Dinuclear Iron Complexes Research Articles

Synthesis and structures of dinuclear iron, molybdenum and tungsten complexes derived from (PhCHCHPh)-coupled bis(cyclopentadiene)

Reductive coupling of phenylfulvene with amalgamated calcium metal followed by hydrolysis yields CpPhCHCHPhCp ( 1) in high yield. Refluxing ligand 1 and Fe(CO) 5 in xylene produces (PhCHCHPh)-coupled bis(cyclopentadienyl) tetracarbonyl diiron (PhCHCHPh)[(η 5-C 5H 4)Fe(CO) 2] 2 ( 2) as a mixture of meso ( 2- meso) and racemic isomers ( 2- rac). The pure racemic isomers of the Mo and W analogues ( 3- rac and 4- rac) have been synthesized by lithiation of ligand 1 and addition of (MeCN) 3M(CO) 3 (M = Mo, W) followed by oxidation with 2 equiv. of ferrocenium tetrafluoroborate. All the new complexes have been fully characterized. The molecular structures of 1- meso, 2- meso, 2- rac, 3- rac, and 4- rac have been determined by X-ray diffraction analysis.

Synthesis and Crystal Structures of Two Dinuclear Iron(III) Complexes with Tripodal Ligands

AbstractBy using the tripodal tetradentate ligands of tris(2‐pyridylmethyl)amine (TPA) or tris(2‐benzimidazolylmethyl)amine (NTB), two dinunclear iron(III) complexes [Fe2L2(μ2‐O)(μ2‐p‐NH2‐C6H4COO)]3+ (L=TPA, 1 and L=NTB, 2) were obtained. Both of the two complexes crystallize in monoclinic system with space group P2(1)/c. The cell parameters of 1: a=1.4529(4) nm, b=1.6622(5) nm, c=2.0625(6) nm, β=100.327(5)°, V=4.900(3) nm3, Z=4, F(000)=2344, Mr=1142.91, Dc=1.549 g/cm3, R1=0.0544, R2=0.0962. The cell parameters of 2: a=1.3378(4) nm, b=2.1174(7) nm, c=2.4351(7) nm, β=97.315(6)°, V=6.842(4) nm3, Z=4, F(000)=3116, Mr=1505.08, Dc=1.444 g/cm3, R1=0.0793, R2=0.1623. In both cases, the central iron(III) metal ions are coordinated to the four nitrogen atoms of TPA (or NTB) and two oxygen atoms from two different bridges to form a distorted octahedral geometry.

Catalytic oxidation of alcohols to carbonyl compounds with hydrogen peroxide using dinuclear iron complexes

Oxidation of primary and secondary alcohols has been studied in the presence of [Fe(ind)Cl] 2O ( 1) and [Fe 2(OMe) 2(PAP)Cl 4] ( 2) (indH = 1,3-bis(2′-pyridylimino)isoindoline; PAP = 1,4-di(2′-pyridyl)aminophthalazine) as catalysts using hydrogen peroxide as primary oxidant. The complexes were found to be suitable catalysts for the oxidation of alcohols to the corresponding carbonyl compounds in acetone as solvent. The reactivity of the alcohols is in the order primary < secondary < cyclic secondary < aromatic. The reaction mechanism in the case of 1 probable involves an iron-based oxidant, while in the case of 2 a free-radical mechanism is suggested.

Synthesis and magnetic properties of new dinuclear iron(II) complexes of a phenylene‐bridge shiff base analogue dinucleating ligand

AbstractThe synthesis and magnetic behavior of four new dinuclear iron(II) complexes Fe22a‐d × 4Py with the iron in an octahedral coordination sphere is presented in this paper. The complex c is a high‐spin complex over the whole temperature range investigated, while the complexes a,b, and d perform a partial low‐spin ⇔︁ high‐spin spin transition. In case of Fe22b × 4Py, X‐ray structure analysis of the HS/LS state was possible, showing that in one molecule both iron centers are either in the low‐spin or sin the high‐spin state. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:391–397, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20108

