Abnormal reactions of N-heterocyclic carbenes with phosphaalkenes


This thesis outlines the results from the project undertaken as a part of my MSc studies: the abnormal reactions of phosphaalkenes with N-heterocyclic carbenes (NHCs) to afford novel 4-phosphino-2-carbenes (IMesP). The focus is on investigating the mechanism of these reactions. Chapter 1 serves as a general introduction of phosphaalkenes, N-heterocyclic carbenes, and abnormal N-heterocyclic carbenes. The possible mechanisms of abnormal reactions of NHCs proposed by other researchers are briefly discussed as well. Chapter 2 describes the kinetic studies of the abnormal reactions. Specifically, the kinetic studies of the reactions of IMes with MesP=CPh2, MesP=C(4-C6H4F)2 and MesP=C(4-OMeC6H4)2, respectively. The kinetic and thermodynamic data are calculated in order to compare with DFT calculations. During the study, it is noticed the abnormal reaction is catalyzed by base whereas hindered by acid. In Chapter 3, the reactions of MesP=CPh2 with other NHCs are discussed. The NHCs include IMes-d2 (IMes with deuterium at C4 and C5 positions), IMesMe2 (IMes with –CH3 groups at C4 and C5 positions) and IMesMe (IMes with a –CH3 group at C4 position). The deuterium labeling experiments with IMes-d2 are designed to gain further insight into the issues with respect to the proton transfer in the abnormal reactions. The result shows the proton transfers intermolecularly in the process to form IMesP. The experiments related to IMesMe2 and IMesMe are conducted in order to expand the scope of reactions of phosphaalkenes with NHCs. It is revealed that IMesMe2 and IMesMe do not react with phosphaalkenes in the abnormal way. Finally, Chapter 4 describes a few metallic complexes synthesized from IMesP. Treating IMesP with excessive W(CO)5CH3CN only affords a product with tungsten binding at the carbene functionality. More interestingly, some dinuclear complexes are obtained by reacting IMesP with Pd(cod)2Cl2 and (tht)AuCl.Science, Faculty ofChemistry, Department ofGraduat

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