Ni-Catalyzed Reductive Dicarbofunctionalization of Nonactivated Alkenes: Scope and Mechanistic Insights
Ni-Catalyzed Reductive Dicarbofunctionalization of Nonactivated Alkenes: Scope and Mechanistic Insights
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DOI：
10.1021/jacs.9b02973
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发表时间：
2019-09-04
影响因子：
15
通讯作者：
Nevado, Cristina
中科院分区：
文献类型：
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作者：
Shu, Wei;Garcia-Dominguez, Andres;Nevado, Cristina
在还原条件下，用两个亲电碳源对不含直接基团或活化基的烯烃进行了二碳官能化。通过镍催化剂和TDAE作为牺牲性还原剂的组合，在各种无偏置的pi体系中同时形成一个C(sp(3))-C(sp(3))和一个C(sp(3))-C(sp(2))键，具有很好的选择性。控制实验和计算研究揭示了两个相互关联的Ni(I)/Ni(III)过程的自由基机理的可行性，并证明了不同的Ni(I)物种(Ni(I)I和PhNi(I))还原C(SP(3))-I键的能力。对还原剂的作用也进行了深入的研究，结果表明，单电子还原Ni(II)物种为Ni(I)在热力学上是有利的。此外，ArNi(I)络合物优先活化烷基对芳基卤化物，以及ArNi(II)对叔基C-中心自由基的高亲和力，解释了在这些转化中没有不需要的同位和直接偶联产物(Ar-Ar，Ar-Alk)。
Olefins devoid of directing or activating groups have been dicarbofunctionalized here with two electrophilic carbon sources under reductive conditions. Simultaneous formation of one C(sp(3))-C(sp(3)) and one C(sp(3))-C(sp(2)) bond across a variety of unbiased pi-systems proceeds with exquisite selectivity by the combination of a Ni catalyst with TDAE as sacrificial reductant. Control experiments and computational studies revealed the feasibility of a radical-based mechanism involving, formally, two interconnected Ni(I)/Ni(III) processes and demonstrated the different ability of Ni(I) species (Ni(I)I vs PhNi(I)) to reduce the C(sp(3))-I bond. The role of the reductant was also investigated in depth, suggesting that a one-electron reduction of Ni(II) species to Ni(I) is thermodynamically favored. Further, the preferential activation of alkyl vs aryl halides by ArNi(I) complexes as well as the high affinity of ArNi(II) for secondary over tertiary C-centered radicals explains the lack of undesired homo- and direct coupling products (Ar-Ar, Ar-Alk) in these transformations.