Synthesis and Structural Characterization of Metallocrown Ethers Containing Butterfly Fe<sub>2</sub>S<sub>2</sub> Cluster Cores. Biomimetic Hydrogen Evolution Catalyzed by Fe<sub>2</sub>(μ-SCH<sub>2</sub>CH<sub>2</sub>OCH<sub>2</sub>CH<sub>2</sub>S-μ)(CO)<sub>6</sub>
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The synthesis, structure, and properties of a series of new metallocrown ethers with butterfly Fe2S2 cluster cores have been investigated. While metallocrown ethers Fe2(μ-SCH2CH2OCH2CH2S-μ)(CO)6 (I) and [Fe2(μ-SCH2CH2OCH2CH2S-μ)(CO)6]2 (I*) were prepared in 30% yield by treatment of dithiol HSCH2CH2OCH2CH2SH with equimolar Fe3(CO)12 in THF at 50−60 °C for 2 h, treatment of dithiols HSCH2(CH2OCH2)nCH2SH (n = 2−4) with equimolar Fe3(CO)12 in THF at reflux for 0.5 h afforded metallocrown ethers Fe2[μ-SCH2(CH2OCH2)nCH2S-μ](CO)6 (II−IV) in 18−33% yields. In addition to a possible pathway for formation of these metallocrown ethers being suggested, all the metallocrown ethers have been fully characterized by elemental analysis and spectroscopy, as well as by X-ray crystallography for I, III, IV, and I*. On the basis of electrochemical study of I−IV, metallocrown ether I was found to be a catalyst for proton reduction to hydrogen under electrochemical conditions. While an EECC mechanism for such catalytic H2 evolution is suggested, the possibility for improving the catalytic activity of this crown ether by its complexation with a metal cations is predicted.
