Synthesis and characterisation of pendant-arm amino derivatives of 1,4,7-triazacyclononane and alkyl-bridged bis(1,4,7-triazacyclononane) macrocycles and complexation to Cu(II)

Abstract

The new pentadentate and bis(pentadentate) ligands 1-methyl-4,7-bis(3-aminopropyl)-1,4,7-triazacyclononane 6 and 1,2-bis[4,7-bis(3-aminopropyl)-1,4,7-triazacyclonon-1-yl]ethane 14 have been synthesised by reaction of acrylonitrile with the corresponding macrocyclic precursors and subsequent reduction of the nitrile groups with BH3·THF. Cu(II) complexes of the two ligands having formulations [Cu(6)][BF4]2 and [Cu2(14)][PF6]4·6MeCN, respectively, have been prepared and structurally characterised. Both complexes exhibit distorted square-based pyramidal geometries about the metal centres with the two primary amino groups belonging to the pendant arms occupying basal positions [Cu–Nap 2.257(6), Cu–Neq 2.026(6)–2.074(5) Å for [Cu(6)]2+, and 2.337(2) and 2.038(3)–2.085(3) Å for [Cu2(14)]4+]. The binuclear complex [Cu2(14)]4+ is centrosymmetric about the ethane bridge with the two pentadentate compartments oriented away from one another to give a transoid anti-configuration with a MeCN molecule interacting with each Cu(II) centre at 2.710(4) Å. Both complexes have also been characterised by electronic and EPR spectroscopy and by cyclic voltammetry, and their properties compared to those of Cu(II) complexes of analogous macrocyclic ligands having 2-methylpyridyl pendant arms.