Iron Carbonyl Complexes Research Articles

Valuable New Cyclohexadiene Building Blocks from Cationic η5‐Iron–Carbonyl Complexes Derived from a Microbial Arene Oxidation Product

Biooxidation of benzoic acid by Ralstonia eutropha B9 provides an unusual cyclohexadiene carboxy diol that contains a quaternary stereocentre. Tricarbonyliron derivatives of this chiron, on treatment with acid, give two isomeric η(5)-cyclohexadienyl complexes as observed by NMR spectroscopy. Both of these can be subjected to the addition of nucleophiles to provide isomeric cyclohexadiene complexes with new substituent patterns, several of which have been characterised crystallographically. De-metallation of these provides a versatile library of cyclohexadiene building blocks, the utility of which is demonstrated by formal syntheses of oseltamivir. The mechanism of product formation and its stereochemical implications are discussed, as are the procedures undertaken to establish the enantiopurity of a representative cyclohexadiene product.

P–N/P–P Bond Metathesis for the Synthesis of Complex Polyphosphanes

A unique hexaphosphane featuring a 2,2'-bi(1,2,3-triphosphacyclopentane) moiety (19) and an ethylene-bridged bis-isotetraphosphane (27(c,m)) were both selectively prepared in efficient one-pot syntheses from easily accessible tris(3,5-dimethyl-1-pyrazolyl)phosphane (14) and 1,2-bis(phenylphosphanyl)ethane (18(c,m)). The formation of 27(c,m) is an example of a highly efficient P-P bond formation via protolysis. In contrast, the formation of 19 comprises P-N/P-P bond metathesis steps. This constitutes a novel synthetic approach toward the preparation of complex polyphosphanes. Detailed spectroscopic investigations form the basis for a mechanistic understanding of this unprecedented methodology. Furthermore, the preparation of a unique dinuclear iron-carbonyl complex which features hexaphosphane 19 as a bridging ligand illustrates the potential use of complex polyphosphanes such as 19 as ligands in transition metal chemistry.

ChemInform Abstract: Iron‐Catalyzed Highly Enantioselective Reduction of Aromatic Ketones with Chiral P2N4‐Type Macrocycles.

AbstractThe catalytic system in situ generated from the iron carbonyl complex and chiral 22‐membered tetraazadiphospha‐macrocycle PAC exhibits high activity and excellent enantioselectivity in the transfer hydrogenation of various aromatic ketones.

ChemInform Abstract: Iron Carbonyl Complex Containing Bis[2‐(diphenylphosphino)phenyl]ether Enhancing Efficiency in the Palladium‐Catalyzed Suzuki—Miyaura Reaction.

AbstractThe combination of a new iron carbonyl complex and PdCl2 catalyzes the cross‐coupling of various aryl bromides with arylboronic acids.

Iron carbonyl complex containing bis[2‐(diphenylphosphino)phenyl]ether enhancing efficiency in the palladium‐catalyzed Suzuki–Miyaura reaction

The reaction of [Fe3(CO)12] with bis[2‐(diphenylphosphino)phenyl]ether (DPEphos) in refluxing THF afforded a mononuclear complex, [Fe(CO)4(η1‐P‐DPEphos)] (1), as major product and a binuclear complex, [Fe2(CO)6(μ‐CO)(μ‐P,P‐DPEphos)] (2), as minor product respectively. The DPEphos ligand acts as a terminal P‐donor in complex 1 and a bridging P,P‐donor in complex 2. Complexes 1 and 2 were characterized by elemental analysis, fast atom bombardment mass spectrometry, FT‐IR, 1H and 31P{1H} NMR spectroscopy. The structure of complex 1 has been tentatively assigned by density functional theory calculations and its analogy with reported complexes. Combination of complex 1 and PdCl2 furnished an active catalyst for the Suzuki–Miyaura cross‐coupling reactions of various aryl halides with arylboronic acids. Interestingly, under the same experimental condition, complex 1/PdCl2 as catalyst showed superior activity over the DPEphos/PdCl2 system. Copyright © 2012 John Wiley & Sons, Ltd.

