Radikalanion-substituierte Kronenether als Käfige für Metallkationen

Bock, Hans; Hierholzer, Bernhard; Vögtle, Fritz; Hollmann, Günter

doi:10.1002/ange.19840960129

Cited by 27 publications

(3 citation statements)

References 8 publications

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“…Radical anions in which a crown-ether moiety is attached to a π system have been described. It was shown that the crown ether may well serve as a ligand to metal cations. − In these systems, like 10 , an oxygen atom carrying a partial negative charge serves as an additional ligand to the metal cation which then is also embedded in the crown-ether moiety. Such an arrangement is not possible in the phanes 4 − 8 .…”

Section: General Conclusionmentioning

confidence: 99%

Radical Ions of Crownophanes Derived from Tetraphenylethene. Solution Structures and Ion-Pairing Phenomena

et al. 1998

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Radical anions and radical cations of parent tetraphenylethene (1) and its cyclophane derivatives 2−8 were generated by chemical methods. These paramagnetic species were characterized by their ESR and simultaneously recorded optical spectra. The hyperfine coupling constants were substantiated by ENDOR and their signs by general TRIPLE spectroscopy. The structures of the radical ions were established with the help of quantum chemical calculations. The electron distribution in the phane radical ions is closely related to that found for 1^•-/1^•+. In the radical anions no specific complexation of alkali-metal counterions, K⁺ and Li⁺, by the crown-ether moieties could be observed. When the radical cations were generated by oxidation with Tl^III trifluoroacetate in 1,1,1,3,3,3-hexafluoropropanol, distinctly different ESR spectra were recorded as with the use of other oxidants. This observation is rationalized by the characteristic solvation properties of 1,1,1,3,3,3-hexafluoropropanol

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Section: General Conclusionmentioning

confidence: 99%

Radical Ions of Crownophanes Derived from Tetraphenylethene. Solution Structures and Ion-Pairing Phenomena

et al. 1998

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“…I) sei angemerkt: Die unerwartete Erniedrigung des ersten Halbstufenpotentials von Tetrakis(ter/-butyl)diphenochinon bei Wechsel des Lösungsmittels Acetonitril zu DMF um etwa 150 mV ist, da Wasserspuren wegen des konstanten zweiten Halbstufenpotentials als Ursa che auszuschließen sind, auf einen spezifischen Solvatationseffekt zurückzuführen [14], Für die Dis proportionierung des Radikalanions, 2M' ^ M + M e e , lassen sich aus den Differenzen der ersten und zweiten Halbstufenpotentiale nach KojSp = /?F/RT exp(Eo -Eq ) [ 15] [3][4][5][6][7][8] nur noch eine quasireversible Wel le, während mit Na*[B (C6H5 )4] (Abb. 1: B) noch zwei erniedrigte, quasireversible HalbstufenReduktionspotentiale meßbar sind.…”

Section: Cyclovoltammetrische Messungen An S^'^^'-tetraalkyldiphenoseunclassified

Elektronentransfer und Kontaktionen-Bildung, 42 [1,2] Cyclovoltammetrische und ESR / ENDOR-Untersuchungen der Einelektronen-Reduktion von Diphenochinonen / Electron Transfer and Contact Ion Pair Formation, 42 [1,2] Cyclovoltammetric and ESR / ENDOR Investigations of the One-Electron Reduction of Diphenoquinones

John

Bock

1995

Zeitschrift Für Naturforschung B

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Semiquinone radical anions are prototype compounds for contact ion pair formation with metal counter cations. In order to investigate the still open question whether bulky alkyl groups can sterically interfere, diphenoquinone derivatives O=C(RC=CH)2C=C(HC=CR)2C=O with R = C(CH3)3, CH(CH3)2 and CH3 have been selected and the following ESR/ENDOR results are obtained for the alkaline metal cations: The tetrakis(tert-butyl)-substituted radical anion only adds Li⊕ and Na⊕, while K⊕ forms no ion pair. The 3,3ʹ,5,5ʹ-tetra(isopropyl)diphenoquinone radical anion is accessible to all cations Me⊕, although Rb⊕ and Cs⊕ seem to be present solvent-separated in solution. The tetramethyl-substituted radical anion unfortunately polymerizes rapidly. Additional information concerns the ESR/ENDOR proof for ion triple radical cation formation [Li⊕ M•⊖Li⊕]•⊕, or the difference in the coupling constants upon Me⊕ docking at one δ⊖O=C group, suggesting that about 87% of the spin density is located in the cation-free molecular half of the diphenoquinone radical anion. Based on the wealth of ESR/ENDOR information, crystallization of the contact ion pairs and their structural characterization should be attempted.

