Precious metal complexes remain ubiquitous in photoredox catalysis (PRC) despite concerted efforts to find more earth‐abundant catalysts and replacements based on 3d metals in particular. Most otherwise plausible 3d metal complexes are assumed to be unsuitable due to short‐lived excited states, which has led researchers to prioritize the pursuit of longer excited‐state lifetimes through careful molecular design. However, we report herein that the C−H arylation of pyrroles and related substrates (which are benchmark reactions for assessing the efficacy of photoredox catalysts) can be achieved using a simple and readily accessible octahedral bis(diiminopyridine) cobalt complex, [1‑Co](PF6)2. Notably, [1‑Co]2+ efficiently functionalizes both chloro‐ and bromoarene substrates despite the short excited‐state lifetime of the key photoexcited intermediate *[1‑Co]2+ (8 ps). We present herein the scope of this C−H arylation protocol and provide mechanistic insights derived from detailed spectroscopic and computational studies. These indicate that, despite its transient existence, reduction of *[1‑Co]2+ is facilitated via pre‐assembly with the NEt3 reductant, highlighting an alternative strategy for the future development of 3d metal‐catalyzed PRC.

中文翻译：

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钴介导的吡咯光化学C−H芳基化

尽管人们共同努力寻找更多地球上丰富的催化剂和特别是基于 3d 金属的替代品，但贵金属配合物在光氧化还原催化 (PRC) 中仍然普遍存在。大多数看似合理的3d金属配合物由于激发态寿命较短而被认为是不合适的，这使得研究人员优先考虑通过仔细的分子设计来追求更长的激发态寿命。然而，我们在此报告，吡咯和相关底物的 C−H 芳基化（这是评估光氧化还原催化剂功效的基准反应）可以使用简单且易于获得的八面体双（二亚氨基吡啶）钴络合物来实现，[1-Co ](PF6)2。值得注意的是，尽管关键光激发中间体 *[1-Co]2+ 的激发态寿命较短（8 ps），[1-Co]2+ 仍能有效地官能化氯芳烃和溴芳烃底物。我们在此介绍了该 C−H 芳基化方案的范围，并提供了从详细的光谱和计算研究中得出的机制见解。这些表明，尽管*[1-Co]2+的存在是短暂的，但通过与NEt3还原剂的预组装促进了*[1-Co]2+的还原，这凸显了3d金属催化PRC未来发展的替代策略。