Iron Hydride Research Articles

Reaction of the Transition Metal Hydrides [Cp*MH2]2 (Cp* = η5-C5Me5; M = Fe, Ru) with BH3·THF to Yield Metallaboranes. Improved Kinetic Control Leads to Novel Ferraboranes

The reactions of [Cp*MH2]2, Cp* = η5-C5Me5; M = Fe, Ru, with BH3·THF have been explored. As with [Cp*RuCl2]2, [Cp*RuH2]2 readily reacts with borane to generate nido-1,2-(Cp*RuH)2B3H7. In contrast to the chloride, intermediates are detectible in the hydride reaction and product selectivity is higher. Benefits of the apparently lower reaction barrier appear in the reaction of [Cp*FeH2]2 with BH3·THF. The formation and isolation of the novel hydrogen-rich ferraborane arachno-1-Cp*FeB4H11 from the iron hydride contrasts with the production of pentamethylferrocene from a pentamethylcyclopentadienyl iron halide. This metastable ferraborane has been characterized spectroscopically as well as by reaction with Co2(CO)8 to give a good yield of the more stable derivative nido-1-(Cp*Fe)-2-{Co(CO)3}B4H8 by metal fragment addition. The latter compound has been spectroscopically characterized in solution as well as in the solid state by a single-crystal X-ray diffraction study as an example of a mixed metal dimetallahexaborane.

High‐Pressure Hydrides of Iron and Its Alloys

AbstractFor Abstract see ChemInform Abstract in Full Text.

The electronic structure of iron hydride

The electronic and bonding properties of iron monohydride were studied using qualitative electronic structure calculations in the framework of the extended hückel tight-binding method. The calculations were performed for a double hexagonal closed-packed structure for the hydride with the hydrogen atoms occupying the octahedral sites. The results were compared with pure hcp Fe and fcc Fe. Analysis of the orbital interaction reveals that H–Fe bonding involves mainly Fe 4s and H 1s orbitals. All s, p and d bands of the FeH present an energy gap at about −12.2 eV. The gap is larger for the p band. The overlap population between Fe atoms is considerably smaller in the hydride than in pure Fe.

Propylene polymerization with a bisiminepyridine iron complex: activation with Ph 3C [B(C 6F 5) 4] and AlR 3; iron hydride species in the catalytic cycle

In this work, the complex 2,6-bis [1-(2-isopropyl-6-methylphenylimino)ethyl]-pyridineiron(II)dichloride was used for propylene polymerization. Activation with Ph 3C [B(C 6F 5) 4] and subsequent treatment with triisobutylaluminium or triethylaluminium generated a very active polymerization catalyst for propylene. The kinetics of this polymerization reaction were investigated with mass-flowmeters. Further we show propagation-time-profiles of this reaction. Depending on the nature of the aluminiumalkyl we are able to determine different aliphatic endgroups in the polymer using 13 C NMR spectroscopy. Addition of hydrogen to the polymerization leads to higher activities and allows us to formulate a complete catalytic reaction cycle containing an iron hydride species. This cycle comprises one starting cycle and two propagation cycles which can be controlled with the aluminiumtrialkyl-propylene ratio.

High-pressure hydrides of iron and its alloys

Hydrides of iron and iron-based alloys are thermodynamically stable only athydrogen pressures in the gigapascal range and rapidly lose hydrogen underambient conditions. At low temperatures, however, these hydrides can be retainedin a metastable state at atmospheric pressure after being cooled under highpressure to liquid nitrogen temperature. This review will discuss the current stateof studies on phase transformations in the Fe–H and related systems and also onthe composition, crystal structure and physical properties of the hydrides, bothunder high hydrogen pressures and in the ‘quenched’ metastable state at ambientpressure. The studies at ambient pressure include magnetization measurements,x-ray and neutron diffraction, Mössbauer spectroscopy and inelastic neutronscattering. In the sections on Mössbauer and structural investigations of hydridesof Fe–Cr and Ni–Fe alloys new experimental results will be presented.

