Study On Catalytic Function Of Rare Earth Complexes

The development of environmentally friendly processes based on carbon dioxide, one ofthe key greenhouseeffect gases, has attracted considerable attention in recent years. Carbondioxide is recognized to be highly naturally abundant, inexpensive, recyclable, and nontoxiccarbon source of various organic reactions. The chemical fixation of carbon dioxide intovaluable chemicals, is generally regarded as an excellent solution both from an environmentalprotection and resource utilization standpoint. Propylene carbonate (PC) is not only a lowtoxicity and high boiling point solvent, but also an important organic product that has beenused widely in the fields of organic synthesis, gas separation, electrochemistry. Although thesynthesis of PC from carbon dioxide and propylene oxide has been applied in industrial scales,the process requires high temperature and pressure(180-206℃,7-8MPa).In this study, twohigh-efficiency homogeneous catalyst systems were designed and fabricated for the synthesisof cyclic carbonates from CO2and propylene oxide.2,2’-dipyridylamine (Hdpa), di(2-pyrazyl)amine (Hdpza),1,13,14-triazadi-benz[a,j]anthracene (Anthy) ligands were synthesized and characterized. Investigated the reaction ofcarbon dioxide with propylene oxide to generate PC with Lgands (Bipy，Hdpa, Hdpza，Napy，Anthy) and rare earth metal salt, and analyzed the influence of the ligand structure for catalyticperformance. The following conclusions have been reached:(1) The amine group of theligands plays minor role and is unnecessary for the catalytic activity, which was indicated bythe similar results of Hdpa and Bipy.(2) The heterocyclic rings in ligands are vital for theirfunction as a catalyst.When ligand Hdpa was changed to Hdpza, the yields increasedsignificantly, which rises from80%to95%.(3) Rigid ligand will be helpful with catalyticperformance. Steric hindrance of ultra-rigid ligand is so large that the reactant can’t to insertthe active site.(4) The catalytic activity is inversely proportional to their ionic radii: with thesmallest radius and the highest charge density among the three metals, Er3+showed the bestyield. This is consistent with that the Er3+is harder and stronger Lewis acid than Nd3+andGd3+, which allows a stronger metal-ligand interactions.(5) When the rare earth nitrate andrare earth acetate were employed instead of chlorides, the catalytic activity reduced markedly.This indicates the importance of the cooperative effect related to anions, and the reactionfavors chlorides other than nitrates and acetates.(6) Different reaction conditions were also investigated. Catalytic reaction tests demonstrated that the incorporation of ErCl3and Hdpzacan significantly enhance the catalytic reactivity of the TBAB (nBu4NBr, tetra-n-butylammonium bromide) towards cycloaddition reaction of CO2and propylene oxide that producecyclic carbonates under mild conditions without any co-solvent.Rare earth of four-phenyl porphyrin complexes, four-phenyl porphyrin erbium，four-phenyl porphyrin neodymium，were synthesized from the corresponding rare-earthacetylacetonates and TPP under reflux in1,2,4-chlorobenzene solvent. The compounds werecharacterized by IR spectrum and their fine structures were analyzed. This synthetic methodshowed feasible for the synthesisof metal porphyrin complexes. Catalytic reaction testsdemonstrated that rare earth of four-phenyl porphyrin complexes efficiently catalystcycloaddition reaction of CO2and propylene oxide.