Porphyrins axial ligand exchange

Both CO2 activation and enolate formation are combined in the preparation of malonic acid derivatives. The reaction of CO2 with methacrylic esters or methacry-lonitrile and under visible light irradiation produced the corresponding aluminum porphyrin malonate complex. When diethylzinc was added to this system, Al(TPP)Et could be regenerated by axial ligand exchange reactions, and the malonic acid derivatives were formed catalytically with respect to the aluminum porphyrins in a one-pot photosynthetic route (Scheme 1). The first step in this... 

Axial ligand exchange at metal(III) porphyrins - In rhodium(III) porphyrins, the rather firmly bound chloride can be exchanged with hydroxide or rhodanide... 

Kinetics of Axial-ligand Exchange on Low-spin Iron(III) Porphyrins... 

The activity of aluminum porphyrins for axial ligand exchange is not only of fundamental interest but is also... 

D Souza, F., G.R. Deviprasad, and M.E. Zandler (1997). Aggregation and axial ligand exchange behavior of water-soluble pyrrole-)ff brominated porphyrins. J. Chem. Soc., Dalton Trans. 3699-3703. 

Ligand substitution kinetics on water-soluble porphyrins have been measured.18,105 106 The Co111 ion of the porphyrin exchanges axial ligands several orders of magnitude more readily than do simple amine or aqua complexes. Relatively low ligand discrimination ratios and positive activation entropies support a dissociative mechanism (equation 18, Table 7). 

When radiolytic reduction of Mn" and Co porphyrins was carried out in frozen MTHF at 77 K, the anionic axial ligands could not diffuse away and thus the optical and ESR spectra of the reduced complexes were quite different from those of the equilibrated reduced products. On the other hand, when the complexes were dissolved in alcohol, the halide axial ligand was exchanged with a solvent molecule and when these solutions were frozen and irradiated, the reduced species were identical with the equilibrated stable products. ... 

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