Coordination chemistry of N-tetraalkylated cyclam ligands—A status report

N-alkylation of macrocyclic amines has a significant impact on their properties as ligands for metal ions. This article examines the development of the coordination chemistry of N-alkylated cyclam ligands from its inception in 1973 with the first report of tetramethylcyclam. Emphasis is on: (1) the stereochemistry of metal complexation, including the effects of inclusion of functional groups in one or two of the N-alkyl groups; (2) the effect of N-alkylation on the metal–donor interaction; (3) the ability of tertiary amine ligands to stabilize complexes of metal ions in unusual oxidation states.