Phenyl-functionalized diiron propanediselenolato complexes containing intramolecular bridging diphosphine ligands

Reactions of [(μ-SeCH₂)₂CHC₆H₅]Fe₂(CO)₆ (A) with 1,1′-bis(diphenylphosphino)ferrocene (dppf) or 1,3-bis(diphenylphosphino)propane (dppp) in refluxing xylene yielded [(μ-SeCH₂)₂CHC₆H₅]Fe₂(CO)₄(μ-dppf) (1) or [(μ-SeCH₂)₂CHC₆H₅]Fe₂(CO)₄(μ-dppp) (2) in moderate yields. The chemical structures of both complexes were characterized by spectroscopic methods and X-ray crystallography, and the electronic structures were further investigated by UV–vis. The redox properties of both complexes in the absence and presence of acetic acid were observed by cyclic voltammetry (CV).     

Phenyl-functionalized diiron propanedithiolato complexes with a chelated 1,2-bis(diphenylphosphino)benzene ligand

Reaction of 1,2-bis(diphenylphosphino)benzene (dppbz) with PhpdtFe₂(CO)₆ (A) in hot acetonitrile yielded a chelated complex, PhpdtFe₂(CO)₄(κ²-dppbz) (1), in moderate yield. Further treatment using an excess of HBF₄·Et₂O resulted in the protonation of 1 at room temperature in dichloromethane solution, forming a hydride [Phpdt(μ-H)Fe₂(CO)₄(κ²-dppbz)]BF₄ (2). The chemical structures of both complexes were fully characterized by spectroscopic methods and X-ray crystallography, and the electronic structures were further investigated by UV-vis spectroscopy. The cyclic voltammetry (CV) of 1 in the absence and presence of acetic acid were also investigated.     

Synthesis and structural characterization of diiron azadithiolate complexes relevant to the active site of [FeFe] hydrogenases

Two N-functionally substituted diiron azadithiolate complexes, [(µ-SCH₂)₂NCH₂CH₂OC(O)C₆H₄I-p]Fe₂(CO)₆ (1) and {[(µ-SCH₂)₂NCH₂CH₂OC(O)C₆H₄I-p]Fe₂(CO)₅Ph₂PCH}₂ (2) as models for the active site of [FeFe] hydrogenases, have been prepared and fully characterized. Complex 1 was prepared by the reaction of [(µ-SCH₂)₂NCH₂CH₂OH]Fe₂(CO)₆ with p-iodobenzoic acid in the presence of 4-dimethylaminopyridine (DMAP) and N,N′-dicyclohexylcarbodiimide (DCC) in 78% yield. Further treatment of 1 with 1 equiv. of Me₃NO?·?2H₂O followed by 0.5 equiv. of trans-1,2-bis(diphenylphosphino)ethylene (dppe) affords 2 in 60% yield. The new complexes 1 and 2 were characterized by IR and ¹H (¹³C, ³¹P) NMR spectroscopic techniques and their molecular structures were confirmed by X-ray diffraction analysis. The molecular structure of 1 has two conformational isomers, in one isomer its N-functional substituent is axial to its bridged nitrogen and in the other isomer its N-functional substituent is equatorial. The crystal structure of 2 revealed that its N-functional substituents are equatorial to its nitrogens and dppe occupies the two apical positions of the square-pyramidal irons.     

Synthesis,characterization, and crystal structures of N-functionalized diiron azadithiolate complexes related to the active site of [FeFe]-hydrogenases

A series of N-functionalized diiron azadithiolate complexes, [(µ-SCH₂)₂NCH₂CO₂Me]Fe₂(CO)_5?L [L?=?CO (1); PPh₃ (2); Ph₂PCH₂PPh₂ (3)], as active site models of [FeFe]-hydrogenases has been prepared and characterized. While 1 was prepared by a sequential reaction of (µ-HS)₂Fe₂(CO)₆ with two equiv. of aqueous HCHO, followed by treatment of (µ-HOCH₂S)₂Fe₂(CO)₆ with one equiv. of H₂NCH₂CO₂Me in 46% yield; 2 and 3 were prepared by a carbonyl substitution reaction of 1 with PPh₃ or Ph₂PCH₂PPh₂ in the presence of Me₃NO?·?2H₂O in 90% and 85% yields, respectively. The crystal structures of 1 and 2 revealed that the substituent attached to the bridgehead nitrogen occupies an equatorial position and the PPh₃ ligand resides in an axial position of the square pyramid of Fe2.     

