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

Several new ferrocenyl secondary phosphine oxides, (η 5 -C 5 H 4 -P(═O)(Ph)(H)) 2 Fe ( 7aB ) and (η 5 -C 5 H 4 -P(═O)(R)(H))(η 5 -C 5 H 5 )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 (η 5 -C 5 H 4 -P(═O)(R)(H)) 2 Fe ( 7bM, b: R = t Bu) led to the formation of the palladium dimer [( 7b′M )( 7b′M-H + )Pd(μ-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 (η 5 -C 5 H 4 -P(OH)(Ph)) 2 Fe ( 7a′B ) indeed took place. This was also true for the case of 7aM and its isomeric form (η 5 -C 5 H 4 -P(OH)(Ph))(η 5 -C 5 H 5 )Fe ( 7a′M ). Palladium-catalyzed Suzuki−Miyaura reactions employing 7aB and 7bM as ligands gave satisfactory results.