Covalent versus noncovalent attachments of [FeFe]­hydrogenase models onto carbon nanotubes for aqueous hydrogen evolution reaction.

In an effort to develop the biomimetic chemistry of [FeFe]­hydrogenases for catalytic hydrogen evolution reaction (HER) in aqueous environment, we herein report the integrations of diiron dithiolate complexes into carbon nanotubes (CNTs) through three different strategies and compare the electrochemical HER performances of the as-resulted 2Fe2S/CNT hybrids in neutral aqueous medium. That is, three new diiron dithiolate complexes [{(µ-SCH2)2N(C6H4CH2C(O)R)}Fe2(CO)6] (R = N-oxylphthalimide (1), NHCH2pyrene (2), and NHCH2Ph (3)) were prepared and could be further grafted covalently to CNTs via an amide bond (this 2Fe2S/CNT hybrid is labeled as H1) as well as immobilized noncovalently to CNTs via π-π stacking interaction (H2) or via simple physisorption (H3). Meanwhile, the molecular structures of 1-3 are determined by elemental analysis and spectroscopic as well as crystallographic techniques, whereas the structures and morphologies of H1-H3 are characterized by various spectroscopies and scanning electronic microscopy. Further, the electrocatalytic HER activity trend of H1 > H2 ≈ H3 is observed in 0.1 M phosphate buffer solution (pH = 7) through different electrochemical measurements, whereas the degradation processes of H1-H3 lead to their electrocatalytic deactivation in the long-term electrolysis as proposed by post operando analysis. Thus, this work is significant to extend the potential application of carbon electrode materials engineered with diiron molecular complexes as heterogeneous HER electrocatalysts for water splitting to hydrogen.

Bulky oxadithiolate-bridged [FeFe]­hydrogenase mimics [Fe2(µ-R2odt)(CO)4(κ2-diphosphine)] (R = Ph and H) with chelating diphosphines.

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 [Fe2(µ-R2odt)(CO)4(κ2-diphosphine)] (3-5) with bulky Ph2odt bridge and their reference counterparts (6-8) with common odt bridge were obtained from the Me3NO-assisted substitutions of diiron hexacarbonyl precursors [Fe2(µ-R2odt)(CO)6] (R2odt = (SCHR)2O, R = Ph (1) and H (2)) with different diphosphines such as (Ph2P)2NBn (labelled PNBnP, Bn = benzyl), (Ph2PCH2)2NBn (PCNBnCP), and (Ph2PCH2)2CH2 (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 (CF3CO2H) as proton source, indicating that the complete protonations of 3, 6 and 5, 8 with higher concentration of CF3CO2H lead to two new catalytic waves for the electrocatalytic proton reduction to hydrogen (H2).

Mononuclear nickel(II) dithiolate complexes with chelating diphosphines: Insight into protonation and electrochemical proton reduction.

Inspired by the metal active sites of [FeFe]- and [NiFe]­hydrogenases, a series of mononuclear Ni(II) ethanedithiolate complexes [{(Ph2PCH2)2×}Ni(SCH2CH2S)] (X = NCH2C5H4N-p (2a), NCH2C6H5 (2b), NCH2CHMe2 (2c), and CH2 (2d)) with chelating diphosphines were readily synthesized through the room-temperature treatments of mononuclear Ni(II) dichlorides [{(Ph2PCH2)2×}NiCl2] (1a-1d) with ethanedithiol (HSCH2CH2SH) in the presence of triethylamine (Et3N) 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 (H2) evolution, the protonation and electrochemical proton reduction of 2a-2c with aminodiphosphines (labeled PCNCP = (Ph2PCH2)2NR) and reference analogue 2d with nitrogen-free diphosphine (dppp = (Ph2PCH2)2CH2) 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 [{(Ph2PCH2)2×}2Ni2(µ-SCH2CH2S)](CF3CO2)2 (3a-3d) and mononuclear Ni(II) N-protonated complexes [{(Ph2PCH2)2N(H)R}Ni(SCH2CH2S)](CF3CO2) (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 Ni2S2 species 3a-3d for electrocatalytic proton reduction to H2.

Diiron and trinuclear NiFe2 dithiolate complexes chelating by PCNCP ligands: Synthetic models of [FeFe]- and [NiFe]-hydrogenases.

