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Kinetic studies, using stopped-flow spectrophotometry, on the reactions of [M4(SPh)10]2- (M = Fe or Co) with PhS- to form [M(SPh)4]2- are described, as are the reactions between [M4(SPh)10]2- and [MOS4]2- to form [S2MoS2Fe(SPh)2]2- or [S2MoS2CoS2MoS2]2-. The kinetics of the reactions with PhS- are consistent with an initial associative substitution mechanism involving attack of PhS- at one of the tetrahedral M sites of [M4(SPh)10]2- to form [M4(SPh)11]3-. Subsequent or concomitant cleavage of a μ-SPh ligand, at the same M, initiates a cascade of rapid reactions which result ultimately in the complete rupture of the cluster and formation of [M(SPh)4]2-. The kinetics of the reaction between [M4(SPh)10]2- and [MOS4]2- indicate an initial dissociative substitution mechanism at low concentrations of [MOS4]2-, in which rate-limiting dissociation of a terminal thiolate from [M4(SPh)10]2- produces [M4(SPh)9]- and the coordinatively unsaturated M site is rapidly attacked by a sulfido group of [MOS4]2-. It is proposed that subsequent chelation of the MOS4 ligand results in cleavage of an M-μ-SPh bond, initiating a cascade of reactions which lead to the ultimate break-up of the cluster and formation of the products, [S2MoS2Fe(SPh)2]2- or [S2MoS2CoS2MoS2]2-. With [Co4(SPh)10]2-, at higher concentrations of [MOS4]2-, a further substitution pathway is evident which exhibits a second order dependence on the concentration of [MOS4]2-. The mechanistic picture of cluster disruption which emerges from these studies rationalizes the "all or nothing" reactivity of [M4(SPh)10]2-.
Author(s): Henderson RA; Cui Z
Publication type: Article
Publication status: Published
Journal: Inorganic Chemistry
Year: 2002
Volume: 41
Issue: 16
Pages: 4158-4166
ISSN (print): 0020-1669
ISSN (electronic): 1520-510X
Publisher: American Chemical Society
URL: http://dx.doi.org/10.1021/ic020284j
DOI: 10.1021/ic020284j
PubMed id: 12160403
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