Synthesis, Structure, and Electrocatalysis of Butterfly [Fe₂SP] Cluster Complexes Relevant to [FeFe]-Hydrogenases

Abstract

The first [Fe 2 SP] model complexes for the active site of [FeFe]-hydrogenases have been prepared. Thus, the μ-CO-containing complex salt [Et 3 NH][(μ-CO)(μ-SCH 2 CH 2 OH)Fe 2 (CO) 6 ] (m 1 ) formed from Fe 3 (CO) 12 , HSCH 2 CH 2 OH, and Et 3 N was treated in situ with PCl 3 and PPhCl 2 followed by treatment with Et 3 N/DBU to give the all-carbonyl complexes (μ-SCH 2 CH 2 OPR-μ)Fe 2 (CO) 6 (1, R = Cl; 3, Ph), whereas the functional transformation of 1 with PhOH/NaH and CO substitution of 3 with PPh 3 or PPh 2 H in the presence of Me 3 NO afforded the corresponding complexes (μ-SCH 2 CH 2 OPOPh-μ)Fe 2 (CO) 6 (2) and (μ-SCH 2 CH 2 OPPh-μ)Fe 2 (CO) 5 L (4, L = PPh 3 ; 5, PPh 2 H), respectively. Similarly, when complex salt [Et 3 NH][(μ-CO)(μ-SC 6 H 4 OH)Fe 2 (CO) 6 ] (m 4 ) generated from Fe 3 (CO) 12 , 2-HOC 6 H 4 SH, and Et 3 N was treated in situ with PCl 3 and PPhCl 2 followed by treatment with Et 3 N/DBU, the expected all-carbonyl complexes (μ-SC 6 H 4 OPR-μ)Fe 2 (CO) 6 (6, R = Cl; 8, Ph) were produced. In addition, further functional transformation of 6 with MeOH/Et 3 N and CO substitution of 8 with t-BuNC in the presence of Me 3 NO yielded the corresponding complexes (μ-SC 6 H 4 OPOMe-μ)Fe 2 (CO) 6 (7) and (μ-SC 6 H 4 OPPh-μ)Fe 2 (CO) 5 (t-BuNC) (9), respectively. However, it should be noted that when complex salt m 4 was treated with PBr 3 under similar conditions, [(μ-SC 6 H 4 OPO(CH 2 ) 4 Br-μ]Fe 2 (CO) 6 (10) was unexpectedly obtained. While the possible pathways for formation of the unexpected 10 were suggested, all complexes 1−10 were characterized by elemental analysis and spectroscopy and for some of them by X-ray crystallography. Interestingly, model complexes 1, 4, and 8 have been found to be catalysts for HOAc proton reduction to H 2 under CV conditions. ■ INTRODUCTION[FeFe]-Hydrogenases (hereafter denoted as [FeFe]Hases) are a class of natural enzymes that catalyze H 2 production at rapid rates in a broad range of prokaryotic and eukaryotic microorganisms. 1−5 The X-ray crystallographic 6−8 and FTIR spectroscopic 9−11 studies revealed that the active site of [FeFe]Hases consists of a butterfly [Fe 2 S 2 ] cluster core and a cubic [Fe 4 S 4 ] cluster core, which are connected together via a cysteine S atom. In addition, the two Fe atoms in the butterfly [Fe 2 S 2 ] core are bridged by a dithiolate ligand and coordinated by three CO and two CN − ligands. Recently, the dithiolate ligand has been identified as an azadithiolate μ-SCH 2 NHCH 2 S-μ ligand, evidenced by 14 N HYSCORE 12 and controlled metalloenzyme activation 13 (Figure 1a). Encouraged by the well-established active site structure, synthetic chemists have prepared a great number of models for the active site of [FeFe]Hases, such as the butterfly [Fe 2 E 2 ] (E = S, Se, Te) and [Fe 2 P 2 ]-type model complexes. 14−17 However, it is worth noting that up to now no butterfly [Fe 2 SP]-type model complex has been prepared, albeit some ordinary butterfly [Fe 2 SP] complexes are known. 18−21 Therefore, to further understand the active site struc...

