Diiron models for the active site of Fe-only hydrogenase with terminal organosulfur ligation: synthesis, structures and electrochemistry

Diiron model complexes (micro-SCH(2)CH(2)CH(2)S)Fe(2)(CO)(5)L with thioether-substitution, L=S(CH(2)CH(3))(2) (2), S(CH(2)CH(3))(CH(2)CH(2)Cl) (3), S(CH(2)CH(3))(C(6)H(5)) (4), or sulfoxide-substitution, L=SO(CH(2)CH(2)CH(3))(2) (5), SO(CH(3))(2) (6), were synthesized as active site analogues of Fe-only hydrogenase. The organosulfur ligands were introduced into the diiron centers via moderately stable intermediates following two routes. The X-ray crystallographic structures of complexes 2-6 show the apical positions of terminal organosulfur ligands. The electrochemical behaviors of the model complexes were investigated, especially for the interesting properties of the derivative of 6 which is proposed to be the first model with weak donor ligand similar to CO.     

Alpha-ketoglutarate protects Streptomyces coelicolor from visible light-induced phototoxicity

It has been known that some Streptomyces species, including the model strain Streptomyces coelicolor, are vulnerable to visible light. Much evidence demonstrated that the phototoxicity induced by visible light is a consequence of the formation of intracellular reactive oxygen species (ROS), which are potentially harmful to cells. In this study, we found that α-ketoglutarate (α-KG) has a protective role against the phototoxicity in S. coelicolor. It could be because that α-KG can detoxify the ROS with the concomitant formation of succinate, which mediates the cells getting into anaerobiosis to produce more NADH and maintain intracellular redox homeostasis, a situation that was demonstrated by overexpressing gdhA in S. coelicolor. This finding, therefore, connects the central metabolites with the bacterial resistance against phototoxicity effect induced by visible light.     

New N-monofunctionalised 1,4,7-triazacyclononane complexes of iron

A series of 1,4,7-triazacyclononane derivatives of Fe(II) been investigated where changing the functionality of a pendant group has created different Fe(II) coordination environments. New examples of triazacyclononane supported iron dibromide complexes are presented as well as an iron complex bearing a novel 1,4,7-triazacyclononane containing a thiophene pendant-arm.     

The synthesis and cyclic voltammetry of select ferrocene piano-stool isocyanide complexes

Ferrocene piano-stool isocyanide complexes ([CpFeL₃]⁺, Cp = η⁵-C₅H₅, L = tert-butyl isocyanide (1), cyclohexyl isocyanide (2), and 2,6-dimethylphenyl isocyanide (3)) are formed by chemical oxidation of ferrocene in the presence of a stoichiometric amount of isocyanide ligand (1:3). The complexes are characterized by elemental analysis, routine spectroscopic methods (IR, ¹H NMR, ¹³C NMR, and UV-Vis), and cyclic voltammetry.     

Iron complexes of dioxoborolanylbutadienes

The first [2,3-dialkyl-1,4-bis(1,3-dioxo-4,4,5,5-tetramethyl-2-borolanyl]-1,3-butadiene]Fe(CO)₃ complexes (2, alkyl=n-butyl; 3, alkyl=cyclopentyl; 4, ‘alkyl’=phenyl; 5, alkyl=3-chloropropyl) have been prepared from the reaction of bis(cis-cyclooctadiene)Fe(CO)₃ (1) with the borolanylbutadienes. The X-ray crystal structures of 2 and 3 are reported. The geometries of the coordinated ligands are compared with those of the free ligands.     

Bio-mimetic hydrogen production from polysaccharide using the visible light sensitization of zinc porphyrin

A biohydrogen production system coupling the polysaccharide such as sucrose and maltose degradation with invertase and glucose dehydrognase (GDH) and hydrogen production with colloidal platinum as hydrogen-evolved catalyst using the visible light-induced photosensitization of water-soluble zinc porphyrin, zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) has been investigated. Continuous hydrogen gas production was observed when the sample solution containing polysaccharide, invertase, GDH, nicotinamide adenine dinucreotide (NAD(+)), ZnTPPS, methylviologen (an electron relay reagent), and colloidal platinum was irradiated by visible light. After 240-min irradiation, the amount of hydrogen production in the system using sucrose and maltose was estimated to be 3.1 and 0.35 micromol, respectively.     

