Tricarbonyl Iron Research Articles

The Umbrella-Shaped Trimethylenemethane Ligand in Iron Carbonyl Chemistry: Comparison with Butadiene and Cyclobutadiene Analogues

Reaction of Fe2(CO)9 with 3-chloro-2-(chloromethyl)propene is known to give the stable iron tricarbonyl complex [η4-(CH2)3C]Fe(CO)3, containing the umbrella-shaped trimethylenemethane ligand. The mononuclear complexes (CH2)3CFe(CO)n (n = 1–4) and the binuclear complexes [(CH2)3C]2Fe2(CO)n (n = 3–5) of this trimethylenemethane ligand have been studied here. The lowest energy [(CH2)3C]2Fe2(CO)5 structure has one bridging CO group and an Fe–Fe single bond but is disfavored with respect to dissociation into the mononuclear fragments [(CH2)3C]2Fe2(CO)3 + [(CH2)3C]2Fe2(CO)2. The lowest energy [(CH2)3C]2Fe2(CO)4 structure has two semibridging CO groups and an Fe═Fe double bond but is disfavored with respect to disproportionation into [(CH2)3C]2Fe2(CO)5 + [(CH2)3C]2Fe2(CO)3. In contrast to [(CH2)3C]2Fe2(CO)5 and [(CH2)3C]2Fe2(CO)4, the tricarbonyl [(CH2)3C]2Fe2(CO)3 appears to be a reasonable synthetic objective. The lowest energy structure has one terminal CO group, one semibridging CO group, one symmetrical bri...

Chemical vapor deposition of polycrystalline Fe3O4 thin films by using the cyclohexadiene iron tricarbonyl liquid precursor

Magnetite (Fe3O4) thin films are synthesized by chemical vapor deposition (CVD) with the cyclohexadiene iron tricarbonyl Fe(C6H8)(CO)3 liquid precursor. The growth of pure, polycrystalline, and stoichiometric Fe3O4 films is confirmed by X-ray diffraction, Raman spectroscopy, time-of-flight secondary ion mass spectrometry, and conversion electron Mössbauer spectroscopy. At 297 K, the resistivity for 24.8 nm (100 nm) Fe3O4 thin film is 17 × 10−3 Ω cm (4.2 × 10−3 Ωcm), indicating the good electrical quality of the as-deposited layers. Magnetoresistance (MR) up to −2.2% is measured at 297 K at 1.1 T, corresponding to 15% electron spin polarization. A gradual increase of MR is observed at low temperature. In particular, the observed MR = −4.4% at 120 K (at 0.8 T) is attributed to an intrinsic enhancement of the electrons spin polarization up to 21.5%.

Calculations of the Effects of Methyl Groups on the Energy Differences between Cyclooctatetraene and Bicyclo[4.2.0]octa-2,4,7-triene and between Their Iron Tricarbonyl Complexes

In accord with experiment, DFT calculations find that cyclooctatetraene (COT, 1a) is lower in energy than its valence isomer, bicyclo[4.2.0]octa-2,4,7-triene (BCOT, 3a) and that the iron tricarbonyl complex of COT [COT-Fe(CO)(3), 2a] is lower in energy than the iron tricarbonyl complex of BCOT [BCOT-Fe(CO)(3), 4a]. Also in agreement with experiment are the DFT findings that 1,3,5,7-tetramethylCOT (TMCOT, 1b) is lower in energy than 1,3,5,7-tetramethylBCOT (TMBCOT, 3b), but that the iron tricarbonyl complex of TMCOT [TMCOT-Fe(CO)(3), 2b] is higher in energy than the iron tricarbonyl complex of TMBCOT [TMBCOT-Fe(CO)(3), 4b]. Calculations of the energies of isodesmic reactions allow the effect of each of the four methyl groups in 1b-4b to be analyzed in terms of its additive contribution to the relative energies of TMCOT (1b) and TMBCOT (3b) and to the Fe(CO)(3) binding energies in TMCOT-Fe(CO)(3) (2b) and TMBCOT-Fe(CO)(3) (4b). Our calculations also predict that the eight methyl groups in octamethylCOT-Fe(CO)(3) [OMCOT-Fe(CO)(3), 2c] should have much more than twice the effect of the four methyl groups in TMCOT-Fe(CO)(3) (2b) on raising the energy of OMCOT-Fe(CO)(3) (2c), relative to that of OMBCOT-Fe(CO)(3) (4c). The effects of the interactions between the methyl groups in OMCOT-Fe(CO)(3) (2c) and OMBCOT-Fe(CO)(3) (4c) are dissected and discussed.