ChemInform Abstract: High‐Pressure Hydrides of Iron and Its Alloys.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Hydride Transfer from (η5-C5Me5)(CO)2MH (M = Fe, Ru, Os) to Trityl Cation: Different Products from Different Metals and the Kinetics of Hydride Transfer

Reactions of the metal hydride complexes Cp*(CO)2MH (M = Fe, Ru, Os) with Ph3C+BF4- in CH2Cl2 were studied. Hydride transfer from Cp*(CO)2FeH to Ph3C+BF4- gives Cp*(CO)2FeFBF3. Hydride transfer from the ruthenium hydride Cp*(CO)2RuH to Ph3C+BF4- produces the bridging hydride complex {[Cp*(CO)2Ru]2(μ-H)}+BF4-, indicating that Cp*(CO)2RuH exhibits significant nucleophilicity in addition to hydridic reactivity of the Ru−H bond. The osmium hydride Cp*(CO)2OsH reacts with Ph3C+BF4- in CH2Cl2 to give a mixture of Cp*(CO)2OsFBF3 and [Cp*(CO)2Os(ClCH2Cl)]+BF4-. The kinetics of these hydride transfer reactions were monitored by stopped-flow methods, leading to the second-order rate law −d[Ph3C+BF4-]/dt = k[Ph3C+BF4-][MH]. The temperature dependence of the rate constants was determined for the iron hydride, the osmium hydride, and the osmium deuteride Cp*(CO)2OsD. Activation parameters for hydride transfer from Cp*(CO)2FeH are ΔH⧧ = 2.6 ± 0.1 kcal mol-1 and ΔS⧧ = −22.1 ± 0.4 cal K-1 mol-1; for Cp*(CO)2OsH the activ...

(η5-C5Me5)Fe(Ph2PCH2CH2CH2PPh2)][SO3CF3], a Stable 16-Electron Complex with a Coordinating Counteranion and without Agostic Interaction: The Dramatic Role of a Trivial Methylene Group

The iron chloro complex Cp*(dppp)FeCl (Cp* = pentamethylcyclopentadienyl, dppp = 1,3-bis(diphenylphosphino)propane; 2) was prepared from FeCl2(dppp) and Cp*Li in 85% yield. The air-stable compound 2 was characterized by IR-FT, 1H, 31P, and 13C NMR, cyclic voltammetry (CV), and X-ray crystal analysis. The experimental data indicate that this complex possesses the same electronic properties as its homologue Cp*(dppe)FeCl (dppe = 1,2-bis(diphenylphosphino)ethane; 2‘), but shorter distances between the chlorine atom and the hydrogen atoms of the dppp ligand give rise to through-space interactions. The hydride 3 was obtained by treatment of the chloro derivative 2 with LiAlH4 (95%). The changes in the Fe−H bond stretching and redox potential induced by replacement of dppe by dppp is in agreement with the existence of two conformers for the iron hydrides 3 and 3‘. The 16-electron species [Cp*(dppp)Fe][OSO2CF3] (4[OTf]) is obtained by treatment of 3 with methyl triflate in diethyl ether (82%). The pseudo-C2v con...

Classical and non-classical iron hydrides: synthesis, NMR characterisation, theoretical investigation and X-ray crystal structure of the iron(IV) dihydride 〚Cp*Fe(dppe)(H) 2〛 +BF 4–

Protonation of Cp*Fe(dppe)H ( 1; Cp* = η 5-C 5Me 5, dppe = Ph 2PCH 2CH 2PPh 2) by HBF 4Et 2O at –80 °C in diethylether affords the dihydrogen complex 〚Cp*Fe(dppe)( η 2-H 2)〛 +BF 4 – ( 2 +BF 4 –) in 90% yield. Its PF 6 – salt analogue ( 2 +PF 6 –) is obtained in 94% yield by reaction between the 16-electron derivative 〚Cp*Fe(dppe)〛 +PF 6 – ( 3 +PF 6 –) with H 2 gas at –80 °C. The presence of a bound dihydrogen ligand in 2 + is indicated by a short T 1 minimum values consistent with a H–H distances of 0.98(1) Å. For the partially deuterated derivative 2 +–d 1, the observed J HD value of 27.0 Hz confirms the presence of the coordinated dihydrogen ligand, which displays an H–H separation of 0.97(1) Å, in complete agreement with the distance calculated using the T 1 static rotation model. Variable temperature NMR study shows the gradual, complete and irreversible transformation of the dihydrogen complex into its classical dihydride isomer trans-〚Cp*Fe(dppe)(H) 2〛 + ( 4 +). Thermal solid state reaction (–20 °C, 48 h) of 2 +BF 4 – gives quantitatively 4 +BF 4 –, whereas 4 +PF 6 – is obtained by simple contact of H 2 with a solution of 3 +PF 6 – in THF at room temperature. The crystal structure of 4 +BF 4 – has been determined and shows a transoid arrangement of hydride ligands, consistent with the formulation of 4 + as an iron(IV) dihydride. DFT calculations on both dihydride and dihydrogen isomers of 〚Cp*Fe(dppe)H 2〛 + indicate that 4 + is more stable than 2 + by 0.19 eV, while this energy difference is reversed in the case of 〚CpFe(dpe)H 2〛 + (dpe = H 2PCH 2CH 2PH 2). The preference for the dihydride form in the case of 〚Cp *Fe(dppe)H 2〛 + and of the dihydrogen one in the case of 〚CpFe(dpe)H 2〛 + is due to the larger π-donor and σ-acceptor abilities of the 〚Cp*Fe(dppe)〛 + fragment, as compared to the 〚CpFe(dpe)〛 + unit.

