TY  - JOUR
A1  - Bock, Hans
A1  - John, Andreas
A1  - Kleine, Markus
A1  - Näther, Christian
A1  - Bats, Jan W.
T1  - Elektronentransfer und Ionenpaar-Bildung, 33 [1, 2]. Die Einelektronen-Reduktion von Tetraphenyl-p-benzochinon mit Alkalimetallen: ENDOR-Spektren von Kontaktionen-Paaren sowie Tripelionen in Lösung und Einkristallstrukturen der Neutralverbindung und ihres Natrium-Salzes
T1  - Electron Transfer and Ion Pair Formation, 33 [1, 2]. The Single Electron Reduction of Tetraphenyl-p-benzoquinone by Alkali Metals: ENDOR Spectra of Contact Ion Pairs as well as Triple Ions in Solution and Single Crystal Structures of Both the Neutral Compound and its Sodium Salt
T2  - Zeitschrift für Naturforschung, B
N2  - Tetraphenyl-p-benzoquinone, according to its single crystal structure, shows some steric congestion: its quinone ring is distorted by 7° to a chair conformation, and its phenyl substituents are twisted around their CC axes between 46° and 72°. The half-wave reduction potentials of -0.57 and -1.25 V in acetonitrile confirm negligible π interaction of the phenyl substituents. Addition of alkalimetal tetraphenylborate salts lowers the second reduction potential due to contact ion formation, which can be confirmed by UV/VIS spectra recorded under aprotic conditions. Extensive ESR/ENDOR investigations prove the formation of the following species in THF solution: Tetraphenyl-p-benzosemiquinone radical anion contact ion pairs [M·⊖ Me⊕solv]' (Me⊕: Li⊕, Na⊕, Rb⊕, Cs⊕) and contact triple ion radical cations both with identical cations [M·⊖ (Me⊕solv)2]·⊕ (Me⊕: Li⊕, Na⊕, Cs⊕) and different cations [M·⊖ (Li⊕solv)(Me⊕solv)]·⊕ (Me⊕: Na⊕, Cs⊕). Addition of crown ethers can lead to external solvation of the Me⊕ counter cations, whereas cryptands form internal solvation complexes. The radical anion of 2,6-diphenyl-p-benzosemiquinone adds cations at its phenyl-free molecular half. The radical anion salt [tetraphenyl-p-benzosemiquinone·⊖ (Na⊕(tetrahydropyrane) 2)] could be crystallized and its structure determined at 200 K. In agreement with the Hirota sign rules for contact radicals in solution, the Na⊕ ion is found 62 pm above the π plane and 29° outside the axis of the CO bound, which is elongated due to one-electron reduction by 5 pm to 127 pm.
KW  - Benzoquinone Radical Anion
KW  - ENDOR Spectra
KW  - Single Crystal Structure
KW  - Ion Pair Formation
Y1  - 2014
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/79809
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-798098
SN  - 1865-7117
SN  - 0932-0776
VL  - 49.1994
IS  - 4
SP  - 529
EP  - 541
PB  - Verlag der Zeitschrift für Naturforschung
CY  - Tübingen
ER  -