Ishida M, Kim SJ, Preihs C, Ohkubo K, Lim JM, Lee BS, Park JS, Lynch VM, Roznyatovskiy VV, Sarma T, Panda PK, Lee CH, Fukuzumi S, Kim D, Sessler JL. Protonation-coupled redox reactions in planar antiaromatic meso-pentafluorophenyl-substituted o-phenylene-bridged annulated rosarins.
Nat Chem 2012;
5:15-20. [PMID:
23247172 DOI:
10.1038/nchem.1501]
[Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Accepted: 10/12/2012] [Indexed: 11/10/2022]
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.
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