Hydrogen atom transfer from iron(II)-tris[2,2'-bi(tetrahydropyrimidine)] to TEMPO: a negative enthalpy of activation predicted by the Marcus equation

Journal of the American Chemical Society
Elizabeth A MaderJames M Mayer

Abstract

The transfer of a hydrogen atom from iron(II)-tris[2,2'-bi(tetrahydropyrimidine)], [FeII(H2bip)3]2+, to the stable nitroxide, TEMPO, was studied by stopped-flow UV-vis spectrophotometry. The products are the deprotonated iron(III) complex [FeIII(H2bip)2(Hbip)]2+ and the hydroxylamine, TEMPO-H. This reaction can also be referred to as proton-coupled electron transfer (PCET). The equilibrium constant for the reaction is close to 1; thus, the reaction can be driven in either direction. The rate constants for the forward and reverse reactions at 298 K are k1 = 260 +/- 30 M-1 s-1 and k-1 = 150 +/- 20 M-1 s-1. Interestingly, the rate constant for the forward reaction decreases as reaction temperature is increased, implying a negative activation enthalpy: DeltaH1 = -2.7 +/- 0.4 kcal mol-1, DeltaS1 = -57 +/- 8 cal mol-1 K-1. Marcus theory predicts this unusual temperature dependence on the basis of independently measured self-exchange rate constants and equilibrium constants: DeltaHcalcd = -3.5 +/- 0.5 kcal mol-1, DeltaScalcd = -42 +/- 10 cal mol-1 K-1. This result illustrates the value of the Marcus approach for these types of reactions. The dominant contributor to the negative activation enthalpy is the favorable enthalpy of reaction...Continue Reading

References

Feb 27, 2003·Journal of the American Chemical Society·Jeffrey C YoderJames M Mayer
Apr 16, 2003·Accounts of Chemical Research·Stephen J Blanksby, G Barney Ellison
Aug 21, 2003·Journal of the American Chemical Society·Jasmine R Bryant, James M Mayer
May 1, 2004·Annual Review of Physical Chemistry·James M Mayer

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Citations

Jan 27, 2006·Photosynthesis Research·James M MayerAntonio G DiPasquale
Oct 28, 2010·Accounts of Chemical Research·James M Mayer
Oct 12, 2010·Chemical Reviews·Jeffrey J WarrenJames M Mayer
Jan 30, 2010·Inorganic Chemistry·Christopher R WaidmannJames M Mayer
Apr 4, 2007·Journal of the American Chemical Society·Elizabeth A MaderJames M Mayer
Mar 19, 2009·Journal of the American Chemical Society·Christopher R WaidmannJames M Mayer
Sep 3, 2009·Journal of the American Chemical Society·Soushi MiyazakiShunichi Fukuzumi
Jul 22, 2009·Journal of the American Chemical Society·Adam WuJames M Mayer
Mar 11, 2010·Proceedings of the National Academy of Sciences of the United States of America·Jeffrey J Warren, James M Mayer
Jul 2, 2016·Journal of the American Chemical Society·Tesia V ChciukRobert A Flowers
Jan 6, 2017·Journal of the American Chemical Society·Marie BergnerFranc Meyer
Jan 19, 2008·Chemistry, an Asian Journal·Hiroki SugiuraMasahiko Yamaguchi
Apr 11, 2008·Dalton Transactions : an International Journal of Inorganic Chemistry·Tatsuya FujiiHideki Masuda
Jan 13, 2021·Inorganic Chemistry·Bronte J CharetteAlan F Heyduk
Nov 15, 2007·Chemical Reviews·My Hang V Huynh, Thomas J Meyer
Jun 9, 2005·Chemical Reviews·Sergey V KryatovSiegfried Schindler
Jun 21, 2011·The Journal of Physical Chemistry Letters·James M Mayer
Feb 11, 2014·Journal of the American Chemical Society·Antonia AlbersFranc Meyer
Mar 6, 2015·Biochemistry·Jeffrey J Warren, James M Mayer
Apr 29, 2020·Inorganic Chemistry·Marie-Louise WindChristian Limberg
Mar 3, 2005·Journal of the American Chemical Society·Bryson R Ussing, Daniel A Singleton
Apr 14, 2005·Journal of the American Chemical Society·Jason ShearerKenneth D Karlin
Mar 10, 2005·Journal of the American Chemical Society·Ahmad DehestaniJames M Mayer
May 5, 2005·Journal of the American Chemical Society·Gino A DiLabio, K U Ingold

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