ANS reactions in aprotic solvents using metal-amine complexes as nucleophilic entity: Experimental and theoretical studies

CECILIA E. S. ALVARO,; NORMA SBARBATI NUDELMAN; SUSANA B. RAMOS; FEDERICO BERGERO

Concón

Conferencia; 14th Latin American Conference on Physical Organic Chemistry. 14a Conferencia Latinoamericana de Físico-Química Orgánica (CLAFQO-XIV).; 2017

Pontificia Universidad Católica de Chile, Chile

Coordination complexes have applications in very diverse scientific and technological fields. Amine complexes exhibit a differential reactivity with respect to free amines depending on, among other factors, the metal center character and the ligand structure. Studies of the Aromatic Nucleophilic Substitution (ANS) mechanism reported in the literature are mainly centered on the nature of substrates, nucleophile basicity and solvent polarity, and the study of coordination complexes as a nucleophilic entity are scarce. The present work describes kinetic studies performed in toluene with 1-chloro-2,4-dinitrobenzene (DNClB) and Cu (II) and Fe (II) complexes with aliphatic bifunctional amines such as ethylenediamine (EDA) and N,N-dimethyl propylamine (DMPA), previously studied in our laboratory in its non-complexed form1. They were chosen considering their characteristics of bi- dentate ligands and the possible size of the metalo-cycle formed. Purification of the solvent, reagents and substitution products1 in addition to the synthesis and characterization of the complexes2 were performed using procedures previously reported. The pseudo-first k, and second order rate constants, kA, were calculated and a differential kA behavior was observed for the metal-amine complexes as the complex concentration increased. Considering the self-aggregation of amines in aprotic solvents, these results suggest a different lability of the complexed amines attributed to stereo-electronic effects, to form free amine dimers that would react with the substrate. In order to interpret kinetic results by means of theoretical calculations, as a first step we performed Density Functional Theory calculations to determine the equilibrium structure and its corresponding formation energy in vacuum for complexes of Cu (II) and Fe (II) with EDA. These calculations were done at the B3LYP/6-31++G(d,p) and LANL2DZ level, and considering one to three ligands. Preliminary results indicate that the most stable complexes are those with three amines for both Cu (II) and Fe (II) complexes, and the Cu (II) ones are more stable than those of Fe (II). These results will be correlated with those obtained experimentally. Further calculations are currently in progress to consider also DMPA complexes and to include the contribution of the basis set superposition errors (BSSE) to the stabilization energies.