Synthesis,Structures And Catalytic CO₂ Cycloaddition Of Pyridine And N-ethyl Pyridine Bromide Based Metalloporphyrins

The rising carbon dioxide?CO₂?in the atmosphere is a greenhouse gas,which mainly comes from the metabolism of living organisms and the emission of industrial production.Greenhouse effect will cause global warming and other phenomena,so many scientific researchers are committed to CO₂ fixation and transformation.Cycloaddition reaction of epoxides with CO₂ plays an important role.It can not only reduce the amount of CO₂ and convert toxic epoxides into non-toxic cyclocarbonates,but also obtain cyclocarbonates which are very important chemicals.It is reported that metalloporphyrin catalysts have good catalytic activity for this reaction.Based on the above research background,this paper selected 5,10,15,20-tetra?4-?3-?4-pyridyl?pyrazolyl?phenyl?porphyrin?H₂TPyP?to study the catalytic activities of pyridyl-based metalloporphyrins and N-ethyl pyridinium bromide-based metalloporphyrins in the cycloaddition of CO₂ with epoxides.The main research work is as follows:?1?Five metalloporphyrins(Zn?II?,Mn?II?,Co?II?,Cu?II?,Ni?II?5,10,15,20-tetra?4-?3-?4-pyridyl?pyrazolyl?phenyl?porphyrins?ZnTPyP,MnTPyP,CoTPyP,CuTPyP,NiTPyP?were synthesized by solvothermal method of H₂TPyP with transition metal acetates.Their crystal structures were determined by X-ray single crystal diffractometer.Among them,ZnTPyP,MnTPyP and CoTPyP are two-dimensional MOFs with six-coordinated central metals formed by coordination bonds,while CuTPyP and NiTPyP are single-molecule stacking structures with four-coordinated central metals formed by weak intermolecular interactions.The successful synthesis of these samples was also confirmed by a series of tests such as elemental analysis?EA?,mass spectrometry?ESI-MS?,ultraviolet-visible?UV-vis?,solid ultraviolet-vis?UV-vis-DRS?and infrared spectroscopy?FT-IR?.X-ray powder diffraction?PXRD?,thermogravimetric analysis?TG?,scanning electron microscopy?SEM?and N₂ adsorption tests show that these samples have good crystal purity,good thermal stability and regular morphology,but small BET specific surface area.Trivalent manganese porphyrin ClMn?III?TPyP was synthesized and characterized by EA,ESI-MS,UV-vis,UV-vis-DRS,FT-IR and TG.?2?N-ethylpyridiniumbromidebasedporphyrin5,10,15,20-tetra?4-?3-?N-ethyl-4-pyridyl?pyrazolyl?phenyl?porphyrin?H2TEtPyP?and its corresponding metal porphyrins(Zn?II?,Mn?III?OAc,Co?II?,Cu?II?,Ni?II?5,10,15,20-tetra?4-?3-?N-ethyl-4-pyridyl?pyrazolyl?phenyl?metalloporphyrins?ZnTEtPyP,MnTEtPyP?OAc?,CoTEtPyP,CuTEtPyP,NiTEtPyP?were synthesized by two-step method.The successful synthesis of these samples was confirmed by a series of characterizations such as ¹H NMR,EA,ESI-MS,UV-vis,UV-vis-DRS and FT-IR.Thermogravimetric analysis showed that these samples had good thermal stability.?3?The catalytic activities of the synthesized metalloporphyrins for cycloaddition of epoxides with CO₂ were tested.Firstly,the optimum reaction conditions?120oC,2 MPa CO₂ pressure,8 h,molar ratio of substrate to catalyst 2222/1?were selected.N-ethyl pyridinium bromide based metalloporphyrins?MTEtPyP?have better catalytic activity than pyridyl-based metalloporphyrins?MTPyP and ClMn?III?TPyP?,probably because pyridine N-ethylation enhances the Lewis basicity of the catalyst and the vacancy sites in the central axis of the metal.The catalytic activity of ZnTEtPyP,MnTEtPyP?OAc?and CoTEtPyP was significantly higher than that of CuTEtPyP and NiTEtPyP,probably because the Lewis acidity of Zn?II?,Mn?III?and Co?II?was stronger than that of Cu?II?and Ni?II?.MTEtPyP was used as catalyst to expand the substrates.It was found that the catalytic activity was related to the structure of the substrates.The stronger the electron pulling property of the substituent was,the higher the conversion rate was found.The cyclic stability of the catalyst was tested with CoTEtPyP as the representative,and the possible mechanism of bimolecular synergy was also proposed.