Electrochemical characterization of ,¡-butanoporphyrins containing sterically hindered meso-2 3 6-dihalorienophenyl substituents and first-row transition metal ions in nonaqueous media

Six beta,beta'-butano substituted metalloporphyrins containing sterically hindered meso-dihalogenophenyl substituents and first-row transition metal ions were synthesized and their electrochemical and spectroelectrochemical properties were characterized in nonaqueous media. The investigated compounds have the general formula butano(Y2Ph)(4)PorM, where Por is a dianion of the porphyrin, M = (MnCl)-Cl-III, (FeCl)-Cl-III, Co-II, Ni-II, Cu-II or Zn-II and Y2Ph is a sterically hindered 2,6-F2Ph or 2,6-Cl-2 Ph group on each of the four meso-positions of the macrocycle. The electrochemistry of each porphyrin was examined in CH2Cl2 or pyridine containing 0.1 M tetra-n-butylammonium perchlorate. The first one-electron reduction is metal-centered for the manganese(III), iron(III) and cobalt(II) porphyrins to generate the Mn(II), Fe(II) and Co(I) porphyrins, but it is porphyrin ring-centered for the other examined M(II) porphyrins to give porphyrin pi-anion radicals under the given solution conditions. The effect of the beta,beta'-butano and sterically hindered meso-Y2Ph substituents on redox potentials and electron transfer mechanisms are discussed and compared to what was previously reported for butano-substituted tetraarylporphyrins without hindered meso-substituents.