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<p>Nickel photocatalysis has recently become vital to organic synthesis, but how the Ni<sup>(II)</sup>X<sub>2</sub>L pre-catalyst (X = Cl, Br; L = bidentate ligand) becomes activated to Ni<sup>(I)</sup>XL has remained puzzling and is typically addressed on a case-by-case basis. Here, we reveal a general mechanism where light induces photolysis of the Ni<sup>(II)</sup>-X bond, either via direct excitation or triplet energy transfer. Photolysis produces Ni<sup>(I)</sup>XL and a halogen radical, X<sup>•</sup>. Subsequent hydrogen atom abstraction, often from the solvent, produces a C(sp<sup>3</sup>) radical, R<sup>•</sup>, that recombines with Ni<sup>(I)</sup> to form organonickel(II) complexes, Ni<sup>(II)</sup>XRL. Rather than acting as a loss pathway, Ni<sup>(II)</sup>XRL behaves as a light-activated reservoir of Ni<sup>(I)</sup> via photolysis of the Ni<sup>(II)</sup>-C bond. These results explain the role of the solvent in protecting the catalyst from off-cycle dimerization, demonstrate that two photons are often required to drive the reaction, and show how tuning the ligand can control the concentration of active Ni<sup>(I)</sup> species.</p>

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Photolytic activation of Ni(II)X2L explains how Ni-mediated cross coupling begins

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年7月1日

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  • Max Kudisch,
  • Reagan X. Hooper,
  • Lakshmy K. Valloli,
  • Justin D. Earley,
  • Anna Zieleniewska,
  • Jin Yu,
  • Stephen DiLuzio,
  • Rebecca W. Smaha,
  • Hannah Sayre,
  • Xiaoyi Zhang,
  • Matthew J. Bird,
  • Amy A. Cordones,
  • Garry Rumbles,
  • Obadiah G. Reid

摘要

Nickel photocatalysis has recently become vital to organic synthesis, but how the Ni(II)X2L pre-catalyst (X = Cl, Br; L = bidentate ligand) becomes activated to Ni(I)XL has remained puzzling and is typically addressed on a case-by-case basis. Here, we reveal a general mechanism where light induces photolysis of the Ni(II)-X bond, either via direct excitation or triplet energy transfer. Photolysis produces Ni(I)XL and a halogen radical, X•. Subsequent hydrogen atom abstraction, often from the solvent, produces a C(sp3) radical, R•, that recombines with Ni(I) to form organonickel(II) complexes, Ni(II)XRL. Rather than acting as a loss pathway, Ni(II)XRL behaves as a light-activated reservoir of Ni(I) via photolysis of the Ni(II)-C bond. These results explain the role of the solvent in protecting the catalyst from off-cycle dimerization, demonstrate that two photons are often required to drive the reaction, and show how tuning the ligand can control the concentration of active Ni(I) species.