Anion radicals in liquid ammonia. III. Activation parameters for the electron transfer between cyclooctatertraene dianion and anion radical

Smentowski, Frank J.; Stevenson, Gerald R.

doi:10.1021/ja01054a031

Cited by 14 publications

(5 citation statements)

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“…In a detailed ESR study by Stevenson et al, [19] the equilibrium constant between COTC À and perdeuterated per- . [20][21][22][23] These observations are in good agreement with numerous results obtained from comparable planar organic electron-self-exchange couples, such as the well-described naphthalene/naphthalene radical-anion system. Most aromatic planar reactants, without significant changes in the molecular configuration upon electron transfer, show these typical rates and activation parameters.…”

Section: à2supporting

confidence: 89%

Electron‐Self‐Exchange Kinetics of the Cyclooctatetraene/Cyclooctatetraene Radical‐Anion Couple

et al. 2008

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Rate constants k(hom) and k(het) are reported for the homogeneous electron-self-exchange and the heterogeneous electrochemical electron-transfer reactions, respectively, of the cyclooctatetraene/cyclooctatetraene(-) (COT/COT(.-)) redox couple. In acetonitrile, the values k(hom) (298 K)=(5+/-3) x 10(5) M(-1) s(-1) and k(het) (295 K)=8 x 10(-3) cm s(-1) are found, whereas slightly faster rates are obtained in dimethylformamide, namely, k(hom) (298 K)=(1.6+/-0.6) x 10(6) M(-1) s(-1) and k(het) (295 K)=2 x 10(-2) cm s(-1). The k(hom) rates are obtained from electron spin resonance (ESR) line broadening whereas the k(het) rates are measured at a mercurized Pt electrode by using Nicolson's method. The slowness of both electron-transfer reactions is caused by the high inner-sphere reorganization energy that results from the inevitable conformational change that takes place upon going from the tub-like COT molecule to the planar COT(.-) anion. The rates are well-understood in terms of Marcus theory, including an additional medium inner-sphere mode which is responsible for the flattening of COT.

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Section: à2supporting

confidence: 89%

Electron‐Self‐Exchange Kinetics of the Cyclooctatetraene/Cyclooctatetraene Radical‐Anion Couple

et al. 2008

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“…Na + /Na, E1 = À2.71 V). [27][28][29][30][31][32][33][34] Structurally characterised alkaline earth complexes comprising the cyclooctatetraenyl dianion are currently limited to examples in which the reducing equivalents of electrons are provided by the unambiguous oxidation of an s-block element centre. The heavier homoleptic alkaline earth complexes, [AeCOT] (Ae = Ca, Sr and Ba), for example, were synthesised by metal vapour co-condensation with 1,3,5,7-C 8 H 8 , whilst the magnesium derivative, [Mg(COT)(THF) 2.5 ], 35,36 was accessed through the direct combination of the [8]annulene and magnesium.…”

mentioning

confidence: 99%

“…The potassium and sodium reduction of 1,3,5,7-C 8 H 8 to the 10p aromatic dianion has been shown to occur in a stepwise fashion via the initial generation of the [COT] À radical anion, which is readily identifiable from its characteristic nine line EPR spectrum [a( 1 H) = 3.2 G (8.9 MHz)]. [27][28][29] The reaction between compound 2 and 1,3,5,7-C 8 H 8 in benzene solution was, thus, repeated between 140 and 298 K within the cavity of an X-band CW EPR spectrometer. Although this procedure again provided for the facile generation of the [COT] 2À dianion, no definitive evidence for any radical intermediates en route to compound 3 were observed.…”

mentioning

confidence: 99%

Reduction of 1,3,5,7-cyclooctatetraene by a molecular calcium hydride: an even electron polarised insertion/deprotonation mechanism

et al. 2019

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“…5 In addition, a large increase in the rate of CT between COT ؒϪ and COT 2Ϫ is observed when the cation is changed from Li ϩ to K ϩ in THF. 6 It has also been observed that upon reduction of COT with K, the 1 H signal from the dianion is very broad while the signals for the neutral COT and the solvent remain sharp throughout the reduction. The dianion signal sharpens just before complete reduction.…”

Section: Differential Line Broadeningmentioning

confidence: 98%

“…2-4 Intermolecular electron transfer (ET) between neutral and anionic COT compounds and related issues about electronic configuration and aromaticity have also been examined. 3,5,6 Further, dianions of bridged diCOT systems have been utilized to investigate various aspects of intramolecular electron and counterion exchange [here denoted charge transfer (CT)] between the dianion and neutral rings, 7-11 such as donor-acceptor distance, orientation of the rings, and electronic properties of the spacer. In addition, the influence of counterion and solvent on the rate constant for CT (k CT ) has been studied.…”

Section: Introductionmentioning

confidence: 99%

Bond shift and charge transfer dynamics in methylene- and dimethylsilyl-bridged dicyclooctatetraene dianions

Boman

Eliasson

Grimm

et al. 2001

J. Chem. Soc., Perkin Trans. 2

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The rate constants for bond shift in dicyclooctatetraenylmethane (1), dicyclooctatetraenyldimethylsilane (2), and their dianions (1 2Ϫ and 2 2Ϫ ) in [ 2 H 8 ]THF, have been determined from the temperature dependence of their 13 C NMR linewidths. The corresponding parameters for intramolecular electron and cation transfer (charge transfer) between the dinegative and neutral rings have been measured by 13 C NMR spin saturation transfer experiments for the dipotassium salts of 1 and 2. Selected structural features of the neutral compounds and the dianions are discussed on the basis of 13 C NMR chemical shifts and ab initio molecular orbital calculations at the HF/6-31G* and HF/3-21G(*) levels of theory. Energy contributions to the ring flattening in the bond shift process are calculated by molecular mechanics methods. The measured rate constants for both bond shift and charge transfer are larger for the methylene-bridged dianion. Approximately half of this difference is due to the greater ease of "gating" (i.e., ring flattening and distortion to the bond shift transition state) in 1 2Ϫ -2K + . A significant portion of the remainder is attributed to a greater inter-ring through-space interaction in 1 2Ϫ , although mediation by the cation and/or throughbridge interactions probably also contribute to some extent. A temperature-dependent differential 13 C NMR line broadening is observed for the dianion ring carbons of the dipotassium salts. Possible mechanisms for this counterion-specific line broadening, which occurs only for carbons with large HOMO coefficients, are discussed.

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Anion radicals in liquid ammonia. III. Activation parameters for the electron transfer between cyclooctatertraene dianion and anion radical

Cited by 14 publications

References 1 publication

Electron‐Self‐Exchange Kinetics of the Cyclooctatetraene/Cyclooctatetraene Radical‐Anion Couple

Electron‐Self‐Exchange Kinetics of the Cyclooctatetraene/Cyclooctatetraene Radical‐Anion Couple

Reduction of 1,3,5,7-cyclooctatetraene by a molecular calcium hydride: an even electron polarised insertion/deprotonation mechanism

Bond shift and charge transfer dynamics in methylene- and dimethylsilyl-bridged dicyclooctatetraene dianions

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