Oxidation by silver salts

The ligand group can be introduced either on the meso or on the /5-pyrrole position of the porphyrin ring, but the synthesis of the meso-functionalized derivatives is easier and has been more widely exploited. Balch (50-53) reported that the insertion of trivalent ions such as Fe(III) (32) and Mn(III) (33) into octaethyl porphyrins functionalized at one meso position with a hydroxy group (oxophlorins) leads to the formation of a dimeric head-to-tail complex in solution (Fig. 11a) (50,51). An X-ray crystal structure was obtained for the analogous In(III) complex (34), and this confirmed the head-to-tail geometry that the authors inferred for the other dimers in solution (53) (Fig. lib). The dimers are stable in chloroform but open on addition of protic acids or pyridine (52). The Fe(III) octaethyloxophlorin dimer (52) is easily oxidized by silver salts. The one-electron oxidation is more favorable than for the corresponding monomer or p-oxo dimer, presumably because of the close interaction of the 7r-systems in the self-assembled dimer. 

Some routes leading to transformation of carbanions into cations were described4585. One of the methods involves capping carbanions with bromine and conversion via Grig-nard into reactive benzyl bromides that could be oxidized by silver salts. Alternatively, phosgene could be used as the reagent4595. Conversion of cations into anions is exemplified by the reaction of living polytetrahydrofuran with lithium salt of cinamyl alcohol,... 

Triaminobenzenes (127) ate oxidized by silver salts, CBr4 or halogens (cf. to yield salts of the dications (55) which seem to be dimerization products of radical-cations (34). With bases, the dications (55) react to hexaaminobiphenyls (126). They may be formed from the salts of triaminobenzenium ions (29) either by hetero-lytic cleavage with subsequent oxidation of triaminobenzene or by the homolytic rupture of the C-Hal bond leading directly to radical cation (34). When heated or kept in polar solvents, dications (55) are converted into triaminobenzenium ions (29b) This may be diK to the dissociation of dications into radical cations (34) which cleave hydrogen atoms from the solvent. 

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