Guillermo Larrazábal

Complexation of sucrose with cobalt(III)bis(phenanthroline)

The delta-[Co(III)bis(phenanthroline)(sucrose)]3+ complex forms with little perturbation of the sucrose conformation, and complexation by HO-2(g) and HO-1(f).

Stereoselectivity and exciton cotton effects in mixed complexes of zinc(II)

Abstract Mixed complexes of Zn(II) with chiral aminoacids and 1,10-phenanthroline have been prepared and their C.D. and O.R.D. spectra measured. All the C.D. spectra exhibited an exciton splitting at 268 nm and their intensities depended on the chiral ligand. These results were interpreted in terms of steric effects through the exciton theory.

Studies of Δ,Λ-[M(1,10-phen)2(S-ala)]qX diastereoisomeric systems of nickel and zinc with different counter-anions

Abstract Δ,Λ-[M(phen) 2 ( S -ala)] + (X q- ) 1/q diastereoisomeric systems, in which M = nickel or zinc, phen = 1,10-phenanthroline, S -ala − = S -alaninate ( q = 1 and 2), with a series of counteranions have been prepared as methanolic solutions and characterized by spectral (CD, ORD, UV-vis) and conductance data. In both nickel and zinc systems the CD spectra in the β′ band region of the diimine ligand exhibit exciton splittings with sign patterns corresponding to a predominance of the Λ isomers. Analysis of the ORD spectra by means of many-term Drude equations suggests the order Zn > Ni for the absolute values of excitation resonance energy. Differences between nickel and zinc systems have been observed concerning the effects of the counter-anion nature upon the formation equilibria. In the nickel systems these effects would consist mainly of outer-sphere interactions affecting the position of the [Λ]/[Δ] equilibrium, whereas in the zinc ones ligand/counter-anion exchange equilibria would also occur to a significant degree. By using the molar-ratio method the stability orders [Zn(phen)( S -ala) 2 ] ≈ [Zn(phen) 2 ( S -ala)] + > [Zn(phen) 3 ] 2+ and [Ni(phen) 3 ] 2+ > [Ni(phen) 2 ( S -ala)] + have been established. The ion-pairing and the third stepwise stability constants for [Zn(phen) 2 ( S -ala)]Cl have also been estimated. The counteranion dependence of the apparent stability constants for the zinc systems, is discussed in terms of the counter-anion basicity and the possible “discriminating qualities” of the [Zn(phen)( S -ala)] + species.

Sucrose bis(1,10-phenanthroline)cobalt (III). Predicted distortion at the octahedral center

Abstract The two 1,10-phenanthroline ligands in the mixed Δ-cobalt(III) complex with sucrose are in different environments relative to the sucrose ligand as shown by differences in their 1H NMR signals and predicted by structural optimization. There is considerable congestion between the glucose moiety and one of the phenanthrolines in the Δ-complex, and the interactions which stabilize it, relative to a Λ-complex, are analyzed. Differences in 1H chemical shifts of the phenanthrolines are related to their mutual interactions and those with the glucose moiety of the sugar, which lead to π-shielding in some of its 1H NMR signals. Absorption and circular dichroism (CD) spectra are analyzed with assignment of the electronic transitions.

Chiral discrimination in diasteroisomeric systems of cadmium with 1,10-phenanthroline and S-amino acidates

Abstract Δ,Λ-[Cd(phen) 2 (S-aa)] + NO − 3 diastereomeric systems (where phen = 1,10-phenanthroline and S-aa = S -alaninate, S -serinate, S -threoninate, S -prolinate, S -valinate, S -leucinate and S -phenylalaninate) have been prepared in the form of methanolic solutions and characterized by spectral (UV, CD, ORD) and conductance measurements. The CD spectra of these systems in the β′ band region of the diimine ligand exhibit residuary exciton splittings, whose intensities and sign patterns suggest the following decreasing order of [Λ]/[Δ] diastereoisomeric equilibrium constants: S -prol > S -phenala > S -val > 1 > S -ala > S -leu > S -ser > S -threo. The same order is inferred from the ORD data over the range 400–600 nm. Comparison with the selectivities observed for some zinc analogues and the analysis of molecular models suggest that in the cadmium systems the chiral discriminations are governed mainly by a balancing between intramolecular steric repulsion, differential solvation and discriminating ion association. Solvent effects on the optical activity of some cadmium and zinc systems in methanol/n-propanol and methanol/benzene mixtures have also been studied. The corresponding results are discussed in terms of the contributions of the above discriminating forces.

Ion-pairing and optical activity of diastereomeric zinc(II) 1, 10-phenanthroline, S-valinate systems

A series of S-valinatobis(1, 10-phenanthroline)zinc salts in methanolic solution have been prepared and their conductivities and ORD spectra measured. A positive linear correlation of optical rotation with conductance was found for salts of non-chelating counter anions. From the application of the Yoe-Jones method on the system Zn, phen, S-val−, Cl− it was concluded that the counter anion dependence of the optical activity is connected mainly with heterocyclic ligand counter anion exchange equilibria.

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).

ISOLATION AND CHARACTERIZATION OF COBALT (III) TRIS-D-AMINOSUGARS

Mixed complexes of aminosugars and 1,10-phenanthroline (phen) with cobalt(III), with the composition Co(III)(phen)2sugar, disproportionate in aqueous solution in approximately one month, giving non ionic tris-aminosugar complexes. The complexes with a-D-glucosamine, a-D-galactosamine and b-D-mannosamine have the L-configuration at Co(III) with facial isomerism, on the bases of molecular composition and absorption and circular dichroism spectra

ELECTROTOPOLOGICAL STATE MODELING OF STABILITY CONSTANTS OF BINARY AND TERNARY COPPER(II) COMPLEXES WITH A-AMINO ACIDS

The second stepwise formation constants of binary and ternary copper(II) complexes with a-amino acidate ligands are modeled by using four-descriptor sets consisting of three indexes defined as linear combinations of the E-states of some skeletal groups of the different species involved in the formation equilibria, and the logarithm of the statistical factor. Hydrophobicity and basicity properties of the ligands are also described. Results indicate that both hydrophobic interactions and ligand basicities, as differential factors over the sequence of copper(II) complexes, would operate mainly through changes in the stability of the copper(II)-carboxylate bonds

ELECTROTOPOLOGICAL STATE STUDIES OF COPPER(II) COMPLEXES WITH alpha-AMINOACIDATES

Descriptor combinations, consisting of the electrotopological state (E-state) indexes of some skeletal groups, the first-order 1c molecular connectivity index and the logarithm of the statistical factor, are employed to describe the second stepwise formation constants of binary and ternary copper(II) complexes with a-aminoacidate ligands. Descriptor sets formed by E-state values of skeletal groups belonging to the chelate rings, 1c and the logarithm of the statistical factor lead to the best regression equations. Results suggest that differences in stability over the series of metal chelates depend mainly upon variations in the coordination tendency of the carboxylate ligand groups