Theoretical Study On The Mechanism Of Dehydrogenation Of Cyclohexane Activated By Transition Metal Ions M~+(M=Sc,Ti,V) In Gas Phase

Transition metal-catalyzed alkanes was a very important chemical reaction in organic chemistry,which removes hydrogen molecules by activating the C-H bond of cyclohexane.For example,a metal ion having a higher reactivity in the first row of transition metal can activate the C-H and C-C bonds in the cyclohexane to obtain the same-surface and different-face dehydrogenation products.In order to further explore the mechanism of transition metal ion catalyzed dehydrogenation of cyclohexane,the reaction mechanism of transition metal ions Sc⁺,Ti⁺and V⁺to cyclohexane was studied.In this paper,the mechanism of Sc⁺,Ti⁺and V⁺catalyzed cyclohexane dehydrogenation has been studied at the B3LYP level of density functional theory?DFT?.The study was based on the reaction potential energy surface,transition state theory in quantum chemistry calculation,and referenced the research results of Schwarz et al.Finally,we obtained the stagnation point,optimizing configuration and related parameters which draw the reaction potential energy and analyzed the reaction mechanism in detail.The whole paper consists of four chapters:The first chapter summarizes the concept,development history and application of quantum chemistry calculation and summarizes the research progress of transition metal-catalyzed alkane molecules and the main work of this paper.The second chapter introduces the theoretical background and methods of quantum chemical calculation in this paper,which laid the foundation for our later research.In the third chapter,the dehydrogenation reaction mechanism of cyclohexane catalyzed by transition metal ions Sc⁺has been investigated.The calculations show the same-face and different-face dehydrogenationof cyclohexane with Sc⁺is a competing reaction.The most favorable reaction path of cyclohexane with Sc⁺is the same-face dehydrogenation and the reaction is a low-barrier or even barrier-free transformation after only one crossing takes place,the exothermicity of the whole reaction is 16 kcal/mol.And we also obtained the minimum energy crossing point?MECP?.And Sc⁺catalyzes the C-H bond in cyclohexane more easily than C-C bond catalysis.This important conclusion is consistent with the experimental data.In the fourth chapter,the dehydrogenation reaction mechanism of cyclohexane,catalyzed by Ti⁺and V⁺have been investigated at the density functional theory.The calculated results show that the frontier molecular orbits?FMO?of Ti⁺and c-C₆H₁₂ can match each other completely.The formation of encounter complex contributes 25 kcal/mol heatto the closed system,which provides sufficient energy to surmount the reaction barriers.The entire dehydrogenation reaction exothermed at 11kcal/mol.As for V⁺,the dehydrogenation reaction proceeds in mixed PES,The results show that V⁺has particularity that only activates C-H bonds.Three molecular dehydrogenation reactions are endothermic reactions,all the reaction is endothermal 6kcal/mol.