Copper(ii) complexes of N-propargyl cyclam ligands reveal a range of coordination modes and colours, and unexpected reactivity. Issue 11 (26th February 2021)

• Record Type: Journal Article
• Authors: Counsell, Andrew J.; Yu, Mingfeng; Shi, Mengying; Jones, Angus T.; Batten, James M.; Turner, Peter; Todd, Matthew H.; Rutledge, Peter J.
• Is Part Of: Dalton transactions. Volume 50:Issue 11(2021)
• Page Start: 3931
• Page End: 3942
• Publication Date: 2021-02-26
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d0dt03736b
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Copper(ii ) complexes of cyclam ligands with 1, 2, 3 or 4 pendant alkynes have been prepared and characterised crystallographically and spectroscopically. An unexpected hydroalkoxylation reaction is observed, affording an enol ether from the alkyne. 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.