Supported tungsten imido and iridium pincer catalysts towards tandem hydrocarbon upgrading
Keywords: Surface organometallic chemistry
Catalysis
Organometallic

The principle aims of this thesis have been to develop well-defined heterogeneous catalysts for potential applications in tandem hydrocarbon upgrading. Catalysts for olefin oligomerisation and metathesis of &alpsha;-olefins and transfer hydrogenation of alkanes based on tungsten mono-imido and PCP pincer iridium complexes have been synthesised and immobilised on solid supports. The reactivity of the immobilised catalysts has been tested and compared with the precursor complexes. Co-immobilisation of the two complexes on the same support has been undertaken.
Chapter One provides a background to the olefin metathesis reaction and the development of highly active tungsten mono-imido and ruthenium alkylidene complexes. A summary of the implementation of the olefin oligomerisation reaction by industry and the development of highly active systems based on group 6 metals is discussed, along with a mechanistic discussion. The SOMC grafting procedure is considered and the immobilisation of catalysts for alkane and olefin metathesis and oligomerisation discussed; with focus on support materials: silica, sMAO and AMO-LDHs. Finally, tandem catalysis and its use in hydrocarbon upgrading and copolymerisation are presented.
Chapter Two details the synthesis of W(NR)Cl4(THF) complexes and their conversion to W(NR)Me3Cl complexes employing TMA. The products are characterised by single crystal X-ray diffraction, NMR and FTIR spectroscopy. W(NR)Me3Cl complexes are shown to be active for the selective dimerisation of ethylene to 1-butene. Attempted formation of possible intermediates in the reaction is presented, and efforts to form mimics for silica supported species are also discussed.
Chapter Three describes the preparation of AMO-LDHs for use as catalyst supports. The effect on the surface hydroxyl content and structural properties of these materials by thermally treating them under vacuum is analysed. Their capability to act as supports for ethylene polymerisation after impregnation with MAO and (nBuCp)2ZrCl2 is described.
Chapter Four investigates the immobilisation and characterisation of synthesised tungsten mono-imido complexes on sMAO, AMO-LDHs and silica, utilising SSNMR, FTIR and X-ray absorption spectroscopy. The reactivity of the grafted complexes towards ethylene oligomerisation is discussed. For the immobilised species effects of varying the imido ligand, temperature and solvent medium are reported. Attempts to immobilise ruthenium carbene complexes on AMO-LDHs and sMAO is detailed.
Chapter Five gives an account of the immobilisation of Ir(tBuPCP)HCl on sMAO which is characterised by SSNMR and FTIR spectroscopy. Molecular analogues of the supported species are synthesised and reactivity for the hydrogenation of ethylene compared. Transfer hydrogenation reaction with sMAO-Ir(tBuPCP)HCl and COA or ethane with TBE as a sacrificial H2 acceptor are discussed. Finally, co-immobilisation of W{N(2,6-F-C6H3)}Cl4(THF) and Ir(tBuPCP)HCl on sMAO was carried out and the solid characterised by SSNMR spectroscopy.
Chapter Six provides experimental details and characterising data for the preceding chapters. An Appendices with crystallographic data, and characterising spectra for each chapter is provided, while the Electronic Appendix contains a combined CIF and checkcif for all the molecular structures presented.