25616-93-7Relevant academic research and scientific papers
Unambiguous identification of Moebius aromaticity for meso-aryl-substituted [28]hexaphyrins(1.1.1.1.1.1)
Sankar, Jeyaraman,Mori, Shigeki,Saito, Shohei,Rath, Harapriya,Suzuki, Masaaki,Inokuma, Yasuhide,Shinokubo, Hiroshi,Kil, Suk Kim,Zin, Seok Yoon,Shin, Jae-Yoon,Jong, Min Lim,Matsuzaki, Yoichi,Matsushita, Osamu,Muranaka, Atsuya,Kobayashi, Nagao,Kim, Dongho,Osuka, Atsuhiro
, p. 13568 - 13579 (2008)
meso-Aryl-substituted [28]hexaphyrins(1.1.1.1.1.1) have been examined by 1H, 13C, and 19F NMR spectroscopies, UV-vis absorption spectroscopy, magnetic circular dichroism spectroscopy, and single-crystal X-ray diffraction analysis. All of these data consistently indicate that [28]hexaphyrins(1.1.1.1.1.1) in solution at 25°C exist largely as an equilibrium among several rapidly interconverting twisted Moebius conformations with distinct aromaticities, with a small contribution from a planar rectangular conformation with antiaromatic character at slightly higher energy. In the solid state, [28]hexaphyrins(1.1.1.1.1.1) take either planar or Moebius-twisted conformations, depending upon the meso-aryl substituents and crystallization conditions, indicating a small energy difference between the two conformers. Importantly, when the temperature is decreased to -100°C in THF, these rapid interconversions among Moebius conformations are frozen, allowing the detection of a single [28]hexaphyrin(1.1.1.1.1.1) species having a Moebius conformation. Detailed analyses of the solid-state Moebius structures of compounds 2b, 2c, and 2f showed that singly twisted structures are achieved without serious strain and that cyclic π-conjugation is well-preserved, as needed for exhibiting strong diatropic ring currents. Actually, the harmonic-oscillator model for aromaticity (HOMA) values of these structures are significantly large (0.85, 0.69, and 0.71, respectively), confirming the first demonstration of stable Moebius aromatic systems consisting of free-base expanded porphyrins without the assistance of metal coordination.
Porphyrins bearing halogens at the meso-phenyl and β-pyrrolic positions: Synthesis and spectral propertiest
Wijesekera, Tilak,Dupre, Daniel,Cader, Mohamed S.R.,Dolphin, David
, p. 765 - 775 (2007/10/03)
The synthesis of symmetrical porphyrins chlorinated at both ortho positions of the meso-aryl substituents, and the chlorination and bromination of the β-pyrrole positions is reported. The β-chlorination of meso-tetraphenylporphyrin via its nickel(II) comp
