Unraveling a Complex Mechanistic Picture of Photochemical Nickel-Catalyzed THF Arylation through Product Enantioselectivity Analysis

Abstract 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. 1 Introduction 2 Enantioselectivity Data Highlights a Complex Mechanistic Scenario 3 Probing the Predominant Pathway with Stoichiometric Experiments 4 MLR Modeling to Understand the Halogen Effect on the Enantioinduction 5 Proposed Prevalent Mechanism 6 Initiation with Ni(0) Precatalyst 7 Conclusion