Synthesis and electrochemistry of 2,3,7,8,12,13,17,18-octachloro-5,10,15,20-tetrakis(3,5-dichloro-2,6-dimethoxyphenyl)porphyrin(H(2)tdcdmpp), [Co-II(tdcdmpp)] and [M(tdcdmpp)Cl] (M=Fe-III or Mn-III)

Four new highly chlorinated porphyrins, 2,3,7,8,12,13,17,18-octachloro-5,10,15,20-tetrakis(3,5-dichloro-2,6-dimethoxyphenyl)porphyrin (H(2)tdcdmpp), [Co-II(tdcdmpp)] and [M(tdcdmpp)Cl] (M = Fe-III or Mn-III) have been prepared. The free base was synthesized by chlorination of H(2)tdmpp [5,10,15,20-tetrakis(2,6-dimethoxyphenyl)porphyrin] and metallated to give the complexes following published procedures. The same transition-metal derivatives of tdmpp were also prepared and all eight synthesized compounds were electrochemically investigated in benzonitrile or pyridine containing 0.1 mol dm(-3) NBu(4)(n)ClO(4). As expected the half-wave potentials of the tdcdmpp complexes are shifted towards positive values while those for oxidation or reduction of the tdmpp species are shifted negatively as compared with E(1/2) for oxidation or reduction of tetraphenylporphyrin (tpp) complexes having the same central metal ions. The magnitude of the anodic shifts in E(1/2) for reduction with respect to pp is among the largest reported for chlorinated porphyrins and ranges between 590 and 860 mV depending upon the specific redox reaction and solvent. A smaller Delta E(1/2) of 330-400 mV is seen for oxidation of the same compounds and these values can be compared to a negligible shift in E(1/2) upon going from planar M(tpp) to distorted M(obtpp) (obtpp = 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrinate) complexes of cobalt and iron where the effect of macrocycle ruffling is known to predominate over the electronic effects of added halide substituents. This result indicates that the core distortion cannot compensate totally for the electron-withdrawing effect of the Cl substituents. The macrocyclic distortion also induces a large red shift of the UV/VIS absorption bands and this shift in lambda(max) ranges up to 40 nm for the chlorinated compounds with respect to the tdmpp complexes.