Tuning of Metal-Metal Interactions in Mixed-Valence States of Cyclometalated Dinuclear Ruthenium and Osmium Complexes Bearing Tetrapyridylpyrazine or -benzene
Tuning of Metal-Metal Interactions in Mixed-Valence States of Cyclometalated Dinuclear Ruthenium and Osmium Complexes Bearing Tetrapyridylpyrazine or -benzene
复制标题
DOI：
10.1021/om500142t
复制
发表时间：
2014-09-22
期刊：
影响因子：
2.8
通讯作者：
Haga, Masa-aki
中科院分区：
文献类型：
--
作者：
Nagashima, Takumi;Nakabayashi, Takuya;Haga, Masa-aki
合成了三齿桥连（BL）或辅助配体（L）中含有环化键的双核钌或锇配合物[（L）M（BL）M（L）]（其中M = Ru，Os; L =双（N-甲基苯并咪唑基）吡啶，-苯; BL=四吡啶基吡嗪（tppz），-苯），并研究了它们的混合价态特征.所有的配合物都表现出连续的单电子氧化还原过程，每个过程对应于M（II/III）（M = Ru，Os）或配体还原波。此外，在环化的[M-2（bis-（benzimidazolyl）benzene）（2）（BL）]配合物（M = Ru，Os）中观察到M（III/IV）对。讨论了环化键对混合价M（Ⅱ）-M（Ⅲ）双核配合物氧化还原行为和可及性的影响。环化键的引入导致双核钌和锇配合物的氧化还原电位发生大的负电位偏移，这取决于环化键的桥接或辅助位点：桥接位点的变化福尔斯为-1.0至-1.2 V，辅助位点的变化范围为-0.65至-0.7 V。这种大的负电位偏移是由于金属C键中苯基阴离子的强供电子性质引起的。在具有相同桥连配体的双核配合物中，锇取代钌可使电位分离增大（Δ E（1））和具有tppz桥连配体的混合价络合物的歧化常数（K-com（Δ E（1）和K-com值：Os > Ru）;然而，具有tpb桥连配体的络合物显示出相反的趋势（Δ E（1）和K-com：Os < Ru）。除了EPR和DFT计算的结果外，还发现混合价配合物中中心金属离子（即Ru或Os）的轨道能级决定了金属d π轨道与桥配体π或π * 轨道之间的轨道混合程度，从而导致空穴或电子转移交换机制.
New dinuclear ruthenium or osmium complexes with cyclometalated bonds in either tridentate bridging (BL) or ancillary ligands (L), [(L)M(BL)M(L)] (where M = Ru, Os; L = bis(N-methylbenzimidazolyl)pyridine, -benzene; BL= tetrapyridylpyrazine (tppz), -benzene (tpb)), were synthesized, and their mixed-valence-state characteristics were investigated. All of the complexes showed successive one-electron redox processes, each of which correspond to M(II/III) (M = Ru, Os) or ligand reduction waves. In addition, an M(III/IV) couple was observed in cyclometalated [M-2(bis-(benzimidazolyl)benzene)(2)(BL)] complexes (M = Ru, Os). Effects of the cyclometalated bonds on the redox behaviors and the accessibility to the mixed-valence M(II)-M(III) dinuclear complexes are discussed. Introduction of a cyclometalated bond induced a large negative potential shift in the redox potentials of dinuclear ruthenium and osmium complexes, depending on either bridging or ancillary sites of the cyclometalated bonds: the change falls within the range of -1.0 to -1.2 V for the bridging sites and -0.65 to -0.7 V for the ancillary ones. This large negative potential shift arises from the strong electron-donating property of the phenyl anion in a metal C bond. Replacing the ruthenium by osmium in the dinuclear complexes with the same bridging ligand results in an increase of the potential separation (Delta E(1)) and the comproportionation constant (K-com) of the mixed-valence complexes having the tppz bridging ligand (Delta E(1) and K-com values: Os > Ru); however, complexes having the tpb bridging ligand showed the opposite trend (Delta E(1) and K-com: Os < Ru). In addition to the results of EPR and DFT calculation, it was found that the orbital energy levels of the central metal ion (namely, either Ru or Os) in the mixed-valence complex determines the degree of orbital mixing between metal d pi orbitals and bridging-ligand pi or pi* orbitals, which leads to either hole- or electron-transfer exchange mechanisms.