This Thesis describes the synthesis and characterisation of titanium and vanadium complexes supported by tris(pyrazolyl)methane and tris(pyrazolyl)methide type ligands. The ethylene polymerisation capability of a selection of these complexes is investigated. Chapter 1 introduces homogenous Ziegler-Natta catalysis, including the role of titanium and vanadium imido complexes. The tris(pyrazolyl)methane ligand is also introduced, along with examples of its use in Group 4 and Group 5 complexes. Chapter 2 describes the synthesis and characterisation of new titanium and vanadium imido synthons. Chapter 3· describes the synthesis of vanadium imido complexes supported by fac-N3 ligands. The ethylene polymerisation capability of a selection of these complexes tested both at room temperature and under industrially relevant conditions will be described Chapter 4 describes the synthesis of new zwitterionic titanium imido complexes, supported by the tris(pyrazolyl)methide ligand. The synthesis of new titanium. imido tris(pyrazolyl)hydroborate complexes will also be described. The ethylene polymerisation capability of the new complexes will be described. Chapter 5 describes the synthesis of new titanium amidinate complexes, along with the ethylene polymerisation studies for selected complexes. A series of new tin-, magnesium- and zinc-tris(pyrazolyl)methide complexes will also be described. Chapter 6 presents full experimental procedures for all of the syntheses and polymerisation studies outlined in Chapters 2 to 5. Chapter 7 contains characterising data for all of the new compounds reported. Appendices A - X contain tables of selected crystallographic data for all new crystallographically characterised complexes described in this Thesis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo