Cross-Coupling of Diarylborinic Acids and Anhydrides with Arylhalides Catalyzed by a Phosphite/N-Heterocyclic Carbene Co-supported Palladium Catalyst System

A highly efficient cross-coupling of diarylborinic acids and anhydrides with aryl chlorides and bromides has been effected by using a palladium catalyst system co-supported by a strong σ-donor N-heterocyclic carbene (NHC), <i>N</i>,<i>N</i>′-bis­(2,6-diisopropylphenyl) imidazol-2-ylidene, and a strong π-acceptor phosphite, triphenylphosphite, in <i>tert</i>-BuOH in the present of K₃PO₄·3H₂O. Unsymmetrical biaryls with a variety of functional groups could be obtained in good to excellent yields using as low as 0.01, 0.2–0.5, and 1 mol % palladium loadings for aryl bromides and activated and deactivated aryl chlorides, respectively, under mild conditions. A ligand synergy between the σ-donor NHC and the π-acceptor phosphite in the Pd/NHC/P­(OPh)₃ catalytic system has been proposed to be responsible for the high efficacy to arylchlorides in the cross-coupling. A scalable and economical process has therefore been developed for synthesis of Sartan biphenyl from the Pd/NHC/P­(OPh)₃ catalyzed cross-coupling of di­(4-methylphenyl)­borinic acid with 2-chlorobenzonitrile