Diverse reactivity of chelating and xanthine-derived copper-N-heterocyclic carbenes : catalytic activity, electrochemical reactivity and non-innocent behaviour

• Main Author: Rungtanapirom, Wasupol
• Other Authors: Willans, Charlotte E.
• Published: University of Leeds 2018
• Subjects: 540
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.752575

This thesis involves the preparation and exploration of the reactivity of a variety of organocopper complexes with N-heterocyclic carbene (NHC) ligands. The ligands contain either pyridyl/picolyl/allyl N-substituents or a xanthine-derived backbone. Structural modifications were made to the NHC ligands which were investigated for their catalytic activity when coordinated with Cu(I) in situ in an Ullmann-type etherification reaction. The ligand found to be the most active in catalysis was 1 allyl-3-picolylbenzimidazol-2-ylidene. The catalytic reaction was studied in more detail to assess deactivation pathways through reductive elimination of aryl imidazolium, dehalogenation and/or homocoupling of aryl iodide. In order to quantify the deactivation pathways, the preparation of novel aryl-imidazolium salts via C 2 selective arylation of imidazole, and of a biaryl via a Pd-catalysed was necessary, which led to more understanding the Cu-catalysed reaction and further side-reactions. The arylation of NHC-related species was exploited in the C 2 arylation of xanthine-derived compounds. The reactions were investigated via Cu NHC complexes, prepared using an electrochemical method. The kinetics of the arylation of a xanthine-derived Cu-NHC complex were studied using in situ 1H NMR and IR spectroscopies. Optimisation and a full understanding of this reaction has potential application in the detection of mismatched DNA bases. Further to the non-innocent behaviour of NHCs, an unusual Cu-mediated annulation reaction involving an allyl N-substituent was investigated. The reaction is proposed to occur via oxidative addition of C-Br to a Cu2Br2 cluster, Br migration and reductive elimination of the annulated product. Although most of the reactions discussed in this thesis are thought to proceed via a Cu(III) intermediate, the isolation of a Cu(III)-NHC has not been achieved to date. Attempts were therefore made to stabilise a Cu(III)-NHC using the macrocyclic effect, which may allow more understanding of the elusive Cu(III) NHC intermediate in a variety of reactions.