Elektron‐Donor‐Acceptor‐Verbindungen, XXXIV. Höhere [n.n]Paracyclophan‐Chinhydrone: Synthese, Molekülstruktur und spektroskopische Eigenschaften

Abstract

Charge-Transfer(CT)-AbsorptionenCharge-transfer(CT) absorptions in dependence on conformation-related donor-acceptor arrangements were investigated for [n.n]paracyclophane quinhydrones with n = 4, 5, and 6. Based on results of the X-ray structure analysis special aspects of the molecular and crystal structure of [4.4]paracyclophane quinhydrone 2 are discussed. -The two stereoisomeric tetramethoxy[5.5]-paracyclophanes 3 and 4 were prepared starting from 5 via 6 -11 as well as by the alternative route via 12 and 13. The structural assignment of 3 and 4 was determined by X-ray structure analysis of 4. A thermal isomerisation 3 + 4 does not occur even at higher temperatures. On the other hand, partial oxidative demethylation of 3 and 4 led to a rapidly equilibrating mixture of the [5.5]paracyclophane quinhydrones 15 and 16. -In the [6.6]paracyclophane series the barrier to the mutual interconversion of pseudoortho and pseudogeminal isomers is further reduced. Therefore, the analogous synthetic route from 17 via 18-22 yielded only one tetramethoxy[6.6]paracyclophane 23 and only one [6.6]paracyclophane quinhydrone 24.Untersuchungen an stereoisomeren Chinhydronen der [3.3]Paracyclophan-Reihe haben gezeigt, daR unterschiedliche Donor-Acceptor-Orientierungen auf die Charge-

Intramolecular Electron Transfer between 2,5-Dimethoxy-1,4-phenylene Units in [n.n]Paracyclophane Radical Cations

“…•ϩ with ∆E Ͻ 0.1 V and interplanar distances Ն 5.1 Å [4] , on the other hand, are localized radical cations at low temperature (ca. 220 K), i.e.…”

“…Previous in-[4.4]paracyclophane radical anion (3 •Ϫ ) generated in dimethoxyethane, clearly indicated a localized species. Based vestigations of these compounds deal, for example, with the dependence of intramolecular charge transfer on the con-on this observation, it was assumed that methylene bridges with n Ͼ 3 prevent intramolecular electron transfer between formation-related donor-acceptor arrangement [1] [2] [3] [4] or with electron transfer of unsubstituted [n.n]paracyclophane the two π-systems. This view is supported by the slow intramolecular electron transfer observed for the 1,2-diphenylradical anions (n ϭ 2, 3 and 4) [5] and related radical ions [6] .…”

“…Furthermore, in both crease in the separation of the electrophores. According to crystal-structure determinations, the interplanar distances the pseudogeminal (5, 6) and the pseudoortho series (10, 11), the first and second oxidation potentials of the correspond-of the pseudogeminal 7 (n ϭ 4) [3] and 8 (n ϭ 5) [4] are 4.01 and 5.11 Å , respectively. This increased separation of the ing [2.2]-and [3.3]paracyclophanes are very similar, indicating virtually uniform intramolecular π-π interactions.…”

“…of the non-deuterated compound NMR Gauss meter and a Hewlett-Packard 5342A microwave fre-181Ϫ182°C [22] [21] , pseudogeminal (5) [1b] , pseudogeminal (7) [3] and pseudoortho 6,9,16,19-tetra-C 8 D 8 ], 167 (13), 138 (35), 112 (13). methoxy [4.4]paracyclophane (12) [3] , pseudogeminal 7,10,18,21-tetramethoxy [5.5]paracyclophane (8) [4] , 9,12,22,paracyclophane: To a boiling, oxy [7.7]paracyclophane-4,17-dione (9) [16] , and 4,7-dimeth-stirred suspension of potassium carbonate (25 g) in ethanol/water oxy [2.2]paracyclophane (15) [22] were available in our laboratory or (95:5, 3 l) a solution containing 1,4-bis(2-bromoethyl)benzene (10.2 were prepared as described in the literature. …”

“…Ϫ EI-MS; (0.5Ϫ1 m) and tetrabutylammonium hexafluorophosphate (0. 4 ]benzene according to proand ENDOR: Bruker ESP 300 spectrometer equipped with the ER cedures described in the literature for the non-deuterated com-252 (ENMR) ENDOR system; g values were determined using an pound [27] , m.p. 185Ϫ186°C (m.p.…”