Mechanisms of Nickel-Catalyzed Coupling Reactions and Applications in Alkene Functionalization.
Mechanisms of Nickel-Catalyzed Coupling Reactions and Applications in Alkene Functionalization.
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DOI：
10.1021/acs.accounts.0c00032
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发表时间：
2020-04-21
影响因子：
18.3
通讯作者：
Diao T
中科院分区：
文献类型：
--
作者：
Diccianni J;Lin Q;Diao T
镍配合物表现出与其他10族金属不同的特性，包括核半径小、对能高、电负性低和氧化还原电位低。这些性质使Ni催化剂能够容纳和稳定顺磁中间体，进入自由基途径，并经历缓慢的β-H消除。我们的研究计划调查了这些基本属性如何影响镍的催化性能，特别是在烯烃功能化的背景下。烯烃是一种用途广泛的官能团，但烯烃的立体选择性碳官能团化反应尚未得到充分的研究。这一挑战可能源于传统的双电子迁移插入途径难以控制选择性。镍催化剂可以通过自由基机制导致不同的立体决定步骤，从而获得难以制备的分子支架。例如，我们小组开发的不对称烯二芳化反应依赖于Ni（III）中间体的自由基性质来控制对映选择性，并获得具有生物活性的手性α，α，β-三芳基乙烷分子库。双组分还原1,2双官能化反应的机理研究揭示了亲电试剂交叉选择性的起源，因为C sp2和C sp3亲电试剂分别通过双电子和自由基途径在Ni(I)上独立激活。催化剂还原已被确定为该系统的周转限制步骤。使用（Xantphos）Ni(I)Ar模型配合物对自由基形成步骤进行更深入的研究表明，Ni(I)通过协调的卤素提取途径引发自由基形成。Ni的低氧化还原电位使我们能够开发一种还原的，反选择的二烯环化，其中经典的双电子机制在Ni(I)/Ni（III）平台上运行，考虑到化学选择性和立体选择性。该反应已被用于高效合成药学相关分子，如3,4-二甲基加巴布丁。Ni倾向于经历单电子氧化还原过程促使我们探索双核Ni介导的键形成。这些研究为Ni-Ni键以及两个金属中心如何协同反应促进C-C， C-X和N-N键形成还原消除提供了见解。最后，分离出β- agagostic Ni和Pd配合物，可以对这些高活性分子进行x射线和中子衍射表征。这些键参数作为β-羟基相互作用的明确证据，有助于解释相对于Pd， Ni中β-H的消除速度较慢。总的来说，我们的研究在几种情况下阐明了Ni配合物的基本性质。更深入的机理理解有助于催化剂的设计，并有助于使镍催化烯烃功能化反应的反应活性和选择性合理化。
Nickel complexes exhibit distinct properties from other group 10 metals, including a small nuclear radius, high paring energy, low electronegativity, and low redox potentials. These properties enable Ni catalysts to accommodate and stabilize paramagnetic intermediates, access radical pathways, and undergo slow β-H elimination. Our research program investigates how each of these fundamental attributes impact the catalytic properties of Ni, in particular in the context of alkene functionalization. Alkenes are versatile functional groups, but stereoselective carbofunctionalization reactions of alkenes have been under-developed. This challenge may derive from the difficulty of controlling selectivity via traditional two-electron migratory insertion pathways. Ni catalysts could lead to different stereo-determining steps via radical mechanisms, allowing access to molecular scaffolds that are otherwise difficult to prepare. For example, an asymmetric alkene diarylation reaction developed by our group relies upon the radical properties of Ni(III) intermediates to control the enantioselectivity and give access to a library of chiral α,α,β-triarylethane molecules with biological activity. Mechanistic studies on a two-component reductive 1,2-difunctionalization reaction have shed light on the origin of the cross-electrophile selectivity, as C sp2 and C sp3 electrophiles are independently activated at Ni(I) via two-electron and radical pathways, respectively. Catalyst reduction has been identified to be the turnover-limiting step in this system. A closer investigation of the radical formation step using a (Xantphos)Ni(I)Ar model complex reveals that Ni(I) initiates radical formation via a concerted halogen-abstraction pathway. The low redox potentials of Ni have allowed us to develop a reductive, trans-selective diene cyclization, wherein a classic two-electron mechanism operates on a Ni(I)/Ni(III) platform, accounting for the chemo- and stereoselectivity. This reaction has found applications in the efficient synthesis of pharmaceutically relevant molecules, such as 3,4-dimethylgababutin. The tendency of Ni to undergo one-electron redox processes prompted us to explore dinuclear Ni-mediated bond formations. These studies provide insight into Ni–Ni bonding and how two metal centers react cooperatively to promote C–C, C–X, and N–N bond forming reductive elimination. Finally, isolation of β-agostic Ni and Pd complexes has allowed for X-ray and neutron diffraction characterization of these highly reactive molecules. The bonding parameters serve as unambiguous evidence for β-agostic interactions and help rationalize the slower β-H elimination at Ni relative to Pd. Overall, our research has elucidated the fundamental properties of Ni complexes in several contexts. Greater mechanistic understanding facilitates catalyst design and helps rationalize the reactivity and selectivity in Ni-catalyzed alkene functionalization reactions.
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影响因子：
15
作者：
Biswas S;Weix DJ
通讯作者：
Weix DJ
DOI：
10.1002/anie.201906005
发表时间：
2019-09-23
期刊：
Angewandte Chemie (International ed. in English)
影响因子：
--
作者：
Diccianni JB;Hu CT;Diao T
通讯作者：
Diao T
影响因子：
15
作者：
Diccianni, Justin B.;Katigbak, Joseph;Diao, Tianning
通讯作者：
Diao, Tianning
影响因子：
0.8
作者：
Batsanov, SS
通讯作者：
Batsanov, SS
影响因子：
2.1
作者：
Diccianni, Justin B.;Chin, Mason;Diao, Tianning
通讯作者：
Diao, Tianning