Theoretical Mechanistic Study Of Decatungstate Photocatalyzed C-C Bond Cross-Coupling Reaction

Chemists have paid more and more attention to the efficient synthesis strategy of C-C bond through cross coupling reaction in organic chemical reactions,which has great application value in drug synthesis and chemical production.Among the single catalyst and synergistic catalysis can successfully activate C-H bond and realize C-C bond coupling reaction.However,it is difficult to capture the reaction intermediates with very short life in the laboratory.As a result,people cannot comprehensively and systematically recognize and understand the reaction mechanism,which hinders the efficient development of synthesis strategy to some extent.At present,theoretical calculation can be used as a means to study the reaction mechanism,simulate the possible intermediates and transition states in the reaction process,and calculate the corresponding thermodynamic and kinetic parameters.Therefore,this paper by using density functional theory（DFT）method to simulate a series of dectungstate（TBADT）photocatalytic C-C bond cross-coupling reaction,determine the different types of reaction mechanism,evaluate the influence factors of TBADT photocatalyst on the reactivity and selectivity,reveal nature of synergistic catalysis,and provide theoretical guidance for the design and development of new type C-C bond coupling reaction.In the first chapter,the basic concepts of catalysis,homogeneous catalysis and synergistic catalysis are introduced,the achievements and challenges of C-C bond coupling reactions in recent years are summarized.In the second chapter,we introduce the basic knowledge of quantum chemistry,density functional theory,transition state theory and enantioselectivity.The third chapter,the fourth chapter and the fifth chapter are the research work done by the author during the three years of studying for the master’s degree,which mainly include:1.The mechanism of TBADT photocatalyzed C-C bond coupling reaction between cyclohexane and quinaldine was studied in detail using density functional theory.The results show that the optimal reaction mechanism includes the excited state of TBADT mediates hydrogen atom transfer（HAT）mechanism,carbon radicals selectively added to quinaldine molecule,reductive dectungstate and oxidizing K₂S₂O₈ through single electron transfer（SET）process to complete the catalytic cycle,and finally through HAT process to obtain the required product.The carbon radical addition process is the rate-determining step,and the energy barrier is 10.0 kcal/mol.The results show that the minimum energy crossing point（MECP）can realize the transition of the ground state potential energy surface from triplet state to singlet state of the closed shell,and effectively reduce the reaction energy barrier.In addition,this chapter reveals the HAT mechanism of TBADT photocatalytic activation of C（sp³）-H bond,which is supported by fragment charge analysis and other means.2.Density functional theory（DFT）has been used to systematically study the synergistic catalysis mechanism for the formation of chiral carbon（R type）products with high selectivity betweenβ-methyl cyclohexenone and benzodiox-ole by TBADT/imine.The TBADT photocatalytic cycle undergoes HAT mechanism to generate carbon radical,the imine catalytic cycle is mainly divided into the following basic steps:β-methyl cyclohexanone and imine happen condensation reaction,carbon radical addition,the catalytic cycle of dectungstate is completed through single electron transfer,isomerization process and the final hydrolysis reaction to produce the target product.Benzoic acid plays a key role as an oxygen bridge in the reaction.In addition,the origin of reaction site selectivity and region selectivity was analyzed from the perspective of electronic effect,spatial effect and weak interaction.3.Density functional theory was used to study the mechanism of TBADT/Ni synergistic catalysis of the highly selective C-C bond coupling reaction between carbamoyl chloride and butanal.The mechanism includes the hydrogen atom transfer mechanism of TBADT activation of C（sp²）-H and the catalytic cycle of nickel(Ni^I-Ni^II-Ni^I-Ni^III-Ni^III-Ni^I).In the nickel catalytic cycle,it is mainly divided into the following basic steps:Ni^I compounds capture radical,single electron transfer between reductive dectungstate and Ni^II compounds to produce reduced Ni^Icompounds,then Ni^I compounds undergo oxidation addition,molecular acylation,and finally reduction elimination to regenerate Ni^I compounds.The molecular acylation process is not only decisive step of selectivity,but also acts as the rate-determining step of the reaction,and the energy barrier is 22.0 kcal/mol.The results provide theoretical assists for the development of new and cheap synergistic catalysis systems.