Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan.
Dalton Trans. 2011 Jan 21;40(3):673-82. doi: 10.1039/c0dt00956c. Epub 2010 Dec 6.
A series of paddlewheel diruthenium(ii, ii) complexes with various fluorine-substituted benzoate ligands were isolated as THF adducts and structurally characterized: [Ru(2)(F(x)PhCO(2))(4)(THF)(2)] (F(x)PhCO(2)(-) = o-fluorobenzoate, o-F; m-fluorobenzoate, m-F; p-fluorobenzoate, p-F; 2,6-difluorobenzoate, 2,6-F(2); 3,4-difluorobenzoate, 3,4-F(2); 3,5-difluorobenzoate, 3,5-F(2); 2,3,4-trifluorobenzoate, 2,3,4-F(3); 2,3,6-trifluorobenzoate, 2,3,6-F(3); 2,4,5-trifluorobenzoate, 2,4,5-F(3); 2,4,6-trifluorobenzoate, 2,4,6-F(3); 3,4,5-trifluorobenzoate, 3,4,5-F(3); 2,3,4,5-tetrafluorobenzoate, 2,3,4,5-F(4); 2,3,5,6-tetrafluorobenzoate, 2,3,5,6-F(4); pentafluorobenzoate, F(5)). By adding fluorine atoms on the benzoate ligands, it was possible to tune the redox potential (E(1/2)) for [Ru(2)(II,II)]/Ru(2)(II,III) over a wide range of potentials from -40 mV to 350 mV (vs. Ag/Ag(+) in THF). 2,3,6-F(3), 2,3,4,5-F(4), 2,3,5,6-F(4) and F(5) were relatively air-stable compounds even though they are [Ru(2)(II,II)] species. The redox potential in THF was dependent on an electronic effect rather than on a structural (steric) effect of the o-F atoms, although more than one substituent in the m- and p-positions shifted E(1/2) to higher potentials in relation to the general Hammett equation. A quasi-Hammett parameter for an o-F atom (σ(o)) was estimated to be ∼0.2, and a plot of E(1/2)vs. a sum of Hammett parameters including σ(o) was linear. In addition, the HOMO energy levels, which was calculated based on atomic coordinates of solid-state structures, as well as the redox potential were affected by adding F atoms. Nevertheless, a steric contribution stabilizing their static structures in the solid state was present in addition to the electronic effect. On the basis of the electronic effect, the redox potential of these complexes is correlated to the HOMO energy level, and the electronic effect of F atoms is the main factor controlling the ionization potential of the complexes with ligands free from the rotational constraint, i.e. complexes in solution.
一系列带有各种氟取代苯甲酸盐配体的桨轮双钌（II, II）配合物被分离为四氢呋喃加合物并进行了结构表征：[Ru(2)(F(x)PhCO(2))(4)(THF)(2)] (F(x)PhCO(2)(-) = 邻氟苯甲酸盐，o-F；间氟苯甲酸盐，m-F；对氟苯甲酸盐，p-F；2,6-二氟苯甲酸盐，2,6-F(2)；3,4-二氟苯甲酸盐，3,4-F(2)；3,5-二氟苯甲酸盐，3,5-F(2)；2,3,4-三氟苯甲酸盐，2,3,4-F(3)；2,3,6-三氟苯甲酸盐，2,3,6-F(3)；2,4,5-三氟苯甲酸盐，2,4,5-F(3)；2,4,6-三氟苯甲酸盐，2,4,6-F(3)；3,4,5-三氟苯甲酸盐，3,4,5-F(3)；2,3,4,5-四氟苯甲酸盐，2,3,4,5-F(4)；2,3,5,6-四氟苯甲酸盐，2,3,5,6-F(4)；五氟苯甲酸盐，F(5))。通过在苯甲酸盐配体上添加氟原子，可以在-40 mV 至 350 mV（相对于 THF 中的 Ag/Ag(+)）的宽电位范围内调谐[Ru(2)(II,II)]/Ru(2)(II,III)的氧化还原电位（E(1/2))。2,3,6-F(3)、2,3,4,5-F(4)、2,3,5,6-F(4)和 F(5)即使是[Ru(2)(II,II)]物种，也是相对稳定的化合物，即使在空气中也很稳定。在 THF 中的氧化还原电位取决于电子效应而不是 o-F 原子的结构（空间）效应，尽管 m-和 p-位的一个以上取代基会使 E(1/2)相对于一般的哈米特方程向更高的电位移动。邻氟原子的准哈米特参数（σ(o)）估计为约 0.2，E(1/2)与包括σ(o)在内的哈米特参数之和的关系图是线性的。此外，基于固态结构的原子坐标计算的 HOMO 能级以及氧化还原电位受到添加 F 原子的影响。然而，除了电子效应之外，还有一个稳定其固态静态结构的空间效应。基于电子效应，这些配合物的氧化还原电位与 HOMO 能级相关，F 原子的电子效应是控制配体无旋转约束的配合物（即溶液中的配合物）电离势的主要因素。