Applications of Synchrotron Science to Chemistry

Synchrotron light sources are highly versatile research tools, with applications in a vast range of science from medicine to earth science. In fact, there are few areas of science to which synchrotron radiation cannot make a contribution, which is a credit to the designers of the many synchrotron light sources around the world and to those who have conceived and implemented the many beamlines and end-stations that make such a diverse range of experiments possible. Australia has recently joined the ranks of countries with an advanced third-generation light source since the opening of the Australian Synchrotron (AS) in Clayton, Victoria, in 2007. Synchrotron science in Australia dates back well before the opening of the AS, from the early days when intrepid scientists travelled to early light sources without the support structures that are taken for granted today, through the period of the Australian National Beamline Facility to the Australian Synchrotron Research Program (ASRP). The ASRP was a visionary programme that provided the experience and much of the impetus needed for Australian scientists to push for the establishment of a synchrotron light source in AustraliaandfromthatcametheASasweknowittoday.Although still in its earlystages of development and with only9 of apossible 38 beamlines,theAS has auser base of over 3000 scientists and an output of over 250 papers with AS data in 2011 alone. Many of the current beamlines are useful to those in the chemical sciences. Some, such as infrared spectroscopy, are methods that are quite familiar to chemists. The synchrotron infrared microspectroscopy beamline offers advantages over its laboratory counterpart such as greatly increased signal-to-noise ratio and the ability to perform mapping rapidly and with high spatial resolution, but is nevertheless quite similar at heart to an instrument that may be found in a lab, albeit with a synchrotron as the source of IR radiation. Others, with the X-ray absorptionspectroscopy(XAS)beamlinebeingagoodexample, rely on the unique properties of synchrotron radiation and offer capabilitiesthatcannotbeachievedwithoutasynchrotron.XAS offers unique opportunities for structural studies of metal centres that are of enormous value to chemists, biologists and materials scientists. This issue of Aust. J. Chem. contains a selection of papers by Australian groups that demonstrate some of the power of synchrotron radiation when applied to chemical problems. While some are more in the style of reviews and others are research articles, all give a useful perspective on how this versatile tool is a powerful weapon in the chemist’s armoury. A short review on applications of synchrotron radiation to medicinal chemistry [1] gives a summary of the way several beamlines (microprobe X-ray fluorescence imaging, XAS and infrared microspectroscopy) can individually and in combinationbeusedtohelpsolveimportantproblemsinthechemistryof health, while applications of infrared spectroscopy to biological systems is the focus of another review. [2] Other papers come from a materials chemistry perspective, highlighting the use of synchrotron powder diffraction for the structural elucidation of perovskite oxides, [3] the application of small angle scattering to the study of superhydrophobic surfaces, [4] structure determination of triiron carbonyl sulfide clusters using X-ray absorption spectroscopy [5] and finally a demonstration of the power of insitu measurements combining electrochemistry and X-ray diffraction to study electrocrystallization. [6] As more sources come into service and beamlines are constructed and upgraded, synchrotron techniques will continue to grow in importance to chemists. It is encouraging to see the breadth and quality of science being produced by Australian scientists using these techniques, and provided governments continue to recognize the importance and power of synchrotron science, there are exciting times ahead.

