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

Abstract

The synthesis of the novel ferrocenyl Schiff base [(η 5 -C 5 H 5 )Fe{(η 5 -C 5 H 4 )CHdN(C 6 H 4 -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{[(η 5 -C 5 H 3 )CHdN(C 6 H 4 -2-SMe)]Fe(η 5 -C 5 H 5 )}Cl] {with M ) Pd (2c) or Pt (3c)}, which are the first examples of cyclopallada-and cycloplatinated compounds containing a mer-terdentate [C(sp 2 , 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.

Relationships between 57Fe NMR, Mössbauer parameters, electrochemical properties and the structures of ferrocenylketimines

“…This indicates that the ferrocenyl Schiff base adopts the anti-(E) conformation in solution. The remaining compounds (1a, 1c-1e and 2d) were characterised by 1 H NMR spectroscopy, and in all cases the number of signals as well as their multiplicities agreed with the results reported in the literature [11][12][13].…”

“…1 (c)) were prepared as described previously [11][12][13][14]. In addition, [(g 5 -C 5 H 5 )Fe{(g 5 -C 5 H 4 )-CH@N-C 6 H 4 -2OH}] (1f) was obtained using the general procedure described before for the synthesis of ferrocenyl Schiff bases of general formula [(g 5 -C 5 H 5 )Fe{(g 5 -C 5 H 4 )-CH@N-R 2 }], where R 2 represents a phenyl, benzyl or naphthyl group [11,12,16]. This procedure consists of the reaction of equimolar amounts of ferrocenecarboxaldehyde and the corresponding amine H 2 N-R 2 in refluxing benzene.…”

“…The most outstanding feature of the infrared spectrum of 1f is the presence of three absorption bands in the range 1550-1650 cm À1 . The band at highest wavenumber was assigned to the stretching of the C@N-functional group [11][12][13][14]16], and the other two were attributed to the stretching of the C@C moieties of the aromatic phenyl group. Proton and 13 C{ 1 H} NMR spectroscopic data for 1f are presented in Section 3.…”

“…In the last decade a wide range of ferrocenyl Schiff bases of the type [(g 5 -C 5 H 5 )Fe{(g 5 -C 5 H 4 )-C(R 1 )@N-R 2 }] {with R 1 = H, Me, C 6 H 5 and R 2 = alkylic or arylic groups} have been described and some of these bases have also been characterised by X-ray diffraction [11][12][13][14]. These compounds are stable and highly soluble in the common solvents used for NMR experiments and so they are especially attractive for 57 Fe NMR studies.…”

Neutral benzoquinolate cyclometalated platinum(II) complexes as precursors in the preparation of luminescent Pt–Ag complexes

“…Metal-metal bonds can act as a link between different subassemblies, making them a valuable tool in molecular or crystal engineering, and giving rise to a variety of structures, from simple linear bimetallic compounds to infinite one-dimensional chains [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Furthermore, some of these complexes show interesting photophysical and photochemical properties [1][2][3][4][5]7,8,11,17,27,[29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48], which in some cases have been exclusively attributed to the presence ...…”