Influence of the basicity of internal bases in diiron model complexes on hydrides formation and their transformation into protonated diiron hexacarbonyl form

Reaction of 2-(1-(pyridin-2-yl)ethyl)propane-1,3-dithiol with tri-iron dodecacarbonyl afforded a diiron pentacarbonyl complex, [Fe₂L(CO)₅] (A and H₂L = 2-methyl-2-(1,2,5,6-tetrahydropyridin-2-yl)propane-1,3-dithiol). In the reaction, the pyridinyl ring of the original ligand was partially hydrogenated during the reaction. This complex was fully characterised by using crystallographic, infrared, and NMR spectroscopic techniques. Formation reaction of its bridging hydride and subsequent conversion into its protonated diiron hexacarbonyl complex, [Fe₂L(CO)₆] (ACOH⁺ in which the N atom of L is decoordinated and protonated), were experimentally and theoretically investigated. Results for this complex alongside with theoretic investigations into other diiron pentacarbonyl analogues revealed positive correlation of basicity of the internal bases of these investigated complexes to bridging hydrides formation. But subsequent conversion of these bridging hydrides into protonated diiron hexacarbonyl complexes was not solely dictated by the basicity. Protophilicity of the internal base and lability of its coordination with the diiron centre play also an important role as revealed by experimental and theoretic investigations.     

Synthesis,characterization, and electrochemistry of diiron ethane-1,2-dithiolate complexes with monosubstituted ethyldiphenylphosphine or dicyclohexylphenylphosphine

Abstract

In this contribution, two diiron ethane-1,2-dithiolate complexes with one ethyldiphenylphosphine or dicyclohexylphenylphosphine ligand have been synthesized and characterized as mimics for the active site of [FeFe]-hydrogenases. Treatment of complex [Fe₂(CO)₆(μ-SCH₂CH₂S)] (1) with ethyldiphenylphosphine or dicyclohexylphenylphosphine and Me₃NO · 2?H₂O as decarbonylating agent gave complexes [Fe₂(CO)₅(Ph₂PCH₂CH₃)(μ-SCH₂CH₂S)] (2) and [Fe₂(CO)₅{PhP(C₆H₁₁)₂}(μ-SCH₂CH₂S)] (3) in 93% and 86% yields, respectively. Complexes 2 and 3 were characterized by elemental analysis, IR, and NMR spectroscopy. X-ray crystallographic studies confirmed the molecular structures of complexes 2 and 3, indicating that they contain a butterfly diiron ethane-1,2-dithiolate cluster with five terminal carbonyl ligands and an apically-coordinated phosphine ligand. Additionally, the electrochemical properties of these complexes were investigated by cyclic voltammetry, suggesting that they can be regarded as electrocatalysts for the reduction of protons to H₂ in the presence of HOAc. A possible mechanism for the proton reduction was proposed.     

Synthesis,crystal structures and electrocatalytic properties of bridgehead-C-functionalized diiron dithiolate complexes

