Metal complexes of macrocyclic ligands. Part XXXIII. Effect of the side‐chain length on the on/off equilibrium in the Ni²⁺ and Cu²⁺ complexes of 11‐(2‐aminoethyl)‐ and 11‐(3‐aminopropyl)‐1,4,7,11‐tetraazacyclotetradecane

Abstract

Abstract Alkylation of 1,4,7‐tritosyl‐1,4,7,11‐tetraazacyclotetradecane with CH 2 O/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 Ni 2+ and Cu 2+ 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 K a values of these protonation/deprotonation equilibria: 1.89 and ∼ 2.0 for the Cu 2+ and Ni 2+ complexes of ligand 1 with the 2‐aminoethyl side chain, and 6.17 and 7.43 for the Cu 2+ and Ni 2+ complexes of ligand 2 with the 3‐aminopropyl side chain.