Synthesis and Structural Characterization of Metallocrown Ethers Containing Butterfly Fe₂S₂ Cluster Cores. Biomimetic Hydrogen Evolution Catalyzed by Fe₂(μ-SCH₂CH₂OCH₂CH₂S-μ)(CO)₆

Abstract

The synthesis, structure, and properties of a series of new metallocrown ethers with butterfly Fe 2 S 2 cluster cores have been investigated. While metallocrown ethers Fe 2 (μ-SCH 2 CH 2 OCH 2 CH 2 S-μ)(CO) 6 ( I ) and [Fe 2 (μ-SCH 2 CH 2 OCH 2 CH 2 S-μ)(CO) 6 ] 2 ( I *) were prepared in 30% yield by treatment of dithiol HSCH 2 CH 2 OCH 2 CH 2 SH with equimolar Fe 3 (CO) 12 in THF at 50−60 °C for 2 h, treatment of dithiols HSCH 2 (CH 2 OCH 2 ) n CH 2 SH ( n = 2−4) with equimolar Fe 3 (CO) 12 in THF at reflux for 0.5 h afforded metallocrown ethers Fe 2 [μ-SCH 2 (CH 2 OCH 2 ) n CH 2 S-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 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.