Synthesis and Characterization of Single, Double, and Triple Butterfly [2Fe2E] (E = Se, S) Cluster Complexes Related to the Active Site of [FeFe]-Hydrogenases

As the active site mimics of [FeFe]-hydrogenases, 14 new butterfly [2Fe2E] (E = Se, S) cluster complexes have been prepared by various synthetic routes. The N-substituted single-butterfly [2Fe2Se] complexes [(μ-SeCH2)2NC(O)R]Fe2(CO)6 (1, R = Me; 2, R = Ph; 3, R = PhCH2O) were prepared by reactions of the in situ formed (μ-LiSe)2Fe2(CO)6 with RC(O)N(CH2Cl)2, whereas the corresponding [2Fe2S] complexes [(μ-SCH2)2NC6H4R-p]Fe2(CO)6 (4, R = CO2Et; 5, R = CH2OH) were produced by reaction of the in situ generated (μ-HS)2Fe2(CO)6 with aqueous CH2O followed by treatment with p-RC6H4NH2. The parent single-butterfly [2Fe2Se] complex [(μ-SeCH2)2NH]Fe2(CO)6 (6) could be prepared by reaction of the N-substituted complex 3 with deprotecting reagent BBr3, BF3·OEt2/EtSH, or BF3·OEt2/Me2S, whereas the N-substituted single-butterfly [2Fe2Se] complexes [(μ-SeCH2)2NC(O)R]Fe2(CO)6 (7, R = Et; 8, R = PhCH2) were produced by reactions of 6 with acylating agents RC(O)Cl in the presence of Et3N. While the known parent single-butterfly [2Fe2S] complex [(μ-SCH2)2NH]Fe2(CO)6 reacted with 2,6-[ClC(O)]2C5H3N to afford double-butterfly [2Fe2S] complex [Fe2(CO)6(μ-SCH2)2NC(O)]2(2,6-C5H3N) (9), the new N-hydroxyethyl-substituted single-butterfly [2Fe2Se] complex [(μ-SeCH2)2N(CH2)2OH]Fe2(CO)6 (10) could be obtained by the in situ reaction of (μ-HSe)2Fe2(CO)6 with (HOCH2)2N(CH2)2OH. Interestingly, complex 10 could react with [ClC(O)]2CH2 or 1,3,5-[ClC(O)]3C6H3 in the presence of Et3N to give the corresponding double-butterfly [2Fe2Se] complex [Fe2(CO)6(μ-SeCH2)2N(CH2)2O2C]2CH2 (11) and triple-butterfly complex [Fe2(CO)6(μ-SeCH2)2N(CH2)2O2C]3(1,3,5-C6H3) (12), whereas the known single-butterfly [2Fe2S] complex [(μ-SCH2)2N(CH2)2OH]Fe2(CO)6 could react with 2,6-[ClC(O)]2C5H3N and 1,3,5-[ClC(O)]3C6H3 in the presence of Et3N to afford the corresponding double-butterfly [2Fe2S] complex [Fe2(CO)6(μ-SCH2)2N(CH2)2O2C]2(2,6-C5H3N) (13) and triple-butterfly complex [Fe2(CO)6(μ-SCH2)2N(CH2)2O2C]3(1,3,5-C6H3) (14), respectively. All the new complexes 1–14 have been characterized by elemental analysis and spectroscopy, as well as by X-ray crystallography for 1–4, 7–9, and 14. In addition, the electrochemical study indicated that complexes 1 and 2 can catalyze the proton reduction of HOAc to give hydrogen.

作为[FeFe]-氢化酶([FeFe]-hydrogenases)的活性位点模拟物，本研究通过多种合成路径制备了14种新型蝶状[2Fe2E]（E=Se、S）簇合物。其中，N-取代单蝶状[2Fe2Se]配合物[(μ-SeCH₂)₂NC(O)R]Fe₂(CO)₆（1，R=Me；2，R=Ph；3，R=PhCH₂O）通过原位生成的(μ-LiSe)₂Fe₂(CO)₆与RC(O)N(CH₂Cl)₂的反应制得；而相应的[2Fe2S]配合物[(μ-SCH₂)₂NC₆H₄R-p]Fe₂(CO)₆（4，R=CO₂Et；5，R=CH₂OH）则先由原位产生的(μ-HS)₂Fe₂(CO)₆与甲醛水溶液反应，再经对-RC₆H₄NH₂处理得到。母体单蝶状[2Fe2Se]配合物[(μ-SeCH₂)₂NH]Fe₂(CO)₆（6）可通过N-取代配合物3与脱保护试剂三溴化硼(BBr₃)、三氟化硼乙醚络合物(BF₃·OEt₂)/乙硫醇(EtSH)或三氟化硼乙醚络合物(BF₃·OEt₂)/二甲基硫醚(Me₂S)反应制得；而N-取代单蝶状[2Fe2Se]配合物[(μ-SeCH₂)₂NC(O)R]Fe₂(CO)₆（7，R=Et；8，R=PhCH₂）则由配合物6与酰化试剂RC(O)Cl在三乙胺(Et₃N)存在下反应得到。已知的母体单蝶状[2Fe2S]配合物[(μ-SCH₂)₂NH]Fe₂(CO)₆与2,6-[ClC(O)]₂C₅H₃N反应，可得到双蝶状[2Fe2S]配合物[Fe₂(CO)₆(μ-SCH₂)₂NC(O)]₂(2,6-C₅H₃N)（9）；而新型N-羟乙基取代单蝶状[2Fe2Se]配合物[(μ-SeCH₂)₂N(CH₂)₂OH]Fe₂(CO)₆（10）可通过(μ-HSe)₂Fe₂(CO)₆与(HOCH₂)₂N(CH₂)₂OH的原位反应制得。值得注意的是，配合物10可与[ClC(O)]₂CH₂或1,3,5-[ClC(O)]₃C₆H₃在三乙胺存在下反应，分别得到对应的双蝶状[2Fe2Se]配合物[Fe₂(CO)₆(μ-SeCH₂)₂N(CH₂)₂O₂C]₂CH₂（11）与三蝶状配合物[Fe₂(CO)₆(μ-SeCH₂)₂N(CH₂)₂O₂C]₃(1,3,5-C₆H₃)（12）；而已知的单蝶状[2Fe2S]配合物[(μ-SCH₂)₂N(CH₂)₂OH]Fe₂(CO)₆可分别与2,6-[ClC(O)]₂C₅H₃N、1,3,5-[ClC(O)]₃C₆H₃在三乙胺存在下反应，得到对应的双蝶状[2Fe2S]配合物[Fe₂(CO)₆(μ-SCH₂)₂N(CH₂)₂O₂C]₂(2,6-C₅H₃N)（13）与三蝶状配合物[Fe₂(CO)₆(μ-SCH₂)₂N(CH₂)₂O₂C]₃(1,3,5-C₆H₃)（14）。所有新型配合物1~14均通过元素分析与光谱学进行了表征，其中配合物1~4、7~9及14还通过X射线晶体衍射(X-ray crystallography)确定了晶体结构。此外，电化学研究表明，配合物1与2可催化乙酸(HOAc)的质子还原反应以生成氢气。