Bis Iron Research Articles

Iron-catalyzed C-H borylation of arenes.

Well-defined iron bis(diphosphine) complexes are active catalysts for the dehydrogenative C-H borylation of aromatic and heteroaromatic derivatives with pinacolborane. The corresponding borylated compounds were isolated in moderate to good yields (25-73%) with a 5 mol% catalyst loading under UV irradiation (350 nm) at room temperature. Stoichiometric reactivity studies and isolation of an original trans-hydrido(boryl)iron complex, Fe(H)(Bpin)(dmpe)2, allowed us to propose a mechanism showing the role of some key catalytic species.

Cyclization of a 1,4-diborabutadiene ligand with both atoms of CO.

A 1,4-dibora-1,3-butadiene iron complex was successfully synthesized through the stoichiometric reaction of an iron bis(borylene) complex with diphenylacetylene. This complex was treated with CO and PMe3 , which led to the formation of an unusual six-membered B2 C3 O ylidic ring bound to both the PMe3 group and zerovalent iron center. The reaction is a very rare example of the incorporation of both atoms of CO into a ring system.

Synthesis and the structure of 8-tetrahydrofuronium and 8-tetrahydropyronium derivatives of iron bis(dicarbollide)(-I) and their cleavage reactions.

8-Tetrahydrofuronium and 8-tetrahydropyronium derivatives of iron bis(dicarbollide)(-I) were synthesized. Their reactions of ring cleavage by MeOH, N3(-), amines and 1,2-bis(diphenylphosphino)ethane were investigated. 8-Tetrahydrofuronium iron bis(dicarbollide)(-I) was found to be more active in these reactions in comparison with 8-tetrahydropyronium and 8-dioxonium species, respectively. The first conjugates of iron bis(1,2-dicarbollide)(-I) with 2'-deoxyadenosine modified via the C-8 position of the purine base were synthesized. Reactions of these oxonium compounds with 1,2-bis(diphenylphosphino)ethane (dppe) led to zwitter-ionic monophosphonium salts. One of these compounds has given rise to a novel ferracarborane/cobaltacarborane hybrid complex.

Synthesis and characterisation of halide, separated ion pair, and hydride cyclopentadienyl iron bis(diphenylphosphino)ethane derivatives.

Treatment of anhydrous FeX2 (X = Cl, Br, I) with one equivalent of bis(diphenylphosphino)ethane (dppe) in refluxing THF afforded analytically pure white (X = Cl), light green (X = Br), and yellow (X = I) [FeX2(dppe)]n (X = Cl, ; Br, ; I, ). Complexes are excellent synthons from which to prepare a range of cyclopentadienyl derivatives. Specifically, treatment of with alkali metal salts of C5H5 (Cp, series ), C5Me5 (Cp*, series ), C5H4SiMe3 (Cp', series ), C5H3(SiMe3)2 (Cp'', series ), and C5H3(Bu(t))2 (Cp(tt), series ) afforded [Fe(Cp(†))(Cl)(dppe)] , [Fe(Cp(†))(Br)(dppe)] , and [Fe(Cp(†))(I)(dppe)] (Cp(†) = Cp, Cp*, Cp', Cp'', or Cp(tt)). Dissolution of in acetonitrile, or treatment of with Me3SiI in acetonitrile (no halide exchange reactions were observed in other solvents) afforded the separated ion pair complexes [Fe(Cp(†))(NCMe)(dppe)][I] . Attempts to reduce , , and with a variety of reductants (Li-Cs, KC8, Na/Hg) were unsuccessful. Treatment of with LiAlH4 gave the hydride derivatives [Fe(Cp(†))(H)(dppe)] . This report provides a systematic account of reliable methods of preparing these complexes which may find utility in molecular wire and metal-metal bond chemistries. The complexes reported herein have been characterised by X-ray diffraction, NMR, IR, UV/Vis, and Mössbauer spectroscopies, cyclic voltammetry, density functional theory calculations, and elemental analyses, which have enabled us to elucidate the electronic structure of the complexes and probe the variation of iron redox properties as a function of varying the cyclopentadienyl or halide ligand.

A heteroleptic push-pull substituted iron(II) bis(tridentate) complex with low-energy charge-transfer states.

