Highly Efficient Pyridylpyrazole Ligands for the Heck Reaction. A Combined Experimental and Computational Study

Several [PdCl 2 (L)] complexes, where L is a pyridylpyrazole ligand, have been used as precatalysts in the Heck reactions between phenyl halides and tert- butyl acrylate. The used ligands differ from each other in the substitution at N1. The best results are obtained when this substituent is a hydroxyethyl group, and the corresponding complexes yield good results even for the reaction of chlorobenzene. Theoretical studies have shown that the presence of an OH group in the N1 substituent favors Pd−X dissociation, since it stabilizes the resulting cationic complex and the dissociation becomes thermodynamically favorable even in the absence of a coordinating solvent molecule.