SYNTHESIS AND ELECTROCHEMISTRY OF CHLORO-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, etrakis(3,5-dichloro-2,6-dimet hoxyphenyl)porphyrin (H(2)tdcdmpp), [Co-II(tdcdmpp)] and [M(tdcdmpp)Cl ] (M = Fe-III or Mn-III) have been prepared. The free base was synthes ized by chlorination of H(2)tdmpp 5,10,15,20-tetrakis(2,6-dimethoxyphe nyl)porphyrin] and metallated to give the complexes following publishe d procedures. The same transition-metal derivatives of tdmpp were also prepared and all eight synthesized compounds were electrochemically i nvestigated in benzonitrile or pyridine containing 0.1 mol dm(-3) NBu( 4)(n)ClO(4). As expected the half-wave potentials of the tdcdmpp compl exes 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) compl exes having the same central metal ions. The magnitude of the anodic s hifts 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 Delt a 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 goi ng from planar M(tpp) to distorted M(obtpp) (obtpp = 7,18-octabromo-5, 10,15,20-tetraphenylporphyrinate) complexes of cobalt and iron where t he effect of macrocycle ruffling is known to predominate over the elec tronic effects of added halide substituents. This result indicates tha t the core distortion cannot compensate totally for the electron-withd rawing effect of the Cl substituents. The macrocyclic distortion also induces a large red shift of the UV/VIS absorption bands and this shif t in lambda(max) ranges up to 40 nm for the chlorinated compounds with respect to the tdmpp complexes.