Department of Chemical Science and Technologies, University of Rome Tor Vergata, Rome 0133, Italy.
Department of Chemistry & Biochemistry, University of Minnesota Duluth, Duluth, Minnesota 55812, United States.
Inorg Chem. 2021 Jun 7;60(11):8227-8241. doi: 10.1021/acs.inorgchem.1c00908. Epub 2021 May 25.
The electronic structure, redox properties, and long-range metal-metal coupling in metal-free 5,10,15,20-tetra(ruthenocenyl)porphyrin (HTRcP) were probed by spectroscopic (NMR, UV-vis, magnetic circular dichroism (MCD), and atmospheric pressure chemical ionization (APCI)), electrochemical (cyclic voltammetry, CV, and differential pulse voltammetry, DPV), spectroelectrochemical, and chemical oxidation methods, as well as theoretical (density functional theory, DFT, and time-dependent DFT, TDDFT) approaches. It was demonstrated that the spectroscopic properties of HTRcP are significantly different from those in HTFcP (metal-free 5,10,15,20-tetra(ferrocenyl)porphyrin). Ruthenocenyl fragments in HTRcP have higher oxidation potentials than the ferrocene groups in the HTFcP complex. Similar to HTFcP, we were able to access and spectroscopically characterize the one- and two-electron oxidized mixed-valence states in the HTRcP system. DFT predicts that the porphyrin π-system stabilizes the [HTRcP] mixed-valence cation and prevents its dimerization, which is characteristic for ruthenocenyl systems. However, formation of the mixed-valence [HTRcP] is significantly less reproducible than the formation of [HTRcP]. DFT and TDDFT calculations suggest the ruthenocenyl fragment dominance in the highest occupied molecular orbital (HOMO) energy region and the presence of the low-energy MLCT (Rc → porphyrin (π*)) transitions in the visible region with energies higher than the predominantly porphyrin-centered Q-bands.
无金属的 5,10,15,20-四（钌茂）卟啉（HTRcP）的电子结构、氧化还原性质和远程金属-金属耦合通过光谱（NMR、UV-vis、圆二色性（MCD）和常压化学电离（APCI））、电化学（循环伏安法、CV 和差分脉冲伏安法、DPV）、光谱电化学和化学氧化方法以及理论（密度泛函理论、DFT 和时间相关的 DFT、TDDFT）方法进行了研究。结果表明，HTRcP 的光谱性质与 HTFcP（无金属的 5,10,15,20-四（二茂铁基）卟啉）有显著差异。HTRcP 中的钌茂片段的氧化电位比 HTFcP 配合物中的二茂铁基团高。与 HTFcP 类似，我们能够进入并对 HTRcP 体系中的单电子和双电子氧化混合价态进行光谱表征。DFT 预测，卟啉π-体系稳定了[HTRcP]混合价阳离子并阻止了其二聚化，这是钌茂体系的特征。然而，[HTRcP]的混合价形成不如[HTRcP]的形成可重现。DFT 和 TDDFT 计算表明，在最高占据分子轨道（HOMO）能量区域中，钌茂片段占主导地位，在可见光区域中存在低能量的 MLCT（Rc→卟啉（π*））跃迁，其能量高于主要以卟啉为中心的 Q 带。