Thermodynamic properties of iron hydride

X-Ray diffraction studies of the iron sample subjected to high hydrogen pressure inside a diamond anvil cell have been carried out in order to determine the equilibrium conditions of formation and decomposition of the iron hydride. Due to hysteresis, commonly observed in transition metal hydrides, the pressure of decomposition of the corresponding hydride describes the equilibrium as decomposition is considered to be a stress-free process. X-Ray diffraction studies have revealed the structural phase transition from the b.c.c. structure of iron metal to the d.h.c.p. of hydride at 3.5 GPa, while the decomposition process has been observed at a hydrogen pressure of about 2.2 GPa. Both processes are accompanied by a volume change of the host lattice of 2.8 Å 3 as compared to the volume of hexagonal iron, extrapolated from high pressure. Free enthalpy of formation of iron hydride was calculated as equal to 23.5 kJ/mol of hydride. Assuming the entropy of formation of 52.25 J/mol/K, enthalpy of iron hydride is positive and equals to 7.9 kJ/mol of FeH.

Near-Infrared Spectroscopy of Brown Dwarfs: Methane and the Transition between the L and T Spectral Types

We report the possible identification of weak methane spectral features in the near-infrared K band in two late L dwarfs, DENIS 0205-11 (L7) and 2MASS 1523+30 (L8). New, high signal-to-noise ratio, flux-calibrated spectra, spanning the wavelength interval 1.10-2.35 μm with an average resolving power R = 1800, were obtained using NIRSPEC on the Keck II telescope. Results are reported and compared for three late L dwarfs (L5, L7, and L8) and two T dwarfs (T1 and T6). The spectra, which are continuous through the atmospheric absorption bands, show the development of deep steam bands and the weakening of iron hydride features through the L dwarfs and the emergence of strong methane bands in the T dwarfs. A detailed comparison of the K-band regions with synthetic spectra suggests that the weak features seen in the L7 and L8 dwarfs at 2.20 μm are likely to be methane. We see no evidence for methane in the H band. At the R = 1800 resolution, significant differences are evident between the spectral signatures of L8 and T1, leaving room for additional transition objects (L9 or T0).

[Fe(PEt(3))(3)](2)(mu-H)(6)B][BPh(4)]: a complex containing octahedral hypercoordinate boron.

The isolation and crystallographic characterization of a dinuclear iron hydride containing a pseudo-octahedrally coordinated boron atom (1) is reported. A description of the bonding in the cation has been obtained from density functional calculations and a topological analysis.

The photolysis of Fe(CO) 3{P(OPh) 3} 2 and reaction of the photoproduct with alkynes: crystal structures of Fe(CO) 2{P(OPh) 3} 2(η 2-PhCCPh), Fe(CO) 2{P(OPh) 3} 2{η 1:η 1-C(O)C(Me)C[CH(OEt) 2]C(O)} and Fe 2(CO) 4{P(OPh) 3} 2(PhCCH) 2

