Hybrid phosphine-carbene ligands and their use in homogeneous catalysis

• Main Author: Lane, Rhian Jane
• Published: Cardiff University 2005
• Subjects: 547
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.583712

Several chelating phosphine-imidazolium salts have been synthesised and their activity tested in a number of palladium catalysed cross-coupling reactions. The in- situ catalyst testing was carried out using parallel screening techniques and moderate catalytic activity was shown by phosphine-imidazolium salts 2, 6 and 16. A number of synthetic routes have been successfully established which have provided viable paths into three main types of phosphine functionalised imidazolium salts. These methodologies have increased the scope for the potential number of interesting chelating phosphine-imidazolium salts. Several group 10 complexes of these new ligands have been prepared and characterised by the reaction of functionalised nucleophilic heterocyclic carbene's (NHC's), which were generated in-situ and reacted with suitable metal precursors. The solid state structure of complex 1 has been obtained, giving an insight into the properties of these chelating ligands. The relative trans influence of the phosphine and carbene functions have been measured for this bidentate ligand. Following the results of the in-situ catalyst testing, two pre-formed palladium(II) complexes, 1 and 2, were tested in the Heck and Suzuki cross-coupling with the reaction performed under stricter anaerobic conditions with more favourable results. The synthesis of several silver(I) complexes was also achieved by the reaction of phosphine- imidazolium salts with Ag2O3. The preparation of a Rh(I) phosphine-NHC complex was achieved via transmetallation.