Models for the Active Site in [FeFe] Hydrogenase with Iron-Bound Ligands Derived from Bis-, Tris-, and Tetrakis(mercaptomethyl)silanes

By Apfel, Ulf-Peter; Troegel, Dennis; Halpin, Yvonne; Tschierlei, Stefanie; Uhlemann, Ute; Görls, Helmar; Schmitt, Michael; Popp, Jürgen; Dunne, Peter; Venkatesan, Munuswamy; Coey, Michael; Rudolph, Manfred; Vos, Johannes G.; Tacke, Reinhold & Weigand, Wolfgang
Published in Inorganic Chemistry NULL 2010

Abstract

A series of multifunctional (mercaptomethyl)silanes of the general formula type RnSi(CH2SH)4-n (n = 0-2; R = organyl) was synthesized, starting from the corresponding (chloromethyl)silanes. They were used as multidentate ligands for the conversion of dodecacarbonyltriiron, Fe3(CO)12, into iron carbonyl complexes in which the deprotonated (mercaptomethyl)silanes act as μ-bridging ligands. These complexes can be regarded as models for the [FeFe] hydrogenase. They were characterized by elemental analyses (C, H, S), NMR spectroscopic studies (1H, 13C, 29Si), and single-crystal X-ray diffraction. Their electrochemical properties were investigated by cyclic voltammetry to disclose a new mechanism for the formation of dihydrogen catalyzed by these compounds, whereby one sulfur atom was protonated in the catalytic cycle. The reaction of the tridentate ligand MeSi(CH2SH)3 with Fe3(CO)12 yielded a tetranuclear cluster compound. A detailed investigation by X-ray diffraction, electrochemical, Raman, Mössbauer, and susceptibility techniques indicates that for this compound initially [Fe2 μ-MeSi(CH2S)2CH2SH (CO)6] is formed. This dinuclear complex, however, is slowly transformed into the tetranuclear species [Fe4 μ-MeSi(CH2S)3 2(CO)8].

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