Yoshimura Takashi, Nishizawa Hayato, Nagata Kojiro, Ito Akitaka, Sakuda Eri, Ishizaka Shoji, Kitamura Noboru, Shinohara Atsushi
Radioisotope Research Center, Institute for Radiation Sciences, Osaka University, Suita 565-0871, Japan.
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan.
ACS Omega. 2022 Jul 21;7(30):26965-26982. doi: 10.1021/acsomega.2c03834. eCollection 2022 Aug 2.
The present study reports that the ground- and excited-state Re(23e)/Re(24e) redox potentials of an octahedral hexanuclear rhenium(III) complex can be controlled by systematically changing the number and type of the -heteroaromatic ligand (L) and the number of chloride ions at the six terminal positions. Photoirradiation of [Re(μ-S)Cl] with an excess amount of L afforded a mono-L-substituted hexanuclear rhenium(III) complex, [Re(μ-S)Cl(L)] (L = 4-dimethylaminopyridine (dmap), 3,5-lutidine (lut), 4-methylpyridine (mpy), pyridine (py), 4,4'-bipyridine (bpy), 4-cyanopyridine (cpy), and pyrazine (pz)). The bis- and tris-lut-substituted complexes, - and -[Re(μ-S)Cl(lut)] and -[Re(μ-S)Cl(lut)], were synthesized by the reaction of [Re(μ-S)Cl] with an excess amount of lut in refluxed ,-dimethylformamide. The mono-L-substituted complexes showed one-electron redox processes assignable to [Re(23e)/Re(24e)] = 0.49-0.58 V versus Ag/AgCl. The ground-state oxidation potentials were linearly correlated with the p of the N-heteroaromatic ligand [p (L)], the H NMR chemical shift of the ortho proton on the coordinating ligand, and the Hammett constant (σ) of the pyridyl-ligand substituent. The series of [Re(μ-S)X (L) ] complexes ( = 0, X = Cl, Br, I, or NCS; = 1-3, X = Cl) showed a linear correlation with the sum of the Lever electrochemical parameters at the six terminal ligands (Σ ). The cyclic voltammograms of the mono-L-substituted complexes (L = bpy, cpy, and pz) showed one-electron redox waves assignable to (L/L) = -1.28 to -1.48 V versus Ag/AgCl. Two types of photoluminescences were observed for the complexes, originating from the cluster core-centered excited triplet state (CC) for L = dmap, lut, mpy, and py and from the metal-to-ligand charge-transfer excited triplet state (MLCT) for L = bpy, cpy, and pz. The complexes with the CC character exhibited emission features and photophysical properties similar to those of ordinary hexanuclear rhenium complexes. The emission maximum wavelength of the complexes with MLCT shifted to the longer wavelength in the order L = 4-phenylpyridine (ppy), bpy, pz, and cpy, which agreed with the difference between [Re(23e)/Re(24e)] and (L/L). The calculated oxidation potential of the excited hexanuclear rhenium complex with the CC character was linearly correlated with p (L), σ, and Σ . The ground- and excited-state oxidation potentials were finely tuned by the combination of halide and L ligands at the terminal positions.
本研究报告称，通过系统地改变-杂芳族配体（L）的数量和类型以及六个末端位置的氯离子数量，可以控制八面体六核铼（III）配合物的基态和激发态Re(23e)/Re(24e)氧化还原电位。用过量的L对[Re(μ-S)Cl]进行光照射，得到单-L-取代的六核铼（III）配合物[Re(μ-S)Cl(L)]（L = 4-二甲基氨基吡啶（dmap）、3,5-二甲基吡啶（lut）、4-甲基吡啶（mpy）、吡啶（py）、4,4'-联吡啶（bpy）、4-氰基吡啶（cpy）和吡嗪（pz））。通过[Re(μ-S)Cl]与过量的lut在回流的N,N-二甲基甲酰胺中反应，合成了双-lut-取代和三-lut-取代的配合物，即α-和β-[Re(μ-S)Cl(lut)₂]以及γ-[Re(μ-S)Cl(lut)₃]。单-L-取代的配合物显示出可归因于[Re(23e)/Re(24e)] = 0.49 - 0.58 V（相对于Ag/AgCl）的单电子氧化还原过程。基态氧化电位与N-杂芳族配体的pKa [pKa(L)]、配位配体上邻位质子的¹H NMR化学位移以及吡啶基配体取代基的哈米特常数（σ）呈线性相关。一系列[Re(μ-S)X₅(L)₁]配合物（n = 0，X = Cl、Br、I或NCS；n = 1 - 3，X = Cl）与六个末端配体处的Lever电化学参数之和（ΣE）呈线性相关。单-L-取代配合物（L = bpy、cpy和pz）的循环伏安图显示出可归因于（L⁺/L）= -1.28至 -1.48 V（相对于Ag/AgCl）的单电子氧化还原波。对于这些配合物观察到两种类型的光致发光，对于L = dmap、lut、mpy和py，源自簇核中心激发三重态（CC），对于L = bpy、cpy和pz，源自金属-配体电荷转移激发三重态（MLCT）。具有CC特征的配合物表现出与普通六核铼配合物相似的发射特征和光物理性质。具有MLCT的配合物的发射最大波长按L = 4-苯基吡啶（ppy）、bpy、pz和cpy的顺序向更长波长移动，这与[Re(23e)/Re(24e)]和（L⁺/L）之间的差异一致。具有CC特征的激发六核铼配合物的计算氧化电位与pKa(L)、σ和ΣE呈线性相关。通过末端位置的卤化物和L配体的组合，可以精细调节基态和激发态氧化电位。
