Three Paramagnetic Reduction Stages of Phenyl Substituted 1,2:9,10 Dibenzo[2.2]paracyclophane-1,9-dienes. Radical Anions, Triplet Dianions and Radical Trianions as studied by ESR and ENDOR Spektroscopy

URN to cite this document:

urn:nbn:de:bvb:355-epub-2552 Copy

DOI to cite this document:

10.5283/epub.255 Copy

Meijere, Armin de ; Gerson, Fabian ; König, Burkhard ; Reiser, Oliver ; Wellauer, Thomas

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Date of publication of this fulltext: 05 Aug 2009 13:22

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Details

Item type:	Article
Journal or Publication Title:	Journal of the American Chemical Society
Volume:	112
Number of Issue or Book Chapter:	19
Page Range:	pp. 6827-6832
Date:	1990
Institutions:	Chemistry and Pharmacy > Institut für Organische Chemie > Lehrstuhl Prof. Dr. Oliver Reiser Chemistry and Pharmacy > Institut für Organische Chemie > Lehrstuhl Prof. Dr. Burkhard König
Identification Number:	Value Type 10.1021/ja00175a013 DOI
Dewey Decimal Classification:	500 Science > 540 Chemistry & allied sciences
Status:	Published
Refereed:	Yes, this version has been refereed
Created at the University of Regensburg:	Unknown
Item ID:	255

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Abstract

Reduction of di- and tetraphenyl-substituted 1,2:9,10-dibenzo[2.2]paracyclophane-1,9-dienes, 3, 3-d'₂, 4,5, and 5-tBu₄ with potassium in ethereal solvents has been monitored by ESR and ENDOR spectroscopy. In each case, the first reduction step yields a radical anion in which the unpaired electron resides in one of the two lateral biphenyl or o-terphenyl mystems orthogonal to the central phane ...

Abstract

Reduction of di- and tetraphenyl-substituted 1,2:9,10-dibenzo[2.2]paracyclophane-1,9-dienes, 3, 3-d'₂, 4,5, and 5-tBu₄ with potassium in ethereal solvents has been monitored by ESR and ENDOR spectroscopy. In each case, the first reduction step yields a radical anion in which the unpaired electron resides in one of the two lateral biphenyl or o-terphenyl mystems orthogonal to the central phane unit. Except under conditions of strong association with the K⁺ counterion, electron exchange between the two π-ystems is fast on the hyperfine time scale. Upon further reduction, a second electron is taken up, as revealed by the appearance of triplet dianions bearing one unpaired electron in each of the two lateral π-ystems (separation ca. 1 nm). The singlet state of the dianion of 5 has been estimated to lie only slightly higher (ca. 2 kJ mol⁻¹) than the triplet state; the simultaneous presence of the singlet dianions of 3 and 5 in the solutions is compatible with evidence from NMR spectroscopy. An even more prolonged contact with potassium metal leads to radical trianions with the unpaired electron accommodated in the central phane unit. These radical trianions can thus be regarded as the radical anions of [2.2]paracyclophane having two negatively charged lateral π-ystems attached to it. Detection of trianions in a quartet state by ESR spectroscopy proved to be difficult under the experimental conditions used. The sequential uptake of three electrons by 3-5 is discussed in the light of the reduction potentials of the constituent π-ystems.

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