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

A series of palladium complexes, trans- [ 1 - ( R ) - pz 3 , 5 - Me 2 ] 2 PdCl2 {R = CH2CONH(2,6-i-Pr2-C6H3) (1b) and 2-(OH)-C6H10 (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:H2O, v/v = 9:1) in moderate to excellent yields. Besides the commonly encountered Csp2–Csp2 coupling, the 1b and 2b precatalysts also catalyzed the relatively difficult Csp2–Csp3 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)PdCl2 in 62–66% yields. The stability of the pyrazole–palladium interaction in the 1b and 2b complexes has been attributed to the deeply buried Npyrazole–Pd interaction as evidenced from the density functional theory (DFT) studies.