N-heterocyclic carbenes and their application as ligands for transition metal mediated synthesis
The present thesis describes a range of studies on the generation and application of N-heterocyclic carbene species capable of acting as ligands to a variety of transition metals. These novel complexes are then applied to a variety of common organic transformations. This thesis opens with two distinct introductory reviews. The first focuses on recent developments on the generation and application of N-heterocyclic carbenes as ligands. The second is concerned with the specific area of hydrogen transfer reactions. The results and discussion section firstly describes the successful generation of free 'pincer' type carbene moieties, their complexation with ruthenium and the application of these new catalysts to oxidation/reduction reactions. This new organometallic complexes are found to undergo hydrogen transfer reactions with a range of substrates (alcohol/carbonyl based) under a variety of conditions to yield the corresponding product (alcohol/carbonyl based). Subsequent studies are directed towards novel syntheses of the parent carbene precursor, the free carbene or the carbene-transition metal complex are then discussed. Preparation of a 'second generation' acac based ligands will be presented in the penultimate results and discussion section of the thesis. From this study, an array of functionalised carbene precursors is prepared, each possessing a masked carbene in a 1,5 relationship to a chelating oxo-substituent. Finally, this thesis discusses the attempted in-situ preparation of several transition metal complexes and their application a range of organic transformations. The thesis terminates with a full description of the experimental procedures used and the compounds prepared.