UV-irradiation of Fe(CO) 3{P(OPh) 3} 2 ( 1) afforded an orthometallated iron hydride HFe(CO) 2{P(OPh) 3}{(PhO) 2POC 6H 4} ( 2) which was reacted in situ with alkynes R 1CCR 2. Internal alkynes reacted to give either η 2-alkyne Fe(CO) 2{P(OPh) 3} 2(η 2-R 1CCR 2) [ 3a, R 1=R 2=Ph; 3b, R 1=Ph, R 2=CH(OEt) 2] or maleoyl Fe(CO) 2{P(OPh) 3} 2{η 1:η 1-C(O)C(R 1)C(R 2)C(O)} [ 4a, R 1=Ph, R 2=Me; 4b, R 1=R 2=Me; 4c, R 1=Me, R 2=CH(OEt) 2; 4d, R 1=Me, R 2=CH 2OH; 4e, R 1=R 2=CH 2OH] complexes. The terminal alkyne HCCPh reacted with 2 to give the ferrole derivative Fe 2(CO) 4{P(OPh) 3} 2(PhCCH) 2 ( 5). The crystal structures of 3a, 4c and 5 were determined. Complex 3a is trigonal bipyramidal about the iron atom with trans apical phosphite ligands and an equatorial arrangement of the CO groups and alkyne CC moiety. Complex 4c is octahedral with trans phosphite ligands and cis carbonyl groups. The alkyne ligand has undergone double carbonylation to generate a ferracyclopentenedione (maleoyl) ring that occupies the remaining two coordination sites at the metal centre. Complex 5 is formally a derivative of Fe 2(CO) 9 in which an Fe(CO) 2{P(OPh) 3} moiety is π-bonded to a ferracyclopentadiene ring arising from the tail-to-tail coupling of two HCCPh ligands.

Very Cool L-Dwarfs

ASTRONOMY Dwarfs are low mass, very cool, main-sequence stars, and recent large-scale star surveys have identified a new spectral class, called the L-dwarfs. The low estimated masses of L-dwarfs suggest that most of these objects are brown dwarfs that are rich in hydrides rather than methane. McLean et al. have obtained high-resolution spectra of six L-dwarfs that range in temperature from 2200-2000 K to 1600-1250 K with the near-infrared cryogenic spectrograph (NIRSPEC) on the Keck II telescope. As the temperature of the star decreases, the spectrum changes systematically: the neutral potassium band broadens and weakens, but persists in the lowest temperature L-dwarf; the iron hydride (FeH) band weakens and disappears at about 1600 K; the water band strengthens, as do the neutral alkali metal bands of Na, Rb, and Cs. These spectral features are consistent with models of a cooling atmosphere in which the iron hydride condenses into iron metal. The less refractory alkali metals can persist as neutral species to lower temperatures than the iron, and because they are present in the L-dwarf spectra to about 1200 K, they will form sulfides rather than chlorides when they do condense.— LR Astrophys. J. 533 , L45 (2000).

J-Band Infrared Spectroscopy of a Sample of Brown Dwarfs Using NIRSPEC on Keck II.

Near-infrared spectroscopic observations of a sample of very cool, low-mass objects are presented with higher spectral resolution than in any previous studies. Six of the objects are L dwarfs, ranging in spectral class from L2 to L8/9, and the seventh is a methane or T dwarf. These new observations were obtained during commissioning of the near-infrared spectrometer (NIRSPEC), the first high-resolution near-infrared cryogenic spectrograph for the Keck II 10 m telescope on Mauna Kea, Hawaii. Spectra with a resolving power of R approximately 2500 from 1.135 to 1.360 µm (approximately J band) are presented for each source. At this resolution, a rich spectral structure is revealed, much of which is due to blending of unresolved molecular transitions. Strong lines due to neutral potassium (K i) and bands due to iron hydride (FeH) and steam (H2O) change significantly throughout the L sequence. Iron hydride disappears between L5 and L8, the steam bands deepen, and the K i lines gradually become weaker but wider because of pressure broadening. An unidentified feature occurs at 1.22 µm that has a temperature dependence like FeH but has no counterpart in the available FeH opacity data. Because these objects are 3-6 mag brighter in the near-infrared compared with the I band, spectral classification is efficient. One of the objects studied (2MASSW J1523+3014) is the coolest L dwarf discovered so far by the 2 Micron All-Sky Survey (2MASS), but its spectrum is still significantly different from the methane-dominated objects such as Gl 229B or SDSS 1624+0029.

