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Nonapentafulvalen
Author(s) -
Escher André,
Neuenschwander Markus
Publication year - 1987
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19870700106
Subject(s) - chemistry , cyclopentadiene , planarity testing , ring (chemistry) , delocalized electron , steric effects , crystallography , deprotonation , molecule , isomerization , cyclopentadienyl complex , stereochemistry , medicinal chemistry , proton nmr , photochemistry , organic chemistry , ion , catalysis
Nonapentafulvalene ( 1 ) has been prepared by oxidative coupling of sodium cyclopentadienide ( 6 ) and sodium cyclononatetraenide ( 7 ) with CuCl 2 in THF, two‐fold deprotonation of cyclopentadienyl‐cyclononatetraene 8 to give dianion 16 , and oxidative treatment of 16 with CuCl 2 ( Schemes 2 and 3 ). Compound 1 is a highly reactive and thermally instable molecule, since valence isomerisation 1 → 17 proceeds easily even at low temperature (the half‐life of 1 is ca. 30 min at −15° in CDCl 3 ). NMR investigations show that nonapentafulvalene is an olefinic molecule with strongly alternating bond lengths, its nine‐membered ring deviating strongly from planarity. Comparison of the NMR data of 1 with those of a series of sterically similar pentafulvenes 18 and nonafulvenes 19 ( Tables 1 and 2 ) demonstrates that ( a ) with regard to the pentafulvene unit of 1 , the cyclononatetraene ring acts as very weak electron‐donating group, while ( b ) with regard to the nonafulvene unit of 1 , the cyclopentadiene ring acts as weak electron‐accepting group. So nonapentafulvalene may be regarded as a ‘nonafulvene of inverse π‐polarisation’.