A heteroleptic iron(II) complex [Fe(dcpp)(ddpd)](2+) with a strongly electron-withdrawing ligand (dcpp, 2,6-bis(2-carboxypyridyl)pyridine) and a strongly electron-donating tridentate tripyridine ligand (ddpd, N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine) is reported. Both ligands form six-membered chelate rings with the iron center, inducing a strong ligand field. This results in a high-energy, high-spin state ((5) T2 , (t2g )(4) (eg *)(2) ) and a low-spin ground state ((1) A1 , (t2g )(6) (eg *)(0) ). The intermediate triplet spin state ((3) T1 , (t2g )(5) (eg *)(1) ) is suggested to be between these states on the basis of the rapid dynamics after photoexcitation. The low-energy π(*) orbitals of dcpp allow low-energy MLCT absorption plus additional low-energy LL'CT absorptions from ddpd to dcpp. The directional charge-transfer character is probed by electrochemical and optical analyses, Mößbauer spectroscopy, and EPR spectroscopy of the adjacent redox states [Fe(dcpp)(ddpd)](3+) and [Fe(dcpp)(ddpd)](+) , augmented by density functional calculations. The combined effect of push-pull substitution and the strong ligand field paves the way for long-lived charge-transfer states in iron(II) complexes.

Activation of Dihydrogen and Silanes by Cationic Iron Bis(phosphinite) Pincer Complexes

Treatment of iron POCOP-pincer hydride complexes cis-[2,6-(iPr2PO)2C6H3]Fe(H)(PMe3)2 (1-H), [2,6-(iPr2PO)2C6H3]Fe(H)(PMe3)(CO) (2-H, trans H/CO; 2′-H, cis H/CO), and cis-[2,6-(iPr2PO)2C6H3]Fe(H)(CO)2 (3-H) with HBF4·Et2O in CD3CN/THF-d8 results in a rapid evolution of H2. Except for the reaction of 1-H, which leads to decomposition of the pincer structure, all other hydrides are converted cleanly to acetonitrile-trapped cationic complexes. Protonation of these hydrides with the weaker acids CF3CO2H and HCO2H establishes the basicity order of 1-H > 2-H > 2′-H > 3-H, with 3-H bearing the least basic hydride ligand. An alternative method of abstracting hydride by [Ph3C]+[BF4]− gives complicated products; the reaction of 2-H generates two pincer products, [HPMe3]+[BF4]− and Gomberg’s dimer, which supports a single electron transfer pathway. Cationic complexes {[2,6-(iPr2PO)2C6H3]Fe(CO)(PMe3)(CH3CN)}+[BF4]− (2+-BF4, trans CO/CH3CN) and cis-{[2,6-(iPr2PO)2C6H3]Fe(CO)2(CH3CN)}+[BF4]− (3+-BF4) are prepared from protonation of 2-H (or 2′-H) and 3-H with HBF4·Et2O, respectively. Both compounds react with H2 with the aid of iPr2NEt to yield neutral hydride complexes and [iPr2N(H)Et]+[BF4]−. In addition, they catalyze the hydrosilylation of benzaldehyde and acetophenone with (EtO)3SiH and show higher catalytic activity than the neutral hydrides 2-H/2′-H and 3-H. The mechanism for the formation of 2+-BF4 and the X-ray structure of 2+-BF4 are also described.

ChemInform Abstract: Iron‐Catalyzed Kinetic Resolution of N‐Sulfonyl Oxaziridines.

We have developed a highly selective kinetic resolution of N-sulfonyl oxaziridines. This reaction utilizes an inexpensive and easily synthesized iron bis(oxazoline) catalyst to promote the efficient rearrangement of oxaziridines to the corresponding N-sulfonyl imides; no sacrificial reagents are required to effect this resolution. This process is readily translated to gram scale, which provides a practical method for the preparation of structurally diverse, enantiopure N-sulfonyl oxaziridines for use as reagents in organic synthesis.

