The redox non-innocent behavior of the diaryl-azo-oxime ligand L^NOH 1 has been accentuated via the synthesis of metastable anion radical complexes of type trans-[Ir(L^NO˙−)Cl(CO)(PPh₃)₂] 2 (CO is trans to azo group of the ligand) by the oxidative coordination reaction of 1 with Vaska's complex. The stereochemical role of co-ligands vis-à-vis 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 via the isolation of quite a few complexes as well as the failure to synthesize some others. The oxidized analogues of type trans-[Ir(L^NO−)Cl(CO)(PPh₃)₂]⁺ 2⁺ (CO and azo group of the ligand are trans) as well as its cis isomer cis-[Ir(L^NO−)Cl(CO)(PPh₃)₂]⁺ 3⁺ (CO and azo group of the ligand are cis) have been structurally characterized but the radical anion congener of the latter could not be synthesized. Furthermore, the closed shell complexes [Ir(L^NO−)Cl₂(PPh₃)₂] 4 and [Ir(L^NO−)₂Cl(PPh₃)] 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 trans influence of ancillary ligands. The anion radical complexes trans-[Ir(L^NO˙−)Cl(CO)(PPh₃)₂] 2 may be rapidly transformed to the metallocarboxylic acids trans-[Ir(L^NO−)Cl(CO₂H)(PPh₃)₂] 6 via 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 via intramolecular –CO₂H⋯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 trans-[Ir(L^NO˙−)Cl(CO)(PPh₃)₂] 2 is primarily azo-oxime centric with very low contribution from the iridium center.

中文翻译：

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偶氮肟金属羰基通过中间体 Ir(III) 自由基同系物转化为金属羧酸：寻求共配体驱动的开壳和闭壳配合物的稳定性

通过合成反式-[Ir(L ^NO ˙- )Cl(CO)(PPh ₃ ) ₂ ]型亚稳态阴离子自由基配合物，^{增强了二芳基偶氮肟配体 L NOH} 1的氧化还原非无辜行为。通过1与 Vaska 配合物的氧化配位反应生成2（CO 与配体的偶氮基团是反式的）。已发现共配体相对于π 键相互作用的立体化学作用对于控制配位氧化还原非无辜配体接受或拒绝电子的能力具有决定性作用。这已通过澄清很多配合物的分离以及其他一些配合物的合成失败。反式-[Ir(L ^NO- )Cl(CO)(PPh ₃ ) ₂ ] ⁺ 2 ⁺类型的氧化类似物（CO 和配体的偶氮基团是反式的）及其顺式异构体cis -[Ir(L ^NO- )Cl(CO)(PPh ₃ ) ₂ ] ⁺ 3 ⁺ (CO和配体的偶氮基团是顺式)已经在结构上进行了表征，但后者的自由基阴离子同系物不能合成。此外，闭壳配合物 [Ir(L^NO- )Cl ₂ (PPh ₃ ) ₂ ] 4和 [Ir(L ^NO- ) ₂ Cl(PPh ₃ )] 5已通过衍射和光谱技术很好地表征，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反式影响。阴离子自由基配合物反式-[Ir(L ^NO˙- )Cl(CO)(PPh ₃ ) ₂ ] 2可以快速转化为金属羧酸反式-[Ir(L ^NO- )Cl(CO ₂H)(PPh ₃ ) ₂ ] 6 通过质子耦合电子转移 (PCET) 过程，从而证明奇数电子在配位配体框架上的作用，以触发金属介导的羰基到羧酸官能化。配合物6通过分子内的 -CO ₂ H⋯ON-（羧酸⋯肟基）氢键进一步稳定。通过TD-DFT和理论分析分析了配合物的光电性质以及跃迁的来源，进一步揭示了反式-[Ir(L ^NO˙- )Cl(CO)(PPh ₃ ) ₂中的奇电子] 2主要以偶氮肟为中心，铱中心的贡献非常低。