Stabilitätsumkehrung im System Benzol/Dewar-Benzol

Abstract

tris(diethy1phosphan) (,,Etriphos") ( I ) haben wir den Eisen(i1)-Komplex [(etriphos)FeZ](BF& (2) erhalten. Z ist das neue heterocyclische Zwitterion 1,1,3,3-Tetraethyl-5,5-dimethyl-1,3-diphosphonia-2,2-cyclohexandithiolat, das sich in situ bildet und als zweizahniger Disulfidoligand fungiert. Forschungsstipendium (1979Forschungsstipendium ( -1980, K. P. C, V. 1st Fellow der A. P. Sloan Foundation (1976-1980) und Camille and Henry Dreyfus Teacher Scholar (1978-1983 Aus den a,o-Diinen (4) und (5) erhalt man so die anellierten Cyclopentadienone (7) bzw. (8); (6) fordert andere Reaktionsbedingungen (Bestrahlen mit einer GE-Projektionslampe, 120 V, 250 W; siedendes 0-Xylol, Infusionspumpentechnik), um das theoretisch interessanter5I, gespannte (9) in geringen Ausbeuten zu liefern (Tabelle l).D a die a-Silyl-substituierten Enone ausgezeichnete Michael-Acceptoren sindI61, konnten die Cyclopentadienon-Liganden von (2). (7) und (8) wertvolle organische Synthone sein, wenn die Dekomplexierung ohne Dimerisierung moglich ware. Sie gelingt in nahezu quantitativer Ausbeute bei Verwendung von Diammoniumcernitrat in einem zweiphasigen Losungsmittelsystem (CH,CN/n-C,H,,), wobei aus (7)-(9) die Verbindungen (11)-(13) (Tabelle 1) erhalten werden. Unter denselben Bedingungen ergibt (2) bei -20 "C das fliichtige (10) (11%) und dessen Dimer (14) (54%), dem die exo-Konfiguration zugeordnet wurdel']. (1 0) dimerisiert spontan bei 37 "C, jedoch kann das Monomer durch BlitzPyrolyse bei 550 "C (10-4-10-5 Torr) (Tabelle 1) quantitativ zuruckgewonnen werden; damit hat man erstmals ein brauchbares Cyclopentadienon-Synthon zur Verfugung.

Organic molecules with abnormal geometric parameters

“…Interestingly, the benzene derivative 162 containing four tert-butyl groups in the adjacent positions is thermodynamically less stable than the isomer 163, which is a Dewar benzene derivative. 289 The twist `conformation' of the benzene ring has been observed in molecules of fused aromatic compounds. Typically, these molecules contain an aromatic polycyclic system twisted to form a helix the axis of which is either perpendicular or parallel to the benzene-ring planes.…”

Organic molecules with abnormal geometric parameters

“…Interestingly, the benzene derivative 162 containing four tert-butyl groups in the adjacent positions is thermodynamically less stable than the isomer 163, which is a Dewar benzene derivative. 289 The twist `conformation' of the benzene ring has been observed in molecules of fused aromatic compounds. Typically, these molecules contain an aromatic polycyclic system twisted to form a helix the axis of which is either perpendicular or parallel to the benzene-ring planes.…”

Organic molecules with abnormal geometric parameters

“…Interestingly, the benzene derivative 162 containing four tert-butyl groups in the adjacent positions is thermodynamically less stable than the isomer 163, which is a Dewar benzene derivative. 289 The twist `conformation' of the benzene ring has been observed in molecules of fused aromatic compounds. Typically, these molecules contain an aromatic polycyclic system twisted to form a helix the axis of which is either perpendicular or parallel to the benzene-ring planes.…”

Organic molecules with abnormal geometric parameters

“…Interestingly, the benzene derivative 162 containing four tert-butyl groups in the adjacent positions is thermodynamically less stable than the isomer 163, which is a Dewar benzene derivative. 289 The twist `conformation' of the benzene ring has been observed in molecules of fused aromatic compounds. Typically, these molecules contain an aromatic polycyclic system twisted to form a helix the axis of which is either perpendicular or parallel to the benzene-ring planes.…”