Palladium-on-Carbon-Catalyzed Coupling of Nitroarenes with Phenol: Biaryl Ether Synthesis and Evidence of an Oxidative-Addition-Promoted Mechanism

Nucleophilic substitution in nitroarenes to form biaryl ethers is of fundamental importance in organic synthesis. Under non-catalytic conditions, this can occur when a highly activated nitroarenes are used, or the nucleophile is activated by strong stoichiometric base. We have established a new method, using ligand-free palladium on carbon (Pd/C) catalyst, for the cross-coupling of activated nitroarenes with relatively non-nucleophilic phenol derivatives, including naphthol, in the absence of harsh bases. Control experiments, hot-filtration, three-phase test and ICP-AES analysis reveals that the catalysis proceeds via a usual oxidative addition step of nitroarene to Pd/C and releases active palladium particles having an extremely high catalytic activity. DFT calculations were made to realize the origin of selectivity of activated nitroarenes.