Kosaka Wataru, Watanabe Yudai, Aliyah Kinanti Hantiyana, Miyasaka Hitoshi
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai 980-8578, Japan.
Dalton Trans. 2021 Dec 20;51(1):85-94. doi: 10.1039/d1dt03791a.
The synthesis of a series of -heteroleptic paddlewheel diruthenium(II,II) complexes with various hydroxy-substituted benzoate ligands, [Ru((OH)PhCO)(2,6-(CF)PhCO)(THF)] ([RuII,II2]) as tetrahydrofuran (THF) adducts is reported, where (OH)PhCO stands for -hydroxybenzoate (o-OH), -hydroxybenzoate (m-OH), -hydroxybenzoate (p-OH), 2,3-dihydroxybenzoate (2,3-(OH)2), 2,4-dihydroxybenzoate (2,4-(OH)2), 2,5-dihydroxybenzoate (2,5-(OH)2), 2,6-dihydroxybenzoate (2,6-(OH)2), or 3,4-dihydroxybenzoate (3,4-(OH)2), and 2,6-(CF)PhCO represents 2,6-bis(trifluoromethyl)benzoate. In this heteroleptic series, the redox potential () of the [RuII,II2]/[RuII,III2] couple in THF varies over a wide range, from -18 mV ( Ag/Ag) for p-OH to 432 mV for 2,6-(OH)2. The redox properties are linearly dependent on the acidity (p) of the OH-substituted benzoic acids, but do not depend on the number of -substituted hydroxy (-OH) groups. This indicates that the steric effect of -substituents is irrelevant in the case of hydroxyl groups, owing to the formation of intramolecular hydrogen bonds between the -OH group and carboxylate oxygens. The value of the Hammett constant for the -OH substituent was determined to be 0.667, indicating a strongly electron-withdrawing character, contrary to the expectation of electron-donating character for an OH group. The redox properties of the compounds were well explained in a framework of Hammett analyses and were also consistent with their HOMO energy levels evaluated by DFT calculations based on the atomic coordinates. The unexpected electron-withdrawing character of the -OH groups could be attributed to the direct effect of intramolecular hydrogen bonding on the charge density on the carboxylate oxygen.
报道了一系列具有各种羟基取代苯甲酸酯配体的 - 异核桨轮二钌（II,II）配合物[Ru((OH)PhCO)(2,6-(CF)PhCO)(THF)]（[RuII,II2]）作为四氢呋喃（THF）加合物的合成，其中(OH)PhCO代表 - 羟基苯甲酸酯（邻位 - OH）、 - 羟基苯甲酸酯（间位 - OH）、 - 羟基苯甲酸酯（对位 - OH）、2,3 - 二羟基苯甲酸酯（2,3-(OH)2）、2,4 - 二羟基苯甲酸酯（2,4-(OH)2）、2,5 - 二羟基苯甲酸酯（2,5-(OH)2）、2,6 - 二羟基苯甲酸酯（2,6-(OH)2）或3,4 - 二羟基苯甲酸酯（3,4-(OH)2），且2,6-(CF)PhCO代表2,6 - 双（三氟甲基）苯甲酸酯。在这个异核系列中，[RuII,II2]/[RuII,III2]电对在THF中的氧化还原电位（）在很宽的范围内变化，从对位 - OH的 - 18 mV（相对于Ag/Ag）到2,6-(OH)2的432 mV。氧化还原性质与OH取代苯甲酸的酸度（p）呈线性相关，但不取决于 - 取代羟基（-OH）的数量。这表明由于 - OH基团与羧酸根氧之间形成分子内氢键， - 取代基的空间效应在羟基的情况下无关紧要。 - OH取代基的哈米特常数的值被确定为0.667，表明具有强吸电子特性，这与OH基团供电子特性的预期相反。化合物的氧化还原性质在哈米特分析框架内得到了很好的解释，并且也与基于原子坐标通过DFT计算评估的它们的HOMO能级一致。 - OH基团意外的吸电子特性可归因于分子内氢键对羧酸根氧上电荷密度的直接影响。