N-methylpyrazinium ion derivatives of an iron (II) dimethylglyoximatoborate complex

New iron (II) bis(dimethylglyoximatoborate) complexes [Fe(dmgBR2)2(MePz)L]+, R = 4-methoxyphenyl and L = N-methylpyrazinium ion (MePz), tetracyanoethylene (tcne), carbon monoxide, or pyridine are described. The dicationic bis MePz derivative is the first example of a complex containing two small cationic ligands. All adopt the C2vconformation in solution, which serves to sandwich one axial ligand between 4-methoxyphenyl groups. Charge transfer spectra, conformational dynamics, and electrospray mass spectrometry studies are reported. Equilibrium and rate constants for ligand substitution reactions give a binding order trans to MePz: MePz ∼ CO < pyridine, CH3CN.

Mechanistic studies of ammonia borane dehydrogenation catalyzed by iron pincer complexes.

A series of iron bis(phosphinite) pincer complexes with the formula of [2,6-((i)Pr2PO)2C6H3]Fe(PMe2R)2H (R = Me, 1; R = Ph, 2) or [2,6-((i)Pr2PO)2-4-(MeO)C6H2]Fe(PMe2Ph)2H (3) have been tested for catalytic dehydrogenation of ammonia borane (AB). At 60 °C, complexes 1-3 release 2.3-2.5 equiv of H2 per AB in 24 h. Among the three iron catalysts, 3 exhibits the highest activity in terms of both the rate and the extent of H2 release. The initial rate for the dehydrogenation of AB catalyzed by 3 is first order in 3 and zero order in AB. The kinetic isotope effect (KIE) observed for doubly labeled AB (k(NH3BH3)/k(ND3BD3) = 3.7) is the product of individual KIEs (k(NH3BH3)/k(ND3BH3) = 2.0 and k(NH3BH3)/k(NH3BD3) = 1.7), suggesting that B-H and N-H bonds are simultaneously broken during the rate-determining step. NMR studies support that the catalytically active species is an AB-bound iron complex formed by displacing trans PMe3 or PMe2Ph (relative to the hydride) by AB. Loss of NH3 from the AB-bound iron species as well as catalyst degradation contributes to the decreased rate of H2 release at the late stage of the dehydrogenation reaction.

High molecular weight poly(lactic acid) produced by an efficient iron catalyst bearing a bis(amidinato)-N-heterocyclic carbene ligand

An iron bis(alkoxide) complex containing a bis(amidinato)-N-heterocyclic carbene ancillary ligand has been synthesized and utilized for the polymerization of (rac)-lactide. This complex was an excellent precatalyst for the controlled polymerization of (rac)-lactide leading to polymer with a number average molecular weight that is approximately four times larger than the analogous bis(imino)pyridine iron complexes while maintaining a similar reaction rate. The unusually high molecular weight observed in these reactions was explained by a fraction of the added complex being the active catalyst for lactide polymerization due to slow initiation versus propagation rates. Mechanistic investigations corroborated this hypothesis revealing an induction period that can be shortened by increasing the concentration of the lactide. This feature of the catalyst system led to a situation where larger observed rate constants were measured as the amount of lactide relative to iron was increased. At the very high lactide to complex ratio of 5000:1 (0.02mol% catalyst loading), the bis(amidinato)-N-heterocyclic carbene iron bis(alkoxide) complex produced very high molecular weight polymer (Mn>350kg/mol, PDI=1.2) within 8h (85% conversion). Kinetic studies revealed that the bis(amidinato)-N-heterocyclic carbene iron complex is approximately seven times more active than the corresponding bis(amino)pyridine iron complex.

Iron-catalyzed kinetic resolution of N-sulfonyl oxaziridines

We have developed a highly selective kinetic resolution of N-sulfonyl oxaziridines. This reaction utilizes an inexpensive and easily synthesized iron bis(oxazoline) catalyst to promote the efficient rearrangement of oxaziridines to the corresponding N-sulfonyl imides; no sacrificial reagents are required to effect this resolution. This process is readily translated to gram scale, which provides a practical method for the preparation of structurally diverse, enantiopure N-sulfonyl oxaziridines for use as reagents in organic synthesis.

β-K3Fe(MoO4)2Mo2O7.

