Synthesis and characterization of transition metal complexes of a 16-membered (N4) macrocycle with tetrapeptide features

A series of macrocyclic complexes of the titled ligand, [16]1,5,6,8,9,13,14,16-octaza-2,4,10,12-tetraoxo-cyclo decahexane (OTCH) with cobalt(II), nickel(II) and copper(II) have been prepared by the action of formaldehyde on the respective bis(1,5-diamino-1,5-diaza-2,4-dioxopentane) metal complexes. The coordination template effect governs the steric course of the reaction. The structure of the complexes has been elucidated on the basis of IR, electronic and ESR spectral data, magnetic properties and electrochemical studies. All the complexes except copper(II) give two well defined reduction steps corresponding to the formation of a species where the metal can be formally assigned to an oxidation state of +1 and zero. Copper(II) complexes show one reduction step corresponding to zero oxidation state.