To investigate the influence of bridgehead-C functionality in diiron dithiolate complexes on the molecular structure and electrocatalytic properties of [FeFe]-hydrogenase models, three new bridgehead-C-functionalized model complexes 1–3 have been synthesized and structurally characterized. Treatments of parent complex [(μ-SCH₂)₂CHCO₂H][Fe₂(CO)₆] (A) with the esterification agents o-MeC₆H₄OH, p-ClC₆H₄OH, or p-HOC₆H₄CHO in the presence of 4-dimethylaminopyridine and dicyclohexylcarbodiimide in CH₂Cl₂ at room temperature resulted in formation of [(μ-SCH₂)₂CHCO₂R][Fe₂(CO)₆] (R = o-MeC₆H₄–, 1; p-ClC₆H₄–, 2; p-OHCC₆H₄–, 3) in 53–55% yields. The new complexes 1–3 were characterized by elemental analysis, IR and NMR spectroscopy, and especially determined by X-ray crystallography. The electrochemical properties of 1–3 and the electrocatalytic H₂ evolution catalyzed by 1 have been investigated by cyclic voltammetry, where 1 is a catalyst for HOAc proton reduction to H₂ under electrochemical conditions.     

Structural studies of diiron complexes with monophosphine ligands tris(4-chlorophenyl)phosphine or diphenyl-2-pyridylphosphine

Four diiron dithiolate complexes with monophosphine ligands have been prepared and structurally characterized. Reactions of (μ-SCH₂CH₂S-μ)Fe₂(CO)₆ or [μ-SCH(CH₃)CH(CH₃)S-μ]Fe₂(CO)₆ with tris(4-chlorophenyl)phosphine or diphenyl-2-pyridylphosphine in the presence of Me₃NO·2H₂O afforded diiron pentacarbonyl complexes with monophosphine ligands (μ-SCH₂CH₂S-μ)Fe₂(CO)₅[P(4-C₆H₄Cl)₃] (1), (μ-SCH₂CH₂S-μ)Fe₂(CO)₅[Ph₂P(2-C₅H₄N)] (2), [μ-SCH(CH₃)CH(CH₃)S-μ]Fe₂(CO)₅[P(4-C₆H₄Cl)₃] (3), and [μ-SCH(CH₃)CH(CH₃)S-μ]Fe₂(CO)₅[Ph₂P(2-C₅H₄N)] (4) in good yields. Complexes 1–4 were characterized by elemental analysis, ¹H NMR, ³¹P{¹H} NMR and ¹³C{¹H} NMR spectroscopy. Furthermore, the molecular structures of 1–4 were confirmed by X-ray crystallography.     

Bis(diphenylphosphino)ferrocene as an intramolecular bridging ligand in N-functionally substituted 1,3-azapropanedithiolate diiron complexes: synthesis and catalysis of proton reduction

Reaction of 1,1′-bis(diphenylphosphino)ferrocene (dppf) with [μ-(SCH₂)₂NCH₂CH₂OH]Fe₂(CO)₆ (A) or [μ-(SCH₂)₂NCH₂CH₂SAc]Fe₂(CO)₆ (C) in refluxing xylene yielded an intramolecular bridging complex [μ-(SCH₂)₂NCH₂CH₂OH]Fe₂(CO)₄(μ-dppf) (1) or [μ-(SCH₂)₂NCH₂CH₂SAc]Fe₂(CO)₄(μ-dppf) (2) in moderate yield. The structures of both complexes were fully characterized by spectroscopic methods and X-ray crystallography, and the electronic structure of 2 was further investigated by UV–vis. The cyclic voltammetry was conducted and the reduction of protons from CF₃SO₃H (TfOH), HBF₄·Et₂O, or CF₃COOH (TFA) catalyzed by 2 was observed.     

Synthesis and characterization of diiron(I) 1,2-dimethylethanedithiolate complexes with bridging or chelating 1,2-bis(diphenylphosphino)ethylene

The reaction of complex [μ-SCH(CH₃)CH(CH₃)S-μ]Fe₂(CO)₆ (1) with trans-1,2-bis(diphenylphosphino)ethylene (trans-dppv) in the presence of Me₃NO?2H₂O in CH₂Cl₂/CH₃CN afforded complex {[μ-SCH(CH₃)CH(CH₃)S-μ]Fe₂(CO)₅}₂(trans-dppv) (2) with a bridging dppv. Complex [μ-SCH(CH₃)CH(CH₃)S-μ]Fe₂(CO)₄(cis-dppv) (3) was prepared by the reaction of 1 with cis-dppv and Me₃NO?2H₂O. The new complexes 2 and 3 were characterized by elemental analysis, spectroscopy, and X-ray diffraction analysis.     

