Santiago Zolezzi

Electrochemical studies of copper(II) complexes with Schiff-base ligands

Abstract The electrochemical reduction of copper(II) complexes with salen Schiff-base ligands derived from ethylenediamine or (R,R) or (S,S)-1,2-diphenylethylenediamine and 5-methoxy, 5-bromo and 5-nitrosalicylaldehyde have been studied by cyclic voltammetry in the potential range +1 to −2.3 V in dimethyl sulfoxide (DMSO) as a solvent. The resulting voltammograms consist of a single quasi-reversible one-electron transfer attributable to the couple [Cu(II)L]/[Cu(I)L]−. Trends in cathodic peak potential (Epc) values are observed which can be correlated with the electronic effects of the 5-substituents of the Schiff-base ligands. Changes in the basicity of the ligand groups are determinant for such electrochemical trends.

SYNTHESES AND CHARACTERIZATION OF COPPER(II) COMPLEXES WITH SCHIFF-BASE LIGANDS DERIVED FROM ETHYLENEDIAMINE, DIPHENYLETHYLENEDIAMINE AND NITRO, BROMO AND METHOXY SALICYLALDEHYDE

Abstract Copper(II) quelates with Schiff bases derived from ethylenediamine, 1R,2R-(+)- or 1S,2S-(−)-1,2-diphenylethylenediamine and 5-X-salicylaldehyde (X=OCH3, H, Br, NO2) have been synthesized and characterized by elemental analysis and IR and UV-visible spectroscopies. The ORD and CD spectra of the chiral ligands and their related complexes have also been measured. The absorption and CD spectra of the metal complexes in the visible region are consistent with near square planar coordination geometries. Trends in absorption spectra over the series of complexes can be correlated with electronic effects of the substituents at position 5 of the salicylaldehyde. The sign patterns of the CD spectra in both UV and visible regions suggest the prevalence of δ and λ conformations for the chelate ring in the complexes of Schiff bases derived, respectively, from R,R- and S,S-diamines. Specific features of the CD spectra of the metal complexes are discussed in terms of the exciton chirality method.

Epoxidation of styrene with iodosylbenzene in the presence of copper(II) Schiff-base complexes

Copper(II) complexes with salen Schiff-base ligands derived from ethylenediamine or (S,S)-1,2-diphenylethylenediamine and salicylaldehyde or 5-methoxy, 5-bromo and 5-nitrosalicylaldehyde have been tested as catalysts for the epoxidation of styrene with iodosylbenzene, in dichoromethane as a solvent. The reactions were followed by gas chromatographic analysis and mass spectrometry. Catalytic activities were found to be dependent upon both the Lewis acidity of the metal complexes and the presence of phenyl substituents on the ethylene moiety. Moderate styrene conversions and epoxide yields were obtained. Pseudo-first-order kinetics was observed for the styrene conversion. Possible reaction mechanisms are outlined.

Tropospheric aerosols above the thermal inversion layer of Santiago, Chile: Size distribution of elemental concentrations

Abstract This paper reports on elemental concentration distribution versus size of particulate matter under 10.2μm, above the thermal inversion layer in Santiago, Chile. Forty-eight-hour samples were collected with Andersen and Berner cascade impactors. Atomic Absorption Spectrophotometry was used to quantify Mg, Ca, Mn, Fe, Zn, Pb, Ni, Cr and Cd. These last three elements were found under the detection limit of the technique. The concentration of Ca, Fe, Mg and Mn increases as the sizes of particles increase, while the concentration of Pb increases as the sizes of particles decrease. Analysis by enrichment factors using Fe from local soils as reference shows that Mg, Ca and Mn have a natural origin, and Pb and Zn an anthropogenic origin. The principal component analysis indicates that Mg, Ca, Mn and Fe are very probably coming from peripheral soils or dust from unpaved roads and streets; Pb from motor vehicles; and Zn and Cu from industrial emissions.

