DFT Investigations On The Mechanism Of Cyclohexane Dehydrogenation By Cluster-ion Dimer M₂⁺?M =V,Cr,Mn? In Gas-phase

In recent years,the transition metal as catalysis to catalyze alkanes are widely used in organic synthesis,these reactions usually involve the removal of hydrogen molecules or small alkane groups by activating C-H or C-C bonds.For example,the metal ions with higher reactivity in the first transition system can activate the C-H bond and the C-C bond of cyclohexane,and thus the surface or different-face dehydrogenation products can be obtained.In the present work,in order to explore the mechanism of cyclohexane dehydrogenation by transition metal dimers cations,we theoretically investigated the dehydrogenation mechanism of cyclohexane by V₂⁺,Cr₂⁺,Mn₂⁺.In the paper,in the light of the tradition transition state theory,the molecular orbital theory,reaction potential energy surface theory and referred to the Schwarz experimental results,the systems?V₂⁺,Cr₂⁺and Mn₂⁺catalyzed cyclohexane?were investigated by the DFT method based on the B3LYP,the structure of each station in the reaction has been optimized to obtain the potential energy surface?PES?and relative parameters,the reaction reactivity and the reaction mechanism has been analysed on the basic of this dates,providing a theoretical basic for further experimental study.The whole paper consists of four chapters.Chapter 1 reviews the background of theory of quantum chemistry,the development of transition-metal catalyzed the alkanes and the major work in this paper.In the second chapter,we summarized the theoretical background and the quantum chemistry calculation methods of this subject that offer us with userful and reliable quantum methods.In chapter 3,the dehydrogenation reaction mechanism of cyclohexane catalyzed by dimer cluster V₂⁺has been investigated at the B3LYP level of density functional theory.The calculations show the reaction is along two different paths after the first dehydrogenation,one is the same-face and the other is different-face dehydrogenation of cyclohexane with V₂⁺.Based on all kinetic data,the most favorable reaction path of cyclohexane with V₂⁺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?.Finally,we compared the dehydrogenation mechanism with Ti₂⁺,although their d orbitals interact with the antibonding orbital of matching symmetry in the set of(C₆H₁₂),the M₂+?M=V,Ti?has different dehydrogenation mechanism of the different-face concerning the?BDE of the M-M bond is different.Chapter 4,the same-face dehydrogenation reaction mechanism of cyclohexane catalyzed by dimer cluster Cr₂⁺and Mn₂⁺have been discussed at the B3LYP level of density functional theory.The calculations show that the reaction of Cr₂⁺takes place more easily along the low-spin potential energy surface and is a low-barrier or even barrier-free transformation,which is exothermic 76 kcal/mol.As for Mn₂⁺,the dehydrogenation reaction proceeds in mixed PES,three molecular dehydrogenation reactions are endothermic reactions,all the reaction is endothermal 16 kcal/mol.