Dinda Soumitra, Pramanik Shuvam, Basu Jaydeep, Patra Sarat Chandra, Pramanik Kausikisankar, Ganguly Sanjib
Department of Chemistry, St. Xavier's College (Autonomous), Kolkata - 700016, India.
Department of Chemistry, Jadavpur University, Kolkata 700032, India.
Dalton Trans. 2022 Jul 5;51(26):10121-10135. doi: 10.1039/d2dt00345g.
The redox non-innocent behavior of the diaryl-azo-oxime ligand L1 has been accentuated the synthesis of metastable anion radical complexes of type -[Ir(L)Cl(CO)(PPh)] 2 (CO is to azo group of the ligand) by the oxidative coordination reaction of 1 with Vaska's complex. The stereochemical role of co-ligands the interplay of π-bonding has been found to be decisive in controlling the aptitude of the coordinated redox non-innocent ligand to accept or reject an electron. This has been clarified the isolation of quite a few complexes as well as the failure to synthesize some others. The oxidized analogues of type -[Ir(L)Cl(CO)(PPh)]2+ (CO and azo group of the ligand are ) as well as its isomer -[Ir(L)Cl(CO)(PPh)]3+ (CO and azo group of the ligand are ) have been structurally characterized but the radical anion congener of the latter could not be synthesized. Furthermore, the closed shell complexes [Ir(L)Cl(PPh)] 4 and [Ir(L)Cl(PPh)] 5 have been well characterized by diffraction as well as spectral techniques but their corresponding azo anion radical complexes could not be isolated and this is attributed to the influence of ancillary ligands. The anion radical complexes -[Ir(L)Cl(CO)(PPh)] 2 may be rapidly transformed to the metallocarboxylic acids -[Ir(L)Cl(COH)(PPh)] 6 a proton-coupled electron transfer (PCET) process, thereby demonstrating the role of odd electron over the coordinated ligand framework to trigger metal-mediated carbonyl to carboxylic acid functionalization. Complexes 6 are further stabilized intramolecular -COH⋯ON- (carboxylic acid⋯oximato) H-bonding. The optoelectronic properties as well as the origin of transitions in the complexes were analyzed by TD-DFT and theoretical analysis, which further disclose that the odd electron in -[Ir(L)Cl(CO)(PPh)] 2 is primarily azo-oxime centric with very low contribution from the iridium center.
通过1与瓦卡配合物的氧化配位反应，二芳基偶氮肟配体L1的氧化还原非无辜行为在合成 -[Ir(L)Cl(CO)(PPh)]₂ 型亚稳阴离子自由基配合物（CO与配体的偶氮基团相连）中得到了突出体现。已发现共配体的立体化学作用以及π键合的相互作用在控制配位的氧化还原非无辜配体接受或拒绝电子的能力方面起决定性作用。这一点通过分离出相当多的配合物以及未能合成其他一些配合物得以阐明。已对 -[Ir(L)Cl(CO)(PPh)]₂⁺ 型（配体的CO和偶氮基团相连）的氧化类似物及其异构体 -[Ir(L)Cl(CO)(PPh)]₃⁺（配体的CO和偶氮基团相连）进行了结构表征，但后者的自由基阴离子同系物无法合成。此外，闭壳配合物 [Ir(L)Cl(PPh)]₄ 和 [Ir(L)Cl(PPh)]₅ 已通过衍射和光谱技术得到很好的表征，但它们相应的偶氮阴离子自由基配合物无法分离，这归因于辅助配体的影响。阴离子自由基配合物 -[Ir(L)Cl(CO)(PPh)]₂ 可能通过质子耦合电子转移（PCET）过程迅速转化为金属羧酸 -[Ir(L)Cl(COH)(PPh)]₆，从而证明了配位配体框架上的单电子在引发金属介导的羰基到羧酸官能化中的作用。配合物6通过分子内 -COH⋯ON-（羧酸⋯肟基）氢键进一步稳定。通过TD-DFT和理论分析对配合物中的光电性质以及跃迁起源进行了分析，这进一步揭示了 -[Ir(L)Cl(CO)(PPh)]₂ 中的单电子主要以偶氮肟为中心，铱中心的贡献非常小。
