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In this work, a new series of azadithiolato‐bridged diiron complexes [Fe2(μ‐adtNOH)(CO)5{P(C6H4R)3}] (adtNOH = (SCH2)2N(C6H4CH2CH2OH‐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 Me3NO‐assisted decarbonylating reactions of all‐CO precursor [Fe2(μ‐adtNOH)(CO)6] (A) with several tertiary phosphines [(P(C6H4R)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 31P{1H} 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(C6H4R)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(C6H4R)3 phosphines coordinated apically to one Fe atom, whereas their Papical‐Fe‐Fe and Capical‐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 (H2). [ABSTRACT FROM AUTHOR]

To further develop the biomimetic chemistry of [FeFe]- and [NiFe]-hydrogenases for the catalytic reduction of protons to hydrogen (H2), two new mononuclear Ni(II) ethanedithiolate complexes [{(Ph2PCH2)2NR}Ni(SCH2CH2S)] (R = tert-butyl (But), 1 and n-butyl (Bun), 2) with pendant amine-containing diphosphines were synthesized in moderate yields from the treatments of mononickel dichlorides [{(Ph2PCH2)2NR}NiCl2] with ethanedithiol (HSCH2CH2SH) with triethylamine (Et3N) as an acid-binding agent at room temperature. The as-prepared complexes 1 and 2 have been fully characterized by means of elemental analysis, nuclear magnetic resonance (NMR) spectrum, and X-ray crystallography. Further, the electrochemical properties of 1 and 2 are investigated in the absence or presence of acetic acid (HOAc) by using cyclic voltammetry (CV), suggesting that they can be considered as the active electrocatalysts for proton reduction to H2. [ABSTRACT FROM AUTHOR]

Two new series of phosphine-substituted diiron complexes Fe2(μ-Rodt)(CO)6−n(PPh3)n (n = 1 for 4–6 and n = 2 for 7–9) bearing desymmetrized oxadithiolate bridges (i.e., Rodt bridges), which can be considered as diiron subsite models of [FeFe]-hydrogenases, were prepared through the Me3NO-induced replacements of all-CO diiron precursors Fe2(μ-Rodt)(CO)6 (Rodt = SCH(R)OCH2S; R = Ph (1), Me (2), and H (3)) with one equivalent or excess PPh3. All the as-obtained complexes have been fully characterized by elemental analysis, various spectroscopy methods, and especially for 4, 7–9 by X-ray crystallography. Further protonation and electrochemistry of 4–6 and 7–9 with Rodt bridges are studied and compared without and with CF3CO2H (TFA) and CH3CO2H (HOAc) as strong and weak acidic proton sources by in situ IR plus NMR spectroscopies and cyclic voltammetry. On the one hand, under excess TFA, the monosubstituted complexes 4–6 are partially protonated to produce a mixture of main precursors 4–6 and minor Fe-protonated species [4(μH)]+ , [5(μH)]+ , and [6(μH)]+ , whereas the disubstituted counterparts 7–9 are completely protonated to form an isomeric mixture of their hydride species [7(μH)]+ , [8(μH)]+ , and [9(μH)]+ in transoid-dibasal and apical-basal fashions. On the other hand, complexes 7–9 show better electrocatalytic proton reduction activities (i.e., higher turnover numbers/TONs) under TFA or HOAc relative to counterparts 4–6, in which the TONs of 4, 5 and 7, 8 with Phodt or Meodt bridges are a little higher than those of 6 and 9 with odt bridges, respectively. These findings reveal that the redox and electrocatalytic behaviors of 4–6 and 7–9 with Rodt bridges are affected not only by phosphine coordination modes (PPh3, mono- vs. di-substitution) but also by desymmetrized dithiolate bridges (Rodt, R = Ph, Me vs. H). [ABSTRACT FROM AUTHOR]

As diiron subsite models of [FeFe]‐hydrogenases for catalytic proton reduction to hydrogen (H2), a new series of the phosphine‐substituted diiron ethanedithiolate complexes Fe2(μ‐edt)(CO)6‐nLn (n = 1, 2) were prepared from the variable substitutions of all‐CO precursor Fe2(μ‐edt)(CO)6 (A) and tertiary phosphines (L1‐L4) under different reaction conditions. While the Me3NO‐assisted substitutions of A and one equiv. ligands L1‐L4 [L = Ph2P(CH2NHBut), Ph2P(CH2CH2NH2), Ph2P(NHBut), and Ph2P(C6H4Me‐p)] produced the monosubstituted complexes Fe2(μ‐edt)(CO)5L (1–4) in good yields, the refluxing xylene solution of A and two equiv. ligand L1 prepared complex Fe2(μ‐edt)(CO)5{κ1‐Ph2P(CH2NHBut)} (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 Fe2(μ‐edt)(CO)4{κ1, κ1‐(Ph2PNHBut)2} (5) in low yield, whereas the Me3NO‐assisted substitution of A and two equiv. ligand L4 afforded the disubstituted complex Fe2(μ‐edt)(CO)4{κ1, κ1‐(Ph2PC6H4Me‐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 H2 in the presence of HOAc. [ABSTRACT FROM AUTHOR]

