Synthesis And Electrochemical Properties Of Extended Macrocyclic Manganese Porphyrins And Iron Porphyrins

Metalloporphyrins are of the conjugated macrocyclic compounds which contain four pyrrolic subunits connected by four methane bridges.These compounds have important applications in the fields of novel medicine and functional materials due to their unique photochemical,photobiological,photophysical,electrochemical and electrocatalytic properties.The research showed that the conjugate system of porphyrin macrocyclic can be expanded,and the electronic and spatial structures can be modified by introducing different substituents onto the meso-and/or?-pyrrole positions of macrocycle,which may tune spectral and electrochemical properties of the compound.Therefore,synthesis and study on the novel porphyrins having different meso-and/or?-substituents have always been the important innovations in the field of porphyrin chemistry.In this thesis,several expanded manganese?III?porphyrins containing methoxy,methyl,chlorine or fluorine substituents on the meso-phenyl rings,and butano and benzo-substituents on the??11??'-pyrrole positions of the macrocycle were synthesized and then characterized by UV-visible and mass spectrometric techniques.The electrochemical and spectroelectrochemical properties of these compounds were examined in methylene chloride and pyridine solvents.The mechanism of electron transfer during the redox reaction and the effect of substituents on properties of the compound were also investigated.Three reductions can be observed for Mn?III?butanoporphyrins in methylene chloride but the Mn?III?benzoporphyrins have only two reductions.The first reduction of theses compounds is metal-centered to generate a Mn?II?porphyrin while the second and third reductions are porphyrin ring-centered to give Mn?II?porphyrin?-anion radicals and dianions.Two oxidations can be observed for Mn?III?butanoporphyrins and benzoporphyrins in CH₂Cl₂ and led to the formation of Mn?II?porphyrin?-cation radicals and dications.The manganes porphyrins undergo three or four reductions in pyridine.Both electrochemical and spectroelectrochemical data suggest that the formation of Mn?II?porphyrin dianions generated from the third reduction is coupled with a chemical reaction to give phlorin anions,the phlorin anions can then be further reduced to give Mn?II?phlorin dianions.In addition,two sereis of Fe?III?butanoporphyrins and benzoporphyrins were also synthesized and characterized.The electrochemical and spectroelectrochemical properties of these compounds were studied in CH₂Cl₂ and pyridine solvents.The effects of solvent and type of fused ring systems?butano or benzo?on the UV-vis spectra and electrochemical properties of the Fe?III?porphyrins are discussed.Up to three reductions were observed for each Fe?III?butanoporphyrin and benzoporphyrin in CH₂Cl₂ or pyridine.The first reduction of the compound is metal-centered to generate an Fe?II?porphyrin.The second reduction is also metal-centered in CH₂Cl₂and leads to formation of an Fe?I?porphyrin,but it is porphyrin ring-centered when pyridine is used as the solvent and gives an Fe?II?porphyrin?-anion radical as the reduction product.