Chloro(aquo)porphyrinmanganese(III) complexes have been synthesized and characterized for a number of different porphyrins, including etioporphyrin I, deuteroporphyrin IX dimethyl ester, mesoporphyrin IX dimethyl ester, hematoporphyrin IX dimethyl ester, protoporphyrin IX dimethyl ester, ,ß, , -tetraphenylporphin, and methyl pheophorbide a. The absorption spectra have been recorded with the complexes in chloroform and pyridine solution. All the porphyrins show the several features typical of manganese(III) porphyrins, i.e., weak near-ir bands, an intense extra absorption around 21.0 kK, and a blue-shifted B band. All the maxima are red-shifted as the donor strength of the macrocycle decreases from etioporphyrin to methyl pheophorbide a. A model for manganese(III) porphyrins is proposed and a tentative assignment of the absorption spectra of all the complexes made. The near-ir bands and extra absorption are assigned to porphyrin-to-manganese charge-transfer bands while other prominent absorptions are assigned to the normal Q and B bands. The intense charge-transfer bands and the blue-shifted B band can be rationalized by invoking strong metal d7i-«-porphyrin eg* mixing.
path with confidence. No conclusion can be drawn as to the nature of the ko path, but the strongly basic nature of the sulfur suggests the possibility of the "tautomeric" mechanism7 in which the leaving group is a protonated ligand, the proton coming from an intermolecular transfer instead of a simple aquation. The activation parameters of the ko' path may elucidate the mechanism present.3 Also at higher excesses of Cr(II) a "tautomeric" path of the form fo[Cr2+] may well be observed.
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