Thermal Reactivity of Neutral and Oxidized Ferrocenyl-Substituted Enediynes


Cinar M. E. , MORBACH G., Schmittel M.

MOLECULES, vol.19, no.11, pp.18399-18413, 2014 (Journal Indexed in SCI) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 19 Issue: 11
  • Publication Date: 2014
  • Doi Number: 10.3390/molecules191118399
  • Title of Journal : MOLECULES
  • Page Numbers: pp.18399-18413

Abstract

The coupling of two equivalents of ethynylferrocene (2) with one equivalent of 1,2-diiodocyclohexene (1) and 1,2-diiodobenzene (4) using Sonogashira cross-coupling conditions led to 1,2-bis(ferrocenylethynyl) cyclohexene (3) and 1,2-bis(ferrocenylethynyl) benzene (5), respectively. At high temperatures enediynes 3 and 5 showed exothermic signals in differential scanning calorimetry (DSC) measurements, suggestive of intramolecular diradicaloid ring formation (Bergman (C-1-C-6) or Schreiner-Pascal (C-1-C-5) cyclizations). The oxidation of 3 and 5 to the mono-oxidized enediynes 3(+) and 5(+) decreased the onset temperatures drastically. Equally, 1-ferrocenylethynyl-2-(p-nitrophenyl) ethynylbenzene (8) displayed a significant decrease in the onset temperature after oxidation to 8(+). Because the insoluble nature of the polymeric material formed in the thermolysis of the oxidized enediynes prevented characterization, the origin of this drastic effect was studied by DFT. Contrary to expectations, one-electron oxidation does not lower the barrier for intramolecular cyclization. Rather, the computations suggest that the polymerization is initiated by a bimolecular process.