Unsymmetrical, Monoanionic Pincer Ligands for Titanium and Palladium

In this thesis, the synthesis, characterisation and coordination chemistry of a series of related [N,NPyN] and [N,NPy O] monoanionic pincer ligands, together with some reaction chemistry of the metal complexes is described. In Chapters 2 and 3, the synthesis and characterisation of novel [N,NPyO] and [N,NPyN] pro-ligands and reaction chemistry with palladium(II) starting materials to form square planar complexes of the type [(N,NPyX)PdL] (X = O, NH, L = OAc, Cl, I, MeCN, Py, Ph) is described. The pro-ligands and the metal complexes have been characterised by a combination of multinuclear NMR spectroscopic techniques, IR spectroscopy, mass spectrometry and, for selected examples, by single crystal X-ray crystallography; salient spectroscopic and structural data are discussed. The stoichiometric reactivity of the [(N,NPyO)PdCl] and [(N,NPyN)PdPh] species towards [p -Tol2I][OTf] and the electrophilic fluorinating agents Selectfluor and XeF2 are disclosed. Thereby, an assessment of the ability of these pincer ligands to support transient high-valent palladium(III) and palladium(IV) complexes has been made. It is established that the N-(4-i-PrC6H4) substituted [(N,NPyO)PdCl] complexes are able to facilitate C-Cl bond forming reactions with greater conversions than their N-(2,6-i-PrC6H3) substituted analogues, and that the reaction of [(N,NPyN)PdPh] [Ar = (4-i-PrC6H4)] with Selectfluor and XeF2 yields biphenyl via complex reaction pathways. In Chapter 4, the use of the same pro-ligands in the synthesis of relatively rare examples of titanium(IV) complexes containing tridentate ligands, [(N,NPyO)TiX3] (X = F, Cl), is described. These complexes have been characterised by multinuclear NMR techniques, mass spectrometry and, for selected examples, by single crystal X-ray crystallography. Investigations reveal that both classes of titanium(IV) complexes are suitable for use as ethylene polymerisation pre-catalysts in the presence of the co-catalyst, MAO. The activity of chloride-containing catalysts is higher than their fluoride-containing analogues. However, the catalysts are highly ligand-dependent; an activity of 340 g(PE) mmol-1 h-1 bar-1 is obtained for an [(N,NPyO)TiF3] complex supported by a sterically bulky tridentate ligand system and these systems are the most active ethylene polymerisation catalysts known which comprise a Ti-F bond.