Synthesis and characterization of two new macrobicyclic salts containing hexahydropyrimidine moieties: experimental and density functional theory studies

Abstract

Two macrocyclic Schiff base ligands (L1, L2) and their related reduced forms (L3 and L4) have been prepared. In the presence of nickel(II) perchlorate in methanol, the reinforced macrobicyclic salts containing hexahydropyrimidine cation moiety have been developed. Here, it seems that Ni(II) perchlorate acts as oxidizing agent converting methanol to the formaldehyde which in turn bridges two nitrogen atoms of reduced forms of macrocycle producing final products. All Schiff base ligands and their reduced forms together with related salts were characterized by elemental analysis, IR spectroscopy, 1H and 13C NMR, EI-Mass and in the case of [L3′](ClO4) salt by X-ray crystallography. The proposed mechanism for the formation of macrobicyclic ligand [L3′] from the reaction of macrocyclic ligand L3 and formaldehyde has also been studied via density functional theory (DFT).