USE OF HYDROPHOBIC LIGANDS FOR THE STABILIZATION OF LOW-VALENT TRANSITION-METAL COMPLEXES .1. THE EFFECT OF N-METHYLATION OF LINEAR TETRAAZAALKANE LIGANDS ON THE PROPERTIES OF THEIR COPPER-COMPLEXES

The electrochemical reduction of the Cu(II) complexes with the ligands 2,5,8,11-tetramethyl-2,5,8,11-tetraazadodecane, 2,5,9,12-tetramethyl-2,5,9,12-tetraazatridecan and 2,6,9,13-tetramethyl-2,6,9,13-tetraazatetradecane in deaerated aqueous solutions yields the corresponding thermodynamically stable copper(I) complexes. The same complexes are obtained also via the comproportionation reaction of CuL(i) (2+) and Cu-0 in the presence of excess ligand. Delta S-0 values of the reduction processes were determined. The basicity constants of L(i) and the stability constants of their Cu(II) complexes were determined potentiometrically. The ESR spectra of CuL(i) (2+) point out that these complexes are not significantly tetrahedrally distorted. The binding constants of axial singly charged anions to the CuL(i) (2+) complexes were determined. Analysis of the data points out that the thermodynamic stabilization of the monovalent copper complexes via N-methylation is mainly due to the destabilization of the CuL(i) (2+) complexes. It is concluded that a major factor contributing to the observed effects is the hydrophobic nature of the tertiary-amine ligands.