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Factors determining the site of electroreduction in nickel metalloporphyrins spectral characterization of nickel i porphyrins nickel ii porphyrin pi anion radicals and nickel ii porphyrin pi anion radicals with some nickel i character

Kadish, K.D.; Franzen, M.M.; Han, B.C.; Araullo Mcadams, C.; Sazou, D.

Journal of the American Chemical Society 113(2): 512-517

1991


ISSN/ISBN: 0002-7863
DOI: 10.1021/ja00002a019
Accession: 007341682

The effect of temperature, porphyrin macrocycle, and solvent on the electroreduction of (P)NiII where P is the dianion of meso-tetrakis(p-(diethylamino)phenyl)porphyrin (T(p-Et2N)PP) or meso-tetrakis(o,o,m,m-tetrafluoro-p-(dimethylamino)phenyl)porphyrin (T(p-Me2N)F4PP) is reported. Both compounds were reduced by controlled potential electrolysis and characterized by ESR and UV-visible spectroscopy. The site of electron transfer varied as a function of experimental conditions and the stable electrogenerated products were assigned as Ni(I) porphyrins, No(I) porphyrins, Ni(II) porphyrin .pi.-anion radicals, or Ni(II) porphyrin .pi.-anion radicals with some Ni(I) character. Ni(I) ESR spectra were obtained for [(T(p-Et2N)PP)Ni]- and [T(p-Me2N)F4PP)Ni]- at low temperature in THF under a CO atmosphere as well as in DMF or pyridine under N2. In contrast, ESR spectra of Ni(II) porphyrin .pi.-anion radicals or Ni(II) prophyrin .pi.-anion radicals with some Ni(I) character were obtained in THF under N2 at room and low temperature, respectively. [(T(p-Et2N)PP)Ni]- catalytically reduces CH3I at room temperture, consistent with the presence of some Ni(I) character in the reactive species. [(T(p-Et2N.PI.P)Ni]- catalytically reduces CH3I at room temperature, consistent with the presence of some Ni(I) character in the reactive species. [(T(p-Me2N)F4PP)Ni]- also reacts with CH3I, but this reaction is not catalytic at room temperature and one or more .beta. pyrrole methylated nickel chlorins are formed as stable products. These species were characterized by UV-visible spectroscopy, 1H-NMR spectroscopy, and mass spectrometry and give data which suggests a high electron density on the porphyrin macrocycle of [(T(p-Me2N)F4PP)]N-.

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