Synthesis of novel diazacyclam copper(II) complexes by template reaction involving sulphonamides as locking fragments

The diazacyclam copper(II) complexes [Cu(5)]2+, [Cu(6)]2+ and [Cu(7)]2+ were prepared by a metal– template synthesis involving ethylenediamine, formaldehyde and an aromatic sulphonamide acting as a ‘‘locking fragment’’. Similarly to other 14-membered macrocyclic ligands, these novel diazacyclam derivatives form square-planar copper(II) complexes. In the molecular structures, diazacyclam rings adopt the stable trans-III(R,R,S,S) configuration, typically observed in cyclam transition metal complexes. The secondary amino groups belonging to the macrocyclic moiety and sulphonyl groups of the pendant arms are involved in intermolecular hydrogen bond interactions which allow the formation of extended chains, as in the case of [Cu(5)]2+ and [Cu(6)]2+, or of a three-dimensional network, as observed for [CuII(7)]2+.
Vibrational and electronic spectra indicate a slight weakening of the metal–ligand interactions com- pared to the ‘‘plain’’ diazacyclam complex [Cu(4)]2+, which can be ascribed to the electron-withdrawing character of sulfonamide groups inserted into the macrocyclic framework.
Nevertheless, the complexes exhibit a considerable inertness toward demetallation even in the pres- ence of strong acid: a decomposition of 4%, 3% and 16% in 24 h was observed for [Cu(5)]2+, [Cu(6)]2+ and [Cu(7)]2+, respectively, when dissolved in DMSO 0.2 M in CF3COOH.
This synthetic route allows the preparation of symmetrical bis-functionalized macrocyclic systems which could be used in the design of more sophisticated supramolecular coordination compounds.