Copper and nickel complexes of 1,8-disubstituted derivatives of 1,4,8,11-tetraazacyclotetradecane

The stereoselective synthesis of various 1,8-disubstituted derivatives of 1,4,8,11-tetraazacyclotetradecane (cyclam) has been achieved and copper and nickel complexes prepared. For the 1,8-dibutyl derivative, the square-planar nickel(II) complex exists as two diastereoisomers, as revealed by crystallographic analysis. The structure of the copper(II) complex of this ligand confirmed that a strong in-plane ligand field was conserved in square-planar complexes notwithstanding the dialkylation at nitrogen. The structures of the copper(II) complexes of two 1,8-dicarboxymethyl derivatives of cyclam also reveal primary N₄ co-ordination with carboxyl oxygens occupying the elongated axial sites. The tricyclic ligand 1,5,8,12-tetraazatricyclo[10.2.2.2^5,8]octadecane is readily prepared from one of these diacids and the copper complex is kinetically stable in solution with respect to attack by hydrogen sulfide and to acid-catalysed dissociation.