The solvent-initiated photochemistry of tris(N,N-diethyldithiocarbamato)iron(III)

The photolysis of [Fe(Et₂dtc)₃], Et₂dtc = diethyldithiocarbamate to yield [Fe(Et₂dtc)₂Cl] proceeds under 313 nm irradiation through a metal complex excited state, as expected. Under 254 nm irradiation, however, the dominant pathway is through a solvent-initiated reaction in which radicals formed after absorption of light by CHCl₃ react thermally with [Fe(Et₂dtc)₃]. The initial rate varies linearly with the light intensity at 313 nm, but at 254 nm varies with the square root of the intensity.     

Antiplasmodial activities of gold(I) complexes involving functionalized N-heterocyclic carbenes

A series of twenty five molecules, including imidazolium salts functionalized by N-, O- or S-containing groups and their corresponding cationic, neutral or anionic gold(I) complexes were evaluated on Plasmodium falciparum in vitro and then on Vero cells to determine their selectivity. Among them, eight new compounds were synthesized and fully characterized by spectroscopic methods. The X-ray structures of three gold(I) complexes are presented. Except one complex (18), all the cationic gold(I) complexes show potent antiplasmodial activity with IC₅₀ in the micro- and submicromolar range, correlated with their lipophilicity. Structure–activity relationships enable to evidence a lead-complex (21) displaying a good activity (IC₅₀ = 210 nM) close to the value obtained with chloroquine (IC₅₀ = 514 nM) and a weak cytotoxicity.     

Iron and manganese complexes of benzothiazolyformazans

A series of Iron (Fe(II)) and manganese (Mn(II)) complexes of 1,3-substituted 5-(2-benzothiazolyl)formazans are reported. The crystal structures of the Fe(II) and Mn(II) complexes of 1,3-diphenyl-5-(2-benzothiazolyl)formazan are very similar and both contain a coordination sphere of four five-membered rings involving the N¹ and N³ nitrogen atoms of the formazan chain and the N² of the heterocyle resulting in a distorted octahedral structure in both cases. The distortions arise primarily from the spatial requirements of the bulky phenyl substituents.     

Effect of visible light on carotenogenesis in arthroconidiating Trichophyton mentagrophytes

The effect of visible light on carotenoid content in the dermatophyte Trichophyton mentagrophytes ATCC 26323 was investigated. The fungus T. mentagrophytes accumulated several carotenoids when arthroconidiated on Sabouraud glucose agar at 37°C. When this fungus was irradiated with moderate fluence rates of white light, the resultant arthroconidia contained considerably less carotenoids in comparison with dark controls although growth and arthroconidiation of this fungus were not at all affected by visible light. The reduction of carotenoid content in arthroconidia was due primarily to blue light, although red light caused a slight decrease in pigmentation. The suppressive effect of visible light on pigmentation was fluence rate dependent. Carotenoid accumulation in arthroconidia was inversely and exponentially related to the fluence rate of light. Carotenoid formation in arthroconidiating T. mentagrophytes was neither photoinducible nor photostimulative. An analysis of isolated carotenoids revealed that visible light caused a quantitative reduction in pigmentation, and no single carotenoid was selectively decreased.Non-standard abbreviations PI pigmentation index - r coefficient of correlation     

A study of binary iron/lithium organometallic complexes as single source precursors to solid state cathode materials for potential Li ion battery application

