Pd-PEPPSI Complexes Bearing Bulky [(1,2-Di‑(tert-butyl)­acenaphthyl] (DtBu-An) on N‑Heterocarbene Backbones: Highly Efficient for Suzuki–Miyaura Cross-Coupling under Aerobic Conditions

With the goal of achieving highly efficient palladium-catalyzed cross-coupling reactions under mild reaction conditions, the Pd-PEPPSI complexes C1 and C2 bearing 1,2-di­(tert-butyl)­acenaphthyl (DtBu-An) backbones were synthesized and characterized, and their use in Suzuki–Miyaura cross-coupling was investigated. The effects of catalyst structure and reaction conditions on the cross-coupling efficiency were evaluated in detail. The significant differences in catalytic activity compared with classical PEPPSI-IPr and PEPPSI-IPrAn precatalysts are discussed, where the axial sterics on the backbone play an important role. At low palladium loadings of 0.05–0.1 mol % and upon the addition of the relatively weak base K3PO4, the palladium complex C1 was found to be highly efficient for the coupling of (hetero)­aryl chlorides with arylboronic acids under aerobic conditions, affording the corresponding biaryls in excellent yields.