Hydrophilic Quaternary Ammonium‐Group‐Containing [FeFe]‐Hydrogenase Models: Synthesis, Structures, and Electrocatalytic Hydrogen Production

“…Complexes 2 and 4 display one irreversible reduction peak at À2.10 and À2.09 V, respectively,a nd one irreversible oxidation peak at À0.06 and 0.40 V, respectively (Table 3a nd Figure 5). Similart op reviously reported cases, [25,35,[58][59][60] 2 NR}] under the reported electrochemical conditions. [23] In addition, it should be noted that:1 )the redox processes for 2 and 4 are irreversible at the scan rates of 50-1613 mV s À1 (see Figures S3 and S4 in the Supporting Information), and 2) the reduction peak currents of 2 and 4 are proportional to the square root of the scan rates (i.e.,5 0-1613mVs À1 ), thus indicatingt hat the electrochemical reduction processes are diffusion controlled (see Figure S5 in the Supporting Information).…”

“…Complexes 2 and 4 display one irreversible reduction peak at −2.10 and −2.09 V, respectively, and one irreversible oxidation peak at −0.06 and 0.40 V, respectively (Table and Figure ). Similar to previously reported cases, bulk electrolysis proved that these redox events are one‐electron processes (see Figures S1 and S2 in the Supporting Information); therefore, these events can be assigned to the Fe Ι Fe Ι to Fe Ι Fe 0 reduction and Fe Ι Fe Ι to Fe Ι Fe ΙΙ oxidation, respectively. Although the dppe‐chelated complex [(μ‐PDT)Fe 2 (CO) 4 (κ 2 ‐dppe)] was reported to undergo electron‐transfer‐catalyzed (ETC) isomerization to afford the bridged isomer [(μ‐PDT)Fe 2 (CO) 4 (μ‐dppe)] upon electrochemical reduction, [ 57] our PNP‐chelated complex 2 cannot undergo such a type of isomerization to give the corresponding bridged isomer 4 .…”

“…Under the guidance of the well‐elucidated H‐cluster structure, synthetic chemists have designed and prepared numerous [FeFe]H 2 ase models; in particular, some of these models have been found to act as catalysts for electrochemical and photoinduced H 2 production in organic solvents, and even in the presence of water . The question is why chemists use water in such catalytic H 2 production, to which the answers are: 1) water may serve not only as a “clean” and cheap solvent, but also as a “clean” and cheap proton source and 2) H 2 production catalyzed by [FeFe]H 2 ases in nature is accomplished in aqueous media at a very low reductive potential (ca.…”

Unexpected Reaction of Fe3(CO)12 with Dialkyldithiophosphate: The Case of P–S Bond Activation

“…One resonance observed at δ = 96.9 and 92.7 ppm can be assigned to the dialkyldithiophosphate ligand, which is high‐field shifted by about 17 ppm compared to the free ligand (δ = 113.8 ppm and 109.9 ppm). The other resonances observed at δ = 263.6 and 257.3 ppm can be ascribed to the bridging P atoms of the P–Fe–CO unit in 1 and 2 , which can compare with the reported [Fe 2 SP] complex ( μ ‐SCH 2 CH 2 OPCl‐ μ )Fe 2 (CO) 6 …”

[Fe2S2–Agx]-Hydrogenase Active-Site-Containing Coordination Polymers and Their Photocatalytic H2 Evolution Reaction Properties

“…The oxidation potentials of L1 and L2 are 0.42 and 0.26 V, respectively, which can be ascribed to the oxidation process of [Fe I Fe I ] to [Fe II Fe I ]. The first reduction potentials of the two ligands are −1.20 and −1.18 V, respectively, which correspond to the reduction process of [Fe I Fe I ] to [Fe 0 Fe I ]. , The second reduction potentials of L1 and L2 are −1.77 and −1.80 V, respectively, which are assigned to the reduction process of [Fe 0 Fe I ] to [Fe 0 Fe 0 ]. As shown in Figure c–e, the polymers retain the electrochemical features of the [Fe 2 S 2 ] cluster, with the oxidation potentials at 0.43, 0.40, and 0.48 V, respectively, and the reduction potentials at −1.13/–1.86, −1.13/–1.82, and −1.04/–1.81 V, respectively, for 1 – 3 .…”