SOLVENT DEPENDENCE OF THE ELECTRON SELF-EXCHANGE OF HEXAKIS(2,6-DIISOPROPYLPHENYL ISOCYANIDE)CHROMIUM(0,I) AND HEXAKIS(2,6-DIISOPROPYLPHENAL ISOCYANIDE)CHROMIUM(I,II) AND A COMPARISON WITH THEORETICAL-MODELS

The rate of electron self-exchange between chromium(I) hexakis(2,6-diisopropylphenyl isocyanide) tetrafluoroborate, Cr-(CNdipp)6BF4, and Cr(CNdipp)6(BF4)2has been measured as a function of reactant concentration, temperature, and solvent (acetone, acetonitrile, nitromethane, methylene chloride, methanol) by1H NMR line broadening. The rate of electron self-exchange between Cr(CNdipp)6and Cr(CNdipp)6BF4has been measured as a function of temperature in acetone. The Cr(0)/Cr(I) rate constants, ca. 108M−1s−1, are a factor of 10 higher than the Cr(I)/Cr(II) values in methylene chloride and acetone. The Cr(I)/Cr(II) rate constants vary little between the solvents at 298 K. The activation parameters do vary, showing a compensating pattern for the solvents studied. The results for the two systems are compared with the predictions of the standard Marcus collision and solvent dynamic models. The experimental electron self-exchange rate constants are in excellent agreement and the activation parameters are in reasonable agreement with the predictions from the Marcus collision model. The calculated activation parameters from the Marcus collision model show no trend with solvent, and thus do not predict the compensation behavior. © 1990, American Chemical Society. All rights reserved.