Iron-Only Hydrogenase Active Site Models Containing a Cysteinyl Group Coordinated through Its Sulfur Atom to One Iron Atom of the Diiron Subsite
✍ Scribed by Li-Cheng Song; Jian-Hua Ge; Jing Yan; Hu-Ting Wang; Xiang Luo; Qing-Mei Hu
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 248 KB
- Volume
- 2008
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
We have developed a simple and convenient method for the synthesis of the first H‐cluster models in which a L‐cysteinyl group is coordinated to one of the two iron atoms of the diiron subsite through its sulfur atom. This synthetic method includes (i) treatment of the Boc‐protected L‐cysteine ester Boc‐NHCH(CH~2~SH)CO~2~Et (1, Boc = tert‐butoxycarbonyl) with EtONa to give the L‐cysteinyl mercaptide NaSCH~2~CH(NH‐Boc)CO~2~Et (2); (ii) further treatment of 2 with [Cp(CO)~2~FeI] to produce the metallothioether ligand Cp(CO)~2~FeSCH~2~CH(NH‐Boc)CO~2~Et (3); and (iii) treatment of the parent diiron complex [Fe~2~(μ‐SCH~2~)~2~CH~2~(CO)~6~] (4), [Fe~2~(μ‐SCH~2~)~2~N(__t__Bu)(CO)~6~] (5), or [Fe~2~(μ‐SCH~2~)~2~N(C~6~H~4~OMe‐p)(CO)~6~] (6) with Me~3~NO·2H~2~O followed by ligand 3 to afford the target model compounds [Fe~2~(μ‐SCH~2~)~2~CH~2~(CO)~5~(ligand 3)] (7), [Fe~2~(μ‐SCH~2~)~2~N(__t__Bu)(CO)~5~(ligand 3)] (8), or [Fe~2~(μ‐SCH~2~)~2~N(C~6~H~4~OMe‐p)(CO)~5~(ligand 3)] (9), respectively. All the new compounds 2, 3, and 7–9 have been characterized by elemental analysis and various spectroscopic techniques. The X‐ray diffraction analysis of 8 has confirmed that these models contain a cysteinyl sulfur atom not only coordinated to one Fe atom of the diiron subsite, but also to the Fe atom of the Cp(CO)~2~Fe moiety to form the linkage [Fe~Cp~‐(μ‐cysteinyl‐S)‐Fe~subsite~], which is similar to [Fe~cubane~‐(μ‐cysteinyl‐S)‐Fe~subsite~] found in natural enzymes. In addition, spectroscopic and electrochemical measurements have further demonstrated that the linkage [Fe~Cp~‐(μ‐cysteinyl‐S)‐Fe~subsite~] can provide substantial electronic communication between the diiron subsite and the Cp(CO)~2~Fe moiety. Under electrochemical conditions, 8 has been shown to be a catalyst for HOAc proton reduction to dihydrogen, and a new type of E*2E2C mechanism for this catalytic reaction is suggested.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)