Switching on elusive organometallic mechanisms with photoredox catalysis.
Switching on elusive organometallic mechanisms with photoredox catalysis.
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DOI：
10.1038/nature14875
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发表时间：
2015-08-20
期刊：
影响因子：
64.8
通讯作者：
MacMillan DW
中科院分区：
文献类型：
--
作者：
Terrett JA;Cuthbertson JD;Shurtleff VW;MacMillan DW
过渡金属催化的交叉偶联反应已成为化学合成中应用最多的碳-碳和碳杂原子成键反应之一。最近，镍的催化作用已被证明参与了多种C-C键形成反应，最著名的是根岸、铃木-宫ura、Stille、Kumada和Hiyama偶联。尽管在C-C片段耦合方面取得了巨大进步，但通过镍催化以一般方式形成C-O键的能力在很大程度上是不成功的。镍介导的醇偶联的挑战是关键的C-O键形成步骤（正式称为还原消除步骤）通过Ni（III）醇氧化物中间体发生的机制要求。在这篇论文中，我们证明了可见光激发的光氧化还原催化剂可以在有效的催化循环中调节镍烷氧化物的首选氧化态，从而提供了容易参与还原消除的Ni（III）物质的短暂途径。利用这种光氧化还原和镍催化的协同合并，我们开发了一种利用大量醇和芳基溴的高效通用碳氧偶联反应。更重要的是，我们已经开发出一种通用策略，通过仅使用弱光和单电子转移（SET）催化剂通过氧化态调制来“开启”重要但难以捉摸的有机金属机制。
Transition metal-catalyzed cross-coupling reactions have become one of the most utilized carbon–carbon and carbon–heteroatom bond-forming reactions in chemical synthesis. More recently, nickel catalysis has been shown to participate in a wide variety of C–C bond forming reactions, most notably Negishi, Suzuki–Miyaura, Stille, Kumada, and Hiyama couplings. Despite the tremendous advances in C–C fragment couplings, the ability to forge C–O bonds in a general fashion via nickel catalysis has been largely unsuccessful. The challenge for nickel-mediated alcohol couplings has been the mechanistic requirement for the critical C–O bond forming step (formally known as the reductive elimination step) to occur via a Ni(III) alkoxide intermediate. In this manuscript, we demonstrate that visible light-excited photoredox catalysts can modulate the preferred oxidation states of nickel alkoxides in an operative catalytic cycle, thereby providing transient access to Ni(III) species that readily participate in reductive elimination. Using this synergistic merger of photoredox and nickel catalysis, we have developed a highly efficient and general carbon–oxygen coupling reaction using abundant alcohols and aryl bromides. More significantly, we have developed a general strategy to “switch on” important yet elusive organometallic mechanisms via oxidation state modulations using only weak light and single-electron transfer (SET) catalysts.