Ferrocene-sesquibicyclic hydrazine cross-electron-transfer rates

Nelsen, Stephen F.; Wang, Yichun; Ramm, Michael; Accola, Molly A.; Pladziewicz, Jack R.

doi:10.1021/j100205a016

Cited by 16 publications

(26 citation statements)

References 2 publications

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“…8, 11 The smallest ratios of k 11 (obs) to k 11 (calc) have been found for reactions involving Cp * CpFe: the ratios are 2.2 for 33N) 2 , 2.0 for 22/u22, and from this work, 1.7 for iPr 2 N) 2 . Electronic factors appear to be surprisingly unimportant in determining k 12 (obs), and the reaction with the aromatic amine TMPD, which has k 22 (obs) 5 × 10 11 times faster than iPr 2 N) 2 , gives a k 11 -(calc) value which is closer to the experimental value than do reactions with three of the four hydrazines studied, which are far closer in structure to iPr 2 N) 2 .…”

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confidence: 43%

“…1 λ is assumed to be the sum of a solvation term, λ out , which is determined by molecular size and the solvent employed, and a solvent-independent structural reorganization term, λ in . 8,11 Marcus showed that if ET is assumed to be adiabatic and λ 12 for a cross-ET is assumed to be the average of λ 11 and λ 22 for the two components, k 12 is given by eqs 2 and 3, where Z 12 is the preexponential factor for the mixed ET. 3 For the particularly well studied tetramethyl-p-phenylenediamine, TMPD, k 11 is 1.5 × 10 9 M -1 s -1 .…”

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confidence: 99%

“…cally, because the parameters V and hν in used in more modern, diabatic ("nonadiabatic") ET theory 1 ought to vary, causing the preexponential factors for k 11 and k 22 to differ. It is not at all clear how Z 12 ought to be predicted in such a case.…”

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Slow Electron Transfer Reactions Involving Tetraisopropylhydrazine

et al. 1996

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Marcus pointed out in 1956 that the fundamental parameter to know for predicting outer-sphere electron transfer (ET) activation free energies is λ, the vertical free energy gap between a non-interacting pair consisting of a neutral species M 0 and its own radical ion (M + or M -) in solution, and the same pair in which an electron has been transferred between the two components without allowing any relaxation. 1 If the relaxed, solvated neutral and radical cation are designated by n and c, and the charge present is shown as a superscript, this energy gap for vertical "self-ET" between n 0 and c + may be written as the sum of the relaxation energies for cationic and neutral species (eq 1). 2 λ corresponds to 4 times the thermal barrier for ET,

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Slow Electron Transfer Reactions Involving Tetraisopropylhydrazine

et al. 1996

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“…Three previous studies of intermolecular electron transfer (ET) reactions involving hydrazines using stopped-flow measurements of rate constants have been reported. − In the work discussed here a purified, isolable cation radical dissolved in acetonitrile containing 0.1 M tetrabutylammonium perchlorate is injected into a stopped-flow cell along with a neutral compound of lower formal redox potential ( E °‘) in the same solvent, and the change in absorbance resulting from the ET reaction which ensues is followed as a function of time. A series of experiments varying the concentrations, carried out under pseudo-first-order conditions if possible, is used to determine the second-order rate constant, k 12 (obsd), for the reaction.…”

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confidence: 99%

Estimation of Self-Exchange Electron Transfer Rate Constants for Organic Compounds from Stopped-Flow Studies

et al. 1997

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Second-order rate constants k 12 (obsd) measured at 25°C in acetonitrile by stopped-flow for 47 electron transfer (ET) reactions among ten tetraalkylhydrazines, four ferrocene derivatives, and three p-phenylenediamine derivatives are discussed. Marcus's adiabatic cross rate formula k 12 (calcd) ) (k 11 k 22 k 12 f 12 ) 1/2 , ln f 12 ) (ln K 12 ) 2 /4 ln(k 11 k 22 /Z 2 ) works well to correlate these data. When all k 12 (obsd) values are simultaneously fitted to this relationship, best-fit self-exchange rate constants, k ii (fit), are obtained that allow remarkably accurate calculation of k 12 (obsd); k 12 (obsd)/k 12 ′(calcd) is in the range of 0.55-1.94 for all 47 reactions. The average ∆∆G ij q between observed activation free energy and that calculated using k ii (fit) is 0.13 kcal/mol. Simulations using Jortner vibronic coupling theory to calculate k 12 using parameters which produce the wide range of k ii values observed predict that Marcus's formula should be followed even when V is as low as 0.1 kcal/mol, in the weakly nonadiabatic region. Tetracyclohexylhydrazine has a higher k ii than tetraisopropylhydrazine by a factor of ca. 10. Replacing the dimethylamino groups of tetramethyl-p-phenylenediamine by 9-azabicyclo[3.3.1]nonyl groups has little effect on k ii , demonstrating that conformations which have high intermolecular aromatic ring overlap are not necessary for large ET rate constants. Replacing a γ CH 2 group of a 9-azabicyclo[3.3.1]nonyl group by a carbonyl group lowers k ii by a factor of 17 for the doubly substituted hydrazine and by considerably less for the doubly substituted p-phenylenediamine.

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“…The Wisconsin group has evaluated self-exchange rate constants for sesquibicyclic hydrazine neutral-radical cation couples in various solvents by 8,9 means of proton NIR line broadening. 8 These hydrazines exhibit much slower self-exchange rates than most organic redox couples, in the range 6.8 x 102 to 6.6 x 104 N1 S-1 (vide infra).…”

Section: Iatmentioning

confidence: 99%