Aebischer Nicolas, Sidorenkova Elena, Ravera Mauro, Laurenczy Gábor, Osella Domenico, Weber Jacques, Merbach André E.
Institut de Chimie Minérale et Analytique, Université de Lausanne, BCH-Dorigny, CH-1015 Lausanne, Switzerland, Département de Chimie Physique, Université de Genève, 30, quai Ernest Ansermet, CH-1211 Genève, Switzerland, and Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Università di Torino, Via P. Giuria 7, I-10125 Torino, Italy.
Inorg Chem. 1997 Dec 17;36(26):6009-6020. doi: 10.1021/ic970783y.
The hexaaqua complex of ruthenium(II) represents an ideal starting material for the synthesis of isostructural compounds with a Ru(H(2)O-ax)(H(2)O-eq)(4)L general formula. We have studied a series of complexes, where L = H(2)O, MeCN, Me(2)SO, H(2)C=CH(2), CO, and F(2)C=CH(2). We have evaluated the effect of L on the cyclic voltammetric response, on the rate and mechanism of exchange reaction of the water molecules, and on the structures calculated with the density functional theory (DFT). As expected, the formal redox potential, E degrees '(+2/+3), increases with the pi-accepting capabilities of the ligands. For L = N(2), the oxidation to Ru(III) is followed by a fast substitution of dinitrogen by a solvent molecule, revealing the poor stability of the Ru(III)-N(2) bond. The water exchange reactions have been followed by (17)O NMR spectroscopy. The variable-pressure and variable-temperature kinetic studies made on selected examples are all in accordance with a dissociative activation mode for exchange. The positive activation volumes obtained for the axial and equatorial water exchange reactions on Ru(H(2)O)(5)(H(2)C=CH(2)) (DeltaV(ax)() and DeltaV(eq)() = +6.5 +/- 0.5 and +6.1 +/- 0.2 cm(3) mol(-)(1)) are the strongest evidence of this conclusion. The increasing cis-effect series was established according to the lability of the equatorial water molecules and is as follows: F(2)C=CH(2) congruent with CO < Me(2)SO < N(2) < H(2)C=CH(2) < MeCN < H(2)O. The increase of the lability is accompanied by a decrease of the E degrees ' values, but no change was found in the calculated Ru-H(2)O(eq) bond lengths. The increasing trans-effect series, established from the lability of the axial water molecule, is the following: N(2) << MeCN < H(2)O < CO < Me(2)SO < H(2)C=CH(2) < F(2)C=CH(2). A variation of the Ru-H(2)O(ax) bond lengths is observed in the calculated structures. However, the best correlation is found between the lability and the calculated Ru-H(2)O(ax) bond energies. It appears, also, that a decrease of the electronic density along the Ru-O(ax) bond and the increase of the lability can be related to an increase of the pi-accepting capability of the ligand. For L = N(2), the calculations have shown that the Ru(II)-N(2) bond is weak. Consequently, the water exchange reaction proceeds through a different mechanism, where first the N(2) ligand is substituted by one water molecule to produce the hexaaqua complex of Ru(II). The water exchange takes place on this compound before re-formation of the Ru(H(2)O)(5)N(2) complex.
钌（II）的六水合配合物是合成通式为[Ru(H₂O - ax)(H₂O - eq)₄L]²⁺的同构化合物的理想起始原料。我们研究了一系列配合物，其中L = H₂O、MeCN、Me₂SO、H₂C=CH₂、CO和F₂C=CH₂。我们评估了L对循环伏安响应、水分子交换反应的速率和机理以及用密度泛函理论（DFT）计算的结构的影响。正如预期的那样，形式氧化还原电位E⁰'( + 2/+3)随着配体的π接受能力的增强而增加。对于L = N₂，氧化成Ru(III)后，二氮会被一个溶剂分子快速取代，这表明Ru(III)-N₂键的稳定性较差。水交换反应通过¹⁷O NMR光谱进行跟踪。对选定实例进行的变压和变温动力学研究均符合解离活化交换模式。在[Ru(H₂O)₅(H₂C=CH₂)]²⁺上轴向和赤道水交换反应获得的正活化体积（ΔV(ax)和ΔV(eq) = + 6.5 ± 0.5和+ 6.1 ± 0.2 cm³ mol⁻¹）是这一结论的最有力证据。根据赤道水分子的活泼性建立了如下增加的顺式效应系列：F₂C=CH₂ ≡ CO < Me₂SO < N₂ < H₂C=CH₂ < MeCN < H₂O。活泼性的增加伴随着E⁰'值的降低，但计算得到的Ru - H₂O(eq)键长没有变化。从轴向水分子的活泼性建立的增加的反式效应系列如下：N₂ << MeCN < H₂O < CO < Me₂SO < H₂C=CH₂ < F₂C=CH₂。在计算的结构中观察到Ru - H₂O(ax)键长的变化。然而，在活泼性与计算得到的Ru - H₂O(ax)键能之间发现了最佳相关性。似乎沿着Ru - O(ax)键电子密度的降低和活泼性的增加可能与配体π接受能力的增加有关。对于L = N₂，计算表明Ru(II)-N₂键较弱。因此，水交换反应通过不同的机理进行，首先N₂配体被一个水分子取代以生成Ru(II)的六水合配合物。水交换在该化合物上发生，然后再形成[Ru(H₂O)₅N₂]²⁺配合物。