The title compound, tripotassium iron(III) bis­(ortho­molyb­date) dimolybdate, was obtained by a solid-state reaction. The main structural building units are one FeO6 octa­hedron, two MoO4 tetra­hedra and one Mo2O7 dimolybdate group, all with point group symmetries m. These units are linked via corner-sharing to form ribbons parallel to [010]. The three K+ cations are located between the ribbons on mirror planes and have coordination numbers of 10 and 12. Two O atoms of one of the MoO4 tetra­hedra of the dimolybdate group are disordered over two positions in a 0.524 (11):0.476 (11) ratio. The structure of the title compound is compared briefly with that of Rb3FeMo4O15.

α-NH4Fe(HAsO4)2.

The title compound α-ammonium iron(III) bis­[hydro­gen arsenate(V)], α-NH4Fe(HAsO4)2 (or poly[ammonium bis­(μ-hydro­gen arsenato)ferrate(III)], {NH4[Fe(HAsO4)2]}n), syn­the­sized hydro­thermally, is isostructural with NH4Fe(HPO4)2. Condensation of the hydro­gen arsenate groups with FeO6 coordination octa­hedra via common corners results in an overall three-dimensional framework containing inter­connected channels parallel to the a-, b- and c-axis directions. The NH4 + cations are located in three inter­secting tunnels, which is promising as an ion exchange. Hydrogen bonding of the types O—H⋯O and N—H⋯O consolidates the packing of the structure. The distortion of the coordination polyhedra is analyzed by means of the effective coordination number and distortion indices. Structural relationships with other compounds of general formula M I M III[HXO4)]2 (X = P, As) are discussed.

KNi0.93FeII0.07FeIII(PO4)2: a new type of structure for a compound of compositionMIMIIMIII(PO4)2

The solid solution KNi(0.93)Fe(II)(0.07)Fe(III)(PO4)2 {potassium [nickel(II)/iron(II)] iron(III) bis(orthophosphate)} has been prepared by the flux method. The compound shows a new type of structure for a phosphate with the general composition M(I)M(II)M(III)(PO4)2. The framework is formed by [(Ni/Fe)O6] polyhedra [Fe site occupancy = 0.069 (14)] linked via shared oxygen vertices forming a cis-like parallel chain stretching along a and [FeO5] polyhedra (located on alternate sides of the chains) connected via two types of PO4 groups into a three-dimensional structure. The K atoms are disordered between two sites, denoted K1A and K1B, with occupancies of 0.930 (9) and 0.070 (9), respectively, and reside inside channels along the a axis. Calculations of the Voronoi-Dirichlet polyhedra of the K atoms give a coordination scheme for K1A of [9 + 3] and for K1B of [10 + 2]. The most remarkable feature of the structure is the splitting of the K-atom site and the population of the K1A and K1B positions due to substitution of Ni by Fe in the (Ni/Fe) position.

β-Li0.37Na0.63Fe(MoO4)2.

The title compound, lithium/sodium iron(III) bis­[ortho­molyb­date(VI)], was obtained by a solid-state reaction. The main structure units are an FeO6 octa­hedron, a distorted MoO6 octa­hedron and an MoO4 tetra­hedron sharing corners. The crystal structure is composed of infinite double MoFeO11 chains along the b-axis direction linked by corner-sharing to MoO4 tetra­hedra so as to form Fe2Mo3O19 ribbons. The cohesion between ribbons via mixed Mo—O—Fe bridges leads to layers arranged parallel to the bc plane. Adjacent layers are linked by corners shared between MoO4 tetra­hedra of one layer and FeO6 octa­hedra of the other layer. The Na+ and Li+ ions partially occupy the same general position, with a site-occupancy ratio of 0.631 (9):0.369 (1). A comparison is made with AFe(MoO4)2 (A = Li, Na, K and Cs) structures.

Activation Energy of the Belousov–Zhabotinsky Reaction in a Gel with [Fe(bpy)3] Catalyst

Abstract We synthesized a novel poly(ACMO-co-[Fe(bpy)3]) gel covalently bonded to an Fe-catalyst moiety for the Belousov–Zhabotinsky (BZ) reaction. The novel gel was composed of acryloyl morpholine (ACMO) and bis(2,2′-bipyridine)(4-vinyl-4′-methyl-2,2′-bipyridine)iron bis(hexafluorophosphate) ([Fe(bpy)3]·2PF6). The period of the BZ reaction in the poly(ACMO-co-[Fe(bpy)3]) gel decreased with increasing temperature. The activation energy of the self-oscillation of the gel was found to be 78 kJ mol−1, which is higher than that of the self-oscillating polymer system with [Ru(bpy)3] (about 60 kJ mol−1).

