Synthesis, characterization, and spectroscopic analysis of antiaromatic benzofused metalloporphyrins

Shun Sugawara, Yusuke Hirata, Satoshi Kojima, Yohsuke Yamamoto, Eigo Miyazaki, Kazuo Takimiya, Shiro Matsukawa, Daisuke Hashizume, John MacK, Nagao Kobayashi, Zhen Fu, Karl M. Kadish, Young Mo Sung, Kil Suk Kim, Dongho Kim

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Abstract

A two-electron oxidation of the Cu II (9) and Zn II (12) complexes of tetraphenyltetrabenzoporphyrin (TPTBP) results in the formation of stable antiaromatic [(TPTBP)Cu II(H 2O)] 2+·2 [SbF 6] - (10) and [(TPTBP)Zn II(H 2O) 2] 2+·2 [SbF 6] - (13) with 16π electrons on the inner ligand perimeter. X-ray structures of the parent TPTBP complexes, the dications, and singly oxidized species [(TPTBP)Cu II] ·+[SbF 6] - (11) reveal that the use of TPTBP rather than a porphyrin ligand reduces the degree of nonplanarity in the 16π-electron species relative to the parent 18π complex. Significant high-field shifts of the 1H NMR signals of the outer ring protons and large positive values in calculations of nucleus-independent chemical shifts on the central cavity of the porphyrin ring provide unambiguous evidence for the antiaromatic character of the 16π Zn II species. A combination of magnetic circular dichroism spectroscopic studies and TD-DFT calculations on both the Zn II and Cu II species demonstrates that the main electronic bands of the dicationic species can be readily assigned by using Michl's 4N perimeter model. Femtosecond transient absorption studies clearly demonstrated that the number of π electrons on the inner ligand perimeter and the configuration of the central metal ion play a critical role in the excited-state relaxation dynamics. Redox potentials for conversion between the 16π, 17π, and 18π systems were measured by cyclic voltammetry in dichloromethane and benzonitrile, and UV/Vis spectra of each oxidation/reduction product were monitored by thin-layer spectroelectrochemistry.

Original languageEnglish
Pages (from-to)3566-3581
Number of pages16
JournalChemistry - A European Journal
Volume18
Issue number12
DOIs
Publication statusPublished - 2012 Mar 19

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All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry

Cite this

Sugawara, S., Hirata, Y., Kojima, S., Yamamoto, Y., Miyazaki, E., Takimiya, K., Matsukawa, S., Hashizume, D., MacK, J., Kobayashi, N., Fu, Z., Kadish, K. M., Sung, Y. M., Kim, K. S., & Kim, D. (2012). Synthesis, characterization, and spectroscopic analysis of antiaromatic benzofused metalloporphyrins. Chemistry - A European Journal, 18(12), 3566-3581. https://doi.org/10.1002/chem.201101846