Mechanistic Evidence of a Ni(0/II/III) Cycle for Nickel Photoredox Amide Arylation
Mechanistic Evidence of a Ni(0/II/III) Cycle for Nickel Photoredox Amide Arylation
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镍光氧化还原酰胺芳基化的 Ni(0/II/III) 循环的机理证据
DOI：
10.1002/anie.202310753
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
Bahamonde, Ana
中科院分区：
文献类型：
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作者：
Bradley, Robert D.;McManus, Brennan D.;Yam, Jessalyn G.;Carta, Veronica;Bahamonde, Ana
这项工作证明了Ni（0/II/III）循环对Ni-光氧化还原酰胺芳基化的主导作用，这与通过Ni（I/III）自维持循环操作的其他Ni-光氧化还原C-杂原子偶联形成对比。当使用不同的Ni预催化剂时收集的动力学数据支持初始Ni（0）介导的氧化加成到芳基溴中。使用NiCl2作为预催化剂导致可观察到的诱导期，发现该诱导期是由生成Ni（0）的光化学活化事件引起的，并且通过Ni（II）预催化剂和原位生成的Ni（0）活性物质之间的非生产性歧化而延长。氧化加成后的配体交换产生的Ni（II）芳基酰胺络合物，这被确定为催化剂的反应的静止状态。化学计量实验表明，需要氧化该Ni（II）芳基酰胺基中间体以产生官能化酰胺产物。所提供的动力学数据支持限速光化学介导的Ni（II/III）氧化，以实现C-N还原消除。基于EPR和动力学测量，丢弃替代Ni（I/III）自持歧管。本文揭示的机理见解将告知社区Ni-光氧化还原反应条件的微妙变化如何影响反应途径，并使我们能够将芳基氯化物作为偶联伙伴，并将Ni负载量减少20倍而没有任何反应性损失。
This work demonstrates the dominance of a Ni(0/II/III) cycle for Ni‐photoredox amide arylation, which contrasts with other Ni‐photoredox C‐heteroatom couplings that operate via Ni(I/III) self‐sustained cycles. The kinetic data gathered when using different Ni precatalysts supports an initial Ni(0)‐mediated oxidative addition into the aryl bromide. Using NiCl2as the precatalyst resulted in an observable induction period, which was found to arise from a photochemical activation event to generate Ni(0) and to be prolonged by unproductive comproportionation between the Ni(II) precatalyst and the in situ generated Ni(0) active species. Ligand exchange after oxidative addition yields a Ni(II) aryl amido complex, which was identified as the catalyst resting state for the reaction. Stoichiometric experiments showed that oxidation of this Ni(II) aryl amido intermediate was required to yield functionalized amide products. The kinetic data presented supports a rate‐limiting photochemically‐mediated Ni(II/III) oxidation to enable C−N reductive elimination. An alternative Ni(I/III) self‐sustained manifold was discarded based on EPR and kinetic measurements. The mechanistic insights uncovered herein will inform the community on how subtle changes in Ni‐photoredox reaction conditions may impact the reaction pathway, and have enabled us to include aryl chlorides as coupling partners and to reduce the Ni loading by 20‐fold without any reactivity loss.