A dinuclear oxygen-bridged Schiff base iron(III) complex derived fromN,N′-bis(2-hydroxybenzylidene)-1,2-diaminopropane

The title compound, μ-oxo-bis({2,2-[propane-1,2-diyl­bis­(nitrilo­methyl­idyne)]diphenolato}iron(III)), [Fe2(C17H16N2O2)2O], is an unusual dinuclear iron(III) complex. Each FeIII ion has a distorted square-pyramidal coordination geometry. In the basal plane, the Fe atom is coordinated by two N atoms and two O atoms of the Schiff base ligand. The apical position is occupied by a bridging O2− ion, which links to the other FeIII ion in the complex. In the crystal structure, pairs of dinuclear iron(III) units form dimers by way of a pair of intermolecular C—H⋯O interactions. The dimers stack along the a axis and there are no other short intermolecular contacts.

Bis(μ-alkoxo)-bridged dinuclear iron(III) complexes of pyrazole-based ligands as models for iron-oxo proteins

The synthesis and characterization of two new bis(μ-alkoxo)-bridged dinuclear iron(III) complexes with the ligands 1-(2-hydroxyethyl)-pyrazole (Hnhep) and 1-(2-hydroxyethyl)-3,5-dimethylpyrazole (Hnhed), [Fe(nhep)Cl 2(EtOH)] 2 ( 1) and [Fe(nhed)Cl 2] 2 ( 2) are reported. The crystal structures of both complexes reveal the presence of centrosymmetric dinuclear units. In compound 1, the iron(III) center has a coordination number of six, with a slightly distorted octahedral geometry. In compound 2, the bulkier nhed ligand, with methyl groups at the 3- and 5-positions of the pyrazole ring, leads to a coordination number of five at the iron(III) center in a distorted square pyramidal geometry. The magnetic properties of both complexes have been investigated in the range 2–300 K and indicate the presence of fairly weak antiferromagnetic exchange interactions between iron(III) ions ( J 1 = −10.04 cm −1 for 1 and J 2 = −12.5 cm −1 for 2). The inactivity of both complexes in the cyclohexane hydroxylation appears to be partly due to the presence of the strong iron(III)–chloride bond that does not allow exchange with the reactant molecules.

Synthesis, crystal structure and properties of dinuclear iron(III) complexes containing terminally coordinated phenolate/H 2O/OH − groups as models for purple acid phosphatases: efficient hydrolytic DNA cleavage

We present here the syntheses of two dinuclear iron(III) complexes with the polydentate N,O-donor ligand H 2BPClNOL ( N-(2-hydroxybenzyl)- N-(2-pyridylmethyl)[(3-chloro)(2- hydroxy)]propylamine). The reaction between Fe III(ClO 4) 3 · 9H 2O, the title ligand and two equivalents of NaOAc · 3H 2O resulted in the complex [ Fe 2 III ( BPClNOL ) 2 ( OAc ) ] ClO 4 ( 1 ) . When the synthesis was performed with a lesser amount of NaOAc · 3H 2O (half equivalent), the complex without bridging acetate, [ Fe 2 III ( BPClNOL ) 2 ( H 2 O ) 2 ] ( ClO 4 ) 2 · 4 H 2 O ( 2 ) was obtained. The complexes were characterized by X-ray structural analysis, magnetochemistry, Mössbauer and UV–Vis spectroscopies, and electrochemistry. Complex 2 was also characterized in solution through potentiometric titration. Both complexes crystallize in the monoclinic system. Complex 2 has one water molecule coordinated to each iron centre. Their p K a values are 5.00 and 7.03 for the first protonation/deprotonation equilibrium of each coordinated water molecule. The UV–Vis and electrochemical techniques showed that the absence of an acetate bridge in 2 results in a significant difference in the Lewis acidity of both iron centres, when compared with 1. The lack of an acetate bridge in 2 also results in changes in the anti-ferromagnetic coupling as revealed by magnetic measurements. Complex 2 is an interesting structural model for the active site of iron containing PAPs, since it has an Fe(-alkoxo) 2Fe core with an Fe III⋯Fe III distance of 3.122(1) Å, containing phenolate and water molecules coordinated to the iron centres and is soluble in aqueous solutions. Furthermore, the UV–Vis properties of 2 are similar to those of PAPs, since the complex absorbs at 580 nm in the oxidized form (550–570 nm for PAPs) and at 499 nm in the mixed-valence form (505–510 nm for PAPs) as revealed through spectroelectrochemical studies. Finally, complex 2 successfully promoted the hydrolytic cleavage of plasmid DNA under aerobic and anaerobic conditions, producing single and double DNA strand breaks at biological pH values.

