Details
Original language | English |
---|---|
Pages (from-to) | 2622-2631 |
Number of pages | 10 |
Journal | European Journal of Organic Chemistry |
Volume | 2015 |
Issue number | 12 |
Publication status | Published - 1 Apr 2015 |
Abstract
Alkynylferrocenes react with tetracyanoethylene (TCNE) to form 2-ferrocenyl-1,1,4,4-tetracyanobutadienes. These reactions occur under mild reaction conditions in almost quantitative yields if the triple bond is electron-rich. Systems with more than one triple bond, namely, 1,1′-dialkynylferrocenes or diynylferrocenes, react once at the more electron-rich triple bond, and the second reaction cannot be achieved, even under more-forcing reaction conditions. For a diyne with the reactivity switched by oxidation of the ferrocenyl moiety to the corresponding ferrocenium salt, the addition of TCNE occurred at the less electron-rich triple bond. This unprecedented reactivity is explained by the resonance stabilization of a diradical intermediate. A push-pull 1,1′-dialkynylferrocene with a [4-(dimethylamino)phenyl]ethynyl and a (4-nitrophenyl)ethynyl substituent reacted exclusively at the [4-(dimethylamino)phenyl]ethynyl triple bond. The additions of tetracyanoethylene (TCNE) to alkynylferrocenes occur selectively at the most electron-rich triple bond. However, this broadly accepted rule is not obeyed when ferrocenium cations come into play.
Keywords
- Alkynes, Conjugation, Redox chemistry, Sandwich complexes
ASJC Scopus subject areas
- Chemistry(all)
- Physical and Theoretical Chemistry
- Chemistry(all)
- Organic Chemistry
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In: European Journal of Organic Chemistry, Vol. 2015, No. 12, 01.04.2015, p. 2622-2631.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Reactions of Alkynyl- and 1,1′-Dialkynylferrocenes with Tetracyanoethylene
T2 - Unanticipated Addition at the Less Electron-Rich of Two Triple Bonds
AU - Krauße, Nico
AU - Kielmann, Marc
AU - Ma, Jingxiang
AU - Butenschön, Holger
N1 - Funding information: N. K. is indebted to the Leibniz Universität Hannover for a graduate fellowship. The authors thank Innospec Deutschland GmbH for a donation of ferrocene. Dr. Michael Wiebcke, Institut für Anorganische Chemie, Leibniz Universität Hannover, is thanked for performing the crystallographic analysis of 32 and David Schmiel, M. Sc. for his help with the characterization of 29 and 30.
PY - 2015/4/1
Y1 - 2015/4/1
N2 - Alkynylferrocenes react with tetracyanoethylene (TCNE) to form 2-ferrocenyl-1,1,4,4-tetracyanobutadienes. These reactions occur under mild reaction conditions in almost quantitative yields if the triple bond is electron-rich. Systems with more than one triple bond, namely, 1,1′-dialkynylferrocenes or diynylferrocenes, react once at the more electron-rich triple bond, and the second reaction cannot be achieved, even under more-forcing reaction conditions. For a diyne with the reactivity switched by oxidation of the ferrocenyl moiety to the corresponding ferrocenium salt, the addition of TCNE occurred at the less electron-rich triple bond. This unprecedented reactivity is explained by the resonance stabilization of a diradical intermediate. A push-pull 1,1′-dialkynylferrocene with a [4-(dimethylamino)phenyl]ethynyl and a (4-nitrophenyl)ethynyl substituent reacted exclusively at the [4-(dimethylamino)phenyl]ethynyl triple bond. The additions of tetracyanoethylene (TCNE) to alkynylferrocenes occur selectively at the most electron-rich triple bond. However, this broadly accepted rule is not obeyed when ferrocenium cations come into play.
AB - Alkynylferrocenes react with tetracyanoethylene (TCNE) to form 2-ferrocenyl-1,1,4,4-tetracyanobutadienes. These reactions occur under mild reaction conditions in almost quantitative yields if the triple bond is electron-rich. Systems with more than one triple bond, namely, 1,1′-dialkynylferrocenes or diynylferrocenes, react once at the more electron-rich triple bond, and the second reaction cannot be achieved, even under more-forcing reaction conditions. For a diyne with the reactivity switched by oxidation of the ferrocenyl moiety to the corresponding ferrocenium salt, the addition of TCNE occurred at the less electron-rich triple bond. This unprecedented reactivity is explained by the resonance stabilization of a diradical intermediate. A push-pull 1,1′-dialkynylferrocene with a [4-(dimethylamino)phenyl]ethynyl and a (4-nitrophenyl)ethynyl substituent reacted exclusively at the [4-(dimethylamino)phenyl]ethynyl triple bond. The additions of tetracyanoethylene (TCNE) to alkynylferrocenes occur selectively at the most electron-rich triple bond. However, this broadly accepted rule is not obeyed when ferrocenium cations come into play.
KW - Alkynes
KW - Conjugation
KW - Redox chemistry
KW - Sandwich complexes
UR - http://www.scopus.com/inward/record.url?scp=85027955557&partnerID=8YFLogxK
U2 - 10.1002/ejoc.201500105
DO - 10.1002/ejoc.201500105
M3 - Article
VL - 2015
SP - 2622
EP - 2631
JO - European Journal of Organic Chemistry
JF - European Journal of Organic Chemistry
SN - 1434-193X
IS - 12
ER -