Topomerisierung des cis , cis , cis , trans ‐[9]Annulen‐Anions

Abstract

Topomerization of the cis,cis,c~,trans-[9]Annulene AnionWe investigated the conformational mobility -a topomerization -of the cis,cis,cis,trans- [9]annulene anion (9) in order to get some insight into the energetic situation of this aromatic compound. Three different temperature ranges afforded almost identical activation enthalpies for this process: 2 7 T , deuterium equilibration: AG* = 22.1 & 0.1 kcal. mol-'; 6 1 T , saturation transfer: AG* = 21.2 kcal .mol-'; 121"C, dynamic nuclear resonance spectroscopy: AG* = 22.2 f 0.2 kcal . mol-'. Reversible valence isomerizations of the trans-anion 9 are not likely to be responsible for the mechanism of the topomerization. Als Annulene werden monocyclische Polyene, deren Ringatome sp'-hybridisiert sind, bezeichnet '). Entsprechendes gilt fur Annulen-Ionen. Nach Hiickel') sollten durchkonjugierte Monocyclen mit 4n + 2 n-Elektronen ,,aromatisch" sein.Mit der Entwicklung der Kernresonanzspektroskopie erlebte die Untersuchung dieser Verbindungen einen enormen Aufschwung. Annulene und Annulen-Ionen mit RinggroDen zwischen 3 und 30 CH-Einheiten wurden dargestellt und auf ihre Ubereinstimmung mit der Hiickel-Regel untersucht 3). Alle Versuche, ein endgiiltiges, alle Molekiile umfassendes, quantitativ meD-und berechenbares Kriterium fur den aromatischen Charakter angeben zu konnen, scheiterten jedoch ' ). So ist man gezwungen, von Fall zu Fall geeignete Merkmale zur Charakterisierung heranzuziehen.Dabei kommt der konformativen Veranderung groDe Bedeutung zu, weil die Ermittlung von Hydrier-und Verbrennungswarmen bei Annulenen -wenn man von Benzol absieht -schwierig 5 * 6 , und bei Annulen-Ionen unmoglich ist '). Die Ermittlung der Aktivierungsparameter ') F. Sondheimer und R. Wolovsky, J. Am. Chem. SOC. 84, 260 (1962).

The Acidity of Brønsted CH Acids in DMSO − The Extreme Acidity of Nonacyanocyclononatetraene

“…This is in full accordance with the previous results of Boche and co-workers, [40,41] who reported a planar D 9h structure of the cyclononatetraenyl anion 13 ؊ as revealed by an NMR experiment. It is interesting to mention that all CϪC bond lengths in 13…”

Calcium, Strontium, Barium, and Ytterbium Complexes with Cyclooctatetraenyl or Cyclononatetraenyl Ligands1

“…Although the cyclononatetraenyl anion (C 9 H 9 - , CNT) and its alkali metal salts have been known for many years, authentic η 9 -C 9 H 9 - containing organometallic compounds are unknown. − The only reported organometallic complex (C 5 H 5 )Ti(C 9 H 9 ) is best described as (η 5 -C 5 H 5 )Ti((η 7 -C 9 H 9 ) on the basis of IR and 1 H NMR studies . The synthesis of neutral main group triple-decker complexes employing the C 8 H 8 2- (COT) ligand, also a 10 π- electron system, spurred the interest in this ligand.…”

Size‐Controlled Hapticity Switching in [Ln(C9H9)(C8H8)] Sandwiches

“…Additionally, Boche et al. gathered, in a comprehensive series of three articles, useful information on the Cnt ligand synthesis, as well as its topomerization and isomerization [19,22] . These studies unveil several questions on the real nature of the isomerization process when assisted by metal complexes.…”

“…gathered, in a comprehensive series of three articles, useful information on the Cnt ligand synthesis, as well as its topomerization and isomerization. [ 19 , 22 ] These studies unveil several questions on the real nature of the isomerization process when assisted by metal complexes. An interesting connection to this is that 1′′ in which one ligand is partially isomerized in the cis‐cis‐cis‐trans form, is obtained in a relatively high‐temperature synthesis (150 °C for 3 h) from the cis‐cis‐cis‐cis ligand, supposedly thermodynamically more stable.…”