The solid-state structure of diiron azadiphosphine complex [Fe2(μ-pdt)(CO)4{(μ-Ph2P)2NH}] (1) bearing a pendant amine, which can be regarded as the diiron subsite model of [FeFe]-hydrogenases, have been well investigated by X-ray crystallography. Notably, in order to explore the potential role of a pendant amine in the bridging azadiphosphine ligand, the electrochemical and electrocatalytic properties of 1 and its reference analog [Fe2(μ-pdt)(CO)4{(μ-Ph2P)2CH2}] (2) have been studied and compared in the absence and presence of acetic acid (HOAc) as a proton source using cyclic voltammetry (CV), indicating that they are active for the electrocatalytic proton reduction to hydrogen (H2). [ABSTRACT FROM AUTHOR]

To further extend diiron subsite models of [FeFe]‐hydrogenases, the various substitutions of all‐carbonyl diiron complex Fe2(μ‐Me2pdt)(CO)6 (A, Me2pdt = (SCH2)2CMe2) with monophosphines or small bite‐angle diphosphines are studied as follows. Firstly, the monodentate complexes Fe2(μ‐Me2pdt)(CO)5{κ1‐P(C6H4R‐p)3} [R = Me (1a) and Cl (1b)] and Fe2(μ‐Me2pdt)(CO)5{κ1‐Ph2PX'} [X' = NHPh (2a) and CH2PPh2 (2b)] are readily afforded through the Me3NO‐assisted reactions of A with monophosphines P(C6H4R‐p)3 (R = Me, Cl) and diphosphines (Ph2P)2X (X = NPh, CH2 (dppm)) in MeCN at room temperature, respectively. Secondly, the chelate complexes Fe2(μ‐Me2pdt)(CO)4(κ2‐(Ph2P)2X) [X = NPh (3a) and NBun (3b)] can be efficiently prepared by the UV‐irradiated reactions of A with small bite‐angle diphosphines (Ph2P)2X (X = NPh, NBun) in toluene. Thirdly, the bridge complexes Fe2(μ‐Me2pdt)(CO)4(μ‐(Ph2P)2X) [X = NPh (4a) and CH2 (4b)] are well obtained from the refluxing solutions of A and diphosphines (Ph2P)2X (X = NPh, CH2) in xylene. Rarely, the diphosphine‐bridge complex 4b may be produced in low yield via the UV‐irradiated solutions of A and the dppm ligand in toluene emitting at 365 nm. Eight new complexes obtained above have been well characterized by using element analysis, FT‐IR, NMR (1H, 31P) spectroscopies, and particularly for 1a, 1b, 2a, 3b, 4a, 4b by X‐ray crystallography. Meanwhile, the electrochemical and electrocatalytic properties of three representative complexes 2a, 3a, and 4a with pendant N‐phenyl groups are investigated and compared by using cyclic voltammetry (CV) in the absence and presence of trifluoroacetic acid (TFA) as a proton source, indicating that they are all found to be active for electrocatalytic proton reduction to hydrogen (H2). [ABSTRACT FROM AUTHOR]

In this paper, five diiron propane-1,3-dithiolate complexes containing substituted phosphine ligands were prepared and structurally characterized. Treatment of [Fe2(CO)6(μ-SCH2CH2CH2S)] (1) with a monophosphine ligand methyl diphenylphosphinite, ethyl diphenylphosphinite, 4-(dimethylamino)phenyldiphenylphosphine, tris(2-methoxyphenyl)phosphine, or tris(4-chlorophenyl)phosphine in the presence of Me3NO·2H2O as the decarbonylating agent gave the corresponding phosphine-substituted analogues [Fe2(CO)5(L)(μ-SCH2CH2CH2S)] [L = Ph2POCH3, 2; Ph2POCH2CH3, 3; Ph2P(4-C6H4 NMe2), 4; P(2-C6H4OCH3)3, 5; P(4-C6H4Cl)3, 6] in 73–93% yields. Complexes 2–6 have been characterized by elemental analysis, spectroscopy, and X-ray crystallography. Additionally, electrochemical studies have shown that 2–6 can catalyze the reduction of protons to H2 in the presence of HOAc. [ABSTRACT FROM AUTHOR]