An approach to water-soluble hydrogenase active site models: Synthesis and electrochemistry of diiron dithiolate complexes with 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane ligand(s)

In order to improve the hydro- and protophilicity of the active site models of the Fe-only hydrogenases, three diiron dithiolate complexes with DAPTA ligand(s) (DAPTA = 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane), (μ-pdt)[Fe(CO)₃][Fe(CO)₂(DAPTA)] (1, pdt = 1,3-propanedithiolato), (μ-pdt)[Fe(CO)₂(DAPTA)]₂ (2) and (μ-pdt)[Fe(CO)₂(PTA)][Fe(CO)₂(DAPTA)] (3), were prepared and spectroscopically characterized. The water solubility of DAPTA-coordinate complexes 1-3 is better than that of the PTA-coordinate analogues. With complexes 1-3 as electrocatalysts, the overvoltage is reduced by 460-770 mV for proton reduction from acetic acid at low concentration in CH₃CN. Significant decrease, up to 420 mV, in reduction potential for the Fe(I)Fe(I) to Fe(I)Fe(0) process and the curve-crossing phenomenon are observed in cyclic voltammograms of 2 and 3 in CH₃CN/H₂O mixtures. The introduction of the DAPTA ligand to the diiron dithiolate model complexes indeed makes the water solubility of 2 and 3 sufficient for electrochemical studies in pure water, which show that the proton reduction from acetic acid in pure water is electrochemically catalyzed by 2 and 3 at ca. −1.3 V vs. NHE.     

Synthetic and structural studies of the diiron toluenedithiolate carbonyl complexes with monophosphine ligands

Four diiron toluenedithiolate complexes 2–5 with monophosphine ligands are reported. Treatment of [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₆ (1) with tris(3-chlorophenyl)phosphine, tris(4-chlorophenyl)phosphine, tris(4-methylphenyl)phosphine or 2-(diphenylphosphino)benzaldehyde, and Me₃NO?2H₂O in MeCN resulted in the formation of [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[P(3-C₆H₄Cl)₃] (2), [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[P(4-C₆H₄Cl)₃] (3), [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[P(4-C₆H₄CH₃)₃] (4), and [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[Ph₂P(2-C₆H₄CHO)] (5) in 64–82% yields. Complexes 2–5 have been characterized by elemental analysis, IR, ¹H NMR, ³¹P{¹H} NMR, ¹³C{¹H} NMR and further confirmed by single crystal X-ray diffraction analysis. The molecular structures show that 2–5 contain a butterfly diiron toluenedithiolate cluster coordinated by five terminal carbonyls and an apical monophosphine.     

Phosphine-substituted diiron 1,2-dithiolate complexes as the models for the active site of [FeFe]-hydrogenases

Abstract

In this article, five diiron 1,2-dithiolate complexes containing phosphine ligands are reported. Treatment of complex [Fe₂(CO)₆(μ-SCH₂CH₂S)] (1) with the phosphine ligands tris(4-methylphenyl)phosphine, tris(4-methoxyphenyl)phosphine, tris(3-chlorophenyl)phosphine, tris(3-methylphenyl)phosphine, or 2-(diphenylphosphino)biphenyl in the presence of Me₃NO·2H₂O as the decarbonylating agent afforded the target products [Fe₂(CO)₅(L)(μ-SCH₂CH₂S)] [L?=?P(4-C₆H₄CH₃)₃, 2; P(4-C₆H₄OCH₃)₃, 3; P(3-C₆H₄Cl)₃, 4; P(3-C₆H₄CH₃)₃, 5; Ph₂P(2-C₆H₄Ph), 6] in 80–93% yields. Complexes 2–6 have been characterized by elemental analysis, spectroscopy, and X-ray crystallography. Additionally, the electrochemical properties were studied by cyclic voltammetry.     

