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 Pdcatalyzed 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 PdI complex, [Pd-I(mu-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 PdI complex and its implications for catalytic reactivity are discussed.