Theoretical Studies On The Formation Of Imidazolium Heterocyclic Carbene-Carbon Dioxide Adducts And Synthesis Of Renzothiazeles Catalyzed By Imidazolium Acetate Ionic Liquid

Ionic liquids(ILs)composed by anions and cations entirely,are a novel class of liquid compounds in the room temperature or near,which exhibit fine properties that traditional liquids incomparable,such as high chemical and thermal stability,non-flammability,nonvolatility,good designability and reusability.These excellent physical and chemical properties make ILs show promising applications in many fields,including biochemistry,functional materials,organic synthesis and catalysis,gas adsorption and separation,electrochemistry and clean energy,and so,ILs are referred to as environmentally friendly and green functional materials.In recent decades,ILs have been attracted more and more attentions in academic and industrial areas.So far,the application and experimental researches upon ILs-catalyzed transformations and gas absorption have made remarkable progresses.However,compared with experimental researches,theoretical studies on ILs are relatively laggard.A lot of catalytic reaction mechanisms are still not clear,and there are no consistent conclusions for rationalization of experimental observations,which will limit utilization and exploitation of new high-efficiency catalysts.Therefore,it is necessary to implement the relevant studies and further to investigate the microscopic nature of the experimental observations.In this dissertation,we carried out a series of theoretical studies based on density functional theory(DFT)calculations.In order to investigate the mechanism details of reactions that imidazolium-based ILs involved:the absorption of CO2 and ILs-catalyzed organic synthesis.We analyzed the properties of dynamics and thermodynamics,and disclosed the micro mechanisms of ILs-catalyzed reactions,as well as aimed at to rationalize some experimental observations.Currently,we have obtained so many creative achievements,and boosted our comprehension and awareness of the significant chemical reactions and phenomena.The presented valuable results would afford important theoretical guidance for the design of new and efficient ILs-catalysts.The primary contributions and innovations of this dissertation can be listed as follows:1.The present work mainly focuses on the formation mechanism of normal and abnormal N-heterocyclic carbene-carbon dioxide adducts(NHC-CO2 and aNHC-CO2)in the reaction of imidazolium-based ionic liquids with CO2.Experimental research shows that,except for the normal NHC-CO2 adduct,the other two aNHC-CO2 adducts also been observed in the reaction system of[C2C1Im][OAc]with CO2.However,under the same experimental temperature and pressure,neither NHC-CO2 adduct nor aNHC-CO2 adducts was observed when the basic acetate anion of[C2C1Im][OAc]was substituted by the less basic[CH3SO3]anion.In order to illustrate the experimental phenomena,we mainly based on DFT calculations which mimicked by employing cluster model and hybrid explicit-implicit solvent model.By analyzing the values of thermodynamics and dynamics,it is indicated that the reaction of imidazolium-based ionic liquids with CO2 proceed via a concerted mechanism.As the solvation effect considered,we reasonably rationalized the competitive formation of NHC-and aNHC-CO2 adducts.Furthermore,compared with[C2C1Im][CH3SO3]-CO2 system,it is shown that the basicity of anion plays an vital role for the formation of the NHC-and aNHC-CO2 adducts.The calculation results will provide some crucial theoretical guidance for designing more efficient functional imidazole ionic liquid to adsorption gas.The corresponding results have been published in J.Phys.Chem.B(2017,121,10276-10284).2.The detailed reaction mechanisms for the synthesis of benzothiazoles catalyzed by imidazolium-based ionic liquids have been studied by DFT calculations.Firstly,the formation of the formoxysilane(FOS)intermediate has been studied.The calculated results show that the most favorable reaction pathway is OAc attacked SN2 mechanism.The Si-H bond is activated via concerted backside SN2 nucleophilic attacked by the negatively charged O atom of OAc-,and meanwhile,hydrogen atoms attack the carbon center of CO2 molecule.In this reaction,OAc acts as a major catalytic role.However,the imidazolium cation only forms hydrogen bond with the acetate anion to stabilize the reaction system.Then,we researched the reaction mechanisms for FOS intermediate reacting with 2-aminothiophenol.The results show that this involves three stages:hydrogen migrations,intramolecular cyclization and intramolecular dehydration.HO Ac molecule acts as a role of hydrogen transfer shuttle,which is very important for the proceeding of reaction.The rate-determining step is intramolecular cyclization.In addition,for the experimental phenomena that 5-nitrobenzothiazole as reactant,the yield is lower,we provide a rational interpretation:due to the nitro induced electron withdrawing effect.The current theoretical calculation results not only can elucidate the experimental phenomena well,but also provide in-depth research on the detailed reaction mechanism for the synthesis of benzothiazoles catalyzed by imidazolium-based ionic liquids.