Discrete Dinuclear Complexes and Two‐Dimensional Architectures from Bridging Polynitrile and Bipyrimidine (bpym) Ligands: Syntheses, Structures and Magnetic Properties of [M2(bpym)(dcne)4(H2O)2] (M = MnII, CoII) and [M2(bpym)(dcne)4(H2O)4]·2H2O (M = FeII, CuII) (dcne− = [(CN)2CC(O)OEt)]−)

AbstractOne‐pot reactions in aqueous solutions of the polynitrile anion dcne− {2,2‐dicyano‐1‐ethoxyethenolate = [(CN)2CC(O)OEt)]−] with the MII ions (M = Mn, Fe, Co, Cu) in the presence of bpym (2,2′‐bipyrimidine) afford the first mixed dcne/bpym compounds [M2(bpym)(dcne)4(H2O)2] (1: M = Mn; 2: M = Co) and [M2(bpym)(dcne)4(H2O)4]·2H2O (3: M = Fe; 4: M = Cu). The new compounds have been characterized by IR spectroscopy and X‐ray crystallography. Compounds 1 and 2 are isostructural, with each metal ion being located in an MN5O pseudo‐octahedral environment with three N atoms coming from three dcne− ligands, two nitrogen atoms from bpym and one oxygen atom from a water molecule. The extended structures of 1 and 2 are best described as dcne‐bridged zigzag chains of MII ions running along the [100] direction; connections of these chains in the [010] direction, by the bis(chelating) bpym ligand, afford 2D structures. Compounds 3 and 4 are isostructural, and consist of discrete dinuclear units involving MN4O2 octahedrally coordinated MII ions bridged by bis(bidentate) 2,2′‐bipyrimidine and terminal dcne ligands. Magnetic measurements for the 2D compounds 1 and 2 exhibit maxima in the χm vs. T plots (at about 4.5 K for 1 and about 20 K for 2) which are characteristic of weak antiferromagnetic exchange interactions between the high‐spin metal centres. While the dinuclear iron complex 3 presents a similar behaviour (maximum in χm vs. T plot at 12 K), the antiferromagnetic exchange interactions are stronger in the copper complex 4. Fits of magnetic data for compounds 1, 3 and 4 with appropriate models led to J values of −0.6, −1.5 and −99.0 cm−1 respectively. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)

A dinuclear Schiff base iron(III) complex with the ligandN,N′-bis(2-oxidophenylmethyleneimino)propane-1,2-diamine

The centrosymmetric title compound, bis­[μ-N,N′-bis(μ-2-oxido­phenyl­methyl­eneimino)­propane-1,2-diaminato(3−)]­iron(III), [Fe2(C17H16ClN2O2)2], is a dinuclear iron(III) complex. Each FeIII atom is six-coordinated by two N atoms and three O atoms from two Schiff base ligands, and one Cl atom, giving an approximately octahedral coordination environment.

Model of the iron hydrogenase active site covalently linked to a ruthenium photosensitizer: synthesis and photophysical properties.

