Molecular propellers that consist of dehydrobenzo[14]annulene blades

Shunpei Nobusue, Yuichi Mukai, Yo Fukumoto, Rui Umeda, Kazukuni Tahara, Motohiro Sonoda, Yoshito Tobe*

*Corresponding author for this work

Research output: Contribution to journalArticle

16 Scopus citations

Abstract

A new class of propel- ler-shaped compound (4), which consisted of dehydrobenzo[14]annulene ([14]DBA) blades, as well as its naphtho homologues (5 and 6), have been prepared. Although NMR studies of compound 4 did not provide useful information regarding its conformation in solution, DFT calculations with different functionals and the 6-31G* basis set all indicated that the D 3-symmetric structure was energetically more favorable than the C 2 conformer. From X-ray crystallographic analysis, it appeared that compound 4 adopted a propeller-shaped-, approximately D 3-symmetric structure in the solid state, in which the [14]DBA blades were twisted substantially owing to steric repulsion between the neighboring benzene rings. On the contrary, in the case of compound 6, although the DFT calculations with the B3LYP functional predicted that the D 3-symmetric conformation was more stable, calculations with the M05 and M05-2X functionals indicated that the C 2 conformer was more favorable because of π-π interactions between the naphthalene units of a pair of neighboring blades. Indeed, X-ray analysis of compound 6 showed that it adopted an approximately C 2-symmetric conformation. Moreover, on the basis of variable-temperature 1H NMR measurements, we found that compound 6 adopted a C 2 conformation and the barrier for interconversion between the C 2-C 2 conformers was estimated to be 16.2 kcal mol -1; however, no indication of the presence of the D 3 isomer was obtained. The relatively small energy barriers to interconversion, despite the large overlapping of neighboring blades, was ascribed to the flexibility of the acetylene linkages, which could be deformed substantially in the transition state of the ring-flip. The propellerheads: The behavior of propeller-shaped compounds with dehydrobenzo[14]annulene rings was investigated. Interconversion between the stereoisomers had relatively small energy barriers owing to the flexibility of the acetylene linkages.

Original languageEnglish
Pages (from-to)12814-12824
Number of pages11
JournalChemistry - A European Journal
Volume18
Issue number40
DOIs
StatePublished - 1 Oct 2012

Keywords

  • activation barrier
  • annulenes
  • density functional calculations
  • fused-ring systems
  • propeller-shaped compounds

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    Nobusue, S., Mukai, Y., Fukumoto, Y., Umeda, R., Tahara, K., Sonoda, M., & Tobe, Y. (2012). Molecular propellers that consist of dehydrobenzo[14]annulene blades. Chemistry - A European Journal, 18(40), 12814-12824. https://doi.org/10.1002/chem.201201061