Detection of Palladium(I) in Aerobic Oxidation Catalysis

Palladium(II)‐catalyzed oxidation reactions exhibit broad utility in organic synthesis; however, they often feature high catalyst loading and low turnover numbers relative to non‐oxidative cross‐coupling reactions. Insights into the fate of the Pd catalyst during turnover could help to address this limitation. Herein, we report the identification and characterization of a dimeric Pd^I species in two prototypical Pd‐catalyzed aerobic oxidation reactions: allylic C?H acetoxylation of terminal alkenes and intramolecular aza‐Wacker cyclization. Both reactions employ 4,5‐diazafluoren‐9‐one (DAF) as an ancillary ligand. The dimeric Pd^I complex, Pd^I(μ‐DAF)(OAc)]₂, which features two bridging DAF ligands and two terminal acetate ligands, has been characterized by several spectroscopic methods, as well as single‐crystal X‐ray crystallography. The origin of this Pd^I complex and its implications for catalytic reactivity are discussed.