In order to develop an attractive generation of bulky oxadithiolate-bridged [FeFe]‑hydrogenase mimics with chelating diphosphines, two new series of asymmetrically diphosphine-substituted diiron model complexes [Fe 2 (μ -R 2 odt)(CO) 4 (κ 2 -diphosphine)] (3 – 5) with bulky Ph 2 odt bridge and their reference counterparts (6 – 8) with common odt bridge were obtained from the Me 3 NO-assisted substitutions of diiron hexacarbonyl precursors [Fe 2 (μ -R 2 odt)(CO) 6 ] (R 2 odt = (SCHR) 2 O, R = Ph (1) and H (2)) with different diphosphines such as (Ph 2 P) 2 NBn (labelled PNBnP, Bn = benzyl), (Ph 2 PCH 2) 2 NBn (PCNBnCP), and (Ph 2 PCH 2) 2 CH 2 (DPPP)), respectively. All the as-prepared complexes have been characterized by elemental analysis, IR plus NMR spectroscopies, and particularly by X-ray crystallography for 3 – 8. It is interesting to note that complexes 3 and 6 chelating by small bite-angle PNBnP diphosphine have the favorable dibasal isomer whereas analogues 4 , 5 and 7 , 8 chelating by flexible backbone PCNBnCP or DPPP ligands possess the main apical-basal isomer in solution or in the solid state. Further, the electrochemical properties of two pairs of representative complexes 3 , 6 and 5 , 8 are explored and compared by cyclic voltammetry (CV) in the absence and presence of trifluoroacetic acid (CF 3 CO 2 H) as proton source, indicating that the complete protonations of 3 , 6 and 5 , 8 with higher concentration of CF 3 CO 2 H lead to two new catalytic waves for the electrocatalytic proton reduction to hydrogen (H 2). A new generation of bulky oxadithiolate-bridged [FeFe]‑hydrogenase mimics 3 – 5 and counterparts 6 – 8 were prepared. Ligand effects (i.e., R 2 odt bridges and chelating diphosphines) on their structures and electrocatalytic H 2 evolution are explored. [Display omitted] • Bulky R 2 odt-bridged [FeFe]‑hydrogenase mimics 1 – 8 were prepared and characterized. • Structural and electrochemical comparisons of 3 – 8 with chelating diphosphines are performed. • Small bite-angle diphosphine (PNP) in 3 and 6 occupy favorable dibasal manner. • Flexible backbone disphosphines (PCNCP or DPPP) in 4 , 5 , 7 , 8 show main apical-basal modes. • Protonations of 3 , 6 and 5 , 8 with higher [CF 3 CO 2 H] lead to the electrocatalytic H 2 evolution. [ABSTRACT FROM AUTHOR]

Two new fungal metabolites, named koninginins L ( 1 ) and M ( 2 ), together with three known koninginins A ( 3 ), E ( 4 ), and trichodermaketone C ( 5 ), were isolated from solid fermentation products of Trichoderma koningii 8662. Koninginins L ( 1 ) and M ( 2 ) were elucidated by extensive spectroscopic methods, including 1D and 2D NMR, HR-EI-MS experiments, and the absolute configuration of compound 1 was confirmed by single-crystal X-ray diffraction analysis using the anomalous scattering of Cu Kα radiation. [ABSTRACT FROM AUTHOR]

As diiron subsite models of [FeFe]-hydrogenases with odt bridge, two new series of PNP-chelate or -bridge diiron oxadithiolate complexes Fe 2 (μ -odt)(CO) 4 {(Ph 2 P) 2 NR} (1 – 3 and 4 – 6) were prepared by selective substitutions of diiron hexacarbonyl complex Fe 2 (μ -odt)(CO) 6 (A , odt = SCH 2 OCH 2 S) with different PNP ligands (PNP = (Ph 2 P) 2 NR, R = (CH 2) 3 Me, (CH 2) 3 NMe 2 and (CH 2) 3 Si(OEt) 3). All the new model complexes have been fully characterized by elemental analysis, various spectroscopies, and particularly for 1 and 4 – 6 by X-ray crystallography. In order to investigate the influence of coordination modes (chelate vs. bridge) of PNP ligands on redox and electrocatalytic properties of diiron model complexes for proton reduction, the protonation and electrochemistry of 1 and 4 as a pair of representative counterparts are well studied and compared in the absence and presence of strong acid (CF 3 CO 2 H) and weak acid (CH 3 CO 2 H) as different proton sources by using in situ IR and NMR spectroscopies as well as cyclic voltammetry (CV). For example, the protonation studies have shown that i) with excess CF 3 CO 2 H, protonations of both 1 and 4 are able to form the respective hydride species 1(μ H) + and 4(μ H) + , but in which the former is completely protonated whereas the latter is less reactive; and ii) with excess CH 3 CO 2 H, complex 1 is unactive yet counterpart 4 is partially protonated to afford species 4(μ H) + . The electrochemical investigations have displayed that i) with CF 3 CO 2 H as a proton source, complex 1 has a very simliar turnover frequency (TOF) and a much lower overpotential for cataytic proton reduction to H 2 in comparison to 4 ; and ii) with CH 3 CO 2 H as a proton source, complex 1 shows a much greater TOF value and a closer overpotential for H 2 evolution in contrast to 4. Image 1 • Two new series of PNP-chelate or -bridge diiron odt complexes 1 – 3 and 4 – 6 were prepared. • The chelate complex 1 is reactive with CF 3 CO 2 H to form [1H N ] + and [1(μ H)] + yet is unreactive with CH 3 CO 2 H. • The bridge complex 4 is reactive with both CF 3 CO 2 H and CH 3 CO 2 H to partially produce [4(μ H)] + . • The chelate complex 1 has a faster catalysis for H 2 evolution relative to its bridge counterpart 4. [ABSTRACT FROM AUTHOR]