Binuclear heptalene iron carbonyl complexes: Comparison with related azulene and pentalene complexes

Reactions of heptalene and its 1,6-dimethyl derivatives with iron carbonyls have been reported to give structurally characterized cis and trans stereoisomers of the bis(tetrahapto)diene complex (η4,η4-C12H10)Fe2(CO)6 in which the uncomplexed CC double bonds form a transoid 1,3-diene unit including the C–C double bond shared by the two heptalene rings. These two structures were found by density functional theory to have essentially identical energies and to lie in energy below any other of the four possible (η4,η4-C12H10)Fe2(CO)6 isomers. The lowest energy structure for C12H10Fe2(CO)5 has a carbonyl-bridged Fe–Fe formal single bond of length ∼2.79 Å. The heptalene ligand in this structure is bonded to one iron atom as a tetrahapto cisoid 1,3-diene unit and to the other iron atom as a tetrahapto Y-shaped trimethylenemethane unit leaving an uncomplexed cisoid 1,3-diene unit. Four higher energy C12H10Fe2(CO)5 structures are found without iron–iron bonds and with one heptalene ring bonded to an iron atom as a hexahapto ligand and to the other iron atom as a tetrahapto ligand leaving one uncomplexed CC bond. In contrast to the related experimentally known (pentalene)Fe2(CO)5 and (azulene)Fe2(CO)5, these (heptalene)Fe2(CO)5 derivatives are predicted to have only marginal stability with respect to disproportionation into (heptalene)Fe2(CO)6 + (heptalene)Fe2(CO)4. This may account for the failure to isolate (heptalene)Fe2(CO)5 from reactions of heptalene with iron carbonyls. The low energy structures for the unsaturated (heptalene)Fe2(CO)n (n = 4, 3, 2) provide examples of triplet and even quintet spin states (the latter for n = 2) as well as variable hapticities of the heptalene rings ranging from trihapto to heptahapto.

Iron and Ruthenium Heterobimetallic Carbonyl Complexes as Electrocatalysts for Alcohol Oxidation: Electrochemical and Mechanistic Studies

Carbonyl-containing Ru and Fe heterobimetallic complexes were prepared and tested as electrocatalysts for the oxidation of methanol and ethanol. GC analysis of the electrolyte solution during bulk electrolysis indicated that CpRu(CO)(μ-I)(μ-dppm)PtI2 (1), CpFe(CO)(μ-I)(μ-dppm)PtI2 (2), and CpRu(CO)(μ-I)(μ-dppm)PdI2 (3) were catalysts for the electrooxidation of methanol and ethanol, while CpFe(CO)(μ-I)(μ-dppm)PdI2 (4), CpRu(CO)I(μ-dppm)AuI (5), and CpFe(CO)I(μ-dppm)AuI (6) did not function as catalysts. The oxidation of methanol resulted in two- and four-electron oxidation to formaldehyde and formic acid, respectively, followed by condensation with unreacted methanol to yield dimethoxymethane and methyl formate as the observed products. The oxidation of ethanol afforded 1,1′-diethoxyethane as a result of two-electron oxidation to acetaldehyde and condensation with excess ethanol. FTIR analysis of the headspace gases during the electrochemical oxidation of methanol indicated formation of CO2. Isotopic labeling experiments demonstrated that the CO2 resulted from oxidation of the CO ligand instead of complete oxidation of CH3OH.

Iron piano-stool phosphine complexes for catalytic hydrosilylation reaction

A family of six cyclopentadienyl–iron carbonyl complexes bearing phosphine ligands (PPh3, PMe2Ph and PCy3) with iodide or PF6 as a counter-anion were prepared and used as catalysts for the hydrosilylation of carbonyl derivatives. Aldehydes were reduced at 30°C, using PMHS as the silane, whereas ketones were reduced at 70°C using PhSiH3.

Syntheses of Iron Carbonyl N‐Heterocyclic Stannylene Complexes

AbstractThe reaction of the β‐diketiminato tin(II) compound LSnCl (1) [L = CH{CMe(NAr)}2, Ar = 2,6‐iPr2C6H3] with diiron nonacarbonyl, Fe2(CO)9, at room temperature led to the iron carbonyl complex LSn(Cl)Fe(CO)4 (2). Complex 2 reacted with AgOSO2CF3 (AgOTf) to yield LSn(OTf)Fe(CO)4 (3). Complex 3 could also be prepared by the reaction of LSnOTf (4) with Fe2(CO)9 at room temperature. Compounds 2 and 3 were characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Both complexes were unambiguously established by single‐crystal X‐ray structural analysis.

