Synthesis and structure of heteroannular cyclopalladated chiral ferrocenylimines: theoretical interpretation of the cyclopalladated complexes based on density functional calculations

Abstract

The reaction of novel chiral ferrocenylimines (η⁵-C₅H₅)Fe(η⁵-C₅H₄)–CH(CH₃)–NCH–2-R (R = furyl (3) and pyridyl (6)) with Li₂PdCl₄ and anhydrous CH₃COONa in dry MeOH produced heteroannular cyclopalladated {Pd[(η⁵-C₅H₄)Fe(η⁵-C₅H₄)–CH(CH₃)–NCH–2-R](μ-Cl)}₂ (R = furyl) (4) and Pd(N^∧N) [(η⁵-C₅H₅)Fe(η⁵-C₅H₄)–CH(CH₃)–NCH–2-R]PdCl₂ (R = pyridyl) (7) complexes, respectively. The Pd(μ-Cl)₂Pd bridge was cleaved by triphenylphosphine to give monomeric derivative 5. The structures of the monomeric and dimeric palladium complexes were confirmed by elemental analyses, IR, 1D and 2D NMR spectra, and X-ray diffraction. All the results led to the conclusion that the palladium atom is bound to the unsubstituted ferrocenyl moiety in compounds 4 and 5, while for compound 7, the palladium atom is coordinated by two nitrogen atoms. The ¹H NMR spectra showed that cyclopalladated complex 4 may exist as two diastereoisomers, with a new axial chirality being induced by the rotation of the two ferrocene rings. To explain these experimental results, detailed DFT computational studies have been carried out.