Activation of σ(C-H) bonds in ferrocenylhydrazones derived from acetylferrocene

Article abstract of DOI:10.1016/S0022-328X(97)00388-4

The synthesis and characterization of the novel ferrocenylhydrazones: [(η⁵-C⁵H⁵)Fe{(η⁵-C₅H₄)-C(CH₃)=N-NHR}] (R = C₆H₄-4-NO₂ (1a), C₆H₄-4-Cl (1b), C₆H₄-2-CH₃ (1c), C₆H₃-2,4-(NO₂)₂ (1d) or C₆H₃-2,5-Cl₂ (1e)) is described. These compounds react in methanol with Na₂(PdCl₄) and sodium acetate trihydrate in a 1:1:1 molar ratio at room temperature, giving the di-μ-chlorobridged cyclopalladated complexes: [Pd{[(η⁵-C₅H₃)-C(CH₃)=N-NHR]Fe(η⁵-C₅H₅)}(μ-Cl)}]₂ (2). Addition of triphenylphosphine (PPh₃) to benzene suspensions of compounds 2, produced the cleavage of the di-μ-chlorobridges and the formation of [Pd{[(η⁵-C₅H₃)-C(CH₃)=N-NHR]Fe(η⁵-C₅H₅)}Cl(PPh₃)}] (3). NMR studies (¹H and ³¹P) on compound 3 revealed the formation of a (5,5) bicyclic system derived from the fusion of a five-membered palladacycle and the ferrocenyl moiety. The X-ray crystal structure of [Pd{[(η⁵-C₅H₃)-C(CH₃)=N-NH(C₆H₃-2,5-Cl₂)]Fe(η⁵-C₅H₅)}Cl(PPh₃)}] (3e) is also reported and confirms the formation of a five-membered palladacycle with a σ(Pd-C_{sp2,ferrocene}) bond.