Pyrazole-tethered arylphosphine ligands for Suzuki reactions of aryl chlorides: how important is chelation?

Pyrazole-derived bidentate ligands (P,N-donor) with bulky substituents at the 3-position of the pyrazole, 1b–d, were used with Pd2(dba)3 to carry out efficient Suzuki coupling reactions with both aryl bromides and chlorides. Enhanced catalytic activity on account of steric crowding in the metal complex suggested participation of a chelated structure in the intermediate catalytic steps.