Copper(II) complexes of 10-methyl-10-amino-1,4,8,12-tetra-azacyclopentadecane. Synthesis, protonation and formation constants and kinetics of the acid-catalysed dissociation

摘要

The ligand 10-methyl-10-amino-1,4,8,12-tetra-azacyclopentadecane has been prepared by the reduction of (10-methyl-10-nitro-1,4,8,12-tetra-azacyclopentadecane)copper(II) nitrate with Zn/HCl. The protonation constants of the ligand at 25 degrees C and I = 0.1 mol dm(-3) are log K-11 = 10.79, log K-12 = 9.37, log K-13 = 5.21, log K-14=2.78 and log K-15= <2.0. The formation constants for the equilibria Cu2+ + L + H+ reversible arrow CuLH3+; log beta(CuLH) Cu2+ + L reversible arrow CuL2+; log beta(CuL) are log 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 the protonated amino group ionises. A new band appears in the visible spectrum of the copper complex at ra. 800 nm as the five-coordinate complex is formed. Spectrophotometric titrations using the 800 nm band give a pK = 3.94 +/- 0.05. The kinetics of the acid-catalysed dissociation of the copper complex have been studied. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 9]