Synthesis, structures, and electrocatalytic properties of phosphine‐monodentate, −chelate, and ‐bridge diiron 2,2‐dimethylpropanedithiolate complexes related to [FeFe]‐hydrogenases

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As diiron subsite models of [FeFe]-hydrogenases for catalytic proton reduction to hydrogen (H 2), a new series of the phosphine-substituted diiron ethanedithiolate complexes Fe 2 (μ-edt)(CO) 6-n L n (n = 1, 2) were prepared from the variable substitutions of all-CO precursor Fe 2 (μ-edt)(CO) 6 (A) and tertiary phosphines (L1-L4) under different reaction conditions. While the Me 3 NO-assisted substitutions of A and one equiv. ligands L1-L4 [L = Ph 2 P (CH 2 NHBu t), Ph 2 P(CH 2 CH 2 NH 2), Ph 2 P(NHBu t), and Ph 2 P(C 6 H 4 Me-p)] produced the monosubstituted complexes Fe 2 (μ-edt)(CO) 5 L (1-4) in good yields, the refluxing xylene solution of A and two equiv. ligand L1 prepared complex Fe 2 (μ-edt)(CO) 5 {κ 1-Ph 2 P(CH 2 NHBu t)} (1) in low yield. Meanwhile, the UV-irradiated toluene solution of A and two equiv. ligand L3 resulted in the rare formation of the disubstituted complex Fe 2 (μ-edt) (CO) 4 {κ 1 , κ 1-(Ph 2 PNHBu t) 2 } (5) in low yield, whereas the Me 3 NO-assisted substitution of A and two equiv. ligand L4 afforded the disubstituted complex Fe 2 (μ-edt)(CO) 4 {κ 1 , κ 1-(Ph 2 PC 6 H 4 Me-p) 2 } (6) in good yield. All the model complexes 1-6 have been characterized by elemental analysis, FT-IR, NMR spectroscopy, and particularly for 1, 3, 5 by X-ray crystallography. Further, the protonations of complexes 1-4 are studied and compared with excess acetic acid (HOAc) and trifluoroacetic acid (TFA) by using FT-IR and NMR techniques. Additionally, the electrochemical and electrocatalytic properties of model complexes 1-6 are investigated and compared by cyclic voltammetry (CV), suggesting that they are electrocatalytically active for proton reduction to H 2 in the presence of HOAc.

Amine‐containing tertiary phosphine‐substituted diiron ethanedithioate (edt) complexes Fe₂(μ‐edt)(CO)_6‐nL_n (n= 1, 2): Synthesis, protonation, and electrochemical properties

Lǐ

Lü

et al. 2020

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Diiron ethane‐1,2‐dithiolate complexes with 1,2,3‐thiadiazole moiety: Synthesis, X‐ray crystal structures, electrochemistry and fungicidal activity

Yang

Liu

et al. 2020

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Four diiron ethane‐1,2‐dithiolate complexes containing 1,2,3‐thiadiazole moiety have been synthesized and characterized. Esterification of the starting complex [Fe2(CO)6{μ‐SCH2CH(CH2OH)S}] (1) with 4‐methyl‐1,2,3‐thiadiazole‐5‐carboxylic acid in the presence of 4‐dimethylaminopyridine and N,N′‐dicyclohexylcarbodiimide yielded the corresponding ester [Fe2(CO)6{μ‐SCH2CHCH2O2C(4‐C2N2SCH3)S}] (2) in good yield. Further treatment of complex 2 with a phosphine ligand triphenylphosphine, tris(2‐methoxyphenyl)phosphine, or tri(p‐tolyl)phosphine and the decarbonylation reagent Me3NO·2H2O resulted in the formation of phosphine‐substituted analogues [Fe2(CO)5L{μ‐SCH2CHCH2O2C(4‐C2N2SCH3)S}] [L = PPh3, 3; P(2‐C6H4OCH3)3, 4; P(4‐C6H4CH3)3, 5] in 60 − 80% yields. The new complexes 2–5 were characterized by elemental analysis, IR and NMR spectroscopy and further confirmed by X‐ray diffraction analysis. The electrochemical properties were studied by cyclic voltammetry, showing that these complexes can catalyse the reduction of protons to H2 in the presence of HOAc. In addition, the fungicidal activity studies revealed that the hydroxy group possibly play a significant role in the biological activity.

Substituent effects of tertiary phosphines on the structures and electrochemical performances of azadithiolato‐bridged diiron model complexes of [FeFe]‐hydrogenases

Liu

Jin

et al. 2022

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In this work, a new series of azadithiolato-bridged diiron complexes [Fe 2 (μadt NOH )(CO) 5 {P(C 6 H 4 R) 3 }] (adt NOH = (SCH 2 ) 2 N(C 6 H 4 CH 2 CH 2 OH-p) and R = Cl-p, 1; Me-m, 2; OMe-p, 3 supported by tertiary phosphines, which may be considered as the active site models of [FeFe]-hydrogenases, has been prepared in 73-81% yields by the Me 3 NO-assisted decarbonylating reactions of all-CO precursor [Fe 2 (μ-adt NOH )(CO) 6 ] (A) with several tertiary phosphines [(P (C 6 H 4 R) 3 ] in MeCN at room temperature. All the new complexes 1-3 are fully characterized by elemental analysis, spectroscopic techniques (Fourier transform-infrared spectroscopy [FT-IR] and nuclear magnetic resonance [NMR]), and especially for 1 and 3 by X-ray crystallography. The IR and 31 P { 1 H} NMR spectroscopic analyses have shown that the electron density of diiron center in 1-3 may be adjusted by the introduction of the different substituents (R) of the P(C 6 H 4 R) 3 ligands into the [2Fe2S] cluster. The X-ray crystallographic investigation has displayed that the typical Fe-Fe, Fe-P, and Fe-C distances of 1-3 are significantly influenced by the electronic effects of the P(C 6 H 4 R) 3 phosphines coordinated apically to one Fe atom, whereas their P apical -Fe-Fe and C apical -Fe-Fe angles are mainly controlled by the steric interaction between the phosphine ligands and the dithiolate bridges. Further, the electrochemical performances of 1-3 are studied and compared in the absence or presence of acetic acid (HOAc) as proton source by using cyclic voltammetry, suggesting that they are active for the electrocatalytic proton reduction to hydrogen (H 2 ).