Five monophosphine‐substituted diiron propane‐1,2‐dithiolate complexes as the active site models of [FeFe]‐hydrogenases have been synthesized and characterized. Reactions of complex [Fe2(CO)6{μ‐SCH2CH(CH3)S}] (1) with a monophosphine ligand tris(4‐methylphenyl)phosphine, diphenyl‐2‐pyridylphosphine, tris(4‐chlorophenyl)phosphine, triphenylphosphine, or tris(4‐fluorophenyl)phosphine in the presence of the oxidative agent Me3NO·2H2O gave the monophosphine‐substituted diiron complexes [Fe2(CO)5(L){μ‐SCH2CH(CH3)S}] [L = P(4‐C6H4CH3)3, 2; Ph2P(2‐C5H4N), 3; P(4‐C6H4Cl)3, 4; PPh3, 5; P(4‐C6H4F)3, 6] in 81%–94% yields. Complexes 2–6 have been characterized by elemental analysis, spectroscopy, and X‐ray crystallography. In addition, electrochemical studies revealed that these complexes can catalyze the reduction of protons to H2 in the presence of HOAc. [ABSTRACT FROM AUTHOR]

Selective substitutions of Fe2(μ‐odt)(CO)6 (odt = 1,3‐oxadithiolate, A) and small bite‐angle diphosphines (Ph2P)2X [X = CH2 (dppm) or N (CH2CHMe2) (dppa)] have been well investigated in this study. With Me3NO·2H2O in MeCN at room temperature, the reaction of A and dppm produced the monodentate complex [Fe2(μ‐odt)(CO)5(κ1‐dppm)] (1), whereas the similar reaction with dppa afforded the chelate complex [Fe2(μ‐odt)(CO)4(κ2‐dppa)] (2). Using UV irradiation in toluene emitting at 365 nm, the treatment of A and dppm rarely resulted in the formation of the bridge complex [Fe2(μ‐odt)(CO)4(μ‐dppm)] (3), whereas the similar treatment with dppa formed the chelate complex 2. Under thermolysis condition, refluxing solution of A with dppm or dppa gave the bridge complex 3 and [Fe2(μ‐odt)(CO)4(μ‐dppa)] (4), respectively, in which the former was formed in toluene (110 °C) but the latter was produced in xylene (138 °C). All the new complexes 1–4 obtained above were characterized by element analysis, FT‐IR, NMR (1H, 31P) spectroscopies, and particularly for 1–3 by X‐ray crystallography. Furthermore, the in situ protonations of 2 with a weak acid HOAc (acetic acid) and a strong acid TFA (trifluoroacetic acid) are explored by means of FT‐IR and NMR (1H, 31P) spectra. In addition, the electrochemical behaviors of 2–4 are studied and compared through cyclic voltammetry (CV) in the absence and presence of a strong acid (TFA) as a proton source, indicating that they all are active for electrocatalytic proton reduction to hydrogen (H2). [ABSTRACT FROM AUTHOR]

• Five di-iron dithiolato complexes with 3-bromothiophene moiety were synthesized. • The new complexes were characterized by spectroscopies and XRD analysis. • Electrochemical and electrocatalytic properties of some complexes were studied. A series of 3-bromothiophene-functionalized di-iron dithiolato complexes was reported. The starting complex [Fe 2 (CO) 6 { μ -SCH 2 CH(CH 2 OH)S}] (1) reacted with 3-bromothiophene-2-carboxylic acid promoting by N,N '-dicyclohexylcarbodiimide and 4-dimethylaminopyridine to yield the corresponding ester [Fe 2 (CO) 6 { μ -SCH 2 CHCH 2 O 2 C(3-C 4 H 2 SBr)S}] (2) in 91.4% yield. The phosphine-containing analogues [Fe 2 (CO) 5 L{ μ -SCH 2 CHCH 2 O 2 C(3-C 4 H 2 SBr)S}] (L = PPh 3 , 3 ; P(4-C 6 H 4 Cl) 3 , 4 ; P(4-C 6 H 4 CF 3) 3 , 5 ; P(C 6 H 11) 3 , 6) were further obtained by the CO-exchange of 2 with the corresponding phosphine ligands and Me 3 NO∙2H 2 O in 68.0–76.7% yields. The new complexes 2 – 6 have been structurally identified by elemental analysis, spectroscopies, and particularly for 2 – 4 by X-ray crystallography. Additionally, the electrochemical and electrocatalytic properties of these products have been explored by cyclic voltammetry, which is showing that they can catalyze the reduction of protons to H 2 by adding an acetic acid as a proton source into MeCN solution. [Display omitted] [ABSTRACT FROM AUTHOR]

Three dioxybiphenyl bridged cyclotriphosphazenes ( 2 – 4 ) containing the (1,1′-biphenyl)-4,4′-diol ( BPD ), 4,4′-sulfonyldiphenol ( SDP ), and 4,4′-(propane-2,2-diyl)diphenol ( PDP ) groups were prepared from the nucleophilic substitution reaction of hexachlorocyclotriphosphazene ( 1 ) with three different diphenols, respectively. All these compounds were structurally characterized using ESI-MS, FTIR, and NMR ( 1 H, 31 P) spectroscopies. Moreover, the molecular structures of 2 – 4 were unequivocally confirmed by X-ray crystallography, in which the two cyclotriphosphazene (N 3 P 3 ) rings are linked via a dioxybiphenyl bridge. [ABSTRACT FROM AUTHOR]

