Diiron Thiadithiolates as Active Site Models for the Iron-Only Hydrogenases: Synthesis, Structures, and Catalytic H₂ Production

The first diiron thiadithiolates as active site models for the Fe-only hydrogenases were prepared. Treatment of Fe3(CO)12 with excess 1,2,4-trithiolane in THF at reflux afforded parent model Fe2 (μ-SCH2)2S(CO)6 (1) in 42% yield. Further treatment of 1 with Cp(CO)2Fe(BF4) prepared in situ from Cp(CO)2FeI and AgBF4 in CH2Cl2 gave cationic model [Fe2(μ-SCH2)2S(CO)6][Cp(CO)2Fe](BF4) (2) in 81% yield, while treatment of 1 with 2 equiv of Et4NCN in MeCN or with t-BuNC in CH2Cl2 produced models (Et4N)2[Fe2(μ-SCH2)2S(CO)4(CN)2] (3) and Fe2(μ-SCH2)2S(CO)4(t-BuNC)2 (4) in 93% and 51% yields, respectively. All the new models 1−4 were characterized by elemental analysis and spectroscopy, as well as by X-ray crystallography for 1, 2, and 4. Furthermore, model 1 has been proved to be a catalyst for proton reduction of a weak acid Et3NHCl to give hydrogen under electrochemical conditions.本研究制备了首例作为铁铁氢化酶(Fe-only hydrogenase)活性位点模型的二铁硫二硫醇盐类配合物。将十二羰基三铁(Fe₃(CO)₁₂)与过量1,2,4-三硫杂环戊烷在四氢呋喃(THF)中回流反应，以42%的收率得到母体模型化合物六羰基(μ-双(亚甲硫基)硫)二铁[Fe₂(μ-SCH₂)₂S(CO)₆]（记为1）。将模型1与原位制备的环戊二烯基(Cp)二羰基铁四氟硼酸盐[Cp(CO)₂Fe(BF₄)]——该试剂由环戊二烯基(Cp)二羰基碘化铁与四氟硼酸银在二氯甲烷(CH₂Cl₂)中原位合成——反应，以81%的收率得到阳离子模型配合物[Fe₂(μ-SCH₂)₂S(CO)₆][Cp(CO)₂Fe](BF₄)（记为2）。将模型1分别与2当量四乙基氰化铵(Et₄NCN)在乙腈(MeCN)中反应，或与叔丁基异腈(t-BuNC)在二氯甲烷中反应，则分别以93%和51%的收率得到模型配合物(Et₄N)₂[Fe₂(μ-SCH₂)₂S(CO)₄(CN)₂]（记为3）与Fe₂(μ-SCH₂)₂S(CO)₄(t-BuNC)₂（记为4）。所有新制备的模型配合物1~4均通过元素分析与光谱表征完成结构确认，其中配合物1、2和4还通过X射线晶体衍射(X-ray crystallography)解析了单晶结构。进一步研究表明，模型配合物1在电化学条件下可作为催化剂，催化弱酸三乙胺盐酸盐(Et₃NHCl)的质子还原反应以制备氢气。