X-Ray Spectroscopy and Structure Elucidation of Reactive Electrogenerated Tri-iron Carbonyl Sulfide Clusters

The design and operation of electrosynthesis cells for generation of samples for X-ray absorption spectroscopy are described. Optimization of continuous-flow methods allows the generation of highly reducing species, which may be combined with spectroscopic validation of the composition of the electrogenerated solution. It is shown that the large sample volume (10 mL) of the 1–10 mM (in the absorbing element) solution required for such experiments can be reduced to ~100 μL using a strategy in which the in situ electrosynthesis cell is amenable to freeze-quenching and transfer to a beamline cryostat. The working electrode in this case doubles as the X-ray absorption spectroscopy sample cell. The application of these techniques is illustrated by the reduction chemistry of Fe3S2(CO)9, 3Fe2S. Spectra recorded in the near-edge region confirm that quantitative preparation of samples of 3Fe2S, 3Fe2S1– and 3Fe2S2– can be prepared by either approach, but samples of a more reduced form, identified as [Fe3S(CO)9]2–, could only be generated using continuous-flow electrosynthesis techniques. Differences in the structural chemistry of the 3Fe2S0/1–/2– redox series were examined from the perspective of their near-edge spectra and the structures of 3Fe2S1– and 3Fe2S2– forms were deduced by a combination of computational (density functional theory), spectroscopic and X-ray absorption fine-structure analyses. These show that addition of the first electron is predominantly localized in one of the Fe–Fe bonds; cleavage of the Fe–Fe bond by addition of a second electron to the Fe–Fe antibonding orbital is associated with a more substantial rearrangement of the molecule. The reduced compounds have structural similarities to the reduced dithiolate-bridged di-iron hexacarbonyl compounds and this is related to the weak electrocatalytic proton reduction exhibited by Fe3S2(CO)9. The methods described provide a strategy for the collection and analysis of experimental data directed towards structure elucidation of redox-activated solution-state complexes.

Acyloxybutadiene tricarbonyl iron complexes as enzyme-triggered CO-releasing molecules (ET-CORMs): a structure–activity relationship study

A series of η(4)-acyloxycyclohexadiene-Fe(CO)(3) complexes was prepared and fully characterized by spectroscopic methods including single crystal X-ray diffraction. For this purpose a new synthetic access to differently acylated 1,3- and 1,5-dienol-Fe(CO)(3) complexes was developed. The enzymatically triggered CO release from these compounds was monitored (detection of CO through GC and/or by means of a myoglobin assay) and the anti-inflammatory effect of the compounds was assessed by a cellular assay based on the inhibition of NO-production by inducible NO synthase (iNOS). It was demonstrated that the properties (rate of esterase-triggered CO release, iNOS inhibition, cytotoxicity) of the complexes strongly depend on the substitution pattern of the π-ligand and the nature of the acyloxy substituent.

Design, construction, and testing of a large-cavity, 1-10 GHz Flygare-Balle spectrometer

A large pulsed-beam, Fourier transform microwave spectrometer employing 48 in. diameter mirrors and 35(") (NHS-35) diffusion pump has been constructed at the University of Arizona. The Fabry-Perot-type cavity, using the large mirrors provides Q-values in the 15,000 to 40,000 range. Test spectra were obtained using transverse and coaxial injection of the pulsed-nozzle molecular beams. The measured molecular resonance linewidths were 8 kHz for the transverse injection and 2 kHz for coaxial molecular beam injection. Good signal to noise ratios were obtained for the test signals. Strong lines for butadiene iron tricarbonyl were seen with a single beam pulse (S/N = 5/1). Transitions were measured as low as 900 MHz and some previously unresolved hyperfine structure is now resolved for the butadiene iron tricarbonyl spectra. The spectrometer is operated using a personal computer with LABVIEW programs, with provisions for automatic frequency scanning. The extended, low-frequency range of this spectrometer should make it very useful for making measurements on significantly larger molecules and complexes than have been previously studied. The improved resolution, in the coaxial beam mode, will allow better resolution of hyperfine structure. The large diffusion pump allows a higher beam pulse frequency to compensate for the generally lower sensitivity at lower frequencies.

Light-Induced Enantioselective Hydrogenation Using Chiral Derivatives of Casey’s Iron–Cyclopentadienone Catalyst

We herein report the first example of an asymmetric ketone hydrogenation using chirally modified derivatives of the homogeneous iron(II)–cyclopentadienone–tricarbonyl system, known as Casey’s catalyst. For the synthesis of the chirally modified catalysts, one of three carbonyl ligands was exchanged for a chiral phosphoramidite. To this end, either oxidative decarbonylation using trimethylamine-N-oxide or photolysis was applied. Photolysis was also used to convert the tricarbonyl iron precatalyst (and, analogously, the dicarbonyl phosphoramidite complexes) to the coordinatively unsaturated dicarbonyl (monocarbonyl, respectively) complexes, which are intermediates in the catalytic cycle of ketone hydrogenation. Hydrogen uptake by the latter species affords the “loaded” hydride, as evidenced by 1H NMR spectroscopy. Thus, the preparation of sensitive iron hydrides by the typically low-yielding Hieber reaction could be avoided. Instead, the catalytic cycle is accessed from air-stable carbonyl precursors. In th...

