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

Abstract

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.