Ferrocenylimidazoline palladacycles: efficient phosphine-free catalysts for Suzuki-Miyaura cross-coupling reaction

A series of new ferrocenylimidazoline ligands 5 with different substituents in the imidazoline ring and their corresponding cyclopalladated complexes 6 were synthesized. Chloride-bridged palladacycle dimers 6, which are thermally stable and insensitive to air and moisture, have been evaluated as effective phosphine-free catalysts for the Suzuki reaction of aryl bromides with arylboronic acid. The catalyst 6b presents the highest efficiency in the coupling processes for less reactive 2-bromothiophene. Moreover, the reactions can be carried out at room temperature under aerobic conditions to give the corresponding biaryls in high yields. Additionally, the triphenylphosphine adduct of cyclopalladated ferrocenylimidazoline 7a was structurally characterized by single-crystal X-ray diffraction.