Theoretical Investigation On The Activation Of C-H And C-C Bonds By Transition Metal Atoms In Gas Phase

The chemical reaction can be considered as the breaking of the old bond and the formation of the new bond. The chemists engage in implementing highly-selective target chemical bond breaking and synthesis for long. In particular, the activation of small molecules involved in transition metal is much more widely studied. The inert chemical bonds of hydrocarbons, C?C bond activation may compete with that of C?H and thus the reaction mechanism research draws wide attentions. For transition metals and their compounds, its chemical properties are closely related to the electronic structure, so the reaction involved in transition metal will appear "spin-forbidden" phenomenon, it doesn't contrary to "spin conservation" law. Due to spin flip of one electron, chemical reactions proceed in different potential energy surfaces, namely the occurrence of the "two-state reactivity" or "multi-state reactivity"(TSR / MSR), which will greatly affect the reaction barrier height and the distribution of resulting product.On the basis of the density functional theory(DFT) and coupled cluster theory, the reaction of 2-butyne catalyzed by second row transition metals Nb and Zr were investigated theoretically using Gaussian program. We successfully complete the geometry optimization along different potential energy surfaces. In addition, according to the calculated results of Crossing 2004 and GAMESS programs, the minimum energy path of titled reaction has been identified.The thesis consists of four chapters. The first chapter introduces the development of quantum chemistry reactions and theoretical background and the definition of two-state reactivity. The second chapter briefly introduces the relevant theoretical knowledge of quantum chemistry, and makes a detailed explanation on theories mentioned in this paper.In chapter 3, in the light of experimental research of Davis et al, the geometry in doublet and quartet of titled reaction pathways has been optimized using theoretical methods. Pathway c, which occurs in two different CH3, is the most favorable pathway among four H2-elimination pathways. Since the C?C bond activation process goes through a high energy barrier, the path c is the main reaction path among all possible pathways. Finally, based on the probabilities of intersystem at minimum energy crossing points(MECPs) along potential energy surfaces, the minimum energy reaction path was ascertained.In chapter 4, on the basis of reaction of 2-butyne catalyzed by Zr in the gas phase, we plotted potential energy surface diagrams both singlet and triplet spin states. Using Curtin-Hammett principle, activation processes of the C?H bond which occurs on the same and different CH3 group were quantitatively analyzed. Finally we only focused on the intersection at the entrance of the reaction, and accordingly determine the minimum energy crossing point(MECP). The probabilities of intersystem crossing at MECPs are calculated by Landau-Zener formula and the optimal path of different path has been certified.