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Molecules 2014, 19(11), 18399-18413;

Thermal Reactivity of Neutral and Oxidized Ferrocenyl-Substituted Enediynes

Department Chemie-Biologie, Universität Siegen, Adolf-Reichwein-Str., Siegen D-57068, Germany
Author to whom correspondence should be addressed.
Received: 18 September 2014 / Revised: 1 November 2014 / Accepted: 3 November 2014 / Published: 12 November 2014
(This article belongs to the Special Issue Free Radicals and Radical Ions)
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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 (C1−C6) or Schreiner-Pascal (C1−C5) 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-nitro-phenyl)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. View Full-Text
Keywords: enediyne; ferrocene; thermal electron transfer; monocation; DFT; differential scanning calorimetry (DSC) enediyne; ferrocene; thermal electron transfer; monocation; DFT; differential scanning calorimetry (DSC)

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Cinar, M.E.; Morbach, G.; Schmittel, M. Thermal Reactivity of Neutral and Oxidized Ferrocenyl-Substituted Enediynes. Molecules 2014, 19, 18399-18413.

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