Search for: All records

This study provides a comprehensive mechanistic understanding of asymmetric THF α-O-arylation via Ni photochemical catalysis, leveraging enantioinduction data to refine the reaction pathway. Originally reported in a racemic fashion by Molander and Doyle, this transformation was re-examined using chiral bis(oxazoline) ligands, revealing distinct enantioselectivity trends depending on the halogen present in the aryl halide and Ni pre-catalyst. Stoichiometric experiments demonstrated that the Ni(II) oxidative addition complex is primarily responsible for trapping the THF radical, while multivariate linear regression modeling confirmed that the halide remains coordinated during the enantiodetermining step. Time-course experiments uncovered an alternative initial pathway when Ni(0) was used as the pre-catalyst, which ultimately converged to the main Ni(II) pathway. EPR analysis further revealed rapid comproportionation between Ni(0) and Ni(II), forming Ni(I) species that engage in radical trapping at early stages, accounting for the observed reactivity differences. By integrating enantioselectivity data with experimental techniques such as EPR spectroscopy, this study establishes enantioinduction analysis as a powerful tool for mechanistic investigations in Ni photochemical catalysis. The insights gained not only refine our understanding of this transformation, but also provide a framework for probing similar Ni/Ir dual photocatalytic systems. 

This perspective details advances made in the field of Ni-catalyzed C–N bond formation. The use of this Earth abundant metal to decorate amines, amides, lactams, and heterocycles enables direct access to a variety of biologically active and industrially relevant compounds in a sustainable manner. Herein, different strategies that leverage the propensity of Ni to facilitate both one- and two-electron processes will be surveyed. The first part of this Perspective focuses on strategies that facilitate C–N couplings at room temperature by accessing oxidized Ni(III) intermediates. In this context, advances in photochemical, electrochemical, and chemically mediated processes will be analyzed. A special emphasis has been put on providing a comprehensive explanation of the different mechanistic avenues that have been proposed to facilitate these chemistries; either Ni(I/III) self-sustained cycles or Ni(0/II/III) photochemically mediated pathways. The second part of this Perspective details the ligand designs that also enable access to this reactivity via a two-electron Ni(0/II) mechanism. Finally, we discuss our thoughts on possible future directions of the field.