COPPER(II) COMPLEXES OF METHYL-10-AMINO-1,4,8,12-TETRA-AZACYCLOPENTADECANE - SYNTHESIS, PROTONATION AND FORMATION-CONSTANTS AND KINETICS OFTHE ACID-CATALYZED DISSOCIATION

The ligand methyl-10-amino-1,4,8,12-tetra-azacyclopentadecane has been prepared by the reduction of itro-1,4,8,12-tetra-azacyclopentadecane) copper(II) nitrate with Zn/HCl. The protonation constants of the ligan d at 25 degrees C and I = 0.1 mol dm(-3) are log K-11 = 10.79, log K-1 2 = 9.37, log K-13 = 5.21, log K-14=2.78 and log K-15= <2.0. The forma tion constants for the equilibria Cu2+ + L + H+ reversible arrow CuLH3 +; log beta(CuLH) Cu2+ + L reversible arrow CuL2+; log beta(CuL) are l og beta(CuLH) = 25.57 +/- 0.03 and log beta(CuL) = 21.63 +/- 0.04. The pK for the ionisation of the protonated 10-amino group in the copper( II) complex, CuLH3+ reversible arrow CuL2+ + H+ is 3.94 +/- 0.05. The protonated complex is four-coordinate and becomes five-coordinate as t he protonated amino group ionises. A new band appears in the visible s pectrum of the copper complex at ra. 800 nm as the five-coordinate com plex is formed. Spectrophotometric titrations using the 800 nm band gi ve a pK = 3.94 +/- 0.05. The kinetics of the acid-catalysed dissociati on of the copper complex have been studied. (C) 1998 Elsevier Science Ltd. All rights reserved.