Remarkable Metal-Complexed Phosphorus Analogues of the Cyclopropenylcarbene–Cyclobutadiene Rearrangement

In situ-generated metal carbonyl-complexed cyclopropenylphosphinidenes undergo a sequence of structural changes leading to phosphorus analogues of Pettit's seminal (η(4)-cyclobutadiene)iron tricarbonyl complex via multiple valence isomers along the reaction pathway and the elimination of one molecule of carbon monoxide.

Corrigendum: Acyloxybutadiene Iron Tricarbonyl Complexes as Enzyme‐Triggered CO‐Releasing Molecules (ET‐CORMs)

In this Communication (), the carbonyl oxygen atom of structure 5 in Scheme 2 was inadvertently omitted. The correct version of the scheme is shown below. The editorial staff apologize for this oversight. Proposed mode of action of enzyme–triggered CO–releasing molecules (ET–CORMs) of type 3.

(Cyclopentadienone)iron Shvo Complexes: Synthesis and Applications to Hydrogen Transfer Reactions

A series of (cyclopendienone)iron tricarbonyl complexes were prepared using an intramolecular cyclization strategy. These were applied to the catalysis of the oxidation of alcohols to aldehydes and ketones. When paraformaldehyde was used as the hydrogen acceptor, formate esters were obtained as coproducts and, in several cases, the major products.

Acyloxybutadiene Iron Tricarbonyl Complexes as Enzyme‐Triggered CO‐Releasing Molecules (ET‐CORMs)

Molecular hazardous materials transport: Enzyme-triggered CO-releasing molecules (ET-CORMs) offer new options for the delivery of CO. The cleavage of dienylester iron tricarbonyl complexes by an esterase under mild oxidative conditions generates CO, which causes a strong inhibiting activity of the compounds to inducible nitric oxide synthase as shown in a cellular assay.

Binuclear Methylborole Iron Carbonyls: Iron−Iron Multiple Bonds and Perpendicular Structures

Methylborole iron tricarbonyl, (η(5)-C(4)H(4)BCH(3))Fe(CO)(3), is known experimentally and is a potential source of binuclear (C(4)H(4)BCH(3))(2)Fe(2)(CO)(n) (n = 5, 4, 3, 2, 1) derivatives through reactions such as photolysis. In this connection the lowest energy (C(4)H(4)BCH(3))(2)Fe(2)(CO)(5) structures are predicted theoretically to have a single bridging carbonyl group and Fe-Fe distances consistent with formal single bonds. The lowest energy (C(4)H(4)BCH(3))(2)Fe(2)(CO)(4) structures have two bridging carbonyl groups and Fe═Fe distances suggesting formal double bonds. Analogously, the lowest energy (C(4)H(4)BCH(3))(2)Fe(2)(CO)(3) structures have three bridging carbonyl groups and very short Fe≡Fe distances suggesting formal triple bonds. The tetracarbonyl (C(4)H(4)BCH(3))(2)Fe(2)(CO)(4) is predicted to be thermodynamically unstable toward disproportionation into (C(4)H(4)BCH(3))(2)Fe(2)(CO)(5) + (C(4)H(4)BCH(3))(2)Fe(2)(CO)(3), whereas the tricarbonyl is thermodynamically viable toward analogous disproportionation. The lowest energy structures of the more highly unsaturated methylborole iron carbonyls (C(4)H(4)BCH(3))(2)Fe(2)(CO)(n) (n = 2, 1) have hydrogen atoms bridging an iron-carbon bond. In addition, the lowest energy (C(4)H(4)BCH(3))(2)Fe(2)(CO) structures are "slipped perpendicular" structures with bridging methylborole ligands, a terminal carbonyl group, and agostic CH(3)→Fe interactions involving the methyl hydrogens. Thus, in these highly unsaturated systems the methyl substituent in the methylborole ligand chosen in this work is not an "innocent bystander" but instead participates in the metal-ligand bonding.