To further develop the biomimetic chemistry of [FeFe]- and [NiFe]-hydrogenases for catalytic proton reduction to hydrogen (H2), two serials of dinuclear diiron and trinuclear NiFe2 dithiolate complexes with chelating PCNCP ligands, namely, Fe2(µ-edt)(CO)4{κ2-(Ph2PCH2)2NR} (1a-1c) and Fe2(CO)6(µ3-S)2Ni{(Ph2PCH2)2NR} (2a-2c) where edt = SCH2CH2S and PCNCP = (Ph2PCH2)2NR [R = Bui (CH2CHMe2), But (CMe3), and Bun (CH2CH2CH2Me)], have been synthesized in moderate yields. All the new complexes 1a-1c and 2a-2c have been fully characterized by elemental analysis, FT-IR, NMR spectroscopy, and single-crystal X-ray diffraction analysis. More importantly, to explore the influence of transition metal cores (i.e., nickel and iron) on the electrochemical and electrocatalytic properties of hydrogenase-inspired molecular catalysts for H2 evolution, the cyclic voltammetries (CVs) of 1a-1c and 2a-2c are studied and compared in nBu4NPF6/DMF solution without and with acetic acid (HOAc) as a proton source. This finding suggests that (i) complexes 1a-1c and 2a-2c are all found to be active for electrocatalytic H2 evolution, but (ii) they display the distinct redox behaviors and electrocatalytic proton reduction abilities.

Sterically Stabilized Terminal Hydride of a Diiron Dithiolate.

The kinetically robust hydride [t-HFe2(Me2pdt)(CO)2(dppv)2]+ ([t-H1]+) (Me2pdt2- = Me2C(CH2S-)2; dppv = cis-1,2-C2H2(PPh2)2) and related derivatives were prepared with 57Fe enrichment for characterization by NMR, FT-IR, and NRVS. The experimental results were rationalized using DFT molecular modeling and spectral simulations. The spectroscopic analysis was aimed at supporting assignments of Fe-H vibrational spectra as they relate to recent measurements on [FeFe]-hydrogenase enzymes. The combination of bulky Me2pdt2- and dppv ligands stabilizes the terminal hydride with respect to its isomerization to the 5-16 kcal/mol more stable bridging hydride ([µ-H1]+) with t1/2(313.3 K) = 19.3 min. In agreement with the nOe experiments, the calculations predict that one methyl group in [t-H1]+ interacts with the hydride with a computed CH···HFe distance of 1.7 Å. Although [t-H571]+ exhibits multiple NRVS features in the 720-800 cm-1 region containing the bending Fe-H modes, the deuterated [t-D571]+ sample exhibits a unique Fe-D/CO band at ∼600 cm-1. In contrast, the NRVS spectra for [µ-H571]+ exhibit weaker bands near 670-700 cm-1 produced by the Fe-H-Fe wagging modes coupled to Me2pdt2- and dppv motions.

(E)-1-Phenyl-3-[4-(trifluoro-meth-yl)phen-yl]prop-2-en-1-one.

In the title compound, C(16)H(11)F(3)O, the dihedral angle between the two rings is 48.8 (2)°. The crystal packing exhibits no classical inter-molecular inter-actions between the mol-ecules.

3-Nitro-2-phenyl-chroman.

In the title compound, C(15)H(13)NO(3), the dihedral angle between the two aromatic rings is 79.25 (16)°.

Synthesis, characterization and some properties of mononuclear Ni and trinuclear NiFe2 complexes related to the active site of [NiFe]-hydrogenases.

The [N(2)S(2)]-type ligand 1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4) (L) is prepared in 84% yield by a new method and its structure has been confirmed by X-ray crystallography. The new synthetic method involves sequential reaction of 1,2-phenylenedithiol with EtONa followed by treatment of the resulting disodium salt of 1,2-phenylenedithiol with in situ generated 2-(chloromethyl)pyridine from its HCl salt. Further treatment of ligand L with NiCl(2)·6H(2)O or NiI(2) affords the expected new mononuclear Ni complexes Ni[1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4)]Cl(2) (1) and Ni[1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4)]I(2) (3) in 87-88% yields, whereas reaction of L with NiBr(2) under similar conditions results in formation of the expected new mononuclear complex Ni[1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4)]Br(2) (2) and one unexpected new mononuclear complex Ni[1-(2-C(5)H(4)NCH(2)S)-2-(2-C(5)H(4)NCH(2)SC(6)H(4)S)C(6)H(4)]Br(2) (2*) in 82% and 5% yields, respectively. More interestingly, the ligand L-containing novel trinuclear NiFe(2) complex Ni{[1,2-(2-C(5)H(4)NCH(2)S)(2)C(6)H(4)}Fe(2)(CO)(6)(µ(3)-S)(2) (4) is found to be prepared by sequential reaction of (µ-S(2))Fe(2)(CO)(6) with Et(3)BHLi, followed by treatment of the resulting (µ-LiS)(2)Fe(2)(CO)(6) with mononuclear complex 1, 2, or 3 in 12-20% yields. The new complexes 1-4 and 2* are fully characterized by elemental analysis and various spectroscopies, and the crystal structures of 1, 2* and 3 as well as some electrochemical properties of 1-4 are also reported.

