Cyclometallated N^C and N^C^N Complexes of Pyridines and Pyridones: Synthesis and Reactivity

In order to develop the applications of transition-metal complexes in the coordination chemistry and catalysis, the synthesis of cyclometallated N^C and N^C^N complexes of pyridines and pyridones are described. Chapter one presents an overview of C-H activation: its importance and mechanisms, ligand types, and multifunctional ligands and their role in catalysis. Chapter two describes the synthesis and characterisation of cyclopalladated complexes with a variety of 6-aryl-2-methoxypyridine ligands (aryl = H 2.5, 4-MePh 2.6, 4-CF3Ph 2.7, 4-FPh 2.8 and 2-MePh 2.9). Further reaction chemistry of these complexes, including disassembly, ligand exchange and stoichiometric reactions are discussed as well. The dimeric PdII complexes are shown to be efficient catalysts for the aerobic oxidation of benzyl alcohol. The reactivity of 2.6 towards two different AuIII sources, H[AuCl4] and K[AuCl4], are described in this chapter. Chapter three shows divergent behaviour in the reactivity of 6-aryl-2-pyridones from those in Chapter 2. Cyclopalladation of the 6-aryl-2-pyridones proceeds smoothly forming the acetate-bridged complexes; however, on standing in solution the dimeric complexes undergo slow pyridinol-pyridonate conversion to the tetrameric species with loss of acetic acid. Different behaviours are also observed in all the subsequent reactions. The electronic effect of different substituents (in particular H vs Me vs CF3) in reactivity is investigated. The role of the ortho-hydroxy group in the stability, reactivity and hydrolysis of PF6 and BF4 is demonstrated as remarkable differences have been shown between the two types, pyridine- and pyridone-based complexes. Chapter four describes the synthesis of novel symmetrical N^C^N pyridine- and pyridone-based ligands and investigates their reactivities and selectivity towards several transition metals, such as PdII, PtII, HgII and AgIII. A new microwave method is developed to afford cyclometallated N^C^N complexes of pyridones. All the experimental work and full characterisation data of the ligands and complexes described in this thesis are detailed in Chapter 5.