Catalytic Effect Of Transition Metal Complexes On Carbon Dioxide Conversion To Polycarbonate

As one of the main gases that cause greenhouse effect,CO₂ has destroyed the ecological balance in nature and threatened the survival of various organisms.Nevertheless,the cheap,abundant and safe characteristics of CO₂ make it one of the main research directions of green chemistry.The conversion of CO₂ into polycarbonate has been extensively studied and has entered the industrialization process.One of the major problems facing the industry at present is the development of new high activity and low-cost catalysts.The synthesis method of schiff base catalyst?SalenMX?is simple and easy to modify.Compared with other catalytic systems,it is characterized by mild reaction conditions,high catalytic activity,high selectivity of polymerization products,narrow molecular weight distribution,and clear catalytic mechanism,thus it is has a wide range of potential applications.In this dissertation,salicylaldehyde derivatives and o-phenylenediamine,3,3'-diaminobenzidine were first introduced to prepare a series of Salen ligand frameworks,which were coordinated with cobalt ions and chromium ions to synthesize a series of novel Single and double metal SalenMX catalyst.The synthesis methods and structural characteristics of bimetallic SalenMX catalysts 4-6b,4-6c and4-6d were reported for the first time.These complexes and PPNX form a bifunctional catalytic system that could efficiently catalyze the copolymerization of CO₂ and propylene oxide?PO?.The impacts of chemical structure,including substituents on the benzene ring,metal ions and axial anions,on the copolymerization reaction were systematically investigated,and the design principles of efficient catalysts were proposed.Moreover,the impacts of reaction conditions such as reaction temperature,reaction pressure and reaction time on the copolymerization were studied,and the ideal conditions for the copolymerization reaction were optimized.Furthermore,effects of catalytic system,including the amount of catalyst,the type of promoter and the amount of promoter,on the copolymerization reaction were explored as well,and the design principles of the catalytic system were proposed.The Guassian 16 calculation program was used to optimize the above complexes by density functional theory?DFT?theoretical calculation method so as to construct an ideal catalyst model for the copolymerization of CO₂ and PO.The results show that the greater the electron donor properties of the substituent on the benzene ring of the benzene ring on the ligand and the greater the steric hindrance of the axial anion,the higher the catalytic activity of the complex.In addition,based on the experimental and calculated results,a possible reaction mechanism for the copolymerization of CO₂and PO by the Salen-type dual-nuclear catalyst system was proposed,and the basic way of bimetallic synergy was explained.