Activation of σ(C–H) bonds in ferrocenyl- and bis(ferrocenyl)-imines promoted by palladium

Abstract

Ferrocenylimines of general formula [Fe(η⁵-C₅H₅){η⁵-C₅H₄CH₂CH₂NCR(R′)}][R = H, R′= Ph 1a, C₆H₄Cl-2 1b, C₆H₃Cl₂-2,6 1c, C₆H₂Me₃-2,4,6 1d or (η⁵-C₅H₄)Fe(η⁵-C₅H₅)1e, R = Me, R′=(η⁵-C₅H₄)Fe(η⁵-C₅H₅)1f] were prepared by condensation of 2-ferrocenylethylamine and the corresponding aldehyde (1a–1e) or acetylferrocene (1f). Cyclopalladation reactions of these substrates gave different kinds of metallacycle depending on the nature of the ligand. In particular, endocyclic five-membered palladacycles containing a σ(Pd–C_sp²,phenyl) or a σ(Pd–C_{sp²,ferrocene}) were obtained from 1a, 1b and 1e, 1f respectively. However, for the ferrocenylimines in which the ortho positions of the aryl ring are blocked by either chlorine (1c) or methyl (1d) groups, mixtures of palladated compounds containing a σ(Pd–C_{sp²,ferrocene}) and a σ(Pd–C_sp²,phenyl)(for 1c) or a σ(Pd–C_{sp³,aliphatic}) bond (for 1d) were obtained. The molecular structure of [[graphic omitted]CH₂CH₂(η⁵-C₅H₄)Fe(η⁵-C₅H₅)}Cl(PPh₃)]·CH₂Cl₂ was determined by X-ray crystallography: triclinic, space group P, with a= 9.995(1), b= 11.308(2), c= 15.747(2)Å, α= 96.85(1), β= 99.05(1) and γ= 95.99(1)°. This confirms the formation of a five-membered palladacycle fused with the phenyl ring.