AMINOCARBONYLATION REACTION USING PALLADIUM COMPLEXES CONTAINING PHOSPHORUS-NITROGEN LIGANDS AS CATALYSTS

The catalytic activities of palladium complexes containing phosphorus-nitrogen ligands is reported. The catalysts studied showed high activities in the aminocarbonylation of aryl iodides. The palladium complexes reported activities between 100% and 58% in the aminocarbonylation reaction. The reactions are very selective for the double carbonylative amination of aryl halides. The major product is N,N-diethyl-α-oxo benzeneacetamide (96/4). The reaction was made under mild conditions of temperature and carbon monoxide pressure.

Studies of the circular dichroism spectra of dissymmetric Schiff-bases by means of the exciton chirality method

Abstract The circular dichroism spectra of some dissymmetrical Schiff-bases derived from condensation of 2 mol salicylaldehyde with 1 mol of a chiral diamine are analyzed in terms of a simple conformational model taking the angle between the aromatic chromophores as a variable. The rotatory strengths of the π→π* transitions are calculated with AM1 molecular orbitals in combination with the dipole-coupling approximation. Calculated CD curves are found to be in reasonable agreement with the experimental CD spectra. Differences in the CD spectra of the Schiff-bases are discussed in relation to variation of the theoretical CD curve of ethylenebis(salicylideneimine) as a function of conformation.

AN ELECTRON SPIN RESONANCE (ESR) INVESTIGATION OF POTENTIAL LIGANDS OF INORGANIC INTEREST WITH NITRO SUBSTITUENTS

ABSTRACT Electron Spin Resonance spectra were obtained of the salicyliden-2-imino-5-nitropyrimidine (1•−), N,N-bis(5-nitrosalicyliden) ethylendiamine (2•−), 2-hydroxy-5-nitro-benzili-den-5-iminoquinoline (3•−) anion radicals produced by electro chemical reduction in DMSO. Hyperfine splitting constants were assigned by comparison with radical anions of similar structure and in some cases with the help of INDO method. For the (2•−) and (3•−) the substitutions in position meta affect greatly some proton coupling constants.

Evolution of lead concentration in the particulate matter of Santiago, Chile, since 1978

Santiago is a city of over 4.5 million inhabitants and about 415000 motor vehicles using leaded gasoline. Twenty-four-hour samples were taken of total and fractionated particulate matter using a low-volume system and two Andersen cascade impactors, between 1978 and 1989 at different sites of the city of Santiago. Lead concentrations were determined by atomic absorption spectrophotometry. The results show that Pb concentrations vary greatly depending on the site selected. Higher values are always detected near the city center. An annual variation with the highest value during the autumn-winter period (May–July) is clearly observed. Lead concentrations versus size are clearly biased to particles smaller than 2 µm. A correlation is observed between Pb concentrations and the suspended particulate matter under 3 µm at different sites of the city. The curves of Pb concentration versus size of the aerosols emitted by the gas exhaust of motor vehicles using leaded gasoline are similar to those of the atmospheric aerosols.

THE STEREOSELECTIVE SYNTHESIS OF THE WERNER COMPLEX WITH SUBSTOICHIOMETRIC SUGARS

ABSTRACT A tetranuclear complex of Co(III) with hydroxo bridges, so-called “Werner Complex”, was synthesized in the presence of several sugars (1-8) with partial resolution of this complex. The sugars in 10 mol % with respect to Co(III) induce maximum resolution of the Werner complex.Keywords: Werner complex, hexol, sugar, Co(III), circular dichroism, dd* transition dd*, enantioselectivity.e-mail: jparada@ciq.uchile.cl. INTRODUCTION The present work is an example of induction of chirality from a chiral “sugar” ligand to the inorganic Werner complex (Fig.1). The Werner complex is a classic example of a chiral compound that does not contain carbon and was one of the first examples of chirality in octahedral complexes. 1, 2 Fig. 1. Structure of ∆-[Co[(OH) 2 Co(NH 3 ) 4 ] 3 ] 6+ .In an earlier publication 2 we showed that sugars induce stereoselective synthesis of the Werner complex, also known as “hexol”. We have now extended the work by synthesizing tetranuclear complex of Co(III) in presence of several sugars (Scheme 1, 1-8).