Theoretical Study On The Mechanisms Of Cobalt-Catalyzed C-H Activation/Oxidation And Rhodium-Catalyzed Carbonyl-Ene Reaction

This thesis focuses on the mechanisms of two representative organometal-catalyzed reactions(high-valent cobalt catalyzed C(sp2)-H activation/oxidation and Rh(III) complex-catalyzed carbonyl-ene reaction). It is composed by four chapters: the first chapter covers the background of these two reactions and the debates around their mechanisms, and briefly introduce the research contents and significance; the second chapter is the theoretical study on the mechanism of the cobalt catalyzed C(sp2)-H activation/oxidation, while the third one performs the DFT calculations on the mechanism and stereoselectivity of Rh(III) complex-catalyzed carbonyl-ene reaction; the last chapter summarizes the work during pursuing the Master degree and shows the perspective on the future studies.Cobalt catalyzed C(sp2)-H functionalization is the subject of extensive interest in synthetic chemistry, but the mechanisms of many of these reactions(such as the Cobalt-catalyzed C-H oxidation) are poorly understood. In the second chapter, possible mechanisms including single electron transfer(SET) and the concerted metalation-deprotonation(CMD) pathways of the CoII/CoIII-catalyzed alkoxylation of C(sp2)-H bonds have been investigated systematically for the first time using the density functional theory(DFT) method. CoII(OAc)2 has been employed as an efficient catalyst in our previously experimental study, but the calculated results unexpectedly indicated that the intermolecular SET pathway with CoIII as the actual catalyst might be the most favorable pathway. To support this theoretical prediction, we have explored a series of Cp*CoIII(CO)I2 catalyzed C(sp2)-H bond alkoxylations, extending the application for cobalt-catalyzed functionalization of C-H bond. Furthermore, kinetic isotope effect(KIE) data, electron paramagnetic resonance(EPR) data, and TEMPO inhibition experiments also support the SET mechanism in both the Co-catalyzed alkoxylation reactions. Thus, this work should support an understanding of the possible mechanisms of the CoII/CoIII-catalyzed C(sp2)-H functionalization, and also provide an example of the rational design of novel catalytic reactions guided by theoretical calculations.The Phebim, a new ligand, is used in synthesis of Rhodium complex which catalyzed the asymmetric carbonyl-ene reaction. As far as we know, there is few mechanistic study on the catalysis involved Pincer Rhodium complex and such tentative work is reported in this thesis. In the third chapter, the possible reaction mechanisms of carbonyl-ene reaction catalyzed by Rh(III)-complex have been investigated using the DFT method. Six possible reaction pathways, including four Lewis acid-catalyzed reaction pathways and two non-catalyzed reaction pathways have been studied in this work. The calculated results indicate that the Lewis acid catalyzed pathways are more energetically favorable than the non-catalyzed pathways. For the Lewis acid-catalyzed pathways, there are four steps including complexation between Rhodium catalyst and trifluoropyuvates, C-C bond formation, proton transfer, and de-complexation processes. Our computational outcomes show that the C-C bond formation step is both the rate- and enantioselectivity-determining step, and the pathway leading to S-configured product is the most favorable one. The dication Rh(III)-complexes with different ligands(i.e., OTf-, Cl-, BF4-, and DCE) were considered as active catalysts, and the computed results indicate that the stereoselectivity can be improved with the presence of the counterion OTf-. All these calculated outcomes align well with the experimental observations. Moreover, the origin of stereoselectivity was elucidated by using second order perturbation theory analysis of Fock matrix in NBO basis and distortion/interaction analysis. Furthermore, the analysis of global reactivity index has also been performed to explain the role of the Lewis acid catalyst.