Catalysis of the Suzuki–Miyaura coupling reaction in water by heteroannular cyclopalladated ferrocenylimine complexes

Catalytic studies on the air- and moisture-stable triphenylphosphine (PPh₃) adducts of heteroannular cyclopalladated ferrocenylimines [PdCl{C₅H₄FeC₅H₄CHRN=CHC₄H₃X}(Ph₃P)] (R = H, CH₃; X = S, O) indicate that they are all effective catalysts for the Suzuki–Miyaura coupling reaction of activated aryl bromides with phenylboronic acid in water under air atmosphere. Typically, using 1 mol‰ of catalyst in the presence of 1.2 equivalents of K₃PO₄ as base in water at 100 °C provided the corresponding biaryls in good to excellent yields. Meanwhile, the structure of [PdCl{C₅H₄FeC₅H₄CH(CH₃)N=CHC₄H₃S}(PPh₃)] has been established by the single-crystal X-ray diffraction technique. According to the crystal structure, the palladium atom is bound to the unsubstituted Cp ring, showing the four-coordinate structure typical of palladium complexes.