Highly efficient pyridylpyrazole ligands for the heck reaction. A combined experimental and computational study

Several [PdCl2(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 Nl. 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 N 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. © 2008 American Chemical Society.