Diastereoselective Spiroketalization: Stereocontrol Using An Iron(0) Tricarbonyl Diene Complex

It has been demonstrated that an element of planar chirality can influence the formation of an adjacent spiroketal stereocenter. Appropriately functionalized enantiomerically pure 1- and 2-sulfinyl 1,3-dien-5-ones and their corresponding iron(0) tricarbonyl complexes (7, 17) have been prepared, and the derived spiroketals (8, 18) are made in good to excellent diastereoselectivity. A preliminary exploration of the combined effects of planar and central chirality upon the diastereoselectivity revealed matched and mismatched combinations (14).

ChemInform Abstract: Tricarbonyl(tropone)iron as a Useful Functionalized Enone Equivalent.

Abstract Tricarbonyl(tropone)iron has been shown to undergo reactions that are characteristic of an isolated enone.

ChemInform Abstract: Synthesis and Reaction of Novel Sulfur-Containing Heterocyclic Systems.

Abstract The strained alkylidene episulfides were synthesized by carbene and alkylidene carbene additions to thiocarbonyl compounds. Thermal, photochemical, and acid catalyzed reactions have been extensively investigated, and and the transition metal-promoted reaction results in the first isolation of thioallyl iron tricarbonyl complex. Germylene and zirconocene also reacted with thioketene to give metallic analogue of alkylidene episulfides, which are excellent synthetic source of a variety of cyclogermanes and stable enethiolizable thioaldehyde. Thermal sulfurization of some 1,2,3-butatriene derivatives and 1,2,3-selenadiazoles with elemental sulfur has been examined to give a variety of novel cyclic polysulfides having an unique structure. Reactive silicon and germanium species also reacted with elemental sulfur and selenium to afford cyclic metallachalcogenides.

ChemInform Abstract: Diastereoselective Alkylation of Tricarbonyl(methyl-3,5-hexadienoate)iron.

Abstract Alkylation of the anion of the title compound with iodomethane, benzylbromide, or allyl bromide proceeds in a highly diastereoselective fashion to afford tricarbonyl(2S*,3R* methyl 2-substituted-3,5-hexadienoate) iron complexes. The relative stereochemistry of the methylation product 2a was determined by single X-ray crystallographic analysis of the corresponding diastereomeric carboxylic acid 4b.

ChemInform Abstract: Highly Stereoselective Total Synthesis of the Natural Leukotriene (-)-( 5S,6S)-LTA4 Methyl Ester and of Its η-7-10 (Tricarbonyl) Iron Complex.

ChemInform Abstract: Highly Stereoselective Total Synthesis of the Natural Leukotriene (-)-( 5S,6S)-LTA4 Methyl Ester and of Its η-7-10 (Tricarbonyl) Iron Complex.

ChemInform Abstract: Chemoselective Arylation of 2′-Deoxyguanosine at N-2 with Organoiron Complexes.

2′-Deoxyguanosine has been directly and chemoselectively arylated at the N2-amino function by treatment with tricarbonyl(η5-cyclohexadienylium)iron or tricarbonyl[η5-2-(n-butyl)cyclohexadienylium]iron cations, followed by decomplexation and dehydrogenation, providing a rapid route to N2-aryl-2′-deoxyguanosine nucleosides.

ChemInform Abstract: The Microwave Spectrum of Cyclobutadiene Iron Tricarbonyl.

Abstract The rotational spectrum of cyclobutadiene iron tricarbonyl was measured using a Flygare-Balle-type microwave spectrometer. Twenty a -dipole transitions were measured in the 5–16 GHz range for this prolate symmetric-top molecule. A least-squares fit of the data to a distortable symmetric top Hamiltonian yielded B = 961.9856(8) MHz, D J = 0.184(8) kHz, D JK = 1.20(3) kHz. These results indicate that the vibrationally averaged structure of the cyclobutadiene ring is square and perpendicular to the a -molecular axis.