Co-tetraphenylporphyrins

Alkali, alkaline-earth, and rare-earth metal cations also catalyze electron transfer reactions. Thus, in the pair of Co -tetraphenylporphyrin complex with BQ, no redox reaction takes place, or it takes place too slowly to be determined. The metal cations promote this reaction. For example, in the presence of 80(0104)3, the corresponding rate constant of 2.7 X 10 M s was observed. BQ transforms into benzosemiquinone under these conditions (Fukuzumi and Ohkubo 2000). Zinc perchlorate accelerates the reaction between aromatic amines and quinones (Strizhakova et al. 1985). This reaction results in the formation of charge-transfer complexes [ArNHj Q ]. The complexes dissociate in polar solvents, giving ion-radicals ... 

Transition metal porphyrins with diatomic ligands have received particular attention in view of their special relevance to biological systems. These diatomic ligands include O2 (obviously, see Section 62.1.12), CO, CS and nq. The IR and resonance Raman spectra of porphyrins with these axial ligands have been well studied, for example Co" tetraphenylporphyrin. ... 

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. ... 

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. 

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