Unraveling the origins of catalyst degradation in non-heme iron-based alkane oxidation.

A series of potentially tetradentate and pentadentate ligands modelled on BPMEN has been prepared and their iron(II) bis(triflate) complexes have been isolated and characterised by spectroscopic and crystallographic techniques (BPMEN = N,N'-bis(pyridylmethyl)ethylenediamine). Changes to the BPMEN ligand have invariably led to complexes with different coordination modes or geometries and with inferior catalytic efficiencies for the oxidation of cyclohexane with H2O2. The reaction of an iron(II) complex containing a pentadentate BPMEN-type ligand with O2 has resulted in ligand degradation via oxidative N-dealkylation and the isolation of a bis(hydroxo)-bridged dinuclear iron(III) complex with a picolinate-type ligand.

EVALUATION OF BALADY BREAD CHARACTERISTICS PREPARED FROM WHEAT FLOUR FORTIFIED WITH TWO DIFFERENT IRON FORTIFICANTS

Iron can be added to flour to replace what is lost from iron during milling or to reach a level higher than naturally found in the whole wheat, which is known as fortification. The criteria for selecting the form of iron to add as fortificant include the effect on the quality of the flour and bread, and the cost. Due to the advantages of iron - amino acid chelate, as organic form, its high bioavailability and its ability to protect the iron from binding with phenols and phytic acid and its resistance to stomach acidity and high temperature of food processing beside its safety, it may be preferred in bread making than iron in its an inorganic form. Therefore, this study was carried out to compare between two wheat flour fortificants, organic form iron (as iron bis- glycinate) and ferrous sulphate (as inorganic form) to prepare balady bread under Egyptian conditions. Physical, chemical, rheological and organoleptic characteristics of the resulted balady bread were evaluated and the resulted data were statistically analysis. The results showed that increasing the level of ferrous addition (organic or inorganic forms) led to an increase in gluten index. It also, was found that no significant differences were observed between control sample (unfortified) and the two fortificants flour samples in all farinograph measurements such as: water absorption (%), arrival time, and dough development time and dough stability. Cost of iron also, fortification for one ton of wheat flour was calculated, in order to encouragement the official authorities such as Ministry of Supply and Internal Trade and Milling Companies. It also aimed to spread the knowledge of wheat flour fortification, which led to obtain a high nutritional value of balady bread.

The (N4C2)2– Donor Set as Promising Motif for Bis(tridentate) Iron(II) Photoactive Compounds

The ground and excited states of iron(II) bis(dipyridylbenzene) were probed by means of DFT and TDDFT. In comparison to the well-known Fe(tpy)2(2+), this neutral complex should not suffer from ligand loss, and it displays a better absorption profile in the visible region. The relative energies of the spectroscopically relevant excited states ((3)MLCT, (3)MC, (5)MLCT, and (5)MC) are quite different from those of its archetypical counterpart and thus make it a promising candidate for photophysics in general.

Redox-Controlled Polymerization of Lactide Catalyzed by Bis(imino)pyridine Iron Bis(alkoxide) Complexes

Bis(imino)pyridine iron bis(alkoxide) complexes have been synthesized and utilized in the polymerization of (rac)-lactide. The activities of the catalysts were particularly sensitive to the identity of the initiating alkoxide with more electron-donating alkoxides resulting in faster polymerization rates. The reaction displayed characteristics of a living polymerization with production of polymers that exhibited low molecular weight distributions, linear relationships between molecular weight and conversion, and polymer growth observed for up to fifteen sequential additions of lactide monomer to the polymerization reaction. Mechanistic experiments revealed that iron bis(aryloxide) catalysts initiate polymerization with one alkoxide ligand, while iron bis(alkylalkoxide) catalysts initiate polymerization with both alkoxide ligands. Oxidation of an iron(II) catalyst precursor lead to a cationic iron(III) bis-alkoxide complex that was completely inactive toward lactide polymerization. When redox reactions were carried out during lactide polymerization, catalysis could be switched off and turned back on upon oxidation and reduction of the iron catalyst, respectively.