低，因此反应性低于 C1。对于带有 2,2'-联吡啶配体的 C3-C6 配合物，aqua 配体位于芳烃配体的反面，因此，它们的反应性根据 η6-芳烃配体上烷基取代基的数量和类型而增加。诱导捐赠到 π 分子轨道，导致协调的 aquo 共配体的反唇化增加。与 triaquo 络合物 (C1) 的反应性相比，(C3) 配合物的辅助联吡啶配体将后面配合物的取代率降低了约 100 倍，这可能是由于其在 Ru(II) 金属中心的空间位阻。显着负的激活熵和正的激活焓表明替代的关联模式。亲核试剂的反应性顺序为 DMTU > TU > TMTU。