Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, Leiden, 2300 RA, The Netherlands.
Inorg Chem. 2013 Aug 19;52(16):9456-69. doi: 10.1021/ic401105v. Epub 2013 Aug 2.
In this work the thermal and photochemical reactivity of a series of ruthenium complexes Ru(terpy)(N-N)(L)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.
在这项工作中，研究了一系列钌配合物Ru(terpy)(N-N)(L)2（terpy = 2,2';6',2″-三联吡啶，L = 2-(甲基硫代)乙醇（Hmte）或水，X 为 Cl(-)或 PF6(-)）与四种不同的双齿螯合剂 N-N = bpy（2,2'-联吡啶）、biq（2,2'-双喹啉）、dcbpy（6,6'-二氯-2,2'-联吡啶）或 dmbpy（6,6'-二甲基-2,2'-联吡啶）的热和光化学反应性。对于每个螯合剂 N-N，测量了在室温下 aqua-和 Hmte-配合物之间的暗平衡的热力学常数、Hmte 的光取代量子产率以及 aqua 和 Hmte 配合物之间的热互变异构的速率常数。通过改变沿 bpy、biq、dcbpy、dmbpy 系列的 spectator N-N 配体的空间位阻和电子性质，暗反应明显从 N-N = bpy 的非稳定平衡转变为 N-N = dmbpy 的非常不稳定的热平衡。根据近 pH = 7 的黑暗条件下的变温速率常数测量，Hmte 取代 H2O 的热取代的活化焓对于所有钌配合物都是相当的，而活化熵对于 bpy 和 biq 是负的，对于 dcbpy 和 dmbpy 配合物是正的。这些数据表明取代机制发生了变化，对于非阻碍或阻碍较小的配合物（bpy、biq）为交换缔合，对于更大体积的配体（dcbpy、dmbpy）为交换解离。对于最不稳定的 dmbpy 体系，热平衡太快，以至于无法使用光显著改变混合物的组成，对于非阻碍的 bpy 配合物，Hmte 可以被 H2O 取代，但 Hmte 在室温下不会与 aqua 配合物发生热结合。相比之下，对于 N-N = biq 或 dcbpy，描述 Ru-S 键形成和断裂的热力学和动力学参数处于一个范围内，在这个范围内，Ru-S 键在黑暗中自发形成，但在光照射下有效地被切断。因此，在室温下可以使用可见光照射有效地控制溶液中 aqua 和 Hmte 配合物的比例。
