Redox-Asymmetric Bisruthenium Complex Bridged by a Pyridin-4-yl Moiety: Synthesis, Characterization, and Electronic Coupling Studies

A polyazine ligand, 5,5′-di­(1-butyl-1,2,3-triazol-4-yl)-2,2′-bipyridine (Bu-dtabpyH), has been prepared by a “click” reaction. The treatment of Bu-dtabpyH with [Ru­(bpy)2Cl2] affords complex [Ru­(bpy)2(Bu-dtabpyH)]2+ (bpy = 2,2′-bipyridine), which has been characterized by single-crystal X-ray analysis. The reaction of [Ru­(bpy)2(Bu-dtabpyH)]2+ with another equivalent of [Ru­(bpy)2Cl2] in the presence of AgOTf gives a redox-asymmetric bisruthenium complex, [Ru­(bpy)2(Bu-dtabpy)­Ru­(bpy)2]3+ (Bu-dtabpy is the 4-deprotonated form of Bu-dtabpyH), with one ruthenium atom binding to the pyridin-4-yl bridge with a Ru–N bond and the other with a Ru–C bond. This complex displays two Ru­(II/III) redox couples at +0.79 and +1.28 V vs Ag/AgCl. After being transformed into a mixed-valence species, [Ru­(bpy)2(Bu-dtabpy)­Ru­(bpy)2]4+, by one-electron oxidation, it exhibits a moderate metal-to-metal charge-transfer band around 1300 nm. Density functional theory and time-dependent density functional theory calculations have been carried out for the model complex [Ru­(bpy)2(Me-dtabpy)­Ru­(bpy)2]3+ and the mixed-valence state [Ru­(bpy)2(Me-dtabpy)­Ru­(bpy)2]4+ to complement these experimental results, where Me-dtabpy is the 4-deprotonated form of 5,5′-di­(1-methyl-1,2,3-triazol-4-yl)-2,2′-bipyridine.一种聚嗪类配体5,5′-二(1-丁基-1,2,3-三唑-4-基)-2,2′-联吡啶（Bu-dtabpyH）通过点击化学反应制备得到。将Bu-dtabpyH与[Ru(bpy)₂Cl₂]（bpy=2,2′-联吡啶，2,2′-bipyridine）进行反应，得到配合物[Ru(bpy)₂(Bu-dtabpyH)]²⁺，该产物已通过单晶X射线衍射分析完成表征。将[Ru(bpy)₂(Bu-dtabpyH)]²⁺与等当量的[Ru(bpy)₂Cl₂]在AgOTf存在下反应，得到氧化还原不对称双钌配合物[Ru(bpy)₂(Bu-dtabpy)Ru(bpy)₂]³⁺，其中Bu-dtabpy为Bu-dtabpyH的4位去质子化形式；该配合物中一个钌原子通过钌-氮键结合于吡啶-4-基桥联位点，另一个则通过钌-碳键结合。该配合物相对于Ag/AgCl参比电极，在+0.79 V与+1.28 V处呈现两组Ru(II/III)氧化还原电对。经单电子氧化生成混合价态物种[Ru(bpy)₂(Bu-dtabpy)Ru(bpy)₂]⁴⁺后，其在约1300 nm处显示出中等强度的金属-金属电荷转移吸收带。为辅助验证上述实验结果，本研究针对模型配合物[Ru(bpy)₂(Me-dtabpy)Ru(bpy)₂]³⁺及其混合价态[Ru(bpy)₂(Me-dtabpy)Ru(bpy)₂]⁴⁺开展了密度泛函理论（Density Functional Theory, DFT）与含时密度泛函理论（time-dependent density functional theory, TD-DFT）计算；其中Me-dtabpy为5,5′-二(1-甲基-1,2,3-三唑-4-基)-2,2′-联吡啶的4位去质子化形式。