title: Protonation-coupled redox reactions in planar antiaromatic meso-pentafluorophenyl-substituted o-phenylene-bridged annulated rosarins.
abstract: Proton-coupled electron transfer (PCET) processes are among the most important phenomena that control a variety of chemical and biological transformations. Although extensively studied in a variety of natural systems and discrete metal complexes, PCET mechanisms are less well codified in the case of purely organic compounds. Here we report that a planar β,β'-phenylene-bridged hexaphyrin (1.0.1.0.1.0), a 24 π-electron antiaromatic species termed rosarin, displays unique redox reactivity on protonation. Specifically, treatment with acid (for example, HI) yields a 26 π-electron aromatic triprotonated monocationic species that is produced spontaneously via an intermediate-but stable-25 π-electron non-aromatic triprotonated monoradical dication. This latter species is also produced on treatment of the original 24 π-electron antiaromatic starting material with HCl or HBr. The stepwise nature of the proton-coupled reduction observed in the planar rosarin stands in marked contrast to that seen for non-annulated rosarins and other ostensibly antiaromatic expanded porphyrinoids.
authors.affiliation: Department of Chemistry, Yonsei University, Seoul                 120-749, Korea.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Ishida
authors.forename: Soo-Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Christian
authors.initials: C
authors.lastname: Preihs
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Jong Min
authors.initials: JM
authors.lastname: Lim
authors.forename: Byung Sun
authors.initials: BS
authors.lastname: Lee
authors.forename: Jung Su
authors.initials: JS
authors.lastname: Park
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Lynch
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Roznyatovskiy
authors.forename: Tridib
authors.initials: T
authors.lastname: Sarma
authors.forename: Pradeepta K
authors.initials: PK
authors.lastname: Panda
authors.forename: Chang-Hee
authors.initials: CH
authors.lastname: Lee
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Sessler
mesh_terms: D018360:Crystallography, X-Ray; D004187:Disaccharides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011522:Protons; D010135:p-Fluorophenylalanine / Q000737:chemistry*
chemical_list: D004187:Disaccharides; D011522:Protons; D010135:p-Fluorophenylalanine; C529149:rosarin