A model of the iron hydrogenase active site with the structure [(mu-ADT)Fe2(CO)6] (ADT = azadithiolate (S-CH2-NR-CH2-S), (2: R = 4-bromophenyl, 3: R = 4-iodophenyl)) has been assembled and covalently linked to a [Ru(terpy)2]2+ photosensitizer. This trinuclear complex 1 represents one synthetic step toward the realization of our concept of light-driven proton reduction. A rigid phenylacetylene tether has been incorporated as the linking unit in 1 in order to prolong the lifetime of the otherwise short-lived [Ru(terpy)2]2+ excited state. The success of this strategy is demonstrated by comparison of the photophysical properties of 1 and of two related ruthenium complexes bearing acetylenic terpyridine ligands, with those of [Ru(terpy)2]2+. IR and electrochemical studies reveal that the nitrogen heteroatom of the ADT bridge has a marked influence on the electronic properties of the [Fe2(CO)6] core. Using the Rehm-Weller equation, the driving force for an electron transfer from the photoexcited *[Ru(terpy)2]2+ to the diiron site in 1 was calculated to be uphill by 0.59 eV. During the construction of the trinuclear complex 1, n-propylamine has been identified as a decarbonylation agent on the [(mu-ADT)Fe2(CO)6] portion of the supermolecule. Following this procedure, the first azadithiolate-bridged dinuclear iron complex coordinated by a phosphine ligand [(mu-ADT)Fe2(CO)5PPh3] (4, R = 4-bromophenyl) was synthesized.

Synthesis, structure and characterization of new complexes [Fe 2(μ-OMe) 2(PAP)(X) 4] (PAP= 1,4-di(2 ′-pyridyl)aminophthalazine, X=Cl, OAc) and their oxidation catalysis

Two dinuclear iron(III) complexes with tetradentate N-donor ligand 1,4-di(2 ′-pyridyl)aminophthalazine (PAP), [Fe 2(μ-OMe) 2(PAP)Cl 4] ( 2) and [Fe 2(μ-OMe) 2(PAP)(OAc) 4] ( 3) were prepared and characterized. Single crystal X-ray molecular structure of [Fe 2(μ-OMe) 2(PAP)Cl 4] · 2MeOH have been elucidated. The six-coordinate iron atoms are in distorted octahedral environment bridged by the oxygen atoms of two methoxy groups and the PAP ligand. The Mössbauer spectra of both complexes show one quadrupole doublet and the isomer shift and quadrupole splitting values indicate the presence of octahedral high-spin Fe III ions. Complex 2 showed catalytic activity for alkane oxidation with hydrogen peroxide.

Electronic and magnetic properties of iron (III) dinuclear complexes with carboxylate bridges

A series of dinuclear iron (III) complexes with carboxylate bridges, of the type [Fe 2L 2(H 20) 4](NO 3) 2(H 2O) m ( m=1–3), where L=Schiff base derived from L-α-amino acids and salicylaldehyde have been prepared and characterised by different spectroscopic techniques, magnetic susceptibility, conductivity, and electrochemical measurements. The dimeric iron complexes contain hexacoordinated iron (III), with the metal ion surrounded by water molecules, the salicylidenimine ligand, and the bridging carboxylate groups. The inequivalence of the iron atoms is detected by Mössbauer spectroscopy and this is reflected by the presence of two overlapping quadrupole doublets ( δ 1∼0.52–0.67 mm s −1, δ 2∼0.64–0.80 mm s −1, Δ E Q1∼0.38–0.80 mm s −1, and Δ E Q2 (∼0.68–1.01 mm s −1), with an approximate intensity ratio of 1:1 for all complexes. The magnetic susceptibilities of the complexes were determined over the temperature interval 5–300 K and revealed a decrease in the effective magnetic moment with decreasing temperature. The plots of the reciprocal of the molar susceptibility versus temperature indicate that the two iron (III) ions are very weakly antiferromagnetically coupled (− J∼0.09–0.21 cm −1). Electrochemical studies show that the first two peaks can be assigned to two consecutive one-electron reduction process, affording Fe IIFe III and Fe IIFe II. The comproportionation constant K c at 298 K is in the 5.3 × 10 3–2.5 × 10 4 range. The values obtained are in agreement with an intermediate electron coupling between redox sites.