Synthesis of uranium complexes incorporating extended azo-imine ligands: Molecular and electronic structure

The new azo-imine ligands 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl)diazenyl) phenylimino)methyl)phenol, H₂L¹, 1a, and 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl) diazenyl)p-chlorophenylimino)phenol, H₂L², 1b, were prepared. Reaction of H₂L¹;1a, and H₂L²;1b, with uranyl nitrate hexahydrate afforded the mononuclear complexes of compositions [U(O)₂(L¹)(H₂O)]; 2a, and [U(O)₂(L²)(H₂O)]; 2b, complexes respectively. The newly synthesised ligands (1a and 1b) and the complexes (2a and 2b) were characterised unequivocally. The x-ray structure of 2a was determined. The tetradentate dianionic ligand (L¹)^2- coordinated the uranium ion equatorially with a water molecule in the same plane. Two axially coordinated oxo ligands completed the overall pentagonal bipyramid geometry around U(VI) ion. Structural pattern, electron transfer properties (oxidation near 1.32 ​V vs Ag/AgCl) and electronic transitions of [U(O)₂(L¹)(H₂O)]; 2a, and [U(O)₂(L²)(H₂O)]; 2b have been rationalized by DFT calculations.     

Synthesis, structure and spectroscopic study of Rh polypyridine complexes with phenylcyanamide derivative ligands

Several new Rh^III complexes, [Rh(tpy)(bpy)L](PF₆)₂ (tpy=2,2′:6′,2″-terpyridine, bpy=2,2′-bipyridine, and L=monoanions of phenylcyanamide(pcyd)), 4-methylphenylcyanamide (4-MePcyd), 2,4-dimethylphenylcyanamide (2,4-Me₂pcyd), 4-methoxyphenylcyanamide (4-MeOPcyd), 2-chlorophenylcyanamide (2-Clpcyd) and 2,5-dichlorophenylcyanamide (2,5-Cl₂pcyd) have been synthesized and characterized by elemental analysis, IR, ¹H NMR and electronic absorption spectroscopies. ORTEP drawing of [Rh(tpy)(bpy)(2,5-Cl₂pcyd)](PF₆)₂·1/2CH₃CN shows three pyridyl rings of the tpy ligand that are nearly coplanar, as are the two rings of bpy. The anionic cyanamide group is coordinated end-on by the nitrile nitrogen to the Rh^III. The Rh^III–NCN bond is bent, having an angle of 125.4°. This bent bond is largely determined by the σ-bonding interaction of a cyanamide non-bonding electron pair in a sp² hybrid orbital.     

含膦配体二铁二硫五羰基配合物的合成、表征及电催化产氢性能

本文报道了4个含膦配体二铁二硫五羰基配合物的合成和结构表征。起始配合物[Fe₂(CO)₆(μ-SCH₂CH (CH₂OOCH) S)](1)与三苯基膦、三环己基膦、三(2-甲氧基苯基)膦或三(4-三氟甲基苯基)膦和脱羰试剂Me₃NO·2H₂O反应,以59%~88%的产率制备了目标产物[Fe₂(CO)₅(L)(μ-SCH₂CH (CH₂OOCH) S)](L=PPh₃(2)、PCy₃(3)、P (2-C₆H₄OCH₃)₃(4)、P (4-C₆H₄CF₃)₃(5))。配合物2~5以元素分析、红外光谱、核磁共振以及单晶X射线衍射进行了表征。电化学性质研究表明配合物1~5均可以实现电化学催化质子还原产生氢气的功能,其中配合物1的催化产氢效率明显优于其它配合物。     

From discrete dinuclear to 1-D and 2-D structures: nickel dipicolinate complexes with flexible bis(imidazole) ligands