Chromium, Iron and Cobalt Carbonyl Complexes with Gallium Halides: Synthesis and Structures

AbstractThe reactions of gallium subhalides Ga2X4·2dioxane (X = Cl, Br) and “GaI” with carbonylmetallates of chromium, iron and cobalt result in the formation of various gallium halide complexes. These are [(CO)5CrGaBr(thf)2] (6), with a terminal GaX unit, and [(CO)4FeGaCl(thf)]2 (1), [(CO)4FeGaCl2Na(thf)2]x (2), [(CO)4FeGaI2Na(thf)3]2 (4) and [Cr2(CO)8(GaI2)INa2(thf)7]x (8) with GaX units in the bridging positions of gallium–transition‐metal rings. In addition, mixed cyclic gallium–iron hydroxides [{(CO)4Fe}2Ga4Cl5(OH)3(thf)] 3 and 4 and gallium oxo/hydroxo cages 5, 9 and 10 were observed. Rings of [{GaCo4(CO)14}K(thf)]6 (11), prepared from Ga4Cl4R4 [R = Si(SiMe3)3] and K[Co(CO)4], are connected through isocarbonyl–potassium interactions to form channels. All compounds were characterized spectroscopically and by X‐ray crystallography. DFT calculations were performed on cobalt–gallium complexes to evaluate their bonding properties.

Synthesis, Characterization, and Reactivity of the Stable Iron Carbonyl Complex [Fe(CO)(N4Py)](ClO4)2: Photoactivated Carbon Monoxide Release, Growth Inhibitory Activity, and Peptide Ligation

Photoactivated carbon monoxide (CO) release by the iron carbonyl complex [Fe(II)(CO)(N4Py)](ClO(4))(2) (1) is described. Compound 1 is a low-spin ferrous complex that is highly stable and soluble in aerobic aqueous solutions. CO release was studied by the substitution of MeCN for CO, which displays saturation kinetics, and by the transfer of CO to deoxymyoglobin, which is slow in the dark but fast upon irradiation with UV light (365 nm). Compound 1 is active against PC-3 prostate cancer cells and shows potent photoinduced cytotoxicity. In addition, the iron carbonyl complex was attached to a short peptide toward the goal of tissue or cell-specific delivery.

Synthesis of Blue Imino(pentafluorophenyl)phosphane

The reaction of AgC(6)F(5) with monomeric iminophosphanes of Mes*-N═P-X (X = Cl, I) in CH(2)Cl(2) at ambient temperature gives imino(pentafluorophenyl)phosphane, Mes*N═P(C(6)F(5)) (1), in almost quantitative yield (96%), which could be isolated as a highly viscous blue oil. The same reaction with LiC(6)F(5) results in the formation of imino(amino)phosphane (C(6)F(5))(2)P-N(Mes*)-P═NMes* (2) (yield 93%). In the second series of experiments the analogous reaction of MC(6)F(5) (M = Ag, Li) with dimeric [Cl-P(μ-N-Dipp)](2) was studied, leading to the formation of [R-P(μ-N-Dipp)](2) (R = C(6)F(5)) (3) for M = Ag, while only decomposition products such as P(C(6)F(5))(3) were observed in the reaction with the Li salt. Highly labile Mes*-N═P-C(6)F(5) (1) decomposes at ambient temperatures, forming among other products the diphosphane (C(6)F(5))(2)P-P(C(6)F(5))(2) (4). Reaction of 1 with Fe(2)(CO)(9) yields the iron carbonyl complexes Mes*-N═P(C(6)F(5))·Fe(CO)(4) (5) and [Mes*-N═P(C(6)F(5))](2)·Fe(CO)(3) (6). The structure, bonding, and potential energy surface are discussed on the basis of B3LYP/6-31G(d,p) computations. According to time-dependent B3LYP calculations, the blue color of 1 arises from an n → π* electronic transition.

Indenyl effect in dissociative reactions. Nucleophilic substitution in iron carbonyl complexes: a case study

The mechanism of carbonyl substitution in [Fe(Ind)(CO)(2)I] (Ind = C(9)H(7)(-), indenyl) by P(OMe)(3) was investigated by means of DFT calculations. The most favourable path involves a spin crossover of the complex from the ground state singlet to the triplet potential energy surface (S = 1), followed by dissociative loss of CO, and phosphite addition to the coordinatively unsaturated intermediate, [Fe(Ind)(CO)I], with S = 1. In the final step, the system returns to the spin singlet surface, affording the product. This dissociative mechanism is in agreement with the experimental findings. Several pathways occurring exclusively along the singlet surface (S = 0) were explored, namely the expected associative mechanism, which is the most favourable among them, and the "pseudo" associative including the participation of solvent (n-octane). In all cases the corresponding energy barriers were significantly higher than the ones involved in the "spin forbidden" mechanism. The rate enhancement observed comparing the Ind complex with the cyclopentadienyl (Cp = C(5)H(5)(-)) analogue reflects the stability difference between the corresponding S = 0 and S = 1 species in the initial step. The larger number of π orbitals and the lower symmetry of the indenyl ligand, compared with Cp, results in a smaller HOMO-LUMO gap, in a more accessible triplet species, and in a smaller barrier for the spin crossover.

