Theoretical Study On The Reactions Of Ethene And Propene With YNH~+ In The Gas Phase

Over the past two decades, gas-phase transition metal cation chemistry with hydrocarbons has been the subject of intensive experimental and theoretical research due to the crucial role that these species play in several fields such as organic chemistry, biochemistry, and catalytic research, which provides important mechanistic information and models for analogous reactions. Generally, among potentially important types of hydrocarbon activation by d-block elements, C-H activation is initiated by electron-rich metal center via oxidative insertion pathway which is predominant. In contrast, low-valence d0 systems preclude the oxidative insertion of the metal center into the C-H bond as the initial step and, hence, must undergo different mechanisms. In order to probe alternative mechanisms of C-H activation by low-valence electron metal complexes in the gas phase besides oxidative insertion, one of our current focuses, therefore, has been on the reaction of YNH+ with olefin.In the paper, on the basis of the molecular orbital theory, the tradition transition state theory as well as Freiser and co-workers' experimental results, the systems choosed have been carefully investigated using Density Functional (DFT) Methods. The structures of the reagents, the reaction products and the transition states along the reaction paths have been obtained, and then obtained the reaction surfaces, the spectrum datum, the thermodynamic datum as well as the information of orbitals. The reaction mechanism has been argued deeply using these data, which could provide helpful evidence for further experimental studies.The whole paper consists of four chapters. Chapter 1 mainly reviews the reactivity patterns of hydrocarbon activation by d-block elements and our main work in this paper. The second chapter summarizes the theory of quantum chemistry and calculation methods of this paper. The contents of two chapters were the basis and background of our studies and offer us with userful and reliable quantum methods.In chapter 3, the reaction of YNH+ with propene was selected as a studied system.The calculated results show that the processes of loss H₂ and CH₄ coexisted in the reaction system and they are parallel reactions. Elimination of H2 corresponds to four reaction paths (path1—4) to yield YC3H5N+ while Elimination of CH4 corresponds to two reaction paths (path 5 and 6) to yield YC2H3N+. All the reaction paths proceed in a two-step manner via two multi-centered transition states. By contrast, dehydrogenation is the predominant process, which shows thatβ-CH₃ transfers are more difficult than theβ-H transfers.In chapter 4, the reaction of YNH+ with ethene was selected as a studied system. The calculated results show that the processes of loss H₂ and NH₃ coexisted in the reaction system and they are competitive reactions, in wich the path 1 proceeds in a two-step manner via two multi-centered transition states and the path 2 proceeds in a four-step manner via four transition states. By contrast, dehydrogenation is the predominant process, which is in good agreement with the experimental observation. Moreover, when ethene is superfluous in the reaction system of YNH⁺ + ethene, the predominant product (YC₂H₃N⁺) of path 1 can further react with it to form more stable six-membered metal-containing ring YC4H5N+, which is feasible thermodynamically and dynamically.