Intramolecular Electron Transfer and Cation Migration in the Dianion of Dicyclooctatetraenyldimethylsilane Studied by Dynamic 13C NMR Spectroscopy.

Boman, Patrik; Eliasson, Bertil; Anulewicz, R.; Rasała, Danuta; Gawinecki, Ryszard; Häfelinger, Günter; Homsi, Muhammed Nour; Kuske, Frank K. H.; Haugg, Monika; Trabesinger-Rüf, Nathalie; Weinhold, Elmar G.

doi:10.3891/acta.chem.scand.50-0816

Cited by 7 publications

(19 citation statements)

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“…8 13 C NMR ([ 2 H 8 ]THF, 0.49 M, 27 ЊC): δ 147.31 (C-1), 141.37 (C-2), 135.51 (C-8), 133.92, 132.70, 132.17, 132.13 (C-5), 129.97, Ϫ3.34 (CH 3 ). 8 Tetrahydrofuran-d 8 ([ 2 H 8 ]THF ) was purchased from Glaser AG Basel and used without further purification. THF employed for the NMR analysis of bond shift in 2 was refluxed over K metal and distilled prior to use.…”

Section: Perkinmentioning

confidence: 99%

“…The C-1 and C-5 assignments followed from their narrow linewidths during BS broadening of the other peaks of the neutral ring and from longer T 1 and smaller NOE values for C-1. 8 Assignment of the 13 C signals of 1 2Ϫ -2K + and 2 2Ϫ -2K + was achieved by 13 C homodecoupling (see SST experiments below), 2D H-C correlation 23 and relayed H-H-C coherence transfer spectroscopy. 24,25 Pulse delays were optimised for 1 J CH = 125 Hz and 3 J HH = 10 Hz.…”

Section: Nmr Signal Assignmentmentioning

confidence: 99%

“…[35][36][37] Some information about the ion-pair structure may be gained from a qualitative relationship between the strength of the cation-anion interaction and the average 13 C chemical shift for the carbons in the dianion ring. 8,10,11 In this simple model, a stronger interaction with the cation is assumed to involve some stabilization of the highest occupied MOs of the anion while the levels of the virtual MOs should be less affected by the interaction. As a result, the average excitation energy of magnetic field-induced mixing of certain filled and virtual MOs will become larger and the paramagnetic moment will decrease according to the Karplus-Pople equation for the paramagnetic contribution to the nuclear shielding.…”

Section: Structure and Ion Pairing Of Dianionsmentioning

confidence: 99%

“…The structural and dynamic properties of annulenes have received considerable attention during the past few decades, with [8]annulene [cyclooctatetraene (COT)] being one of the most studied compounds. [1][2][3] Ring inversion (RI) and bond shift (BS) mechanisms (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the influence of counterion and solvent on the rate constant for CT (k CT ) has been studied. 8,11 Intramolecular two-electron-cation transfer in such species is relatively slow, with k CT in the range of 10 Ϫ2 -10 2 s Ϫ1 at ambient temperature, which is explained by the requirement for flattening the neutral ring. Rate constants have been obtained by 1 H and 13 C dynamic NMR methods.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Perkinmentioning

confidence: 99%

Section: Nmr Signal Assignmentmentioning

confidence: 99%

Section: Structure and Ion Pairing Of Dianionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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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Carbanion Chemistry

Grutzner

2007

Encyclopedia of Magnetic Resonance

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

et al. 1998

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The rate constants for ring inversion (k r.i.) and bond shift (k b.s.) in 1 and 2 were determined by dynamic NMR spectrometry while the rate constants for bond shift and intramolecular charge transfer (k c.t.) were determined for 1 2-/2K+ and 2 2-/2K+. These processes were modeled by HF/3-21G(*) ab initio molecular orbital calculations of the ground states and of several transition states for 3, 4, 3 2-, 4 2-, 3 2-/2K+, and 4 2-/2K+. The results indicate that k r.i. and k b.s. are ca. 2.5 times greater (at 240 and 280 K, respectively) for 2 compared to 1 due to larger steric repulsions in the ground state of 2. Contrariwise, k b.s. and k c.t. are 1.7 and 166 times greater, respectively, at 280 K for 1 2-/2K+ than for 2 2-/2K+. These differences are attributed to less twisting and therefore greater π delocalization between the cyclooctatetraenyl rings and the aryl ring in the bond shift and charge-transfer transition states of 1 2- compared to 2 2-. The greater difference between 1 2- and 2 2- for k c.t. compared to k b.s. is postulated to result from looser ion pairing in the charge-transfer transition state relative to the bond shift transition state.

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Intramolecular Electron Transfer and Cation Migration in the Dianion of Dicyclooctatetraenyldimethylsilane Studied by Dynamic 13C NMR Spectroscopy.

Cited by 7 publications

References 0 publications

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

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

Carbanion Chemistry

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

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