Three new complexes, [Ni₂(dpc)₂(L₁)₂(H₂O)₂]?·?4H₂O (1), [Ni(dpc)(L₂)_1.5] _n (2), and {[Ni(dpc)(L₃)_1.5]?·?2H₂O} _n (3), where H₂dpc?=?dipicolinic acid, L₁?=?1,4-bis(2-methylimidazol-1-yl)butane, L₂?=?4,4′-bis(2-methylimidazol-1-ylmethyl)biphenyl, and L₃?=?1,4-bis(benzimidazol-1-yl)-2-butylene, have been synthesized by hydrothermal methods and characterized by elemental analyses, infrared spectra, thermogravimetric analysis, and X-ray crystallography. The common structural characteristic of the three complexes is that the Ni²⁺ is coordinated by tridentate dipicolinate through nitrogen of pyridine and oxygen of carboxylate, serving as a terminal ligand. In 1, two L₁ link two [Ni(dpc)(H₂O)] units to a discrete binuclear metallomacrocycle with a 22-membered ring, which is assembled through multiple O–H?···?O hydrogen bonds to form a 3-D supramolecular framework. Complex 2 exhibits a 1-D ladder-like chain structure constructed by cis/trans-conformation L₂ linking metal centers; 3 displays a 2-D (6,3) topology, being constructed from the linking of [Ni(pdc)] by L₃. These results indicate the merits of flexible bis(imidazole) ligands as building blocks with dipicolinate for the construction of complexes with diverse structural motifs.     

Syntheses,structures, and characterizations of three Ag(I) complexes constructed by length-modulated pyrazole-based ligands

Three coordination complexes with N-donor ligands, Ag₂(L1)_1.5(NO₃)₂ (1), Ag₃(L2)₂(NO₃)₃ (2), and Ag(L1)₂NO₃ (3) {L1?=?1,4-bis(pyrazole-1-ylmethyl)benzene, L2 = 4,4′-bis(pyrazole-1-ylmethyl)biphenyl}, have been synthesized and structurally characterized by elemental analysis, IR spectroscopy, TGA, and X-ray single crystal diffraction. Complex 1 shows a 3-D fsh-3,4-P2₁/c structure with brevity code {8³}²{8⁵·10}. Complex 2 has a 3-D framework with a 2-D layer penetrated by an infinite 1-D zigzag chain. Complex 3 exhibits a (4,4)-net racemizing layer structure with nitrate anions filling the cavity. The results indicate that L1 and L2 can adopt varied conformations in formation of the complexes, and the length of the ligands plays a key role in configuring and directing the corresponding structure of the complexes.     

Synthesis and structures of two molybdenum(VI) complexes derived from similar benzohydrazone ligands with catalytic properties

Two new structurally similar molybdenum(VI) complexes, [MoO₂L¹(CH₃OH)] (1) and [MoO₂L²(CH₃OH)] (2), where L¹ is the dianionic form of N′-(2-hydroxy-5-nitrobenzylidene)-2-methylbenzohydrazide and L² is the dianionic form of N′-(2-hydroxy-4-methoxybenzylidene)-2-methylbenzohydrazide, were prepared and structurally characterized by elemental analysis, infrared spectra, and single-crystal X-ray diffraction. 1 crystallizes in the monoclinic space group P2₁/c, with unit cell dimensions a?=?7.941(1), b?=?14.337(2), c?=?15.141(2)?Å, β?=?92.782(2)°, V?=?1721.8(4)?ų, Z?=?4, R₁?=?0.0286, wR₂?=?0.0650, GOOF?=?1.028. 2 crystallizes in the triclinic space group P-1, with unit cell dimensions a?=?8.003(1), b?=?10.608(1), c?=?10.880(1)?Å, α?=?95.745(2)°, β?=?97.627(2)°, γ?=?105.762(2)°, V?=?872.0(2)?ų, Z?=?2, R₁?=?0.0226, wR₂?=?0.0595, GOOF?=?1.116. X-ray analysis indicates that Mo in the complexes are coordinated by the phenolate oxygen, imino nitrogen, and enolate oxygen of the benzohydrazone, methanol, and two oxo groups, generating octahedral coordination. The oxidation of olefins with the complexes as catalysts was evaluated, indicating that the complexes showed excellent catalytic efficiency in oxidation of most aliphatic and aromatic substrates under mild conditions using tert-butyl hydrogen peroxide as oxidant.