An efficient protocol for the direct synthesis of N-tetraalkylated derivatives of the azamacrocycles cyclam and cyclen has been developed, using a partially miscible aqueous–organic solvent system with propargyl bromide, benzyl bromide, and related halides. The method works most effectively when the reaction mixture is shaken, not stirred. A crystal structure of the N-tetrapropargyl cyclam derivative 1,4,8,11-tetra(prop-2-yn-1-yl)-1,4,8,11-tetraazacyclotetradecane diperchlorate is reported.
The coordination chemistry of N-functionalised cyclam ligands has a rich history, yet cyclam derivatives with pendant alkynes are largely unexplored. This is despite the significant potential and burgeoning application of...
<p>Herein we describe single crystal
X-ray diffraction and spectroscopic investigations of the coordination
chemistry of copper(II) complexes of cyclam derivatives with between 1 and 4
pendant alkynes. The crystal structures of these copper complexes unexpectedly reveal
a range of coordination modes, and the surprising occurrence of five unique
complexes within a single recrystallisation of the tetra-<i>N</i>-propargyl cyclam ligand. One of these species exhibits weak
intramolecular copper-alkyne coordination, and another is formed by a surprising
intramolecular copper-mediated hydroalkoxylation reaction with the solvent
methanol, transforming one of the pendant alkynes to an enol ether. Multiple
functionalisation of the tetra-<i>N</i>-propargyl
ligand is demonstrated <i>via</i> a ‘tetra-click’
reaction with benzyl azide, and the copper-binding behaviour of the resulting
tetra-triazole ligand is characterised spectroscopically.</p>
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