PHOTOCATALYSIS, PHOTOREDUCTION, PHOTOOXIDATION AND PHOTOREDOX HYDROGEN TRANSFER REACTIONS OF METALLOPORPHYRINS

Abstract— Hydrogen transfer from tertiary amines to nitroaromatics is photocatalysed by Sn^IV and Ge^IV complexes of tetraphenylporphyrin. There are two photochemical steps, one involving hydrogen transfer to the catalyst, and the second 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 quertchirjg of the fluorescence of the intermediate by nitrobenzene.