Theoretical (DFT) Insights Into The Mechanism Of Nickel Catalyzed Chromium Carbene Transfer, Cyclopropane And Elimination Reactions

It is also generally accepted that transition metal-catalyzed cyclopropanation reactions proceed via a metal-carbene complex, which is formed by association of the diazo compound and the catalyst with concomitant extrusion of nitrogen. However, the transfer of heteroatom-stabilized carbene transformation also forms the metal carbene. The chromium carbene complex likely in equilibrium with the nickel carbenoids is postulated to represent the active form of the cyclopropane reaction. Alao, the dimerization reactions can occur between the nickel carbenoids and chromium carbene, which have been comprehensively studied of experiment, but there is little theoretical report about the reaction.In the paper, we chose several typical reactions that have been carefully studied using the molecular orbital theory, the tradition transition state theory as well as quantum chemistry theory, the selected systems have been investigated using comparison DFT- B3LYP and the polarized continuum model (PCM). The structures of the intermediates and the transition states along the reaction paths were fully optimized. The thermodynamic datums were all used to obtain the potential surface. The information of orbitals was also used to explain the reaction mechanism.The whole paper consists of four chapters. Chapter 1 is mainly about the development and application of quantum chemistry and the characteristics of organic gas-phase anion molecule reaction are also concerned. The second chapter, we will introduce the theory and computation methods that we based on. The contents of two chapters were the basis the background of our studies and offer us with useful and reliable quantum methods.In Chapter 3, a theoretical investigation the nickel-catalyzed transmetalation from chromium carbene complex has been presented. Firstly, nckel carbenoids were obtained by the chromium carbene transfer process. The nickel carbenoids can exist in two forms, namely (PH3)2NiCH2Cl)Cl and PH3Ni(CH2PH3)Cl2. Also, the chromium carbene complex is in equilibrium with the nickel carbenoids. So, the cyclopropane product comes from nickel carbenoids and chromium carbene. Nickel carbenoids proceeds through three pathways: methylene transfer, carbometalation and the reaction of a monophosphinic, chromium carbene also have the methylene transfer channel. The most favored reaction channel is chromium carbene with a barrier height only 9.63 kcal mol-1. The dimerization process occurs between nickel carbenoids and chromium carbene and between chromium. The most favored reaction channel barrier height is 5.41 kcal mol-1. So, the cyclopropanation reactions and the dimerization reactions are competitive. The solvent effect, which mimic dichloromethane, THF, and benzene, both have negligible consequence on the activation barriers.In Chapter 4, a theoretical investigation the cyclopropanation reactions catalyzed by nickel(0) and nickel(II) have been extensively investigated. The computation results show that the active catalytic species formed by a CH2 fragment and the Cl2Ni(PH3)2 is carbenoids (PH3)2Ni(CH2Cl)Cl (IMA) and (PH3)Ni(CH2PH3)Cl2 (IMB), but both the carbenes (Cl2NiCH2 (IMC), (PH3)3NiCH2 (IME) and (PH3)2NiCH2 (IMG)) and carbenoids (ClNiCH2Cl (IMD), Ni(CH2PH3)(PH3)2 (IMF) and Ni(CH2PH3)PH3 (IMH)) are active catalytic species obtained from NiCl2, Ni(PH3)3, Ni(PH3)2 and a CH2 fragment.The cyclopropanation reaction proceeds through either concerted or multistep reaction pathway. The computed results show that the two-coordinated nickel(II) catalyst is more active than the four-coordinated nickel(II) catalyst, but the two-coordinated nickel(0) catalyzed cyclopropanation reaction is similar with the four-coordinated nickel catalyst, because the four-coordinated nickel catalyst is formed two-coordinated nickel(0) catalyst in the cyclopropanation reaction by loss of a PH3 ligand. The nickel(0) catalyzed cyclopropanation reactions proceed easer than nickel(II). From the kinetic and thermodynamic viewpoints, the most favored reaction pathway is that nickel(0) catalyzed cyclopropanation reaction.