Bens Tobias, Kübler Jasmin A, Walter Robert R M, Beerhues Julia, Wenger Oliver S, Sarkar Biprajit
Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
Institut für Chemie und Biochemie, Freie Universität Berlin, Fabeckstraße 34-36, 14195 Berlin, Germany.
ACS Org Inorg Au. 2023 May 3;3(4):184-198. doi: 10.1021/acsorginorgau.3c00005. eCollection 2023 Aug 2.
We present here new synthetic strategies for the isolation of a series of Ru(II) complexes with pyridyl-mesoionic carbene ligands (MIC) of the 1,2,3-triazole-5-ylidene type, in which the bpy ligands (bpy = 2,2'-bipyridine) of the archetypical [Ru(bpy)] have been successively replaced by one, two, or three pyridyl-MIC ligands. Three new complexes have been isolated and investigated via NMR spectroscopy and single-crystal X-ray diffraction analysis. The incorporation of one MIC unit shifts the potential of the metal-centered oxidation about 160 mV to more cathodic potential in cyclic voltammetry, demonstrating the extraordinary σ-donor ability of the pyridyl-MIC ligand, while the π-acceptor capacities are dominated by the bpy ligand, as indicated by electron paramagnetic resonance spectroelectrochemistry (EPR-SEC). The replacement of all bpy ligands by the pyridyl-MIC ligand results in an anoidic shift of the ligand-centered reduction by 390 mV compared to the well-established [Ru(bpy)] complex. In addition, UV/vis/NIR-SEC in combination with theoretical calculations provided detailed insights into the electronic structures of the respective redox states, taking into account the total number of pyridyl-MIC ligands incorporated in the Ru(II) complexes. The luminescence quantum yield and lifetimes were determined by time-resolved absorption and emission spectroscopy. An estimation of the excited state redox potentials conclusively showed that the pyridyl-MIC ligand can tune the photoredox activity of the isolated complexes to stronger photoreductants. These observations can provide new strategies for the design of photocatalysts and photosensitizers based on MICs.
我们在此展示了一系列用于分离具有1,2,3 - 三唑 - 5 - 亚基型吡啶基 - 中离子卡宾配体（MIC）的Ru(II)配合物的新合成策略，其中典型的[Ru(bpy)]中的bpy配体（bpy = 2,2'-联吡啶）已被一个、两个或三个吡啶基 - MIC配体依次取代。通过核磁共振光谱和单晶X射线衍射分析分离并研究了三种新配合物。在循环伏安法中，引入一个MIC单元会使以金属为中心的氧化电位向更负的电位移动约160 mV，这表明吡啶基 - MIC配体具有非凡的σ - 供体能力，而电子顺磁共振光谱电化学（EPR - SEC）表明，π - 受体能力主要由bpy配体主导。与已确立的[Ru(bpy)]配合物相比，用吡啶基 - MIC配体取代所有bpy配体导致以配体为中心的还原电位发生390 mV的阳极位移。此外，紫外/可见/近红外光谱电化学（UV/vis/NIR - SEC）结合理论计算，考虑到Ru(II)配合物中引入的吡啶基 - MIC配体的总数，对各个氧化还原态的电子结构提供了详细的见解。通过时间分辨吸收和发射光谱测定了发光量子产率和寿命。对激发态氧化还原电位的估计最终表明，吡啶基 - MIC配体可以将分离出的配合物的光氧化还原活性调节为更强的光还原剂。这些观察结果可为基于MICs的光催化剂和光敏剂的设计提供新策略。