Solid state and solution phase decomposition of organometallic half sandwich and sandwich complexes of type [CpFeCODLi × DME] 1, [CpFeCODLi × TMEDA] 2 and [(Cp)₂FeLi₂ × 2 TMEDA] 3 (Cp = cyclopentadienyl, COD = 1,5-cyclooctadiene, DME = dimethoxyethane, TMEDA = tetramethylethylenediamine) derived from ferrocene, yield different kinds of lithium ferrites under oxidative and inert conditions. Thermogravimetry (TG) and TG coupled mass spectrometry of these compounds indicate that the decomposition begins above 170 °C for 1, 185 °C for 2 and 190 °C for 3 with removal of all the organic ligands. In the absence of oxygen, compounds 1, 2 and 3 decompose to a mixture of Fe, Fe₃C and Li₂O/Li₂CO₃ at temperatures above 200 °C. Amorphous α-LiFeO₂ is formed in the temperature range of 200-400 °C in the presence of oxygen. Crystalline α-LiFeO₂ is formed only above 400 °C using 1. Elemental analysis of the LiFeO₂ obtained from 1 indicates a drastic decrease in the carbon and hydrogen content with the increase in the oxidation temperature. XRD reveals the presence of Li₂CO₃ as second phase formed for precursors 1, 2, and 3 under oxidative conditions. Solution phase decomposition of 2 and 3 in the absence of oxygen followed by annealing at 600 °C yields Li₂Fe₃O₅, Li₅FeO₄ and Fe₃C depending on the solvent to precursor ratio in contrast to the α-LiFeO₂ phase formed under pure solid state decomposition conditions. However, all lithium ferrites (Li₂Fe₃O₅, Li₅FeO₄) are converted to α-LiFeO₂ when oxidized above 500 °C. The α-LiFeO₂ products were further characterized by IR, XPS, and TEM. Electrochemical analysis of the α-LiFeO₂ was performed, showing a moderate initial capacity of 13 mAh/g.     

Charge transfer photochemistry of quadruply bonded ditungsten halophosphine complexes

The quadruple metal-metal bonded complexes, W₂Cl₄(PR₃)₄ (PR₃ = PMe₃, PMe₂Ph, PBu₃), photoreact in dichloromethane with near-UV excitation (λ>375 nm) to yield a mixed valence W₂(II,III) photoproduct. Electronic absorption and EPR spectra of photolyzed solutions are identical to those obtained from the thermal oxidation of W₂Cl₄(PR₃)₄ by PhICI₂, which is known to yield W₂Cl₅(PR₃)₃. Subsequent reaction of the photolyzed solution yields the oxidized, confacial biotahedral W₂(III,III) halophosphine. Analysis of the organic photoproduct reveals that the halocarbon solvent is reduced by one electron to yield the chloromethyl radical. When the radical is produced in low yields, hydrogen abstraction from solvent appears to be sufficiently efficient to compete with dimerization and only chloromethane is observed; however, at higher concentrations, the chloromethyl radicals couple to produce dichloroethane. Photoreaction is observed only with near-UV excitation of the LMCT absorption manifold of W₂Cl₄(PR₃)₄. At lower energy wavelengths, transient absorption spectroscopy shows the production of the ¹δδ^* excited state, which decays to ground state over times commensurate with the decay of ¹δδ^* luminescence. In hydrocarbon solutions, no transient intermediate or photochemistry is observed, indicating that the LMCT excited state, although capable of reducing a C---X bond, cannot activate the stronger C---H bonds of hydrocarbons. The photochemistry and transient absorption spectroscopy results of the W₂Cl₄(PR₃)₄ complexes are compared to our previous studies of the homologs.     

Gold acyls and imidoyls prepared from anionic Fischer-type carbene complexes

Reaction of [(CO)₅WC(O)Ph]Li or [(CO)₅WC(O)Ph]NBu₄ with Ph₃PAuCl affords acyl complexes of gold. In the latter conversion, both the crystalline products [(CO)₅WCl]NBu₄ (2) and Ph₃PAuC(O)Ph (3) have been isolated and fully characterised. Similarly, imidoyl gold compounds (4-8) result from deprotonated aminocarbene complexes, [(CO)₅MC(NR²)R¹]Li (M = Cr, W; R¹ = Ph, Me; R² = H, Me) and Ph₃PAuCl. Crystal and molecular structure determinations of dinuclear [Ph₃PAuC(NH)Ph] · Cr(CO)₅ (6) show N-coordination of the chromium carbonyl unit that selectively affords a Z-isomer.     

Iron release analyses from ferritin by visible light irradiation

We investigated the iron release from ferritin by irradiation from a white fluorescent light in the absence or presence of ADP. Irradiation of a ferritin solution at 17,000 lx in the absence of ADP slightly induces iron release from ferritin but only at acidic pH conditions (pH 5.0 or pH 6.0). Irradiation in the presence of ADP markedly enhances iron release from ferritin under the same conditions. In the absence of irradiation, the iron release from ferritin was low even in the presence of ADP. The induction of the iron release by irradiation in the presence of ADP was also affected by various factors such as irradiation dose and acidity, but not temperature (4-47°C), oxygen concentration, or free radical generations during the irradiation. The iron release during the irradiation ceased to increase by turning off the light and was found to increase again after additional irradiation. These results suggest that visible light directly induces iron release from ferritin via the photoreduction of iron stored inside ferritin.     