To further develop the active site models of [FeFe]‐hydrogenases, a new series of diiron model complexes [{(μ‐SCH2)2CHCH2OC(O)C6H4I)}Fe2(CO)6] (I is located at ‐para for 1, ‐meta for 2, and ‐ortho for 3) bearing dithiolato‐bridgehead functionality were successfully prepared by treatments of bridghead‐hydroxyl‐containing parent complex [{(μ‐SCH2)2CHCH2OH)}Fe2(CO)6] (A) and three different iodobenzoic acids (IC6H4CO2H) in the presence of 4‐dimethylaminopyridine (DMAP) as catalyst and dicyclohexylcarbodiimide (DCC) as dehydrating reagent. All these new complexes 1–3 have been fully characterized through elemental analysis, FT‐IR and NMR (1H, 13C) spectroscopies, and X‐ray crystallography. Further electrochemical and electrocatalytic properties of complexes 1–3 are studied and compared in the absence and presence of acetic acid (HOAc) as a proton source by cyclic voltammetry (CV), indicating that they may be considered as the active biomimetic electrocatalysts for proton reduction to hydrogen (H2). [ABSTRACT FROM AUTHOR]

A new series of the asymmetrically PNP-chelate diiron edt complexes 1 – 3 were prepared and especially an electrocatalytic comparison with all-CO precursor A is investigated, aiming to better explore the role of the asymmetrically PNP-chelate ligands in diiron subsite models of [FeFe]-hydrogenases. • A new series of the PNP-chelate diiron edt complexes 1‒3 were prepared. • The molecular structures of 1‒3 have been fully characterized. • Electrochemical and electrocatalytic properties of 1‒3 and A are investigated. • Complexes 1‒3 all display a higher TOF and a lower overpotential in contrast to A. As a further exploration of the desirable diiron subsite models of [FeFe]-hydrogenases for hydrogen (H 2) evolution, the asymmetrically PNP-chelate diiron ethanedithiolate complexes Fe 2 (μ -edt)(CO) 4 { κ2 -(Ph 2 P) 2 NR} (1 – 3) can be synthesized in good yields through the substitution reactions of diiron all-carbonyl complexes Fe 2 (μ -edt)(CO) 6 (A , edt = SCH 2 CH 2 S) with different PNP ligands (PNP = (Ph 2 P) 2 NR, R = (CH 2) 2 CHMe 2 , (CH 2) 3 OMe, (CH 2) 3 SMe) in the presence of Me 3 NO·2H 2 O as decarbonylating agent. These new complexes 1 – 3 have been fully characterized by elemental analysis, FT-IR, NMR spectroscopy, and particularly for 1 by X-ray crystallography. Further, the electrochemical and electrocatalytic properties of complexes 1 – 3 and their precursor A as a reference compound are studied and compared through cyclic voltammetry (CV) in the absence and presence of HOAc as a proton source, suggesting that they are all found to be electrochemically active but show the distinct electrocatalytic abilities for proton reduction to H 2. [ABSTRACT FROM AUTHOR]

A novel diiron S-(−)-1-phenylethylazadithiolate complex, Fe 2 [( μ -SCH 2 ) 2 NCH(CH 3 )Ph](CO) 6 ( 1 ), has been prepared by the condensation of Fe 2 ( μ -SH) 2 (CO) 6 , CH 2 O and S-(−)-1-phenylethylamine. Furthermore, the reaction of complex 1 and phosphine ligands (PPh 3 , P(C 6 H 4 -4-F) 3 , dppe) in the presence of the decarbonylation agent Me 3 NO·2H 2 O resulted in the formation of the phosphine-substituted diiron S-(−)-1-phenylethylazadithiolate complexes Fe 2 [( μ -SCH 2 ) 2 NCH(CH 3 )Ph](CO) 5 (PPh 3 ) ( 2 ), Fe 2 [( μ -SCH 2 ) 2 NCH(CH 3 )Ph](CO) 5 [P(C 6 H 4 -4-F) 3 ] ( 3 ) and {Fe 2 [( μ -SCH 2 ) 2 NCH(CH 3 )Ph](CO) 5 } 2 (Ph 2 PCH 2 CH 2 PPh 2 ) ( 4 ). Complexes 1 – 4 have been fully characterized by elemental analysis, FTIR and NMR ( 1 H, 13 C, 31 P) spectroscopies, and for 1 , 2 and 4 by X-ray crystallography. Moreover, complexes 1 and 2 were found to be catalysts for hydrogen production in the presence of acid under electrochemical conditions. According to the electrochemical observations, a possible catalytic mechanism for complexes 1 and 2 was proposed. [ABSTRACT FROM AUTHOR]

