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-Me2)](2) PdCl2 {R = CH2CONH(2,6-i-Pr-2-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 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) 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 N-pyrazole-Pd interaction as evidenced from the density functional theory (DFT) studies. (C) 2010 Elsevier B.V. All rights reserved.