Suzuki-Miyaura cross-coupling of aryl chlorides catalyzed by palladium precatalysts of N/O-functionalized pyrazolyl ligands

摘要

A series of palladium complexes, trans-[1-(R)-pz3,5-Me2]2PdCl_2 {R = CH_2CONH(2,6-i-Pr_2-C_6H_3) (1b) and 2-(OH)-C_6H_(10) (2b)}, supported over N/O-functionalized pyrazole derived ligands effectively catalyzed the more challenging Suzuki-Miyaura cross-coupling of a variety of activated aryl chlorides with phenyl boronic acid in air in a mixed-aqueous medium (DMF:H_2O, v/v = 9:1) in moderate to excellent yields. Besides the commonly encountered C _(sp2)-C_(sp2) coupling, the 1b and 2b precatalysts also catalyzed the relatively difficult C_(sp2)-C_(sp3) coupling of benzyl chloride with phenyl boronic acid. The 1b and 2b complexes were synthesized by the direct reaction of the respective N/O-functionalized pyrazolyl ligands, 1a and 2a, with (COD)PdCl_2 in 62-66% yields. The stability of the pyrazole-palladium interaction in the 1b and 2b complexes has been attributed to the deeply buried N_(pyrazole)-Pd interaction as evidenced from the density functional theory (DFT) studies.