Copper(II) promoted imidazolidine ring formation and complexation: A unique reaction course

The reaction of Cu(II) ions with a sodium salt of new Schiff base ligand NaL1, sodium N-2-methyl pyridine-2-imine benzoate, in alkaline medium produced an imine bond coupled ligand and a novel complex, Na2[Cu(L3)2], L3 = 2,5-di(2-benzoic acid)-4-(2-pyridine)-1-(2-methyl-2-pyridine)-imidazolidine. When the reduced form of the sodium salt of the Schiff base ligand, NaL2, is employed, a simple hexacoordinated copper(II) complex, [Cu(L2)2], [L2]− = bis(N-(2-methylpyridine)-2-aminomethylbenzoate), was isolated. The compounds were characterized by spectroscopic methods and the molecular structures of [Cu(L2)2] and Na2[Cu(L3)2] were determined by single-crystal X-ray diffraction methods. Reaction mechanism for the synthesis of, Na2[Cu(L3)2], copper(II) promoted imine bond coupling is proposed and discussed. The redox behavior of [Cu(L2)2] and Na2[Cu(L3)2], studied using cyclic voltammetry and electron paramagnetic resonance spectroscopic methods, are also discussed.