Synthesis and structural characterization of metallocrown ethers containing butterfly Fe2S2 cluster cores.: Biomimetic hydrogen evolution catalyzed by Fe2(μ-SCH2CH2OCH2CH2S-μ)(CO)6

The synthesis, structure, and properties of a series of new metallocrown ethers with butterfly Fe2S2 cluster cores have been investigated. While metallocrown ethers Fe-2(mu-SCH2CH2OCH2CH2S-mu)(CO)(6) (I) and [Fe-2(mu-SCH2CH2OCH2CH2S-mu)(CO)(6)](2) (I*) were prepared in 30% yield by treatment of dithiol HSCH2CH2OCH2CH2SH with equimolar Fe-3(CO)(12) in THF at 50-60 degrees C for 2 h, treatment of dithiols HSCH2(CH2OCH2)(n)CH2SH (n = 2-4) with equimolar Fe-3(CO)(12) in THF at reflux for 0.5 h afforded metallocrown ethers Fe-2[mu-SCH2(CH2OCH2)(n)CH2S-mu](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 H-2 evolution is suggested, the possibility for improving the catalytic activity of this crown ether by its complexation with a metal cations is predicted.