As the active site models of [FeFe]-hydrogenases, two new aminophosphine-monosubstituted diiron dithiolate compelxes with the general formulae Fe 2 ( μ -pdt)(CO) 5 {PPh 2 NH(C 6 H 4 R- p )} (pdt = SCH 2 CH 2 CH 2 S; R = Br ( 1 ), Me ( 2 )), were prepared by the oxidative decarbonylation of parent Fe 2 ( μ -pdt)(CO) 6 ( A ) with monophosphines Ph 2 PNH(C 6 H 4 Br- p ) or Ph 2 PNH(C 6 H 4 Me- p ) in the presence of decarbonylating agent Me 3 NO·2H 2 O in MeCN. Interestingly, the ambient temperature treatment of A and aminodiphosphine Ph 2 PN(C 6 H 4 Me- p )PPh 2 resulted in the formation of the major chelated complex Fe 2 ( μ -pdt)(CO) 4 { κ 2 -Ph 2 PN(C 6 H 4 Me- p )PPh 2 } ( 3 ) concomitant with the minor complex 2 . All the complexes 1 - 3 have been well characterized by elemental analysis, FTIR, NMR ( 1 H, 31 P) spectroscopies, and X-ray crystallography. Additionally, the electrochemical and electrocatalytic properties of complexes 1 - 3 are studied using cyclic voltammetry, where the ratios of the catalytic current ( i cat ) to the reductive peak current ( i p ) for similar complexes 1 , 2 , and parent A at 10 mM HOAc exhibit a ranking of 2 ≈ 1 > A . [ABSTRACT FROM AUTHOR]

Three novel diiron azadithiolate complexes Fe 2 [( μ -SCH 2 ) 2 NCH 2 CH 2 CH(CH 3 ) 2 ](CO) 6 ( 1 ), Fe 2 [( μ -SCH 2 ) 2 NCH(CH 2 CH 3 ) 2 ](CO) 6 ( 2 ) and Fe 2 [( μ -SCH 2 ) 2 NCH 2 CH 2 CH 2 SCH 3 ](CO) 6 ( 3 ) have been synthesized by treatment of Fe 2 ( μ -SCH 2 OH) 2 (CO) 6 with primary amines RNH 2 (R = CH 2 CH 2 CH(CH 3 ) 2 , CH(CH 2 CH 3 ) 2 , CH 2 CH 2 CH 2 SCH 3 ). Meanwhile, reaction of Fe 2 ( μ -SCH 2 OH) 2 (CO) 6 and diphosphine ligand Ph 2 PCH 2 PPh 2 (dppm), followed by the addition of amines NH 2 CH 2 CH 2 CH(CH 3 ) 2 and NH 2 CH(CH 2 CH 3 ) 2 resulted in the formation of the target phosphine-substituted diiron azadithiolate complexes Fe 2 [( μ -SCH 2 ) 2 NCH 2 CH 2 CH(CH 3 ) 2 ](CO) 5 (dppm) ( 4 ) and Fe 2 [( μ -SCH 2 ) 2 NCH(CH 2 CH 3 ) 2 ](CO) 5 (dppm) ( 5 ). Complexes 1 – 5 have been fully characterized by elemental analysis, FTIR, and NMR ( 1 H, 13 C, 31 P) spectroscopies, and particularly for 1 – 3 by X-ray crystallography. In addition, complexes 1 – 5 were found to be catalysts for hydrogen production under electrochemical conditions. [ABSTRACT FROM AUTHOR]

Three diiron and tetrairon azadithiolate complexes as models for the active site of [FeFe] hydrogenase were prepared. Reaction of complex Fe2(SCH2OH)2(CO)6 and NH2CH2CH2CH2OCH3 resulted in the diiron azadithiolate hexcarbonyl complex Fe2[(SCH2)2- NCH2CH2CH2OCH3](CO)6 (1) in moderate yield. Furthermore, treatment of complex 1 with mono phosphine ligand PPh3 and diphosphine ligand PH2PCH2CH2PPH2 in the presence of decarbonylation reagent Me3NO·2H2O yielded the phosphine-substituted azadithiolate complexes Fe2[(SCH2)2NCH2CH2CH2OCH3]CO)5(PPh3) (2) and {Fe2[(SCH2)2NCH2CH2CH2OCH3](CO)5}2(PH2PCH2CH2PPH2) (3) respectively. The new complexes 1-3 were fully characterized by elemental analysis, IR, ¹H, 13C, 31P NMR spectroscopy and X-ray crystallography. It is worthy to note that the crystallographic studies show the unusual difference of the methoxypropanyl substituent on the N atom of complexes 1 and 2, largely because of the affection of phosphine ligand PPh3. In addition, complex 1 was found to be a catalyst for H2 production under electrochemical condition. [ABSTRACT FROM AUTHOR]

