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Copper(ii) complexes of N-propargyl cyclam ligands reveal a range of coordination modes and colours, and unexpected reactivity†
Andrew J. Counsell,Mingfeng Yu,Mengying Shi,Angus T. Jones,James M. Batten,Peter Turner,Matthew H. Todd,Peter J. Rutledge
Dalton Transactions Pub Date : 02/08/2021 00:00:00 , DOI:10.1039/D0DT03736B
Abstract

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 N-propargyl cyclams and related compounds in the creation of diversely functionalised cyclam derivatives via copper-catalysed azide–alkyne ‘click’ reactions. 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-N-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-N-propargyl ligand is demonstrated via a ‘tetra-click’ reaction with benzyl azide, and the copper-binding behaviour of the resulting tetra-triazole ligand is characterised spectroscopically.

Graphical abstract: Copper(ii) complexes of N-propargyl cyclam ligands reveal a range of coordination modes and colours, and unexpected reactivity
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