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“…M it den zu ihrer Untersuchung zu nehm end eingesetzten ESR-und vor allem EN-DOR-spektroskopischen Meßtechniken [5] sind zahlreiche biologisch aktive Semichinon-Radikalanionen nachgewiesen und charakterisiert worden [4,5]. Im Gegensatz hierzu konnten für ihre Radikal-K ontaktionenpaare wie [M'e Me®]' oder ihre Tripelion-Radikalkationen [Me®M'e Me®]'®, die bei einfachen ortho-und para-C hm ontn um fang reich untersucht sind [5][6][7], keine Literaturhinwei se aufgefunden werden. Die folgenden vier W irk stoffe m it para-und orfAo-Benzochinon-Unterein- Sie sollten daher in weitgehend aprotischen Lö sungen zu ihren Radikalanionen oder nach Zusatz löslicher Salze Me®"X® zu ihren Radikal-Ionenpaaren reduzierbar und diese ESR/EN DOR-spektroskopisch nachweisbar sein.…”

unclassified

Elektronentransfer und Ionenpaar-Bildung, 28. ESR/ENDOR-Untersuchungen an Radikalanionen und Kontakt-Ionenpaaren der Naturstoff-Chinone Mitomycin C, Streptonigrin, Entobex^® und 10,11-Dioxobrucin/Electron Transfer and Ion Pairing, 28. ESR/ENDOR Studies of Radical Anions and Contact Ion Pairs of the Naturally Occurring Quinones Mitomycine C, Streptonigrine, Entobex^® and 10,11-Dioxobrucine

Bock

Hänel

Herrmann³

1992

Zeitschrift Für Naturforschung B

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Reduction of naturally occurring para-and ortho-benzoquinone derivatives M to their respective radical anions M·⊖ can be accomplished under largely aprotic conditions either by cautious low-temperature reaction in THF containing an excess of (2.2.2) cryptand at a potassium mirror or by using the "mild" single electron transfer reagent tetrabutylammonium boranate R4N⊕BH4⊖ in DMF. On addition of soluble alkali tetraphenylborates Me⊕[B(C6H5)4]⊖ , their hitherto unknown radical ion pairs [M·⊖ Me⊕]· and/or triple ion radical cations [Me⊕M·⊖Me⊕]·⊕ form, which might be of biological relevance in molecular carrier and "turn off -turn on" switch processes. On addition of metal perchlorates Me⊕n(ClO4⊖)n with multiply charged counter cations Me⊕n the respective paramagnetic species [M·⊖Me⊕n]·(n-1)⊕ result. Assuming exclusive one-electron transfer reductions without any redox fragmentation reactions, ESR, ENDOR and GENERAL TRIPLE spectra are presented and discussed for the following radical anions and radical ion pairs: mitomycin C (M·⊖ and [M·⊖Mex⊕]·(x-1)⊕ with Me⊕ = Li⊕, Na⊕), streptonigrine (M·⊖ and [M·⊖Lix⊕]·(x-1)⊕), Entobex® (M·⊖ and [M·⊖Me⊕n]·(n-1)⊕ with Me⊕n = Li⊕, Na⊕, Cd⊕⊕, (H5C6)2Tl⊕) as well as brucinequinone ([M·⊖ Me⊕n]·(n-1)⊕ with Me⊕n = Li⊕, Cd⊕⊕, Pb⊕⊕, La⊕⊕⊕).

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Radikalanion-substituierte Kronenether als Käfige für Metallkationen

Abstract: Die Fixierung von Metallkationen im Solvatkäfig – wie in 1 – gelingt durch Reduktion der entsprechenden neutralen Verbindung mit Alkalimetallen M. Die von Ladung und Radius der Kationen abhängige Spinverteilung wurde erstmals durch ESR‐ und ENDOR‐Spektroskopie untersucht.

Cited by 27 publications

References 8 publications

Radical Ions of Crownophanes Derived from Tetraphenylethene. Solution Structures and Ion-Pairing Phenomena

Radical Ions of Crownophanes Derived from Tetraphenylethene. Solution Structures and Ion-Pairing Phenomena

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