Synthesis Of Cobalt And Palladium Complexes And Their Applications In CO₂ Conversion And Azole Arylization

The continuous advancement of the industrial process and the improvement of people’s living standards have brought a series of environmental problems.Among them,global warming and rising sea levels caused by the massive emission of greenhouse gas carbon dioxide seriously threaten the living environment of human beings,how to achieve CO₂ efficient utilization has become a research hotspot for scientists.CO₂ can be used as a raw material in the synthesis of various high value-added chemicals,and the atomic economy can reach 100%,which is in line with the concept of green and efficient development.However,as an inert gas,the chemical methods used to convert CO₂ into high-value-added chemicals is subject to harsh reaction conditions such as high temperature and pressure.In order to overcome the harsh conditions,it is necessary for us to research highly active catalyst.Our group reports a series of highly active metal complex catalysts or organic catalysts based on an asymmetric pyridine bridged pincer ligand.Therefore,based on the research of our group,we designed and synthesized a series of highly active heteroligand cobalt complex catalysts based on inversion effect methods,and successfully applied them to the synthesis of cyclic carbonates and oxazolidone,and excellent reaction effects were obtained.1.Based on the asymmetric pyridine bridged pincer-type ligand synthesized in our laboratory,with an inverse effect between the ligands,this pincer-type ligand was reacted with Co（acac）₂ to synthesize six kinds different heteroligand cobalt complex catalysts,which are used in the reaction of CO₂ with epoxides to synthesis cyclic carbonates.We also use different methods to verify the inverse effect between the pincer ligand and the acetylacetone ligand.2.Cobalt complexes of this kind of heteroligand were used in the synthesis of cyclic carbonates.Through further research,it was found that this cobalt complex catalyst exhibits extremely excellent catalytic effect under the conditions of 30°C,0.3 MPa CO₂ pressure,and 0.2 mol%catalyst amount.Higher yields were obtained for different substrates in the catalytic system.The mechanism of action of the catalyst was also studied.Infrared spectroscopy,electronic paramagnetic resonance spectroscopy,and DFT calculations have verified the role of the catalyst in the reaction,and the inverse effect between the acetylacetone ligand and the pincer ligand has also been verified.Firstly,the acetylacetone group in the cobalt complex is removed due to the presence of the inverse effect during the reaction,which exposes the center of the cobalt metal,and then the cobalt coordinates with the Br^-present in the system to form an active intermediate.The substrate was activated by the active intermediate,and the co-catalyst tetrabutylammonium bromide（TBAB）in the system further accelerated the reaction process.3.The oxazolidinone compound has a wide range of applications in chiral auxiliaries,pharmaceutical synthesis and other fields.The synthesis of oxazolidinone compounds based on the reaction of alkynamine compounds and CO₂ is an efficient,green and sustainable way.The cobalt complex of heteroligand was also used in the reaction of alkynylamine and CO₂ for the synthesis of oxazolidinone.It was found that the cobalt complex catalyst showed a high performance under relatively mild conditions（60°C,1 atm CO₂）.At the same time,there are 11 different substituents were extended,and higher conversion rates were obtained.4.In addition,based on the previous research results in the carbazole field of our group,a carbazole-pyridine compound was used as a ligand to design and synthesize 6 different metal palladium complex catalysts.This catalysts were used in the direct arylation reactions of azoles and brominated aromatic hydrocarbons.The direct arylation reactions of imidazole,oxazole,thiazole,pyrazole with brominated aromatic hydrocarbons were studied respectively.The reaction effect is universal with the substrate,and 61different substrates have been expanded.Comparative experiments found that the active intermediate of the palladium catalyst in the reaction is the Pd（0）species,this part enriches the research content of this paper.