Steric and Electronic Control of Dynamic Processes in Aryl-Bridged Dicyclooctatetraenes and Their Dianions

Staley, Stuart W.; Kehlbeck, Joanne D.; Grimm, Russell A.; Sablosky, Rachel A.; Boman, Patrik; Eliasson, Bertil

doi:10.1021/ja980931z

Cited by 11 publications

(26 citation statements)

References 27 publications

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“…[35] These values are in good agreement with experimental data, following from NMR measurements. [41] Gas-phase reactions yield 63 kJ mol À1 [42] for the flattening and delocalization of COT, which is comparable with the corresponding NMR data of 53 kJ mol…”

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confidence: 82%

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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confidence: 82%

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

et al. 2008

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“…They recently studied the dipotassium salts of 1,4-dicyclooctatetraenyl-benzene (A) and 1,4-dicyclooctatetraenylnaphthalene (B) in THF-d 8 , where they exist as (K + ) 2 (COT -2 )-bridge-(COT 0 ) pairs. 17 The rate constant ratio (A/B) for two electron and potassium charge transfer that they observed is 166 (at 280 K).…”

Section: Discussionmentioning

confidence: 95%

“…The result for 1 + / 4 + result resembles that observed by Staley and co-workers for the same change in bridge, using very different, ion-paired CBU. They recently studied the dipotassium salts of 1,4-dicyclooctatetraenyl-benzene ( A ) and 1,4-dicyclooctatetraenylnaphthalene ( B ) in THF-d 8 , where they exist as (K + ) 2 (COT -2 )−bridge-(COT 0 ) pairs . The rate constant ratio ( A / B ) for two electron and potassium charge transfer that they observed is 166 (at 280 K).…”

Section: Discussionmentioning

confidence: 99%

Temperature Effects on Electron Transfer within Intervalence Bis(Hydrazine) Radical Cations

et al. 1999

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Analyses of the shape of intervalence charge-transfer bands at various temperatures (∼255-325 K in most cases) in acetonitrile are reported for the radical cations of bis(2-tert-butyl-2,3-diazabicyclo[2.2.2]-oct-3-yl) hydrazines that are bridged by 2,5-xylene-1,4-diyl (2 + ), durene-1,4-diyl (3 + ), naphthalene-1,4-diyl (4 + ), biphenyl-4,4′-diyl (5 + ), and 9,9-dimethylfluorene-2,7-diyl (6 + ) aromatic rings. Electron-transfer (ET) rate constants measured by ESR as a function of temperature are reported for 4 + -6 + . Despite the fact that the ET barriers for these compounds are dominated by vibrational reorganization, explicit inclusion of vibronic coupling effects is not necessary for the prediction of their ET rate constants from the optical spectra. Rate constants in excellent agreement with the measured ones are predicted by a classical analysis of chargetransfer band shape, if the diabatic surfaces are changed from the usual assumption that they are parabolas to ones that fit the shape of the charge-transfer bands.

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“…Details of this procedure are given elsewhere. 8, 9 The progress of reduction was followed by 1 H NMR and (in some cases) by 13 C NMR spectroscopy. Because of extensive disproportionation of the radical anion to the neutral compound and dianion, 5 reduction does not have to proceed until exactly two equiv.…”

Section: Perkinmentioning

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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Steric and Electronic Control of Dynamic Processes in Aryl-Bridged Dicyclooctatetraenes and Their Dianions

Cited by 11 publications

References 27 publications

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

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

Temperature Effects on Electron Transfer within Intervalence Bis(Hydrazine) Radical Cations

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

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