• New diiron monophosphine precursors FePR (R = F , H, and Me) were prepared and characterized. • A new family of CNT-supported diiron monophosphine hybrids CNT- f -FePR was fabricated and characterized. • Substituent effects of FePR on electrocatalytic HER behaviros of CNT- f -FePR were investigated systematically. • Electrochemical studies indicate hybrid CNT- f -FePF exhibits a better HER activity in 0.1 M H 2 SO 4. • DFT calculation reveals hybrid CNT- f -FePF has a lower Δ G H* value relative to homologues CNT- f -FePR (R = H , Me). In order to explore substituent effects of PR 3 -phosphine ligands of diiron dithiolato complexes on the catalytic performances of [FeFe]-hydrogenase mimics for hydrogen evolution reaction (HER) in an aqueous medium, three new diiron monophosphine complexes [{(μ -SCH 2) 2 N(C 6 H 4 CH 2 CH 2 OH)}Fe 2 (CO) 5 {P(C 6 H 4 R- 4) 3 }] (labeled as FePR ; R = F , H, and Me) were prepared and can be further linked covalently into carbon nanotube (CNT) to construct the target CNT-supported hybrids denoting as CNT- f -FePR. The molecular structures of diiron complexes FePR are well characterized through element analysis, fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and X-ray crystallography, whereas the formations of target hybrids CNT- f -FePR have been confirmed by using X-ray photoelectron spectroscopy (XPS), Raman and FT-IR. Notably, the electrochemical HER performances of target hybrids CNT- f -FePR (R = F , H, and Me) are studied and compared in 0.1 M H 2 SO 4 aqueous solution by means of linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and density functional theory (DFT) calculation. Among these hybrids, the CNT- f -FePF hybrid exhibits a more efficient HER activity in an aqueous media based on their electrochemical observations that the CNT- f -FePF hybrid with F-substituted phosphine has lower applied overpotential, smaller Tafel slope, larger electrochemical active surface area, smaller charge transfer resistance, and lower hydrogen chemisorption free energy relative to its analogues CNT- f -FePH and CNT- f -FePMe with H- or Me-substituted phosphines. A new family of CNT-supported diiron monophosphine complexes denoting as CNT- f -FePR (R = F vs. H vs. Me) was constructed in order to investigate the substituent effects of diiron phosphine clusters FePR on the electrochemical HER performances of hydrogenase-inspired catalysts CNT- f -FePR in aqueous medium. [Display omitted] [ABSTRACT FROM AUTHOR]

The potential influence of pendant amine of phosphine ligands on the structural, protophilic, and electrocatalytic properties of diiron model complexes for proton reduction to H 2 are described. [Display omitted] • Diiron monophosphine complexes 1 and 2 were prepared and characterized. • Complexes 1 and 2 are partially protonated with CF 3 CO 2 H but are unreactive with CH 3 CO 2 H. • Complex 1 shows a faster catalysis of proton reduction to H 2 in contrast to reference 2. To explore the influence of pendant amine of phosphine ligands on the structural, protophilic, and electrochemical properties of diiron model complexes related to [FeFe]-hydrogenases, one new aminophosphine-substituted diiron oxadithiolate (odt) complex Fe 2 (μ -odt)(CO) 5 {Ph 2 P(CH 2 NMe 2)} (1) and its new reference analogue Fe 2 (μ -odt)(CO) 5 {Ph 2 P(CH 2 Ph)} (2) were synthesized and characterized through elemental analysis, FT-IR as well as NMR spectroscopies, and X-ray crystallography. Notably, a comparative study on the protonation and electrochemistry of 1 and 2 is performed in the absence or presence of strong acid CF 3 CO 2 H and weak acid CH 3 CO 2 H by using in situ spectroscopic techniques (IR and NMR) and cyclic voltammetry (CV). The protonation study reveals that complexes 1 and 2 are treated with excess CF 3 CO 2 H to form a small amount of their respective Fe-protonated products [(μ -H)Fe 2 (μ -odt)(CO) 5 {Ph 2 P(CH 2 NMe 2)}](CF 3 CO 2) ([1(μ H)]+) and [(μ -H)Fe 2 (μ -odt)(CO) 5 {Ph 2 P(CH 2 Ph)}](CF 3 CO 2) ([2(μ H)]+), but they are unreactive with excess CH 3 CO 2 H. The CV investigation suggests that complexes 1 and 2 are found to be active biomimetic electrocatalysts for proton reduction to hydrogen (H 2) with CF 3 CO 2 H and CH 3 CO 2 H, in which complex 1 shows a slightly greater turnover frequency (TOF) value for H 2 evolution in contrast to its reference 2. [ABSTRACT FROM AUTHOR]

