Ni-Catalyzed Reductive Dicarbofunctionalization of Nonactivated Alkenes: Scope and Mechanistic Insights

Olefins devoid of
directing or activating groups have been dicarbofunctionalized
here with two electrophilic carbon sources under reductive conditions.
Simultaneous formation of one C­(sp3)–C­(sp3) and one C­(sp3)–C­(sp2) bond across
a variety of unbiased π-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(sp3)–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.

不含导向基团或活化基团的烯烃，在还原条件下可与两种亲电碳源发生双碳官能化转化。本研究通过镍催化剂与作为牺牲还原剂的四(二甲氨基)乙烯（TDAE）的协同作用，在多种无偏π体系上同时构建C(sp³)-C(sp³)与C(sp³)-C(sp²)键，且反应选择性极佳。对照实验与计算研究证实，该反应遵循自由基机理，形式上包含两个相互关联的Ni(I)/Ni(III)循环过程，并揭示了不同Ni(I)物种——碘化亚镍（NiI）与苯基镍(I)（PhNi(I)）——在还原C(sp³)-I键时的能力差异。研究还对还原剂的作用进行了深入剖析，结果表明将Ni(II)物种经单电子还原为Ni(I)的过程在热力学上有利。此外，芳基镍(I)配合物优先活化烷基卤化物而非芳基卤化物，且芳基镍(II)对仲碳中心自由基的结合亲和力强于叔碳中心自由基，这一发现解释了该转化过程中未生成非目标均偶联与直接偶联产物（Ar-Ar、Ar-Alk型）的原因。