Iron Complexes with the Alcoholato Donor‐Rich Ligand 4‐tert‐Butyl‐2,6‐bis(hydroxymethyl)phenol: Synthesis and Characterization of a Tetra‐Anionic Fe2 Complex and a Neutral Fe10Na4 Complex

AbstractThe reaction of 4‐tert‐butyl‐2,6‐bis(hydroxymethyl)phenol (H3L) with FeIII ions in methanol in the presence of an excess of NaOH afforded the tetra‐anionic dinuclear complex Na4[(HL)4FeIII2(CO3)]·11MeOH·3H2O (1). Changing the solvent to an ethanol/dme (dme = 1,2‐dimethoxyethane) mixture led to the formation of the decanuclear complex [(HL)12FeIII10Na4(µ4‐O)4(µ3‐OH)2(dme)2(EtOH)2]·2dme·8EtOH (2). The Mössbauer spectra of 1′ and 2 at 80 K are consistent with high spin FeIII sites in distorted octahedral O6 coordination environments. Compound 1 consists of a tetra‐anionic dinuclear iron complex with the unprecedented [FeIII(μ2‐OBz)2(μ2‐CO3)FeIII]2+ core. Compound 2 contains a core of hydrous ferric oxide produced by a modified hydrolysis of FeIII ions in the presence of the ligand. Eight benzyl alcohol groups are located on the surface of 2 leading to a 2D network structure by intermolecular hydrogen bonding. The temperature dependence of the magnetic susceptibilities of 1′ and 2 indicates antiferromagnetic interactions between the ferric ions. The data for 1′ were fitted with J = −4.4 cm−1 and g = 1.98, H = −2JS1S2. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)

Chemistry and reactivity of dinuclear iron oxamate complexes: alkane oxidation with hydrogen peroxide catalysed by an oxo-bridged diiron(III) complex with amide and carboxylate ligation

A new dinuclear iron(III) complex with the tetradentate ligand N, N ′- o-phenylenebis(oxamate) (opba) has been synthesised, and structurally, magnetically and electrochemically characterised. It possesses an unprecedented triply bridged Fe 2(μ-O)(μ-RCO 2⋯H 2O⋯O 2CR) 2 core, whereby two N-amides from the opba ligand complete the square-pyramidal coordination sphere of the O-carboxylate rich iron site (Fe–N=2.053 Å and Fe–O=2.015 Å). The antiferromagnetic exchange interaction between the two high-spin Fe III ions through the oxo bridge ( J=−190 cm −1; H=− JS 1· S 2) is weaker than that found in related μ-oxo singly bridged diiron(III) complexes. The lessened antiferromagnetic coupling correlates to the remarkably long Fe–O distance ( R=1.808 Å), which is associated to the relatively bent Fe–O–Fe angle ( α=131.8°) in the Fe 2O unit. It experiences an irreversible one-electron oxidation process in acetonitrile at 25 °C ( E=0.63 V versus SCE) to give the putative mixed-valent diiron(III,IV) species which is unstable under the experimental conditions. The reactivity of this unique oxo-bridged diiron(III) oxamate complex toward hydrogen peroxide activation and hydrocarbon oxidation in the presence of dioxygen has been examined. It catalyses the oxidation of alkanes like cyclohexane and adamantane to the corresponding alcohols and ketones by H 2O 2 and O 2 in acetonitrile at room temperature with limited catalytic activities (total yields of ca. 5% after 24 h) and modest selectivities ( A/ K=0.9, KIE=2.4, tert/ sec=3.0). Overall, these results are more in line with a mechanism involving alkyl radicals as transient intermediates, although they do not exclude the possibility that a metal-based active oxidant is also involved in this C–H bond oxidation chemistry.

Novel dinuclear iron(0) complexes from α,β-unsaturated ketones β-positioned with sulfide and sulfoxide groups

The reaction of Fe 2(CO) 9 with α,β-unsaturated ketones analogues containing β-positioned sulfoxide group 2a– 2d afforded dinuclear Fe(0) complexes 3a–3d and 5 which were characterized by IR, mass spectrometry, 1H and 13C NMR spectroscopy, the structures of 3a, 3c and 5 were established by X-ray diffraction analysis.