Inspired by the metal active sites of [FeFe]- and [NiFe]‑hydrogenases, a series of mononuclear Ni(II) ethanedithiolate complexes [{(Ph 2 PCH 2) 2 ×}Ni(SCH 2 CH 2 S)] (X = NCH 2 C 5 H 4 N- p (2a), NCH 2 C 6 H 5 (2b), NCH 2 CHMe 2 (2c), and CH 2 (2d)) with chelating diphosphines were readily synthesized through the room-temperature treatments of mononuclear Ni(II) dichlorides [{(Ph 2 PCH 2) 2 ×}NiCl 2 ] (1a - 1d) with ethanedithiol (HSCH 2 CH 2 SH) in the presence of triethylamine (Et 3 N) as acid-binding agent. All the as-prepared complexes 1a - 1d and 2a - 2d are fully characterized through elemental analysis, nuclear magnetic resonance (NMR) spectrum, and by X-ray crystallography for 1b , 2a - 2d. To further explore proton-trapping behaviors of this type of mononuclear Ni(II) complexes for catalytic hydrogen (H 2) evolution, the protonation and electrochemical proton reduction of 2a - 2c with aminodiphosphines (labeled PCNCP = (Ph 2 PCH 2) 2 NR) and reference analogue 2d with nitrogen-free diphosphine (dppp = (Ph 2 PCH 2) 2 CH 2) are studied and compared under trifluoroacetic acid (TFA) as a proton source. Interestingly, the treatments of 2a - 2d with excess TFA resulted in the unexpected formation of dinuclear Ni(II)-Ni(II) dication complexes [{(Ph 2 PCH 2) 2 ×} 2 Ni 2 (μ -SCH 2 CH 2 S)](CF 3 CO 2) 2 (3a - 3d) and mononuclear Ni(II) N-protonated complexes [{(Ph 2 PCH 2) 2 N(H)R}Ni(SCH 2 CH 2 S)](CF 3 CO 2) (4a - 4c), which has been well supported by high-resolution electrospray ionization mass spectroscopy (HRESI-MS), NMR (31P, 1H) as well as fourier transform infrared spectroscopy (FT-IR) techniques, and especially by X-ray crystallography for 3d. Additionally, the electrochemical properties of 2a - 2d are investigated in the absence and presence of strong acid (TFA) by using cyclic voltammetry (CV), showing that the complete protonation of 2a - 2d gave rise to dinuclear Ni 2 S 2 species 3a - 3d for electrocatalytic proton reduction to H 2. A new series of dinuclear Ni(II)-Ni(II) dication complexes 3a - 3d were unexpectedly formed from the facile protonations of mononuclear Ni(II) complexes 2a - 2d with excees CF 3 CO 2 H (TFA) and they as electroactive species are responsible for the electrocatalytic proton reduction to H 2. [Display omitted] • Mononuclear Ni(II) complexes 2a - d and precursors 1a - d were prepared and characterized. • Protonation and electrocatalytic properties of 2a - d are studied and compared. • Dinuclear Ni 2 S 2 complexes 3a - d were formed via protonation of 2a - d with excess CF 3 CO 2 H. • Electroactive species 3a - d are responsible for electrocatalytic proton reduction. [ABSTRACT FROM AUTHOR]

A new series of diiron aminophosphine complexes 1 – 5 with the adtNPh bridge and reference analogue 7 have been obtained, aiming to better observe and compare the influence of pendant amines of phosphine ligands on the structures and electrocatalytic properties of diiron model complexes related to [FeFe]-hydrogenases in this work. • New diiron aminophosphine complexes 1 – 5 and reference analogues 6 , 7 were synthesized. • All the complexes are characterized by elemental analysis, various spectroscopies, and X-ray crystallography for 1 , 2 , 4 , 7. • Structural and electrochemical comparisons of 1 – 5 and 7 are studied. Me 3 NO-assisted substitution reactions of precursor Fe 2 (μ -adtNPh)(CO) 6 (A , adtNPh = SCH 2 N(Ph)CH 2 S) and aminodiphosphines (Ph 2 P) 2 NR with different N -aryl substituents (R) resulted in the unexpected formation of five new diiron aminophosphine complexes Fe 2 (μ -adtNPh)(CO) 5 { κ1 -Ph 2 P(NHR)} (R = C 6 H 5 (1), C 6 H 4 Me- p (2), C 6 H 4 OMe- p (3), C 6 H 4 CO 2 Me- p (4), and C 6 H 4 Cl- p (5)) with adtNPh bridge, which may be regarded as the active site models of [FeFe]-hydrogenases. In order to further observe the influence of the pendant amines of phosphine ligands on the formation, structures, and electrochemical properties of model complexes 1 – 5 obtained above, two reference analogues Fe 2 (μ -adtNPh)(CO) 5 (κ1 -dppm) (6 , dppm = (Ph 2 P) 2 CH 2) and Fe 2 (μ -adtNPh)(CO) 5 { κ1 -Ph 2 P(CH 2 Ph)} (7) were prepared from the similar treatment of A with the dppm or Ph 2 P(CH 2 Ph) ligands, respectively. Meanwhile, these new complexes 1 – 5 and 7 have been characterized by elemental analysis, FT-IR and NMR (1H, 31P) spectroscopies, and particularly for 1 , 2 , 4 , 7 by X-ray crystallography, in which the P atoms of the Ph 2 P(NHR) ligands in 1 , 2 , 4 reside in an apical position whereas that of the Ph 2 P(CH 2 Ph) ligand in 7 occupies at a basal site in the solid state. In addition, the electrochemical and electrocatalytic behaviors of 1 – 5 and 7 are investigated and compared in the absence and presence of acetic acid (HOAc) as proton source using cyclic voltammetry (CV), indicating they are all found to be active eletrocatalysts for proton reduction to hydrogen (H 2). [ABSTRACT FROM AUTHOR]