Direct Observation of C–F Bond Formation from Isolable Palladium(IV) Systems via an Outer-Sphere Pathway

Abstract

Despite recent advancements in synthetic methods for palladium-catalyzed C–F couplings, the mechanistic understanding─particularly concerning high-valent palladium species─remains underexplored. In contrast to the commonly proposed inner-sphere mechanism, which involves C–F reductive elimination at a palladium(IV) center, the outer-sphere pathway is poorly understood, and little experimental evidence has been provided using well-defined, isolable high-valent Pd systems. In this study, we present the design and synthesis of a series of isolable and characterizable palladium(IV) alkyl systems. Their reactivity in C–F bond formation has been investigated and systematically compared. Through the isolation of intermediates, reactivity comparisons, kinetic studies, and DFT calculations, this work presents, for the first time, isolable palladium(IV) model systems that enable the direct observation of C–F bond formation via an outer-sphere pathway.