METAL-COMPLEXES OF MACROCYCLIC LIGANDS .33. EFFECT OF THE SIDE-CHAIN LENGTH ON THE ON OFF EQUILIBRIUM IN THE NI-2+- AND CU-2+- COMPLEXES OF 11-(2-AMINOETHYL)-1,4,7,11-TETRAAZACYCLOTETRADECANE AND 11-(3-AMINOPROPYL)-1,4,7,11-TETRAAZACYCLOTETRADECANE

Alkylation of 1,4,7‐tritosyl‐1,4,7,11‐tetraazacyclotetradecane with CH2O/KCN or acrylonitrile gave the corresponding cyanomethyl or 2‐cyanoethyl derivatives, which, by treatment with Na in BuOH, were detosylated and reduced to the macrocyclic pentaamines 1 and 2. The Ni2+ and Cu2+ complexes with 1 and 2 show a reversible pH‐dependent change in geometry, in which the side‐chain amino group is either coordinated to the metal ion (basic form) or protonated and, thus, non‐coordinated (acidic form). The length of the side chain determines the log Ka values of these protonation/deprotonation equilibria: 1.89 and ∼ 2.0 for the Cu2+ and Ni2+ complexes of ligand 1 with the 2‐aminoethyl side chain, and 6.17 and 7.43 for the Cu2+ and Ni2+ complexes of ligand 2 with the 3‐aminopropyl side chain. Copyright © 1990 Verlag GmbH & Co. KGaA, Weinheim