Ana Maria Leiva

Nouvell préparation, propriétés electrochimiques et etude structurale des phosphaferrocenes η5-C5Me5Fe-η5-PC4(R4)

Abstract A new synthesis of phosphaferrocenes is described. It involves nucleophilic attack of a phospholyl anion on a metastable cyclopentadienyliron acetylacetonate. The monoelectronic oxidation of the phosphaferrocenes thus obtained has been studied by cyclic voltammetry in various solvents. The X-ray structures of [η 5 -C 5 Me 5 Fe-η 5 -PC 4 (C 6 H 5 ) 4 ] is discussed and compared with the structure of [η 5 -C 5 H 5 Fe-η 5 -PC 4 H 2 (CH 3 ) 2 ].

ELECTRONIC EFFECTS OF DONOR AND ACCEPTOR SUBSTITUENTS ON DIPYRIDO(3,2-a:2′,3′-c)PHENAZINE (dppz)

Abstract The chelate ligands 11-R-dipyrido[3,2-a:2′,3′-c]phenazine, dppz-R (R = NH2, CH3, H, COOH, NO2) and the Re(dppz-R)(CO)3Cl (R = NH2, COOH, NO2) complexes were synthesized and characterized by conventional techniques. The influence of the donor and acceptor properties of the R substituents on the ligand properties were studied by spectroscopic techniques such as 1H-NMR and UV-Vis. Theoretical calculations were also achieved, mainly to interpret and understand the experimental spectra.

Synthesis of a new polypyridinic highly conjugated ligand with electron-acceptor properties

Abstract A new acceptor polypyridinic ligand functionalized with a quinone fragment is reported. The ligand, dipyrido[3,2- a :2′,3′- c ]-benzo[3,4]-phenazine-11,16-quinone, Nqphen, was synthesized by condensation of 1,10-phenanthroline-5,6-dione and 2,3-diamino-1,4-naphthoquinone. The syntheses of two rhenium complexes with this ligand are also reported.

Synthesis, characterization and crystal structure of [Ru(tppz)(4,4′-(CH3)2bpy)Cl](PF6), (tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine)

Abstract The synthesis and characterization of the complex [Ru(tppz)(4,4′-(CH 3 ) 2 bpy)Cl] + , where tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine, is reported. The ion was obtained in a one pot synthesis by reduction of Ru(4,4′-(CH 3 ) 2 bpy)Cl 4 with triethylamine in the presence of tppz, and isolated as the hexafluorophosphate salt. The structure of [Ru(tppz)(4,4′-(CH 3 ) 2 bpy)Cl](PF 6 ), 1 , was established by X-ray diffraction. The ruthenium atom is in a highly distorted octahedral environment with the 4,4′-(CH 3 ) 2 bpy nitrogens, the pyrazine central nitrogen of tppz, and chlorine defining the best mean equatorial plane. The axial positions are occupied by the nitrogens of the coordinated pyridyl rings of tppz. The Ru—N(tppz) bond to the central ring is short [1.962(9) A], while the Ru—N(4,4′(CH 3 ) 2 bpy) bond trans to it is lengthened towards a single bond distance [2.096(10) A]. This enhances the distortion in coordination of the octahedron, mainly produced by the bite angle of tppz. The distortions in 1 are evident in the 1 H-NMR spectra by the shifts of characteristic resonances upfield and downfield relative to the ligand.

Experimental evidence of the disproportionation equilibrium in copper mixed-valence complexes

Abstract Experimental evidence for a dismutation equilibrium in the mixed-valence (MV) [M n + –M ( n +1)+ ] system type has been elusive and its existence can be established only when the oxidation–reduction processes involved are reversible. Previous research in the field of binuclear Cu(II)Cu(II), Cu(I)Cu(I) and the related MV Cu(II)Cu(I) complexes allowed us to obtain electrochemical evidence for the disproportionation equilibrium in some of these systems. In this communication we report and discuss experiments with [(RCOO) 2 Cu(II)Cu(I)(OOCR) 2 ] − (R=CH 3 , Ph) type MV complexes that give direct non-electrochemical experimental evidence for the presence in solution of the disproportion equilibrium: 2[( RCOO ) 2 Cu ( II ) Cu ( I )( OOCR ) 2 ] − ⇔( RCOO ) 4 Cu 2 ( II )+[( RCOO ) 4 Cu ( I ) 2 ] 2 − It was possible to isolate the different components of the disproportionation equilibrium by varying temperature and solvent conditions. To our knowledge, this is the first non-electrochemical experimental evidence of this equilibrium for copper MV complexes in solution. Furthermore, as is discussed in the text, these results may be the basis for giving an alternative point of view to that given in some studies already reported in the literature, which relate to solvent and temperature effects on the intensity and energy of the intervalence transfer bands and also to changes in the EPR spectra of MV species.

Solvent effect on N-methylthiourea. A 1H NMR study

Abstract The solvent influence on the spectroscopic properties of the solute can be used to obtain information about its configuration in solution. With this objective the influence of the temperature on the 1 H-nmr spectra of N-methylthiourea was studied in the following solvents 1,2-propanodiolcarbonate, trimethylphosphate, tributylphosphate, tributylphosphate and dimethylsulfoxide mixed with CCl 4 in a ratio 1:1 in volume. At low temperature the methyl group signals of thiourea split showing the signals corresponding to cis and trans positions of methyl protons. These results with the behaviour reported for other solvents. However, the low field spectra corresponding to NH and NH 2 protons show higher complexity as is shown in Fig. 1. The splitting of the NH 2 signal in two signals with different intensities. A and B, indicates the presence of two non equivalent configurations of Fig. 1. The nmr spectra of NH and NH 2 protons of N-methylthiourea in 1,2-propanodiol-carbonate–carbonate–CCl 4 mixture at different temperatures. thiourea. The relative concentrations and the equilibrium constant between both configurations can be obtained from the areas under the signals. Both, enthalpy and entropy changes - calculated from the temperature dependence of the equilibrium constant - show a clear dependence on solvent basicity (DN). The influence of solvent basicity on the thermodynamics of the interconversion between forms A and B, added to the effect of the pure solvents and solvent mixtures on the chemical shifts at room temperature show that the two observed configurations differ on the planarity in the thiourea molecule. The planarity grade on the substrate would be mainly determined by the solute–solvent interaction through hydrogen bonds.