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 compared 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 presence 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.

Bis-functionalised 14-membered macrocycles can be prepared by a metal template synthesis involving [Cu(en)2]2+, formaldehyde and aromatic sulphonamides. The resulting CuII-diazacyclam derivatives exhibit a high inertness. In the solid state, the symmetrical macrocyclic units form extended chains or three-dimensional networks, due to hydrogen bonds involving NH and SO2 groups.Figure optionsDownload as PowerPoint slideHighlights
► Novel bis-functionalised CuII macrocyclic complexes prepared by a template synthesis.
► Aromatic sulphonamides act as efficient molecular padlocks in the cyclization process.
► The resulting CuII-diazacyclam derivatives exhibit a high inertness.
► In the solid state the macrocyclic units form extended chains or 3D networks.
► Diazacyclam units can be used in the design of supramolecular coordination compounds.