Reactions of Alkynyl- and 1,1′-Dialkynylferrocenes with Tetracyanoethylene: Unanticipated Addition at the Less Electron-Rich of Two Triple Bonds

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Original languageEnglish
Pages (from-to)2622-2631
Number of pages10
JournalEuropean Journal of Organic Chemistry
Volume2015
Issue number12
Publication statusPublished - 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

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Reactions of Alkynyl- and 1,1′-Dialkynylferrocenes with Tetracyanoethylene: Unanticipated Addition at the Less Electron-Rich of Two Triple Bonds. / Krauße, Nico; Kielmann, Marc; Ma, Jingxiang et al.
In: European Journal of Organic Chemistry, Vol. 2015, No. 12, 01.04.2015, p. 2622-2631.

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title = "Reactions of Alkynyl- and 1,1′-Dialkynylferrocenes with Tetracyanoethylene: Unanticipated Addition at the Less Electron-Rich of Two Triple Bonds",
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",
author = "Nico Krau{\ss}e and Marc Kielmann and Jingxiang Ma and Holger Butensch{\"o}n",
note = "Funding information: N. K. is indebted to the Leibniz Universit{\"a}t Hannover for a graduate fellowship. The authors thank Innospec Deutschland GmbH for a donation of ferrocene. Dr. Michael Wiebcke, Institut f{\"u}r Anorganische Chemie, Leibniz Universit{\"a}t 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.",
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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

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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 -

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