Applications of Amido-N-Heterocyclic Carbene Ligands in Bifunctional Catalysis
thesisposted on 12.03.2013, 15:47 by Christopher Gary Daly
This thesis describes the synthesis of amino/amido-N-heterocyclic carbene (NHC) complexes of late transition metals, in order to investigate bifunctional catalysis involving a metal-amido bond. Chapter one introduces bifunctional catalysis, with an emphasis on the mechanism of bifunctional bond-breaking during catalytic reactions. Mechanisms of C-H activation are described and the features of bifunctional C-H activation (AMLA) discussed. The ligand properties, and methods of synthesis, of NHC and amido ligands are described, and the choice of ligand to investigate bifunctional catalysis rationalised. Finally, the detailed aims and objectives of this research are stated. Chapter two gives an overview of the synthesis of N-donor functionalised imidazolium salts, as precursors to functionalised NHC ligands. The synthesis of imidazolium salts that are precursors to tridentate (CNC) amido-bisNHC pincer ligands and bidentate (C,NR) amino/amido-NHC ligands are described. Chapter three introduces the synthesis of pincer complexes containing NHC or amido donors. The syntheses of (CNC) amido-bisNHC complexes of palladium, platinum and nickel are described. Investigations into the stoichiometric bifunctional reactivity of a (CNC) Pd complex are also discussed. Chapter four describes the synthesis of complexes containing an amino/amido-NHC (C,NR) ligand of palladium, platinum, ruthenium, rhodium and iridium. The stoichiometric reactivity of an iridium amido complex towards electrophiles is reported. Chapter five reports the reactivity of amino/amido-NHC complexes in bifunctional catalysis. (C,NR) ruthenium, rhodium and iridium complexes are shown to be active precatalysts for the transfer hydrogenation (TH) of ketones. Evidence is presented that suggests that the metal-amido bond is participating in a bifunctional mechanism for TH. (C,NR) complexes of palladium are shown to be active precatalysts for the direct arylation (DA) of 2-n-butylfuran; however, DA of oxazole and thiazole proceeds only on addition of cocataytic pivalic acid. Evidence suggests that a metal-amido species is not involved in a bifunctional mechanism; a palladium-pivalate species is implicated in the C-H activation step of DA. Chapter six summarises the conclusions of the work reported in this thesis; potential future work is highlighted and discussed.