Chemistry of vinylidene complexes XI. Synthesis of trinuclear MnFePt complexes by means of consecutive assembling out of mono- and dimetal vinylidene precursors

The dimetal μ-vinylidene complexes Cp(CO)₂MnPt(μ-C = CHPh)L₂ (L = tert.-phosphine or -phosphite), which have been obtained by coupling of the mononuclear complex Cp(CO)₂Mn=C=CHPh and unsaturated PtL₂ unit, add smoothly the Fe(CO)₄ moiety to produce trimetal MnFePt compounds. The μ₃-vinylidene cluster CpMnFePt(μ₃-C=CHPh)(CO)₆(PPh₃) was prepared in quantitative yields from the reactions of Cp(CO)₂MnPt(μ-C=CHPh)(PPh₃)L (L = PPh₃ or CO) with Fe₂(CO)₉ in benzene at 20 °C. The phosphite-substituted complexes Cp(CO)₂Mnpt(μ-C=CHPh)L₂ (L = P(OEt)₃ or P(OPrⁱ)₃) react under analogous conditions with Fe₂(CO)₉ to give mixtures (2:3) of the penta- and hexacarbonyl clusters, CpMnFePt(μ₃-C = CHPh)(CO)₅L₂ and CpMnFePt(μ₃-C = CHPh)(CO)₆L, respectively. The similar reaction of the dimetal complex Cp(CO)₂MnPt(μ-C = CHPh)(dppm), in which the Pt atom is chelated by dppm = Ph₂PCH₂PPhPin2 ligand, gives only a 15% yield of the analogous trimetal μ₃-vinylidene hexacarbonyl product CpMnFePt(μ₃-C = CHPh)(CO)(dppm), but the major product (40%) is the tetranuclear μ₄-vinylidene cluster (dppm)PtFe₃(μ₄-C = CHPh)(CO)₉. The IR and ¹H, ¹³C and ³¹P NMR data for the new complexes are reported and discussed.     

A convenient synthesis of isocyclam and [16]aneN4 and the photophysics of their dicyanochromium(III) complexes

The syntheses of the tetraazamacrocyclic ligands 1,4,7,11-tetraazacyclotetradecane (isocyclam) and 1,5,9,13-tetraazacyclohexadecane ([16]aneN₄) in two steps starting from the corresponding tetraamine and diethylmalonate is reported. The trans-dicyanochromium(III) complexes, trans-[Cr(isocyclam)(CN)₂]PF₆ and trans-[Cr([16]aneN₄)(CN)₂]PF₆ have also been prepared. Both are ²E_g emitters with 0-0 band emission wavelengths at 721.2 and 704.8 nm, respectively. The isocyclam complex has a room temperature excited state lifetime of 147 μs in aqueous solution which increases to 215 μs upon macrocyclic N-H deuteration, whereas the corresponding lifetime of the [16]aneN₄ complex is 25 μs and is unaffected by macrocyclic N-H deuteration. The implications of the temperature dependence of the excited state lifetimes are also presented.     

Molecular structure and reactions of azobenzene complexes with iron-lithium compounds

Reactions of azobenzene have been studied with heteronuclear iron-lithium compounds formed in the reaction of FeCl₃ with LiPh, one of the dinitrogen reducing systems of the Vol'pin type: Ph₄FeLi₄(OEt₂)₄ (1) and (H₂)FePh₄Li₄(OEt₂)₄ (2). The structures of the azobenzene complexes formed, (N₂Ph₂)₃FeLi₃(OEt₂)₃ (3) and (N₂Ph₂)₃FeLi₂(THF)₂ (4), as well as an ether-containing analog of the latter, (N₂Ph₂)₃FeLi₂(OEt₂)₂ (5), were determined by X-ray analysis of single crystals. Coordination of azobenzene at FeLi₃ and FeLi₂ clusters was shown to result in a sigificant elongation of the NN bond; partial cleavage of this bond on protolysis of the complexes resulted in the formation of hydrazobenzene and aniline. Magnetic susceptibility measurements and theoretic analysis of a similar model complex leads to the conclusion that the iron oxidation state in 3 may be considered between iron (I) and iron(III) (close to iron(I)), whereas in 4 and 5 it is close to iron(II).     

