Novel Five-Membered Pallada- and Platinacycles Containing a [C(sp2, ferrocene), N, S]- Terdentate Ligand. Theoretical Interpretation of Their Electrochemical and Electronic Properties Based on Density Functional Calculations

The synthesis of the novel ferrocenyl Schiff base [(η5-C5H5)Fe{(η5-C5H4)CHN(C6H4-2-SMe)}] (1c) and the study of its reactivity versus palladium(II) or platinum(II) salts are reported. These studies have allowed us to isolate and characterize [M{[(η5-C5H3)CHN(C6H4-2-SMe)]Fe(η5-C5H5)}Cl] {with M = Pd (2c) or Pt (3c)}, which are the first examples of cyclopallada- and cycloplatinated compounds containing a mer-terdentate [C(sp2, ferrocene), N, S]- ligand. Mössbauer spectroscopic studies and the X-ray crystal structures of 1c−3c are reported. The crystal structures of 2c and 3c confirmed the mode of binding of the ligand and revealed that the molecules are associated in pairs, which interact by C−H···π interactions forming a chain that stacks along the [101] plane. Electrochemical studies, based on cyclic voltammetry, reveal that the ease with which the oxidation of the ferrocenyl moiety occurs increases according to the sequence 1c < 2c < 3c. Molecular orbital calculations at a DFT level have also been carried out to rationalize the influence of the nature of the Pd(II) (in 2c) or Pt(II) in (3c) on the electrochemical properties of these compounds, and theoretical studies using time-dependent density functional theory (TD-DFT) calculations have also been carried out in order to assign the bands observed in the electronic spectra of the cyclometalated compounds.