Study On Electrochemistry And Axial Coordination Of Multi-substituted Extended Porphyrins

Porphyrins are a class of heterocyclic aromatic compounds with 18?electron conjugated system,and the internal cavity of macrocycle can selectively binds various metal ions to form porphyrin complexes with different physical and chemical properties.Porphyrin derivatives with different properties can be obtained by modifying the four meso and eight?-pyrrole positions on the porphyrin ring,which can be applied in the field of clinical medicine,catalytic oxidation,liquid crystal materials,solar cells,etc.Compared with regular porphyrin compounds,the extended porphyrin compounds have a larger?-electron conjugated system,which has more complex coordination properties and photoelectric properties,so its potential applicationsare immeasurable.However,the properties of coordination chemistry,electrochemistry and application of extended porphyrins are relatively limited,therefore,it is of great importance to study the electrochemical and coordination properties of multi-substituted extended porphyrins.Porphyrin compounds studied in current synthesis contains the following four series:1)Four kinds of multi-substituted iron porphyrin compounds.5,10,15,20-?4-CH₃Ph?₄PorFeCl 1,2-NO₂-5,10,15,20-?4-CH₃Ph?₄PorFeCl 2,5,10,15,20-?3,5-diCH₃O?₄PorFeCl 3 and 2-NO₂-5,10,15,20-?3,5-diCH₃O?₄PorFeCl 4;2)Zinc butanoporphyrins and benzoporphyrins.Butano?YPh?₄PorZn5a-5c and benzo?YPh?₄PorZn 6a-6c?Y=-CH₃,-H or-Cl?;3)Butanoporphyrins.Butano?4-CH₃Ph?₄PorH₂ 7,butano?Ph?₄PorH₂ 8 and butano?4-ClPh?₄PorH₂ 9;4)Four copper or manganese butanoporphyrin and benzoporphyrin compounds.Butano?2,6-diFPh?₄PorM 10a-11a and benzo?2,6-diFPh?₄PorM 10b-11b,M represents Cu?II?or Mn?III?Cl.In this work,axial coordination reactions between the multi-substituted iron porphyrins 1-4and certain nitrogenous base molecules were studied in dichloromethane?CH₂Cl₂?by micro-spectral titration,and the equilibrium constant?logb_n?were determined at different temperatures,and the thermodynamic constants standard molar enthalpy change??_rH_m^??,standard molar entropy change??_rS_m^??and standard molar Gibbs free energy change??_rG_m^??were calculated at 298 K.The result shows that each iron porphyrinaxially binds to one or two ligand molecules to form five-or six-coordinated porphyrin derivative,and the specific coordination number depends on the properties of the nitrogenous bases.Moreover,by measuring the equilibrium constants of reactions at different reaction temperatures,it is known that the axial coordination reactions of these four iron porphyrins with nitrogenous bases are spontaneous exothermic reactions.Secondly,the axial coordination reaction of the six zinc porphyrin compounds 5a-6c with seven nitrogenous bases were determined in CH₂Cl₂.It suggests that these six compounds all axially coordinate with one nitrogenous base molecule to form five-coordinate derivatives.The effect of pKa value of the nitrogenous base and the type of?,?'-fused substituent of macrocycle on the equilibrium constant logK are also discussed.Then,the protonation and deprotonation reaction of tetrabutanoporphyrins 7-9 in dimethyl sulfoxide were determined.Compared with the spectrum of corresponding non?,?'-fused porphyrins,the UV-visible spectrum of butanoporphyrins have a large red shift due to the?,?'-fused butano group.These bases have strong electron-donating effect,so it is easier to form a stable porphyrin cation.In conclusion,porphyrins containing electron-donating meso-substituents will have a greater protonation constant.Finally,the metal porphyrins 10a-11b were synthesized and electrochemically characterized.The tetrabutanoporphyrins and tetrabenzoporphyrins 10a-11b were determined by cyclic voltammetry and thin-layer spectroelectrochemistry in CH₂Cl₂ or pyridine containing 0.1M TBAP.The copper butanoporphyrins and benzoporphyrins all contain two reversible oxidation reaction and one reversible reduction reaction in CH₂Cl₂,and contain two oxidation reaction and three reduction reaction in pyridine.The results showed that the second reduction of butanoporphyrins compound generate a phlorin anion in pyridine containing 0.1M TBAP.Compared with the corresponding butanoporphyrins and regular porphyrin compounds,the HOMO-LUMO energy gap of benzoporphyrins is the smallest.