Browse by author
Lookup NU author(s): Adrain John Dunford, Professor Richard Henderson
Full text for this publication is not currently held within this repository. Alternative links are provided below where available.
The kinetics of the substitution reaction between [Fe4S4Cl4](2-) and (BuNC)-N-t to form [Fe4S4Cl2 (CNBut)(6)], in the presence of [H2N(CH2)(3)CH2](+), [NHEt3](+) or [lutH](+) (lut = 2,6-dimethylpyridine) have been studied. With the weakest acid, [H2N(CH2)(3)CH2](+) (pK(a) = 21.5), (BuNC)-N-t binds before the transfer of the proton. Analysis of the kinetics yields the rate constant for the binding of (BuNC)-N-t to [Fe4S4Cl4](2-) (k = 2.1 +/- 0.5 x 10(3) dm(3) mol(-1) s(-1)). With the stronger acids, [NHEt3](+) (pK(a) = 18.5) and [lutH](+) (pK(a) = 15.4), two protons bind to the cluster. Earlier work indicated that for a thermodynamically favourable proton-transfer reaction, the rate of the first proton transfer to [Fe4S4Cl4](2-) is at least 10(4) times slower than the diffusion-controlled limit (i.e. k = ca. 1 x 10(6) dm(3) mol(-1) s(-1)). Studies presented herein on the reactions between [Fe4S4Cl4](2-) and (BuNC)-N-t or Br- indicate that the rate of the second proton transfer is about 10(7) times slower than the diffusion-controlled limit (i.e. k = ca. 1 x 10(3) dm(3) mol(-1) s(-1)). One consequence of these slow rates of proton transfer to [Fe4S4Cl4](2-) is that the rate of binding (BuNC)-N-t or Br- to the cluster is slower than the initial proton transfer, but faster than the second one. The results of these studies are compared with those reported earlier for the reaction of [Fe4S4Cl4](2-) with PhSH in the presence of [lutH](+), where the poor nucleophilicity of the thiol results in PhSH binding to the cluster only after diprotonation. The possible relevance of these studies to the mechanisms of substrate binding and transformation at both synthetic and natural Fe-S clusters is discussed.
Author(s): Dunford AJ, Henderson RA
Publication type: Article
Publication status: Published
Journal: Journal of the Chemical Society: Dalton Transactions
Year: 2002
Issue: 14
Pages: 2837-2842
ISSN (print): 1472-7773
ISSN (electronic): 1364-5447
Publisher: Royal Society of Chemistry
URL: http://dx.doi.org/10.1039/b202850f
DOI: 10.1039/b202850f
Altmetrics provided by Altmetric
