title: Triarylporphyrin meso-Oxy Radicals: Remarkable Chemical Stabilities and Oxidation to Oxophlorin π-Cations.
abstract: 5-Hydroxy-10,15,20-triarylporphyrin (oxophlorin) and its Ni(II) and Zn(II) complexes were oxidized with PbO2 to give the corresponding porphyrin meso-oxy radicals as remarkably stable species. These radicals were fully characterized with X-ray diffraction analysis, UV/vis/NIR absorption and ESR spectroscopies, magnetic susceptibility measurement, electrochemical studies, and theoretical calculations. Free-base radical and its Ni(II) complex have been shown to exist as a monoradical in solution, while the Zn(II) complex exists in an equilibrium between monomer (doublet monoradical) and dimer (a non-Kekulé singlet biradicaloid) with a dimerization constant of KD = 3.0 × 10(5) M(-1) in noncoordinating CH2Cl2 but becomes a pyridine-coordinated monoradical upon addition of pyridine. Variable temperature magnetic susceptibility measurements of these radicals revealed different magnetic interactions in the solid-states, which has been interpreted in terms of their different packing structures in a microscopic sense. These radicals undergo one-electron oxidation and reduction in a reversible manner within narrow potential windows of 0.57-0.82 V. Finally, one-electron oxidation of Ni(II) and Zn(II) porphyrin meso-oxy radicals with tris(4-bromophenyl)aminium hexachloroantimonate furnished oxophlorin π-cations, which displayed nonaromatic closed-shell character, NIR absorption, and significant double bond character of the C-O bond.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University , Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Daiki
authors.initials: D
authors.lastname: Shimizu
authors.affiliation: Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University , Seoul 120-749, South Korea.
authors.forename: Juwon
authors.initials: J
authors.lastname: Oh
authors.affiliation: Center for Instrumental Analysis, Niigata University , Nishi-ku, Niigata 950-2181, Japan.
authors.forename: Ko
authors.initials: K
authors.lastname: Furukawa
authors.affiliation: Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University , Seoul 120-749, South Korea.
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University , Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Atsuhiro
authors.initials: A
authors.lastname: Osuka