Theoretical Investigation On The Activation Of CH₃CN And HCN By Ti And U In Gas Phase

In recent years,it has been found that the reaction of transition metal catalyzed organic small molecules with the phenomenon on ground state reactants and ground state products in different spin state,that is,the reaction does not comply with the law of conservation of spin.This reaction has been named two-state/multiple-state reaction?TSR/MSR?.In order to understand the detailed process of this kind of reaction?including potential energy surface crossing,spin inversion and competing reactions?,achieve the desired response highly selective,the researchers have never stopped exploring them.Transition metals withunfilled valence d orbitals,whose atoms and ions as well as weak ligand coordination complexes generally have high-spin ground state,which is easy to form complex compounds with the electron-rich organic molecules,there may be structural rearrangements or spin flip during the period to avoid the high energy barrier to allow the reaction into the low energy reaction channel,therefore,the reaction mechanism between the transition metal and the electron-rich organic matter is very meaningful for understanding the spin inhibition reaction.In this paper,based on density functional theory?DFT?and coupled cluster theory,the Gaussian program is used to calculate the reaction of transition metal with acetonitrile and nitrile in gas phase,all stationary point on the potential energy surfaces are optimized;the minimum energy crossing point is obtained by means of Crossing 2004 program and GAMESS program,the spin-orbit coupling effect is analyzed,and finally the lowest energy path has been identified.This paper is divided into four chapters.The first chapter briefly introduces the development background of quantum chemistry,the background and progress of the TSR/MSR,and the research purpose and content of this paper.The second chapter mainly introduces some basic theories and methods of quantum chemistry used in this paper,which provides strong theoretical support for the research work of this paper.In the third chapter,Reaction mechanism of transition metal Ti,actinide element U and CH₃CN in the gas phase is studied.The geometrical configuration of the stationary points on all potential energy surfaces of the reaction system is optimized,the crossing points and the lowest energy crossing point?MECP?of different spin potentials are determined,the spin-orbit coupling constants?SOC?,the probability of intersystem crossing of different potential surfaces and the rate constants are discussed.In addition,for a deeper explanation of the reaction path,the chemical bonding evolution in this intriguing reaction was also analyzed by different methods including electronic localization function?ELF?,atoms in molecules?AIM?and natural bond orbital?NBO?,finally,the minimum energy response path is determined.In the fourth chapter,the reaction mechanism of HCN catalyzed by Ti in the gas phase are studied,all the possible intermediates and transition states in the reaction system are optimized,and the corresponding configuration and energy are obtained.;initial reaction site was predicted;all possible paths were analyzed by means of the activation strain model and Curtin-Hammett principle,finally,the main product and the most likely reaction path are identified.