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Kinetics of the reactions between [(RS)₂Fe(μ-S)₂M(μ-S)₂Fe(SR)₂]ⁿ- (M = Mo, R = Ph, n= 2; M = V, R = Et, n = 3) and [Fe(SR)₄]²-: Key steps in the assembly of cuboidal Fe - S-based clusters

Lookup NU author(s): Professor Richard Henderson

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Abstract

The reaction of [S2Mo(μ-S)2Fe(SPh) 2]2- with [Fe(SPh)4]2- produces the dicuboidal cluster [{MoFe3S4(SPh)3}2 (μ-SPh)3]3- in a three stage process studied by 1H-n.m.r. spectroscopy and stopped-flow spectrophotometry. The initial stage involves the formation of the linear trinuclear [(PhS) 2Fe(μ-S)2Mo(μ-S)2Fe(SPh) 2]2- and the kinetics indicate an equilibrium reaction (k1Mo = 2.5±0.3×102 dm3 mol-1 s-1, k-1Mo, = 0.8±0.1 s-1). The second stage involves the reduction of [(PhS) 2Fe(μ-S)2Mo(μ-S)2Fe(SPh) 2]2- by [Fe(SPh)4]2- to form [(PhS)2Fe(μ-S)2 Mo(μ-S)2Fe(SPh) 2]3- which subsequently rearranges to form the voided cuboidal [MoFe2S4(SPh)3]2-. The kinetics of the second stage exhibits a simple first order dependence on the concentrations of both [(PhS)2Fe(μ-S)2Mo(μ-S) 2Fe(SPh)2]3- and [Fe(SPh)4] 2-(k2Mo = 25±2 dm3 mol -1 s-1). The kinetics of the third stage have not been studied but must involve incorporation of the final Fe and formation of the dicuboidal [{MoFe3S4(SPh)3}2(μ- SPh)3]3-. The kinetics of the reaction between [(EtS) 2Fe(μ-S)2V(μ-S)2Fe(SEt)23- and [Fe(SEt)4]2- to form [{VFe 3S4(SEt)3}2(μ-SEt)3] 3- have also been studied. An important difference between this reaction and the formation of the analogous [{MoFe3S 4(SPh)3}2(μ-SPh)3]3- is that the formation of [{MoFe3S4(SPh)3} 2(μ-SPh)3]3- from [(PhS)2Fe(μ- S)2Mo(μ-S)2Fe(SPh)2]2- involves a change in the redox state of the cluster, whilst the formation of [{VFe 3S4(SEt)3}2(μ-SEt) 3]3- from [(EtS)2Fe(μ-S)2V(μ- S)2Fe(SEt)2]3- requires no change in redox state. The reaction between [(EtS)2Fe(μ-S)2V(μ-S) 2Fe(SEt)2]3- and [Fe(SEt)4] 2- involves two stages. The kinetics of the faster phase is associated with a rate law analogous to that observed for the reaction between [(PhS)2Fe(μ-S)2Mo(μ-S)2Fe(SPh) 2]2- with [Fe(SPh)4]2-: a first order dependence on the concentrations of [(EtS)2Fe(μ-S) 2V(μ-S)2Fe(SEt)2]3- and [Fe(SEt)4]2- (k2V = 1.1±0.1 × 103 dm3 mol-1 s-1). This observation indicates that whilst there is no change in redox state between [(EtS)2Fe(μ-S)2V(μ-S)2Fe(SEt) 2]3- and [{VFe3S4(SEt) 3}2(μ-SEt)3]3-, reduction is necessary to catalyse the conversion of the linear [(EtS)2 Fe(μ-S)2V(μ-S)2Fe(SEt)2]3- into the voided cuboidal [VFe2S4(SEt)3] 3-. The results of the studies reported in this paper together with those on other putative reactions involved in the assembly of cuboidal clusters, have been combined to present a scheme of the mechanism of cuboidal cluster assembly. © Springer 2006.

Publication metadata

Author(s): Cui Z, Henderson RA

Publication type: Article

Publication status: Published

Journal: Transition Metal Chemistry

Year: 2006

Volume: 31

Issue: 4

Pages: 530-540

ISSN (print): 0340-4285

ISSN (electronic): 1572-901X

Publisher: Springer

URL: http://dx.doi.org/10.1007/s11243-006-0020-6

DOI: 10.1007/s11243-006-0020-6

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