Copper N-heterocyclic carbenes: novel electrochemical synthesis, stabilisation of variable oxidation states and unusual carbene reactivity

This thesis concerns the synthesis, structural characterisation and reactivity of a range of novel organometallic complexes. The research primarily focuses on N-heterocyclic carbenes as ligands, and their coordination to copper cations. A novel electrochemical synthetic procedure for the synthesis of CuI-NHC complexes is described. It was found that this procedure was suitable for the synthesis of a wide range of CuI-NHC complexes, containing either bulky, non-bulky or base sensitive functional groups. Furthermore, the synthetic procedure was found to be highly selective, producing [Cu(NHC)X]- type complexes when X is a coordinating anion, and [Cu(NHC)2]X-type complexes when X is a non-coordinating anion. The structural chemistry of CuI-NHC complexes containing pendant N-allyl groups was explored, with the resultant complexes displaying an array of coordination geometries about the CuI centres. By careful modification of these ligands, the first example of a CuI -NHC complex containing a CuI-alkene interaction was observed. The coordination chemistry of NHC ligands containing pyridyl substituents, which act as ancillary donors, was investigated. CuI -NHC complexes containing these ligands were found to be catalytically competent in an Ullmann-type etherification reaction. Additionally, exposure of solutions of some of these CuI-NHC complexes to atmospheric conditions allowed the crystallographic characterisation of rare examples of CuII-NHC complexes. Finally, the rational synthesis of a range of unusual CuII-NHC complexes was performed, with the resulting complexes being structurally characterised. It was found that, under certain circumstances, oxidative decomposition of the NHC ligand within the coordination sphere of a copper centre can occur. The formation of 2-haloimidazolium and C-C coupled bis-imidazolium salts, via oxidative degradation, was investigated using a combined experimental and computational study.