Application of Tautomerism of Ferrocenyl Secondary Phosphine Oxides in Suzuki-Miyaura Cross-Coupling Reactions

Several new ferrocenyl secondary phosphine oxides, (eta(5)-C5H4-P(=O)(Ph)(H))(2)Fe (7aB) and (eta(5)-C5H4-P(=O)(R)(H))(eta(5)-C5H5)Fe (7M, a: R = Ph; c: R = Cy), were prepared and characterized by spectroscopic means. Further reaction of Pd(COD)Cl-2 with 2 molar equiv of (eta(5)-C5H4-P(=O)-(R)(H)(2)Fe (7bM, b: R = Bu-t) led to the formation of the palladium dimer [(7b'M)(7b'M-H+)Pd(mu-Cl)](2), 8. In addition, the reaction of Pd(OAc)(2) With 1 molar equiv of 7bM yielded a bis-7bM-coordinated palladium acetate, [(7b'M)(7b'M-H+)Pd(OAc)], 9. The molecular structures of 7aB, 7aM, 7bM, 8, and 9 were determined by single-crystal X-ray diffraction methods. A tautomeric equilibrium between 7aB and its isomeric form (eta(5)-C5H4-P(OH)(Ph))(2)Fe (7a'B) indeed took place. This was also true for the case of 7aM and its isomeric form (eta(5)-C5H4-P(OH)(Ph))(eta(5)-C5H5)Fe (7a'M). Palladium-catalyzed Suzuki-Miyaura reactions employing 7aB and 7bM as ligands gave satisfactory results.