LIANG-CHU GONG and DAVID DOLPHIN. Can. J. Chem. 63, 401 ( 1 985). The reaction of zinc octaethylporphyrin with N z 0 4 in dichloromethane gives, in a stepwise reaction, the zinc complexes of mono-, di-, tri-, and tetra-nitrooctaethylporphyrins. Demetallation, under acidic conditions, gives the corresponding free base porphyrins. The meso-nitro groups exert both steric and electronic effects on the porphyrin macrocycle. Thus N-protonation of the nitrated species causes a distortion of the ring and gives an optical spectrum similar to that of protonated meso-arylsubstituted porphyrins. In addition, the nitro groups make the oxidation of the porphyrin ring more difficult and at the same time facilitate the ring reductions.LIANG-CHU GONG et DAVID DOLPHIN. Can. J. Chem. 63, 401 ( I 985). La rkaction du sel de zinc de I'octaCthylporphyrine avec le N204 dans le dichloromCthane conduit, par I'intermCdiaire d'une sCrie de rCactions, aux complexes de zinc des mono-, di-, tri-et tCtra-nitrooctaCthylporphyrines. La dCmCtalation, en utilisant des conditions acides, conduit aux porphyrines correspondantes qui existent sous forme de bases libres. Les groupes nitro en positions mPso exercent des effets la fois stCriques et Clectroniques sur le macrocycle de porphyrine. La N-protonation des espkces nitrCes provoque donc une distortion du cycle et fournit un spectre optique semblable a celui des porphyrines protontes portant des substituants aryles en position meso. De plus, les groupes nitro rendent le cycle porphyrine moins susceptible a I'oxydation et ils facilitent les reductions des cycles.[Traduit par le journal]Porphyrins, like most other aromatic systems, undergo electrophilic substitution. However, as with all heteroaromatic systems, the competition between the basicity of the heteroatom and the nucleophilicity of the aromatic a-system can prevent many substitution reactions from occurring. A striking example of this is the faster rate of meso-substitution of octaethylporphyrin (OEP) in CH3COzD compared to CF3C02D (I)! ~, Electrophilic substitution at the porphyrin periphery has been recently reviewed (2) and, while a wide variety of reactions have been described, few high-yield reactions have been reported. The usually large effort that must be expended to prepare any porphyrin, other than the trivially easy reactions to generate tneso-arylporphyrins (3), requires that further manipulations should be as efficient as possible. We report here on the convenient preparation of the nitrooctaethylporphyrins and the effect the electron-withdrawing groups have on the redox properties of the free bases and some metal complexes.The direct nitration of OEP in fuming nitric acidlacetic acid gives good yields of 5-nitrooctaethylporphyrin (5-(N02)OEP (1)) with considerably diminished yields of the dinitroporphyrins 5,10-(N0)z0EP (2) and 5,15-(NOz)OEP (3). Under more forcing conditions (HN03/H2S04), 20% of the 5,10,15-trinitrooctaethylporphyrin (4) can be formed but isolable amounts of the 5,10,15,20-tetranitroporphyrin (5) are not ob...

LIANG-CHU GONG and DAVID DOLPHIN. Can. J. Chem. 63, 406 (1985). Nitrooctaethylporphyrins readily undergo nucleophilic aromatic substitution in the presence of HCI or HBr. In the presence of methoxide, nucleophilic addition to give a porphodimethane occurs, followed by autoxidation to the methoxyporphyrin. Unlike the nitrated complexes, the chlorosubstituted porphyrins exhibit redox potentials similar to those of unsubstituted analogs. Meso-halogenated porphyrins do, however, show steric distortion due to the bulk of the halogen atoms.LIANG-CHU GONG et DAVID DOLPHIN. Can. J. Chem. 63, 406 (1985). En presence de HCI ou de HBr, les nitrooctaethylporphyrines subissent facilement des rhctions de substitutions aromatiques nucleophiles. En presence d'ions methylates, il se produit une addition nuclCophile conduisant ii un porphodimCthane; cette rCaction est suivie d'une auto-oxydation qui conduit i une mkthoxyporphyrine. Contrairement au comportement observe avec les complexes nitrts, les potentiels redox des chloroporphyrines sont semblables h ceux de leurs analogues qui ne sont pas substituCs. Par contre, les porphyrines portant des halogenes dans les positions mPso presentent une distortion stkrique qui est due ii I'encombrement des atomes d'halogenes.[Traduit par le journal]