Premium
Reactions of Alkynyl‐ and 1,1′‐Dialkynylferrocenes with Tetracyanoethylene – Unanticipated Addition at the Less Electron‐Rich of Two Triple Bonds
Author(s) -
Krauße Nico,
Kielmann Marc,
Ma Jingxiang,
Butenschön Holger
Publication year - 2015
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201500105
Subject(s) - triple bond , chemistry , tetracyanoethylene , reactivity (psychology) , moiety , substituent , medicinal chemistry , diradical , photochemistry , double bond , stereochemistry , organic chemistry , medicine , physics , alternative medicine , pathology , nuclear physics , singlet state , excited state
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.