Photochemical reactions of transition metal organyl complexes with olefins Part 10. Light-induced formal [5+2] cycloadditions at manganese

Tricarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-manganese (1) forms upon UV irradiation in THF at 208 K solvent stabilized dicarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-tetrahydrofurane-manganese (2). With butynedioic acid dimethyl ester (3) and diphenylacetylene (5) complex 2 yields tricarbonyl-η⁵-1,2-dimethoxycarbonyl-4,6-dimethyl- cyclohepta-2,4-dien-1-yl-manganese (4) and tricarbonyl-η-4,6-dimethyl-1,2-diphenyl-cyclohepta-2,4-dien-1-yl- manganese (6) in a formal [5+2] cycloaddition. Addition of carbon monoxide and a 1,4-H shift completes the reaction. Propynoic acid methyl ester (7) forms the 2:1 adduct dicarbonyl-η^5:2-1,3-dimethyl-6-methoxycarbonyl-6- (E-2′-methoxycarbonylvinyl)-cyclohepta-2,4-dien-1-yl-manganese (8). The crystal and molecular structure of 8 was determined by X-ray structure analysis. The molecular structures of the complexes 4 and 6 were established by IR and NMR spectroscopy. Formation mechanisms of 4, 6 and 8 are discussed. Crystal data for 8: monoclinic space group P2₁/c, a=802.6(3), b=1136.6(1), c=8872.3(3) pm, β=93.14(2)°, V=1.705 nm³, Z=4.     

Two cyano-bridged heterotrinuclear complexes built from [(Tp)Fe(CN)3] (Tp = hydrotris(pyrazolyl)borate): synthesis, crystal structures and magnetic properties

Using an anionic precursor [(Tp)Fe^III(CN)₃]⁻ (1) as a building block, two cyano-bridged centrosymmetric heterotrinuclear complexes, (2) and (3) (en = ethylenediamine), have been synthesized and structurally characterized. In each complex, [TpFe(CN)₃]⁻ acts as a monodentate ligand toward a central [Mn(C₂H₅OH)₄]²⁺ or [Ni(en)₂]²⁺ core through one of its three cyanide groups, the other two cyanides remaining terminal. The intramolecular Fe-Mn and Fe-Ni distances are 5.2354(4) and 5.0669(11) Å, respectively. The magnetic properties of complexes 2 and 3 have been investigated in the temperature range of 2.0-300 K. A weak antiferromagnetic interaction between the Mn(II) and Fe(III) ions has been found in complex 2. The magnetic data of 2 can be fitted with the isotropic Hamiltonian: where J and J′ are the intramolecular exchange coupling parameters between adjacent and peripheral spin carriers, respectively. This leads to values of J = −1.37 cm⁻¹ and g = 2.05. The same fitting method is applied to complex 3 to give values of J = 1.2 cm⁻¹ and g = 2.25, showing that there is a ferromagnetic interaction between the Fe(III) and Ni(II) ions.     

Copper(II) PMDTA and copper(II) TMEDA complexes: precursors for the synthesis of dinuclear dicationic copper(II) complexes

Copper(II) cations coordinated with PMDTA (pentamethyldiethylenetriamine) and TMEDA (tetramethylethylenediamine) possess a high synthetic potential. The synthesis of these cations was carried out by metathesis reactions with silver salts. The cationic copper(II) complexes, [Cu(PMDTA)(Me₂CO)Cl]⁺, [Cu(PMDTA)(H₂O)Cl]⁺, [Cu(PMDTA)(DMF)]⁺, [Cu(PMDTA)Cl]⁺, [Cu(PMDTA)OAc]⁺, [Cu(PMDTA)(MeCN)₂]²⁺, [Cu₂(TMEDA)₂Cl₃]⁺ and [Cu(TMEDA)(MeCN)₃]²⁺ were synthesised as PF₆ salts, crystallised and characterised by single-crystal X-ray diffraction.