Electrochemistry of nickel and copper beta-octahalogeno-meso-tetraarylporphyrins. Evidence for important role played by saddling-induced metal(d(x2)-(y2))-porphyrin("a(2u)") orbital interactions

This is an electrochemical study of the Ni(II) and Cu(II) complexes of a se ries of beta -octahalogeno-meso-tetrakis(p-X-phenyl)porphyrins, M[Y8T(p-X-P )P] (M = Ni, Cu; Y = Cl, Br; X = CH3, H, F, Br, COOMe, CF3, NO2). We have a nalyzed the oxidation and reduction potentials by means of the Hammett equa tion. The Ni and Cu series exhibit significant differences in electrochemic al behavior in terms of the absolute values of the redox potentials and sub stituent effects. DFT calculations suggest that these differences may be as cribed to differences in saddling-induced metal(d(x2-y2))-porphyrin(a(2u)) orbital interaction between the Ni and Cu porphyrins.