Push-Pull Buta-1,2,3-trienes: Exceptionally Low Rotational Barriers of Cumulenic C=C Bonds and Proacetylenic Reactivity

Przemyslaw Gawel, Yi Lin Wu, Aaron D. Finke, Nils Trapp, Michal Zalibera, Corinne Boudon, Jean Paul Gisselbrecht, W. Bernd Schweizer, Georg Gescheidt*, François Diederich

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

A variety of asymmetrically donor-acceptor-substituted [3]cumulenes (buta-1,2,3-trienes) were synthesized by developed procedures. The activation barriers to rotation ΔG were measured by variable temperature NMR spectroscopy and found to be as low as 11.8 kcal mol-1, in the range of the barriers for rotation around sterically hindered single bonds. The central C=C bond of the push-pull-substituted [3]cumulene moiety is shortened down to 1.22 Å as measured by X-ray crystallography, leading to a substantial bond length alternation (BLA) of up to 0.17 Å. All the experimental results are supported by DFT calculations. Zwitterionic transition states (TS) of bond rotation confirm the postulated proacetylenic character of donor-acceptor [3]cumulenes. Additional support for the proacetylenic character of these chromophores is provided by their reaction with tetracyanoethene (TCNE) in a cycloaddition-retroelectrocyclization (CA-RE) cascade characteristic of donor-polarized acetylenes.

Original languageEnglish (US)
Pages (from-to)6215-6225
Number of pages11
JournalChemistry - A European Journal
Volume21
Issue number16
DOIs
StatePublished - Apr 13 2015

Keywords

  • [3]cumulenes
  • bond length alternation
  • proacetylenic
  • push-pull chromophores
  • rotational barrier
  • zwitterions

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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