Synthesis and characterization of a new [4.0.4.0] porphyrin-like antiaromatic macrocycle

Martin R. Johnson, Carla Slebodnick, James A Ibers*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

The antiaromatic macrocycle 2 has been prepared by the reaction of the bipyrrole dialdehyde 1 with hydrazine. In the crystal structure of 2-DMSO molecule 2 is nearly planar, the mean deviation of the 28 atoms of the core from the best least-squares plane being 0.227 Å. AM1 geometric optimization of the core of 2 leads to a fully planar macrocycle. Attempts to oxidize 2 to 3 were largely unsuccessful, yielding only limited evidence for the formation of 3. The antiaromatic precursor 2 turns out to be much more stable than the putative aromatic product 3. Molecular orbital calculations at the AM1/PM3 level indicate the S0-T1 gap for 3 is only about 0.2 eV and hence is readily accessible via intersystem crossing from any visible transition. This small band gap of 3 contrasts starkly with the much larger S0-T1 band gap of 1.86 eV calculated for 2 itself. Paratropicity in antiaromatic systems is usually attributed to a low-lying paramagnetic state, with band gaps ranging up to 2.1 eV. For the 2/3 system the S0-T1 band gap is substantially larger for the paratropic species than for the putative diatropic species.

Original languageEnglish (US)
Pages (from-to)87-92
Number of pages6
JournalJournal of Porphyrins and Phthalocyanines
Volume1
Issue number1
DOIs
StatePublished - Jan 1 1997

Keywords

  • Antiaromatic, paratropic
  • Band gap
  • Molecular orbital calculations
  • Porphyrin-like macrocycle

ASJC Scopus subject areas

  • Chemistry(all)

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