C 9. Bürokommunikation

Hamacher, Bernd

doi:10.1515/9783110961355.377

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“…Similar redox activity has been observed and characterized in (bpy)Ni(Mes) 27 and (terpy)Ni(Mes) complexes. 28 The EPR spectrum of the reduction mixture of 21 by Zn displays an isotropic signal with a g value of 2.009, close to the free-electron value of 2.0023 ( Figure 9). This observation indicates the ligand character of the SOMO, consistent with the previous characterization of (phen)Ni(Mes) 25.…”

Section: Reduction Of Ni By Zn Characterized By Spectroscopy and Cycmentioning

confidence: 55%

Mechanism of Ni-Catalyzed Reductive 1,2-Dicarbofunctionalization of Alkenes

2019

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Ni-catalyzed cross-electrophile coupling reactions have emerged as appealing methods to construct organic molecules without the use of stoichiometric organometallic reagents. The mechanisms are complex: plausible pathways, such as "radical chain" and "sequential reduction" mechanisms, are dependent on the sequence of the activation of electrophiles. A combination of kinetic, spectroscopic, and organometallic studies reveals that a Ni-catalyzed, reductive 1,2dicarbofunctionalization of alkenes proceeds through a "sequential reduction" pathway. The reduction of Ni by Zn is the turnover-limiting step, consistent with Ni(II) intermediates as the catalyst resting-state. Zn is only sufficient to reduce (phen)Ni(II) to a Ni(I) species. As a result, commonly proposed Ni(0) intermediates are absent under these conditions. (Phen)Ni(I)-Br selectively activates aryl bromides via two-electron oxidation addition, whereas alkyl bromides are activated by (phen)Ni(I)-Ar through single-electron activation to afford radicals. These findings could provide insight into achieving selectivity between different electrophiles.

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Section: Reduction Of Ni By Zn Characterized By Spectroscopy and Cycmentioning

confidence: 55%