Theoretical Investigation On The CO₂-splitting Reaction Mechanism Catalyzed By Transition Metal Rhenium Complex In Gas Phase

In recent years,it has been found that there is such a phenomenon in the reactions in which most transition metal compounds participate,and the reactants and products are on different spin state potential energy surfaces.As more and more reaction mechanisms are discovered,chemists Schr?der,Shaik,and Schwarz called such reactions"two-state reactions".In other words,for reactions involving transition metal complexs,the electrons are arranged in parallel on the d orbit of the transition metal by unpaired ways.It is easy to cause the electrons to spin over due to the spin orbit coupling interaction,causing the spin state change of the reaction system.Therefore,the corresponding reaction sructure in the region where the spin state changes is called the minimum energy crossing point?MECP?.In addition to considering the local minima?products and intermediates?and saddle points?transition states?on the reaction coordinates,we also need to consider all MECPs in order to more properly describe the reaction mechanism and more fully understand the kinetics of the spin-forbidden reaction.The current research hotspots of the two-state/poly-state reaction in theoretical chemistry are focused on the inter-system crossing probability and the transition mechanism of transition metal d-orbital electrons.These studies can help us better understand the two-state reaction.Whether electrons can undergo spin transitions or not,we generally use the transition probability of crossing point to evaluate.Here we need to focus on the spin-orbit coupling and the slope between the two potential energy surfaces.It is well known that the magnitude of the spin-orbit coupling?SOC?constant determines the magnitude of the transition probability of crossing point.Therefore,in this paper,Crossing packages are used respectively to find the minimum energy crossing point,then the spin-orbit coupling constant and inter-system crossover probability also are calculated.Based on density functional theory?DFT?,this paper uses Gaussian 09 program to study the gas-phase reaction of transition metal compounds and CO₂.The relevant transition states and intermediates were found to determine reaction paths,and the structure of all saddle points in the reaction system was optimized.Later,a high-precision coupled cluster method was used to obtain more accurate thermodynamics and kinetics energy and molecular orbital information.The full text consists of four chapters.The first chapter mainly introduces the development process of quantum chemistry,the research status of metal ion,metal oxides,metal clusters,and metal hydride catalyzed CO₂.The second chapter mainly introduces quantum basic theory of chemistry.In Chapter 3,in order to further explore the detailed reaction mechanism of[Re?CO?₂]⁺complex activated carbon dioxide,the CCSD?T?method was used to determine the relevant potential energy surface.The crossing point is determined by using a partially optimized method.The results show that the larger SOC(155.37cm^-1)in the spin forbidden region and the probability of intersystem crossing cause electrons to spin at the MECP and enter the low singlet potential energy surface.The non-adiabatic rate constant k is estimated very fast,so the transition state?¹TS1?is the speed-determining step.In addition,the electronic structure of the oxygen atom transfer process was further analyzed by localized molecular orbitals and Mayer bond levels.The analysis found that the main bonding orbital is the electron contribution from p?O?in carbon dioxide to the empty d?Re?orbital.In chapter 4,we mainly studied the two-state reaction mechanism of ReO₂-catalyzed CO₂,determined the appropriate related functionals and basis sets,and used the activation tension model to make correlations to the path transitions of important transition states.Analysis and related electronic structure analysis using NBO program.The calculation results show that the transition states with lower barriers are due to the relatively small activation deformation energy?E_strain of[ReO₂]^-and CO₂,and their interaction energy is quite large.Therefore,the decrease in the activation energy barrier ³TS1 is due to the more stable interaction energy?E^?_int.However,this interaction energy is mainly because Re atoms behave as both electron acceptors and electron donors,forming a special the electron donor-acceptor interaction with CO₂.The difference between[ReO₂]^-,[ReO₃]^-and[ReO₄]^-catalyzed CO₂ depends on the energy difference between the rhenium oxide LUMO and the HOMO orbit of CO₂,that is,the 5d empty orbit energy of[ReO_x]^-.Therefore,the reaction of[ReO₃]^-and[ReO₄]^-catalyzed CO₂ does not easily occur?In addition,a weighted average with statistical concepts based on the Landau-Zener?LZ?model was used to evaluate the probability of MECP,the reaction rate was calculated,and the reaction path was explained.