Intramolecular aromatic hydroxylation mediated by a dinuclear iron complex: an oxo-Feiv Feiv active intermediate is suggestedElectronic supplementary information (ESI) available: ESI-MS of 1 with theoretical isotopic pattern. Multiple-stage tandem ESI-MS analysis of the ligand recovered after extraction of the iron. 1H NMR spectra in CD3CN of [1]2+ under different conditions and [2]+. See http://www.rsc.org/suppdata/nj/b4/b402403f/

In the presence of oxygen atom donors [XO, e.g., m-chloroperbenzoic acid (m-CPBA), o-tert-butylsulfone iodosyl benzene (ArIO)] the benzyl group of the ligand in a mixed-valent FeIIFeIII complex is almost quantitatively ortho-hydroxylated to a phenolate terminally bound to one iron in the derived FeIIIFeIII complex. All available experimental evidence concurs to suggest that this reaction involves an oxo-FeIVFeIV intermediate.

Structure and magnetism of a new pyrazolate bridged iron(II) spin crossover complex displaying a single HS-HS to LS-LS transition.

The dinuclear iron(II) complex [(pypzH)(NCSe)Fe([micro sign]-pypz)(2)Fe(NCSe)(pypzH)].2H(2)O displays a single, sharp spin crossover transition between the [HS-HS] and [LS-LS] states and is structurally characterised above and below the T(1/2)= 225 K value

Nickel and iron complexes with oxazoline- or pyridine-phosphonite ligands; synthesis, structure and application for the catalytic oligomerisation of ethylene.

The bis(oxazolinyl)phenylphosphonite ligand (bis(4,4-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydrooxazole)phenylphosphonite, NOPONMe2)) and the new pyridine-phosphonite ligand (2-ethyl(1'-methyl-1-hydroxy)pyridine-6H-dibenz[c,e][1,2]oxaphosphorin) have been used for the preparation of the mononuclear complexes [NiCl2(NOPONMe2)] 18 and [NiCl2(6)2] 19, respectively, which catalyze the oligomerisation of ethylene with activities up to 57300 mol C2H4 mol Ni(-1) h(-1) (19 in the presence of only 6 equivalents of AlEtCl2). The selectivities for C4 dimers were as high as 90% (18 in the presence of only 2 equivalents of AlEtCl2) with selectivities for 1-butene of 21-22% of the C4 fraction. In the presence of 400 or 800 equivalents of MAO as cocatalyst, complex 19 yielded turnover frequencies of 7400 mol C2H4 mol Ni(-1) h(-1) and 13200 mol C2H4 mol Ni(-1) h(-1), respectively. The selectivities for 1-butene and ethylene dimers were similar to those obtained with AlEtCl2. The fact that 19 with a cyclic phosphonite moiety leads to higher activities and selectivities than 18 which contains an acyclic phosphonite group underlines the importance of the ligand on the catalytic properties of its metal complex. An unprecedented dinuclear iron complex [FeCl2(4,4-dimethyl-2-[(1-hydroxy-1-methyl)ethyl]-4,5-dihydrooxazolate)]2 20 was also obtained which contains two pentacoordinated metal centers coordinated by a bridging-chelating oxazoline-alcoholate. Complexes 18-20 are paramagnetic in solution, as determined by the Evans method.

Preparation and charactarization of dinuclear iron(III) and vanadium(IV) complexes with bridging salbn or salpentn ligands

Preparation and charactarization of dinuclear iron(III) and vanadium(IV) complexes with bridging salbn or salpentn ligands

Synthesis and properties of an iron hydrogenase active site model linked to a ruthenium tris-bipyridine photosensitizer

A dinuclear iron complex, related to the active site of Fe hydrogenases, has been covalently linked to a redox active ruthenium tris-bipyridine type photosensitizer. Photophysics and electrochemistry of this system are studied in solution. IR spectra of this complex together with its precursor, the dinuclear iron complex, were also shown.