Theoretical Study On Nickel-catalyzed Coupling Reaction And Photocatalytic Oxidation Reaction Based On Density Functional Theory

Quantum chemistry is a fundamental subject that focuses on studying chemical problems at the microscopic level.In the development of chemical subject,the proposal of quantum chemistry is regarded as one of the most influential advances.Density functional theory as one of a mainstream quantum chemical calculation method.With the gradual improvement of theoretical chemistry research and the rapid development of computer technology,it plays an increasingly significant role in promoting the development of modern chemistry.Moreover,the combination of density functional theory research and experimental research has brought great changes to the development of the entire field of chemistry.At present,density functional theory has been successfully applied in many aspects such as chemical research,environment and biomedicine.It has irreplaceable advantages in compound property analysis,interpretation of experimental phenomena,elucidation of reaction mechanism,and prediction of reaction activity.The theoretical results obtained not only greatly enrich the research content of theoretical chemistry,but also have a good guiding role in experimental work.The research work of this thesis is based on the density functional theory to conduct in-depth theoretical research on some problems in nickel-catalyzed coupling reactions and photocatalytic oxidation reactions.Firstly,the mechanism of Ni-Catalyzed cyclization/carboxylation of bromoalkynes with CO₂ was studied in detail.Bromoalkynes play important roles in coupling reactions because they can show obvious stereoselectivity to form E-and Z-isomers when substituents are different.However,the origin of stereoselectivity is still unclear.By comparing the mechanism of syn-insertion of alkynes and E/Z isomerization and the radical process,it is found that the radical process is the dominant mechanism.Moreover,the NBO charge analysis of the intermediates in the reaction shows that the electrostatic effect caused by the difference in charge distribution of different intermediates is the main reason that leads to the syn-insertion of alkynes in Ni（I）species more easily than Ni（II）species.At the same time,the Ni（I）species and alkenylation products has two different directions in the radical process,thus forming products of different configurations.In addition,it was determined that the steric hindrance effect of different substituents is the main reason for the generation of stereoselectivity through the distortion/interaction analysis.The distortion energy of the substrate plays a leading role in the formation of the dominant product,and the steric hindrance effect becomes more and more obvious with the increase of the substituent structure.The second part of the thesis mainly uses density functional theory to study the process of visible light activation of potassium permanganate to degrade sulfamethazine.Firstly,the molecular properties of sulfamethazine were studied by Fukui function and Dual descriptor,and the possible reaction sites of sulfamedimethyldiazine were predicted as N₂₆,N₃₁,H₃₃ and H₂₇,respectively.According to the significance of f⁺,f^-and CDD values,it was determined that the degradation process of sulfamedimethyldiazine was mainly electrophilic reaction,which is also consistent with the properties of active species such as·OH,·O₂^-and Mn（III）measured in the experiment match.Further mechanism study found that different active species will degrade sulfamethazine through different mechanisms.The degradation of sulfamethazine is more favorable when·O₂^-forms·O₂H with H⁺in the system first,while Mn（III）participates in the reaction through electron transfer with Mn（IV）.In addition,·OH mainly attacks the hydrogen atom in the sulfamethazine molecule to undergo a hydrogen extraction reaction.The intermediate product generated in this process is very prone to Smiles-type rearrangement,which breaks the S-N bond in the molecule.By comparing the energy barrier in different reaction processes,it can be determined that sulfamedimethylpyrimidine degradation process is the dominant path.