Bioinorganic chemistry of copper(II) complexes of N-salicylidene-aminoacidato: associative versus dissociative mechanism in the formation of copper ternary complexes with 2-aminopyridine (or pyrimidine). An ab initio study

Abstract

[eng] An ab initio computational study has been performed in order to evaluate the associative versus dissociative mechanism in the formation of ternary complexes of copper(II) N-salicylidene-aminoacidato with 2-aminopyridine (or pyrimidine). In order to diminish the extent of the calculations involved, 3-hydroxypropenal (for N-salicylidene) and guanidine (for 2-aminopyridine or pyrimidine) moieties have been used. In both mechanisms, only one transition state is detected, which corresponds to the increase of the coordination number (5 to 6 and 4 to 5 in the associative and dissociative pathways, respectively). These calculated transition states represent the coordination of the guanidine moiety to the copper complex. Although theoretical results indicate that the associative mechanism is more likely to occur (energy barrier=16.9 kcal/mol), the dissociative mechanism cannot be completely discarded (energy barrier=25.3 kcal/mol). The development of the hydrogen bond between the O(2) (carboxylate) and NH2 (guanidine) is seemingly the first step in the formation of the ternary complex.