Palladium‐Catalyzed Cross‐Dehydrogenative Coupling of o‐Xylene: Evidence of a New Rate‐Limiting Step in the Search for Industrially Relevant Conditions

An efficient cross‐dehydrogenative coupling of o‐xylene under neat conditions, which brings important industrial benefits towards the synthesis of a monomer used in polyimide resins, is reported. The catalyst based on the combination of Pd/N ligand/carboxylate=1:1:2 does not require a Cu cocatalyst and proceeds at 11 bar of O2 pressure. Evaluation of the deuterium kinetic isotope effect (KIE) provides evidence for three different rate‐determining steps, which depend on the reaction conditions (medium, temperature). Under the reported neat conditions, the dissociation of a carboxylate‐bridged dimer to generate a more reactive monometallic Pd species is proposed to be the rate‐limiting step.