Monodentate phosphine substitution in [Pd(κ3-dppf)(PR3)][BF4]2 (dppf = 1,1′-bis(diphenylphosphino)ferrocene) compounds

Abstract

The ligand 1,1′-bis(diphenylphosphino)ferrocene (dppf) is commonly employed in a variety of catalytic systems. There are a variety of coordination modes known for dppf, the least studied being the κ³ coordination mode, in which both phosphorus atoms and the iron atom of dppf interact with another metal center. One such compound is the previously reported [Pd(κ³-dppf)(PPh₃)]²⁺. A series of related compounds, [Pd(κ³-dppf)(P(p-C₆H₄R)₃)]²⁺ (R = OCH₃, CH₃, F and CF₃), has been synthesized and characterized. The X-ray crystal structure of [Pd(dppf)(P(p-C₆H₄F)₃)][BF₄]₂ was determined. Electrochemical and computational studies indicate that the electron donor ability of the P(p-C₆H₄R)₃ ligands influences the properties of these compounds. Substitution reactions of the P(p-C₆H₄R)₃ ligands have been examined, and, in general, the more electron donating P(p-C₆H₄R)₃ ligands completely replace the less electron donating ones. The kinetics of the reaction of [Pd(κ³-dppf)(P(p-C₆H₄F)₃)]²⁺ with P(p-C₆H₄OCH₃)₃ indicate that the reaction proceeds through a dissociative mechanism, contrary to the associative substitutions prevalent in square planar palladium(II) chemistry.