Gas-Phase Thermochemistry of Iron Oxides and Hydroxides: Portrait of a Super-Efficient Flame Suppressant

In the search for non-ozone-depleting Halon (CF3Br) replacements, several metals, including iron, have been identified as super-efficient flame suppressants. Although some thermochemical data exist for the species that are thought to be most important in iron's flame chemistry, a more complete and accurate characterization of the thermochemistry of iron oxides, hydrides, and hydroxides is required to improve kinetic flame models. In this investigation predicted enthalpies (Δrxn ) and free energies (Δrxn ) of the reactions of several FeOxHy species in methane flames are reported. Heats of formation (Δf ) for the FeOxHy species of interest are also recommended. The hybrid B3LYP density-functional method and the CCSD(T) coupled-cluster method are employed in conjunction with a relativistic effective core potential on the iron center and a valence triple-ζ basis on all atoms in order to characterize the relative energetics of the important species.

The mechanism of displacement of dihydrogen and dinitrogen from iron, ruthenium and osmium hydrides and implications for models of nitrogenase action

The substitution of dihydrogen in complexes [FeH(H2)(phosphine)x]+ [phosphine = R2PCH2CH2PR2 (R = Et or Me) or P(CH2CH2PR′2)3 (R′ = Me or Ph)] by ligands L (MeCN, PhCN, or Cl–) has been shown to be first order in the concentration of complex and zero order in the concentration of L, in both acetone and thf. Activation parameters have been determined, and the mechanism of substitution is proposed to involve rate-determining loss of H2 from the parent complexes and subsequent rapid co-ordination of L. This mechanism differs from that recently proposed for an analogous complex of Ph2PCH2CH2PPh2, and the reasons for this are discussed. Less thorough studies of some related dinitrogen complexes, and of some homologous complexes of Ru and Os, are consistent with a similar loss of dinitrogen or dihydrogen being rate determining.

The melting temperature of iron hydride at high pressures and its implications for the temperature of the Earth's core

The Earth's core is about 10% less dense than pure iron under the relevant pressure and temperature conditions, so elements lighter than iron should exist in it. Recent experiments support the hypothesis that hydrogen dominates this light component. The hydrogen dissolved in metallic iron has a large potential to reduce its melting temperature. To estimate the melting temperature of the iron-hydrogen core, experiments were carried out at pressures up to 10 GPa by means of a new technique to determine the melting temperature and chemical composition from the textures of rapidly decompressed iron hydride grains. The rate of reduction of the melting temperature induced by adding hydrogen to iron was obtained as per unit mole fraction. If this behaviour of hydrogen persists to the much higher pressure deep inside the Earth, the isentrope in the iron-hydrogen core is about 600 K lower than the previous estimates based on experiments on the iron-sulphur-oxygen system.

New chiral zwitterionic iron hydride complexes with ‘ephosium’ and ‘valphosium’ ligands

New chiral cationic phosphinite ligands based on ephedrine or valinol skeletons, and corresponding zwitterionic hydridotricarbonylferrate complexes are described. IR data indicate an unusual cis-H–Fe–P arrangement in these complexes, and NMR studies show an unusual variation of 2 J PH with temperature and solvent. The possibility that both these rare features are dictated by a stabilizing back folding of the [NMeR 2] + terminus onto the [FeH] − center is discussed.

Ab initio study of iron and iron hydride: II. Structural and magnetic properties of close-packed Fe and FeH

The energetical ordering and magnetic states of hexagonal and double-hexagonal close-packed (hcp, dhcp) as well as face-centred cubic (fcc) Fe and FeH crystals are studied via spin-polarized ab initio total-energy calculations in the local spin-density approximation and with generalized gradient corrections by means of the mixed-basis pseudopotential and the all-electron LMTO-ASA methods. In all three structures, the magnetic spin moments go to zero under volume compression. For pure Fe in the compressed non-magnetic state, the hcp structure is found to have the lowest energy, fcc the highest, and the dhcp structure lies in between. The two hexagonal structures have significantly smaller than ideal ratios. For compressed non-magnetic FeH the energetical ordering of the structures is reversed, compared to that for pure Fe, with fcc ground-state structure and almost ideal ratios for both hexagonal structures. In the ferromagnetic states at expanded volumes, the energetical orderings are again opposite to those of the non-magnetic states both for Fe and FeH. In ferromagnetic FeH these energy differences are particularly small, yielding almost an energetical degeneracy of all three close-packed structures.