Diphenyl-methyl isothio-cyanate.

The asymmetric unit of the title compound, C(14)H(11)NS, contains two mol-ecules in which the dihedral angles between the phenyl rings are 77.23 (7) and 86.30 (7)°. No aromatic π-π stacking inter-actions are observed.

1-Bromo-2-[(E)-2-nitro-ethen-yl]benzene.

In the title compound, C(8)H(6)BrNO(2), the dihedral angle between the planes of the benzene ring and the nitro group is 22.99 (12)°. In the crystal, inversion dimers associated by pairs of short Br⋯O contacts [3.2319 (17) Å] occur.

4-(Diphenyl-phosphan-yl)benzoic acid.

In the title compound, C(19)H(15)O(2)P, the dihedral angles between the benzoic acid ring and the phenyl rings are 75.64 (7) and 80.88 (7)°; the dihedral angle between the phenyl rings is 81.35 (7)°. In the crystal, inversion dimers linked by pairs of O-H⋯O hydrogen bonds generate R(2) (2)(8) loops between the head-to-head carb-oxy-lic acid groups.

2-Isonicotinoyl-N-phenyl-hydrazine-carbothio-amide dimethyl-formamide hemisolvate.

The title compound, C(13)H(12)N(4)OS·0.5C(3)H(7)NO, contains four hydrazine mol-ecules and two solvent mol-ecules in the asymmetric unit. The dihedral angles between the pyridine and phenyl rings in the hydrazine mol-ecules are 67.51 (16), 68.28 (16), 81.36 (15) and 83.32 (15)°. In the crystal, the mol-ecules are linked by N-H⋯N, N-H⋯O and N-H⋯S hydrogen bonds.

Diphenyl chloro-thio-phospho-nate.

The complete mol-ecule of the title compound, C(12)H(10)ClO(2)PS, is generated by crystallographic mirror symmetry, with the P, S and Cl atoms lying on the mirror plane. The resulting PO(2)SCl tetra-hedron is significantly distorted [O-P-O = 96.79 (9)°]. The crystal packing exhibits no directional inter-actions.

A novel trinorguaiane-type sesquiterpene from Dictamnus radicis.

A novel trinorguaiane-type sesquiterpene named radicol (1), together with a known sesquiterpene dictamnol (2), was isolated from the petroleum ether-EtOAc-MeOH extracts of the root of Dictamnus radicis Cortex. The structure of 1 was elucidated as 1 alpha,5 alpha-dimethyl-4 alpha,10 alpha-bicyclo[3.5.0]dec-8-en-1 beta,5 beta-diol (1) on the basis of IR, HRESIMS, 1H and 13C NMR, DEPT, 1H-1H COSY, HMQC, HMBC and NOESY.

Limonoids from the root of Dictamnus radicis cortex.

Chemical investigation of the roots of Dictamnus radicis Cortex led to the isolation of a new limonoid isodictamdiol (1) and a known dictamdiol (2), the first 5S/9S-type degraded limonoids, together with other six known limonoids (3-8). The chemical structures were identified on the basis of modern spectroscopic methods, including IR, MS, NMR ((1)H-NMR, (13)C-NMR, (1)H-(1)H COSY, HMQC, HMBC, NOESY). Additionally, the absolute configurations of limonoid isodictamdiol (1) and dictamdiol (2) were separately elucidated by single crystal X-ray diffraction, as well as their circular dichroism spectra. Furthermore, all compounds were evaluated for antibacterial activity against three bacterial cultures.

Antibacterial constituents from Pedicularis armata.

A new neolignan glycoside named armaoside (1), together with six known compounds (2-7), have been isolated from the whole plant of Pedicularis armata Maxim. The structure of 1 was elucidated as erythro-(7S,8R)-1-(4-O-beta-D-glucopyranosyl-3-methoxyphenyl)-2-[3,5-dimethoxyl-4-oxo-cinnamic aldehyde]propane-1, 3-diol by spectroscopic and chemical methods. All compounds were assayed against Bacillus subtilis, Escherichia coli, and Staphylococcus aureus.