Benzoquinone-promoted reaction of O2 with a Pd(II)-hydride.

Benzoquinone (BQ) and O(2) are among the most common stoichiometric oxidants in Pd-catalyzed oxidation reactions. The present study provides rare insights into mechanistic differences between BQ and O(2) in their reactivity with a well-defined Pd-hydride complex, Pd(IMes)(2)(H)(O(2)CPh) (1). BQ promotes the reductive elimination of PhCO(2)H from 1 and catalyzes the formation of a Pd(II)-OOH complex when this reaction is carried out under aerobic conditions. These results have important implications for Pd-catalyzed oxidation reactions.