Tatarin Sergei V, Kalle Paulina, Taydakov Ilya V, Varaksina Evgenia A, Korshunov Vladislav M, Bezzubov Stanislav I
N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky pr. 31, Moscow 119991, Russia.
P.N. Lebedev Physical Institute, Russian Academy of Sciences, 53 Leninsky Prospect, Moscow 119991, Russia and G.V. Plekhanov Russian University of Economics, 36 Stremyanny Per., Moscow, 117997 Russian Federation.
Dalton Trans. 2021 May 25;50(20):6889-6900. doi: 10.1039/d1dt00820j.
A series of bis-cyclometalated iridium(iii) complexes with 2-arylphenanthroimidazole "antenna" ligands containing electron-donor or withdrawing substituents and a more flexible ancillary aromatic β-diketone bearing the "anchoring" carboxymethyl function has been prepared. Thorough X-ray study of the complexes revealed significant structural strains caused by bulky cyclometalated 2-arylphenanthroimidazoles resulting in dramatic distortions of the iridium octahedron and even in twist of the phenanthrene fragment. The crystal data were corroborated by gas-phase DFT calculations whereby the geometry of the complexes was distorted in the same way. While redox potentials, absorption and emission maxima of the complexes displayed expected change upon the variation of the electron-donating ability of the cyclometalated ligands, the complexes readily exchanged the bidentate ancillary ligand in the presence of a negligible amount of protons that was inspected in solution by UV-Vis spectroscopy. Moreover, after hydrolysis of the carboxymethyl group the resulting complexes readily react with the surface of titanium dioxide giving unique binuclear structures in which the deprotonated carboxy group of the coordinated β-diketonate binds the second bis-cyclometalated unit by forming a four-membered metallacycle. Though the enhanced reactivity of the complexes is contrary to the common idea of the high inertness of iridium(iii) compounds it can be seen as a consequence of the interplay between the steric hindrance induced by the ligands and the strong preference of the iridium(iii) ion for octahedral geometry. This study demonstrates that the use of bulky ligands provides access to light-harvesting iridium(iii) complexes with required extent of lability which may be promising as photocatalysts and biologically active molecules.
制备了一系列双环金属化铱（III）配合物，其具有含电子供体或吸电子取代基的2-芳基菲并咪唑“天线”配体，以及带有“锚定”羧甲基官能团的更具柔性的辅助芳香族β-二酮。对这些配合物进行的全面X射线研究表明，庞大的环金属化2-芳基菲并咪唑会引起显著的结构应变，导致铱八面体发生剧烈扭曲，甚至菲片段发生扭曲。晶体数据通过气相DFT计算得到证实，由此配合物的几何结构以相同方式发生扭曲。虽然配合物的氧化还原电位、吸收和发射最大值在环金属化配体供电子能力变化时呈现出预期变化，但在极少量质子存在下，这些配合物很容易交换双齿辅助配体，这一点通过紫外-可见光谱在溶液中进行了检测。此外，羧甲基水解后，所得配合物很容易与二氧化钛表面反应，形成独特的双核结构，其中配位β-二酮酸酯的去质子化羧基通过形成四元金属环与第二个双环金属化单元结合。尽管配合物的反应活性增强与铱（III）化合物高度惰性的普遍观念相反，但这可以看作是配体引起的空间位阻与铱（III）离子对八面体几何构型的强烈偏好之间相互作用的结果。这项研究表明，使用庞大的配体能够获得具有所需不稳定程度的光捕获铱（III）配合物，这些配合物作为光催化剂和生物活性分子可能具有前景。
