Metallized N-Heterocyclic Carbene Polymer Catalyzes The Conversion Of CO₂ To Oxazolidinones

Industrial waste gas emissions were the main reason for the increase in CO₂concentration in the atmosphere.The primary goal of reducing the content of CO₂ in the atmosphere was to reduce the emission of CO₂ from industrial waste gas into the atmosphere.Converting CO₂ into high value-added organic chemicals was one of the main means to reduce CO₂ emissions from industrial waste gases.However,due to the complex gas composition and low CO₂ content in industrial waste gas,catalysts with good selectivity and high efficiency were needed to convert CO₂ directly into high value-added organic chemicals.Porous organic polymers（POPs）have abundant porous channels and adjustable skeleton structure,and have the ability to absorb and enrich CO₂,and were prone to embed active groups and metal catalytic centers that activate CO₂.It was also ideal heterogeneous catalysts for CO₂.In this study,a novel porous organic polymer of Imidazoles,N-heterocyclic carbene porous catalyst,has been prepared and used to catalyze the reaction of CO₂ and nitrogen nucleophilic centers to achieve chemical fixation of CO₂under mild conditions.The specific contents and results were as follows:（1）Preparation of silver-containing N-heterocyclic carbene polymer（Ag OAc@NHC-1）and catalyzed the synthesis of oxazolidinones by the reaction of CO₂ with amines and alkanesThe porous N-heterocyclic carbene polymer NHC-1 was synthesized by copolymerization method,and the Ag OAc@NHC-1 catalyst was prepared by loading Ag OAc as the metal catalytic center.The BET surface area of the catalyst was 390.3 m²·g^-1.The adsorption capacity of CO₂ was 10.88 cm³·g^-1.The catalyst has good thermal stability when the temperature is less than 400℃.The basic skeleton structure of the catalyst was determined by solid state NMR and FTIR characterization.Finally,the successful loading of metal in the polymer was determined by TEM,XPS and ICP-MS,and the metal content was 1.93×10³ mg·kg^-1.Using AgOAc@NHC-1 as catalyst,the reaction of CO₂ with three-component reactionof 4-methoxyaniline and 1,2-dichloroethane was used as model reaction.The results show that Ag OAc has the best catalytic effect.The type and amount of catalyst,the type and amount of base,the amount of 1,2-dichloroethane,temperature and time were optimized by single factor method,and the optimum reaction conditions of the reaction system were determined as follows:When CO₂（100 vol.%）reacted with 4-methoxyaniline（1 mmol）,Ag OAc@NHC-1（40 mg）,Cs₂CO₃（3 mmol）,1,2-dichloroethane（2 m L）at 80℃and 0.1MPa atmospheric pressure for 24 h,the maximum yield of the model reaction was 91%.Under the optimal reaction conditions,9 oxazolidinones with different substituent groups were synthesized with amines with different electronic effects and steric hindrance,and the yield was between 71-93%.The product was obtained with 80%yield in gram-scale reaction.The catalyst can be recycled at least 5 times and still has good catalytic activity.The reaction mechanism was explored through the control experiment and the determination of intermediate products,and the possible reaction mechanism of the reaction system was proposed:CO₂ and substrate were adsorbed and activated by Ag OAc@NHC-1 catalyst,the generated compound intermediate reacted with activated CO₂ to produce oxazolidone compounds,and the catalyst was regenerated.（2）Preparation of copper based N-heterocyclic carbene polymer（Cu@NHC-5）and catalytic synthesis of oxazolidone compounds with low concentration CO₂ and propargylaminesThe porous N-heterocyclic carbene polymer NHC-5 was synthesized by copolymerization method and Cu（OAc）₂ was used as the metal catalytic center to prepare Cu@NHC-5 catalyst.The BET surface area of the catalyst was 341.4 m²·g^-1.The adsorption capacity of CO₂ was 13.39 cm³·g^-1.The catalyst has good thermal stability below 400℃.The basic skeleton structure of the catalyst was determined by solid state NMR and FTIR characterization.Finally,the successful loading of metal in the polymer was determined by TEM,XPS and ICP-MS,and the metal content was 1.04×10⁴ mg·kg^-1.Using Cu@NHC-5 as catalyst,the cyclization reaction of low concentration CO₂ with propargylamines compounds was studied under continuous bubbling condition.First,the reaction between CO₂ and N-benzylprop-2-yn-1-amine was taken as the model reaction.The results show that Cu（OAc）₂ has the best catalytic effect.The single factor method was used to optimize the type and amount of catalyst,the type of solvent,temperature and time,and the best reaction conditions were determined as follows:CO₂（30 vol.%）reacted with N-benzylprop-2-yn-1-amine（1 mmol）,Cu@NHC-5（80 mg）and acetonitrile（Me CN,4m L）as solvents at 50℃and 0.1 MPa atmospheric pressure for 7.5 h,and the optimal yield of the model reaction was 96%.Under optimized reaction conditions,the applicability of different reaction substrates was explored,and 21 oxazolidone compounds were successfully synthesized,with yields ranging from 36%to 98%,and most yields>80%.It contains three amino acid derivatives that play important roles in medicine and biology.Then,six different reaction substrates were reacted with CO₂ in lime kiln waste gas,and satisfactory yields were obtained.The gram test also obtained excellent yield of 92%;The catalyst can be recycled at least 5 times and still has good catalytic activity;The reaction mechanism was investigated by controlled experiments,in situ FTIR spectroscopy and HRMS,and the possible reaction mechanism of the catalytic system was proposed as follows:CO₂ and the reaction substrate are adsorbed by Cu@NHC-5 catalyst,the nitrogen in the catalyst activates CO₂ and the copper catalytic center activates C≡C in the substrate,and then cyclization reaction occurs with activated CO₂ to form oxazolidone compounds,and the catalyst regeneration.The application of this system in the study of chemical fixation reaction of CO₂ in lime kiln waste gas provides a research idea and theoretical basis for the realization of direct chemical conversion of CO₂ in industrial waste gas.