Spontaneous Formation in the Dark, and Visible Light-Induced Cleavage, of a Ru-S Bond in Water: A Thermodynamic and Kinetic Study
Spontaneous Formation in the Dark, and Visible Light-Induced Cleavage, of a Ru-S Bond in Water: A Thermodynamic and Kinetic Study
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DOI：
10.1021/ic401105v
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发表时间：
2013-08-19
影响因子：
4.6
通讯作者：
Bonnet, Sylvestre
中科院分区：
文献类型：
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作者：
Bahreman, Azadeh;Limburg, Bart;Bonnet, Sylvestre
在这项工作中，描述了一系列钌配合物[Ru(terpy)(N - N)(L)](X)₂（terpy = 2,2';6',2'' - 三联吡啶，L = 2 - （甲硫基）乙醇（Hmte）或水，X为Cl⁻或PF₆⁻）与四种不同的双齿螯合物（N - N = bpy（2,2' - 联吡啶）、biq（2,2' - 联喹啉）、dcbpy（6,6' - 二氯 - 2,2' - 联吡啶）或dmbpy（6,6' - 二甲基 - 2,2' - 联吡啶））的热化学反应性和光化学反应性。对于每种螯合物N - N，在室温下测量了水合配合物和Hmte配合物之间暗平衡的热力学常数、Hmte光取代量子产率以及水合配合物和Hmte配合物之间热相互转化的速率常数。通过沿着bpy、biq、dcbpy、dmbpy系列改变旁观N - N配体的空间位阻和电子性质，暗反应性明显从N - N = bpy的非不稳定平衡转变为N - N = dmbpy的非常不稳定的热平衡。根据在pH约为7的黑暗中变温速率常数测量，对于所有钌配合物，Hmte对H₂O的热取代活化焓相当，而bpy和biq的活化熵为负，dcbpy和dmbpy配合物的活化熵为正。这些数据表明取代机制发生了变化，对于无阻碍或阻碍较小的螯合物（bpy、biq）是交换缔合机制，对于体积更大的配体（dcbpy、dmbpy）是交换解离机制。对于最不稳定的dmbpy体系，热平衡太快，以至于无法利用光显著改变混合物的组成，而对于无阻碍的bpy配合物，H₂O对Hmte的光取代是可能的，但在室温下Hmte与水合配合物不会发生热结合。相比之下，当N - N = biq或dcbpy时，描述Ru - S键形成和断裂的热力学和动力学参数处于这样一个范围：该键在黑暗中自发形成，但在光照下能有效断裂。因此，在室温下利用可见光照射可以有效地控制溶液中水合配合物和Hmte配合物之间的比例。
In this work the thermal and photochemical reactivity of a series of ruthenium complexes [Ru(terpy) (N-N)(L)](X)(2) (terpy = 2,2';6',2 ''-terpyridine, L = 2-(methylthio)ethanol (Hmte) or water, and X is Cl- or PF6-) with four different bidentate chelates N-N = bpy (2,2'-bipyridine), biq (2,2'-biquinoline), dcbpy (6,6'-dichloro-2,2'-bipyridine), or dmbpy (6,6'-dimethyl-2,2'-bipyridine), is described. For each chelate N-N the thermodynamic constant of the dark equilibrium between the aqua- and Hmte- complexes, the Hmte photosubstitution quantum yield, and the rate constants of the thermal interconversion between the aqua and Hmte complexes were measured at room temperature. By changing the steric hindrance and electronic properties of the spectator N-N ligand along the series bpy, biq, dcbpy, dmbpy the dark reactivity clearly shifts from a nonlabile equilibrium with N-N = bpy to a very labile thermal equilibrium with N-N = dmbpy. According to variable-temperature rate constant measurements in the dark near pH = 7 the activation enthalpies for the thermal substitution of H2O by Hmte are comparable for all ruthenium complexes, whereas the activation entropies are negative for bpy and biq, and positive for dcbpy and dmbpy complexes. These data are indicative of a change in the substitution mechanism, being interchange associative with nonhindered or poorly hindered chelates (bpy, biq), and interchange dissociative for more bulky ligands (dcbpy, dmbpy). For the most labile dmbpy system, the thermal equilibrium is too fast to allow significant modification of the composition of the mixture using light, and for the nonhindered bpy complex the photosubstitution of Hmte by H2O is possible but thermal binding of Hmte to the aqua complex does not occur at room temperature. By contrast, with N- N = biq or dcbpy the thermodynamic and kinetic parameters describing the formation and breakage of the Ru-S bond lie in a range where the bond forms spontaneously in the dark, but is efficiently cleaved under light irradiation. Thus, the ratio between the aqua and Hmte complex in solution can be efficiently controlled at room temperature using visible light irradiation.