Mechanistic Study Of Transition-metal Catalyzed C-H And C-C Bond Activation Reactions

Transition-metal catalyzed C-H and C-C bond activation/functionalizations are significant for organic synthesis. In this thesis, theoretical study was conducted to solve the mechanistic issues of important organic reactions emerging in C-H and C-C acti-vation areas. The first chapter of this thesis reviews the advantages, challenges and achievements of C-H and C-C activation, together with the development of quantum chemistry. From the second chapter to the fourth chapter are the summary of research projects during my PhD study.The second chapter of this thesis describes the theoretical study of regio-selectivity in Cu(I)-catalyzed heteroarenes C-H activation. Through examining the relationship be-tween C-H activation barrier and varies factors (i.e., pKa, bond dissociation energy, re-action energy), we found that the linear relationship exists between the activation barrier and the reaction energy. This indicates that the regio-selectivity of C-H activation could be predicted by calculating the reaction energy. Furthermore, the relationship between reaction energy and the energy difference of Ar-[Cu] and Ar-H bonds was illustrated after deducing equations. Therefore, it is possible to predicte the regioselectivity in C-H activation by simply calculating the bond dissociation energies of Ar-[Cu] and Ar-H bonds. This study also denotes that the dissociation of Ar-H bond and the formation of Ar-[Cu] bond make important contributions to the activity of C-H bond.In the third chapter, we conducted a mechanistic study on Ni-catalyzed decar-bonylative/C-H coupling and C-H/C-O coupling reactions between azoles and aryl carboxylates. These two reactions reflect an interesting chemo-selectivity determined by different carboxylic ester, such as aryl carboxylates and phenolic ester. Considering the commonly accepted decarbonylative/C-H mechanism cannot explain the result of kinetic isotope experiment, we proposed a new mechanism, which includes C(acyl)-O bond, base-promoted C-H activation of azole, CO migration, and reductive elimina-tion. Meanwhile, the C-H/C-O coupling reaction proceeds through oxidative addition of C(phenyl)-O bond, base-promoted C-H activation, and reductive elimination steps. The steric hindrance of acyl substituent determines the observed chemo-selectivity. In details, the decarbonylative C-H coupling product is favored for less-bulky group sub-stituted C-O electrophiles (such as aryl ester), while C-H/C-O coupling product is pre-dominant for the bulky group substituted C-O electrophiles (such as phenyl pivalate).The fourth chapter of this thesis concentrates on the mechanistic research on Rh-catalyzed direct coupling and decarbonylative coupling reactions of alkene- benzocy-clobutenone. The computational results indicate that both the direct and decarbonylative coupling reactions start with the oxidative addition of C(acyl)-C(sp2) bond of alkene-benzocyclobutenone. The following C-C reductive elimination or β-H elimination-decarbonylation-reductive elimination leads to the direct or decarbonylative coupling reaction, respectively. Furthermore, the coordination features of different ligands were found to significantly influence C-C reductive elimination and decarbonylation step: the bidentate ligand (DPPB) facilates reductive elimination, leading to the direct cou-pling reaction; the monodentate ligand favors decarbonylation, thus decarbonylative coupling is facile.