Ligands derived from C-aryl substituted derivatives of cyclen: Formation of kinetically unstable complexes with lanthanide(III) ions

The synthesis of C-aryl monosubstituted derivatives of 1,4,7,10-tetraazacyclododecane (cyclen) by metal templated reductive amination of triethylenetetramine with aryl glyoxals has been developed and shown to be widely applicable. Octadentate ligands derived from these C-substituted macrocycles form relatively labile eight-coordinate complexes, which dissociate when challenged with EDTA in aqueous solution at pH 5.5, suggesting their use in metal-transport processes rather than for applications in vivo.