Photo catalysis photo reduction photo oxidation and photo redox hydrogen transfer reactions of metallo porphyrins

Harel, Y.; Manassen, J.

Photochemistry and Photobiology 31(5): 451-458


ISSN/ISBN: 0031-8655
Accession: 006108359

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Hydrogen transfer from tertiary amines to nitroaromatics is photocatalyzed by SnIV and GeIV complexes of tetraphenylporphyrin. There are 2 photochemical steps, one involving hydrogen transfer to the catalyst, and the 2nd being a hydrogen donation from the intermediate formed. The photoredox properties of para-substituted tin tetraphenyl porphyrin dichlorides can be correlated with the one electron oxidation-reduction potentials of the porphyrins and of the reduced intermediates. The steady-state concentration of intermediate and rate of product formation depend also on the electron donor and acceptor properties of, respectively, the amine and nitro-compound. Fluorescence results indicate that in both photochemical steps excited singlet states of porphyrins are involved and there is evidence for exciplex formation with ground state amine. Acetic anhydride has a cocatalytic effect but does not influence the quenching of porphyrin fluorescence by amine or the quenching of the fluorescence of the intermediate by nitrobenzene. [Such photochemical reactions are closely related to the role played by chlorophyll in the primary events of photosynthesis.].