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Substitution reactions of [Fe4S4Cl4]2- with ButNC or Et2NCS2-: Trapping intermediates and detecting new pathways

Lookup NU author(s): Adrain John Dunford, Professor Richard Henderson


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Kinetic studies on the substitution reaction between [Fe4S4Cl4]2- and ButNC or Et2NCS2- are reported. The binding of small molecules and ions to Fe-S clusters is a fundamental step in substitution reactions but can be difficult to follow directly because these reactions are rapid and often associated with small spectroscopic changes. A novel kinetic method is reported which allows the time course of molecule and ion binding to Fe-S clusters to be followed by monitoring the lability of the cluster. Using a stopped-flow, sequential-mix apparatus, [Fe4S4Cl4]2- and L (L = Et2NCS2- or ButNC) are rapidly mixed, and after a known time (δ) the resulting solution is mixed with a solution of PhS-. The thiolate substitutes for the chloro ligands on the cluster, in a reaction which is easy to follow because of the large change in the visible absorption spectrum. The rate of this substitution is extremely sensitive to whether L is bound to the cluster or not. By correlation of δ with the rate of the reaction with PhS-, the time course of the reaction between [Fe4S4Cl4]2- and L can be mapped out. In studies where L = ButNC this technique has allowed the detection of an intermediate {[Fe4S4Cl4(CNBut)]2-} which cannot be detected spectrophotometrically. In further studies, the substitution reactions of [Fe4S4Cl4]2- with PhS-, Et2NCS2-, or ButNC are all perturbed by the addition of Cl-. In all cases a common pathway for substitution is evident, but with Et2NCS2- an additional, slower pathway becomes apparent under conditions where the common pathway is completely inhibited by Cl-.

Publication metadata

Author(s): Henderson RA; Dunford AJ

Publication type: Article

Publication status: Published

Journal: Inorganic Chemistry

Year: 2002

Volume: 41

Issue: 21

Pages: 5487-5494

ISSN (print): 0020-1669

ISSN (electronic): 1520-510X

Publisher: American Chemical Society


DOI: 10.1021/ic0202110

PubMed id: 12377044


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