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

Abstract

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°C and I = 0.1 mol dm −3 are log K 11 = 10.79, logK 12 = 9.37, logK 13 = 5.21, log K 14 = 2.78 and log K 15 = < 2.0. The formation constants for the equilibria Cu 2++ L+ H +⇄ CuLH 3+; logβ CuLH Cu 2++ L⇄ CuL 2+; logβ CuL are log β CuLH = 25.57 ± 0.03 and log β CuL = 21.63 ± 0.04. The pK for the ionisation of the protonated 10-amino group in the copper(II) complex, CuLH 3+⇄ CuL 2++ H + is 3.94±0.05 . The protonated complex is four-coordinated and becomes five-coordinate as the protonated amino group ionises. A new band appears in the visible spectrum of the copper complex at ca 800 nm as the five-coordinate complex is formed. Spectrophotometric tritrations 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.