Longest C–C Single Bond among Neutral Hydrocarbons with a Bond Length beyond 1.8 Å

Yusuke Ishigaki, Takuya Shimajiri, Takashi Takeda, Ryo Katoono, Takanori Suzuki

研究成果: Article

22 引用 (Scopus)

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On the basis of the intramolecular “core-shell strategy,” we designed dihydropyracylene with two spiro(dibenzocycloheptatriene) units, for which theoretical calculations predicted a very weak C–C bond with a bond length around 1.8 Å. This bond is expanded by the forced adoption of an eclipsed conformation and by angle strain through a “scissor effect.” The highly strained hydrocarbon was isolated as a thermally stable compound with no signs of diradical contribution because the weak C–C bond (core) is protected by the shape-persistent fused-ring structure (shell). A Raman shift corresponding to the C–C stretching vibration (587 cm−1) was very different from that for ethane (993 cm−1). The bond length determined by X-ray (1.806(2) Å) was greater than the shortest non-bonded intramolecular CC contact (1.80(2) Å). The assumed limit for a C–C bond (1.803 Å) by supposing linear correlation between bond length and bond-dissociation energy for covalent bonding was proven to be invalid. The nature of chemical bonds is of fundamental importance in chemistry. Clarifying the new facets of covalent bonds is also helpful to promote green chemistry by allowing chemists to design novel chemical products and new processes to advance sustainability. We have successfully synthesized highly strained “core-shell”-type hydrocarbons and demonstrated that the C–C covalent bond can be expanded beyond 1.80 Å, which is 1.17 times greater than the standard length (1.54 Å). By the discovery of such a “hyper covalent bond,” the covalently bonded state and non-bonded state are seamlessly connected in terms of the interatomic distance. Compounds with the hyper covalent bond are potential candidates for making a novel class of materials whose crystals, films, or polymers can respond to external mechanical stimuli with anisotropic contraction or expansion of the matter, accompanied by reversible compression, extension, or fission of the “bond” in the molecule. Compounds with an ultralong C–C single bond have been successfully constructed in three steps from commercially available dihalo aromatics. The intramolecular “core-shell strategy” is a key tactic for stabilizing compounds with an ultralong C–C bond. Using this concept could lead to an even longer C–C bond (“hyper covalent bonds” with a bond length of 1.8–2.0 Å) because the covalently bonded state and non-bonded state are seamlessly connected in terms of the interatomic distance.

元の言語English
ページ(範囲)795-806
ページ数12
ジャーナルChem
4
発行部数4
DOI
出版物ステータスPublished - 2018 4 12

ASJC Scopus subject areas

  • Chemistry(all)
  • Biochemistry
  • Environmental Chemistry
  • Chemical Engineering(all)
  • Biochemistry, medical
  • Materials Chemistry

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