Organic Guanidines Involved Carbon Dioxide Activation And Catalytic Transformation

Carbon dioxide?CO₂?is the cheapest,non-toxic,and abundant resource in the carbon family.The conversion of carbon dioxide into high value-added fine chemicals with has become one of the research hotspots of scholars.As we all know,CO₂ is highly thermodynamically stable,and the key issue for CO₂ catalytic conversion is its activation.One of the most effective ways to activate CO₂ is to attack the carbon atom in the center of the carbon dioxide by nucleophiles or electron donors.Organic guanidine is one of the most basic organic bases due to resonance stabilization of the corresponding conjugate acids.The skeleton of guanidines can be easily modified into a variety of derivatives by introducing various functional groups onto the three nitrogen atoms of the molecule.As a commonly used organic strong base,it plays an important role in CO₂ activation and catalytic conversion,but there are problems such as singular reaction system,harsh reaction conditions?high temperature and high pressure?and low catalytic activity in most catalytic systems.This thesis focuses on the design and development of a novel reaction system for CO₂ activation and conversion based on organic guanidine compounds,thus providing a new way for the green transformation of CO₂.?1?In this thesis,the carboxylative cyclization of propargylic amides with CO₂ to oxazolidine-2,4-diones was achieved for the first time employing commercial available organic guanidine 1,5,7-triaza-bicyclo-[4.4.0]dec-5-ene?TBD?as an organocatalyst.This method allows for the efficient and selective synthesis of a variety of?Z?5-alkylidene1,3-oxazolidine-2,4-diones.Through the investigation of guanidine catalysts,solvents,reaction time and so on,the optimized reaction conditions were established as follow:TBD?5mol%?as catalyst,CO₂?1.0 atm?and reaction in THF at 25 ^oC for 1 h.Under optimal conditions,a series of propargylamide compounds containing different substituents can react with CO₂ to obtain the corresponding oxazolidine-2,4-dione products with high yields.The reaction mechanism was explored through in-situ infrared experiments,density functional theory?DFT?calculation and other means.Theoretical studies reveal that the bifunctional activity?base/H-bond donor?of TBD plays a key role in accelerating this reaction.?2?A series of N,N'-bis?imidazolyl?guanidine bases?BIG bases?were successfully designed and synthesized.The BIG bases system can efficiently activate CO₂ and its analogues CS₂ and COS to obtain the zwitterionic adducts.The corresponding structures were characterized by NMR,MS,IR and X-ray single crystal diffraction analysis.In the presence of water or tert-butanol,BIGs-CO₂ adducts will be converted into the corresponding ammonium bicarbonate or alkylcarbonate.The thermal stability of BIGs-CO₂ adducts was systematically investigated by thermogravimetric analysis?TGA?,and the decarboxylation temperature range was between 129¹59 ^oC.The BIGs system can effectively capture CO₂ in the simulate fule gas?10%CO₂,90%Ar?and even in the air.On this basis,a new organic catalyst system for the chemical conversion of CO₂ by BIGs-CO₂ adducts was developed.The cyclization reaction of propargylamidines with CO₂ to 4-imino-oxazolidine-2-ones was achieved for the first time.Under simulated flue gas?10%CO₂,90%Ar?,a series of4-imino-oxazolidine-2-ones containing different functional groups were prepared in moderate to high yields.