University of Tasmania
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Organolanthanide complexes of the calix[2]phenylene[2]pyrrolide macrocyclic ligand

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posted on 2023-05-27, 10:47 authored by Wilson, AJ
This thesis describes the synthesis and characterisation of lanthanide complexes of the macrocyclic ligand calix[2]phenylene[2]pyrrolide. The reactivity of these complexes is investigated and discussed. The reductive abilities of these complexes are tested through reaction with a series of pyridines and diazines. The flexibility and reactivity of the macrocyclic ligand is contrasted with a related, more rigid ligand. Chapter 1 establishes a background of the lanthanide metals and organolanthanide chemistry. Organolanthanide complexes of the ubiquitous cyclopentadienyl and pentamethylcyclopentadienyl ligands are introduced. Non-cyclopentadienyl ligands are briefly discussed, with a focus on the use of calix[4]pyrrolide as a macrocyclic ligand. Modifications of the calix[4]pyrrolide ligand are introduced, with a focus on trans-N,N'-dimethyl-meso-octaethylcalix[4]pyrrolide and meso-octamethyl-calix[2]phenylene[2]pyrrolide. Chapter 2 discusses the preparation and characterisation of precursors, key reagents and benchmark lanthanide(II) and (III) reference complexes. Conformational characteristics of these complexes are compared, with a focus on detail of the solid state structures obtained by single crystal X-ray diffraction. The contrasting structures of dilithiated calix[2]phenylene[2]pyrrole and an analogous potassium complex are described. Metathesis of the dilithiated macrocycle with samarium diiodide is shown to form complexes with samarium bound within the macrocyclic cavity. The effect of ancillary coordinated solvent molecules on the conformation of these complexes is investigated. The oxidation state of lanthanides in macrocyclic complexes is discussed. Unambiguous europium(II) and samarium(III) complexes are synthesised and characterised in order to identify whether conformational changes to the macrocycle indicate the oxidation state of the lanthanide metal centre. An interesting polymeric samarium complex free of ancillary ligands is described. Chapter 3 focuses on the preparation of a series of samarium calix[2]phenylene[2]pyrrolide complexes with pyridine and pyridine-based ligands. Where possible, analogous europium complexes are also described in order to compare their structural characteristics in the solid state. This investigation produced some unexpected results, such as an easily-reducible molecule observed acting as neutrally charged ancillary ligand. This Chapter covers the reactivity of selected pyridines, diazines, and sterically bulky linked- or fused-ring heterocyclic molecules with a samarium macrocyclic complex. Where relevant, comparisons are drawn with analogous samarium cyclopentadienyl-based complexes and complexes of the related macrocyclic ligand trans-N,N'-dimethyl-meso-octaethylcalix[4]pyrrolide. Concluding remarks and avenues of work warranting future investigation are presented in Chapter 4. The experimental syntheses and characterisation data of complexes prepared in this thesis are provided in Chapter 5. Single crystal X-ray diffraction data has been included electronically in the form of crystallographic information files (.CIF) in Appendix A.


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