Redox Properties of Tetraphenylporphyrin Complexes

Abstract

The redox‐properties of tetraphenylporphyrin‐complexes were studied as a function of substituents on the phenyl group. Electron‐withdrawing chlorine substituents cause a rise of approximately 100 mV for the first ligand oxidation and electron‐donating methoxy‐substituents cause a decrease of about the same magnitude. The redox‐properties of the central metal ion are much less sensitive to these substituents. The Fe3+/Fe2+ transition on the other hand, is seen to depend on the anion used. Taking these effects into account a tentative mechanism is proposed for the oxidation‐behaviour of μ‐oxo‐bis (tetraphenyl)porphyrin‐iron(III).

Significant Effect of Electronic Coupling on Electron Transfer between Surface-Bound Porphyrins and Co2+/3+ Complex Electrolytes

“…Zn 2+ in the porphyrin ring is electrochemically inert (it is not oxidized or reduced in the electrochemical window of the porphyrin ring), therefore the redox potential of the Zn porphyrin typically shifts negatively by only 200 mV as compared to the free-base porphyrin . It is well-known that Zn 2+ ions in porphyrins provide a fifth coordination site, − which in the absence of specific ligands can be occupied by solvent molecules .…”

“…Zn 2+ in the porphyrin ring is electrochemically inert (it is not oxidized or reduced in the electrochemical window of the porphyrin ring), therefore the redox potential of the Zn porphyrin typically shifts negatively by only 200 mV as compared to the free-base porphyrin. 36 It is well-known that Zn 2+ ions in porphyrins provide a fifth coordination site, 37−39 which in the absence of specific ligands can be occupied by solvent molecules. 38 It is at this site of lone N electron pairs where we expect to see a difference in the electrostatic force between the free-base porphyrins and the positively charged Co 2+ redox species in the electrolyte.…”

Protonation and Electrochemical Properties of Pyridyl‐ and Sulfonatophenyl‐Substituted Porphyrins in Nonaqueous Media

“…The “split” redox reactions at E pc =−0.42 V and E pc =0.00 V in Figure and the associated oxidation/reduction mechanisms are associated in each case with an electrochemical EC mechanism, where the electron transfer step (E) is reversible and the chemical reactions following both oxidation and reduction (the C step) involves the gain or loss of an axial ligand …”

“…The "split" redox reactions at E pc = À0.42 V and E pc = 0.00 V in Figure 9 and the associated oxidation/reduction mechanisms are associated in each case with an electrochemical EC mechanism, where the electron transfer step (E) is reversible and the chemical reactions following both oxidation and reduction (the C step) involves the gain or loss of an axial ligand. [30,[40][41][42][43] The split reductions and oxidations of 1Co in pyridine involve metal-centered reactions and the proposed mechanism for the Co II /Co III and Co II /Co I processes is given in Scheme 3. Only the metal center (Co III , Co II or Co I ) and the bound pyridine (abbreviated as Py) axial ligand are shown in the Scheme.…”

Study of a mixed-valence hemin dimer

“…(2) Treatment of the violet copper-penicillamine complex with 3% H202 produces a material whose XPS now shows the presence of Cu(II) and oxidized sulfur (S 2p = 169.2 eV).4,5 (3) If in the preparation of the violet copper-penicillamine complex a threefold excess of Cu(II) is used in the reaction, then the XPS of the resultant brown-green reaction mixture shows the presence of large quantities of Cu(II) in addition to Cu(I).5,15 (11) Frost, D. C.; Ishitani, A.; McDowell, C. A. Mol.…”