Porphyrins complexes in solution

Cobalt porphyrins have been used for several studies and exhibit catalytic activity . For example when Co-tetraphenylporphyrin (5.15) and Co-octamethylporphyrin complexes are used, CO is obtained catalytically whereas palladium and silver porphyrins in DCL produced oxalate. However, demetallation of the complexes rapidly deactivates the catalyst . In these cases, the catalytic process was interpreted in terms of the anion radical species of the reduced state of Pd (II) and Ag (II) porphyrins rather than the Pd(I) and Ag(I) states.  

Also Co porphyrins have been studied by photophysical , photochemical and electrochemical techniques . The authors found that 

Structure 5.15. Co-tetraphenylporphyrin. Reprinted from Structure 5.15 J. Costamagna, G. Ferraudi, J. Canales and J. Vargas, Carbon dioxide activation by aza-macrocyclic complexes. Coordination Chemistry Reviews 148 (1996) 221-248. Copyright 1996, with permission of Elsevier. 

It has been reported that the macrocycle known as Corrole is an effective catalyst toward CO2 reduction , (5.16). The Co (II) corrole [PhsPCo (tpfc)] (tpfc = 5, 10, 15-tris(pentafluorophenyl) corrole) exhibit catalytic activity in ACN. Stepwise reduction to the [Co (tpfc)] and [Co (tpfc)] states was 

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Zr(IV), and Ce(IV) as the central metal ion. Copper(II) porphyrins are among the most studied of the paramagnetic metalloporphyrins. The Cu(II) complexes show a low-temperature luminescence that arises from the and states that exist in thermal equilibrium. These two states are derived from the lowest excited triplet state on the porphyrin ring, which is split because of the presence of a unpaired electron on the Cu(II) center. Transient absorption measurements show that the ambient temperature excited-state decay times are lowered when a ligand is associated with the axial coordination positions of the tetracoordinate Cu(Il) porphyrin complex. The excited state lifetimes of Cu(II) porphyrin complexes in solution can be either dependent or independent of the temperature and solvent. For the octaethylporphyrin complex Cu(OEP) the excited state lifetime increases as the temperature is lowered, and also as the solvent polarity is increased. By contrast, the excited state lifetime of the tetraphenylporphyrin Cu(TPP) is insensitive to both the temperature and the polarity of the solvent. This difference in their photophysical behavior is likely due to a difference in the energy gap between the charge transfer state and the T/ T states in the pair of complexes. 

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