New donor-acceptor chromophores by formal [2+2] cycloaddition of donor-substituted alkynes to dicyanovinyl derivatives

Peter D. Jarowski, Yi Lin Wu, Corinne Boudon, Jean Paul Gisselbrecht, Maurice Gross, W. Bernd Schweizer, Franois Diederich*

*Corresponding author for this work

Research output: Contribution to journalArticle

49 Scopus citations

Abstract

The efficient methodology of the cycloaddition between electron-rich alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ), followed by retro-electrocyclisation, is extended to dicyanovinyl derivatives to produce new donor-acceptor push-pull 1,1-dicyanobutadienyl chromophores in excellent to quantitative yield (63-98%) that express strong charge-transfer (CT) absorptions from 300 to 600 nm. The scope of this reaction is established by both varying the nucleophilic and electrophilic components. Electrochemical studies show that the CT properties of these systems are readily tunable by substitution on the electrophile, which has the largest effect on the lowest unoccupied molecular orbital (LUMO). Non-reversible reduction potentials range from ca.-1.2 to -1.9 V in CH2Cl2, against the ferricinium/ferrocene couple (Fc+/Fc) according to cyclovoltammetry (CV) and rotating disk voltammetry (RDV). The chromophores show a significant non-planarity between the N,N-dimethylanilino donor and the 1,1-dicyanovinyl acceptor moieties, with torsional angles around 40° from X-ray analysis, but retain strong quinoidal character. The mechanism of this reaction has been studied computational using density functional methods in the gas-phase and using the polarizable continuum model (PCM) for addressing solvent effects. The complete reaction free-energy profile has been determined for the reaction of 1,1-dicyanoethene and 4-ethynyl-N,N-dimethylaniline. The process proceeds through formal [2+2] cycloaddition followed by retro- electrocyclisation. The formation of a zwitterionic intermediate in the cycloaddition step is shown.

Original languageEnglish (US)
Pages (from-to)1312-1322
Number of pages11
JournalOrganic and Biomolecular Chemistry
Volume7
Issue number7
DOIs
StatePublished - Jul 1 2009

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry
  • Organic Chemistry

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    Jarowski, P. D., Wu, Y. L., Boudon, C., Gisselbrecht, J. P., Gross, M., Schweizer, W. B., & Diederich, F. (2009). New donor-acceptor chromophores by formal [2+2] cycloaddition of donor-substituted alkynes to dicyanovinyl derivatives. Organic and Biomolecular Chemistry, 7(7), 1312-1322. https://doi.org/10.1039/b821230a