Models for the Active Site in [FeFe] Hydrogenase with Iron-Bound Ligands Derived from Bis-, Tris-, and Tetrakis(mercaptomethyl)silanes

A series of multifunctional (mercaptomethyl)silanes of the general formula type R(n)Si(CH(2)SH)(4-n) (n = 0-2; R = organyl) was synthesized, starting from the corresponding (chloromethyl)silanes. They were used as multidentate ligands for the conversion of dodecacarbonyltriiron, Fe(3)(CO)(12), into iron carbonyl complexes in which the deprotonated (mercaptomethyl)silanes act as μ-bridging ligands. These complexes can be regarded as models for the [FeFe] hydrogenase. They were characterized by elemental analyses (C, H, S), NMR spectroscopic studies ((1)H, (13)C, (29)Si), and single-crystal X-ray diffraction. Their electrochemical properties were investigated by cyclic voltammetry to disclose a new mechanism for the formation of dihydrogen catalyzed by these compounds, whereby one sulfur atom was protonated in the catalytic cycle. The reaction of the tridentate ligand MeSi(CH(2)SH)(3) with Fe(3)(CO)(12) yielded a tetranuclear cluster compound. A detailed investigation by X-ray diffraction, electrochemical, Raman, Mössbauer, and susceptibility techniques indicates that for this compound initially [Fe(2){μ-MeSi(CH(2)S)(2)CH(2)SH}(CO)(6)] is formed. This dinuclear complex, however, is slowly transformed into the tetranuclear species [Fe(4){μ-MeSi(CH(2)S)(3)}(2)(CO)(8)].

Catalytic Hydrogen Evolution from Mononuclear Iron(II) Carbonyl Complexes as Minimal Functional Models of the [FeFe] Hydrogenase Active Site

How much iron does it take? Mononuclear complexes [FeII(3,6-R2bdt)(CO)2(PMe3)2] (bdt=1,2-C6H4(S−)2; R=H, Cl) can be reversibly protonated at the sulfur ligands, can catalyze the electrochemical reduction of protons, and are thus minimal functional models of the [FeFe] hydrogenases (see scheme). DFT calculations show that cleavage of an FeS bond leads to the generation of a free coordination site, which is crucial for the formation of hydrides that are key intermediates in the generation of hydrogen.

ChemInform Abstract: Synthesis of Pyrrole Derivatives from 5,6-Dihydro-4H-1,2-oxazines via Reductive Deoxygenation by Use of Fe3(CO)12.

α-Bromooximes such as α-bromoacetophenone oxime and ethyl 3-bromo-2-(hydroxyimino)propanoate react with enamines to give 5,6-dihydro-4H-1,2-oxazines in good yields. Dihydro-1,2-oxazine derivatives are also obtained by the reaction of α-bromooximes with vinyl ethers and silyl enol ethers in the presence of Na2CO3. Dihydro-1,2-oxazines can be converted into pyrrole derivatives via reductive deoxygenation by treating with Fe3(CO)12 in moderate to excellent yields. Iron carbonyl complexes other than Fe3(CO)12 are also effective for the pyrrole-forming reaction. The efficiency of the complexes for this reaction decreases in the order: Fe3(CO)12>>Et3NH[HFe3(CO)11]>Fe2(CO)9>>Fe(CO)5. Both of the dihydro-1,2-oxazine- and pyrrole-forming reactions can be carried out in a single flask, giving pyrrole derivatives in good yields.

ChemInform Abstract: Iron Carbonyl Complexes of 2-(Phenylazo)pyridines. The First Example of a Six-Electron, Bridging 2-(Phenylazo)pyridine Ligand.

ChemInform Abstract: Iron Carbonyl Complexes of 2-(Phenylazo)pyridines. The First Example of a Six-Electron, Bridging 2-(Phenylazo)pyridine Ligand.

ChemInform Abstract: Transition Metal Complexes in the Chemistry of Vinylcyclopropanes

The special structure of the cyclopropane ring con- fers on it an unusually strong tendency to conjugate with a double bond. This is due to internal strain that imparts distinctive p-characteristics to the compound. A 1,3-dienic system is modeled by coupling of cyclo- propane to an olefin or acetylene, and this was clearly confirmed by photoelectron spectroscopy [1,2], and electron diffraction [3] and also by a lot of the chemical reactions [4]. Thus, vinylcyclopropane (VCP) and its substituted derivatives show promising and interesting transformations catalyzed by transition metal com- plexes (TM0 Sarel and his coworkers carried out the first research in this field [4,6-91 with studies on the reactions of VCP with iron carbonyl complexes which were summarized in a comprehensive review published in 1978 [4]. Subsequently the TMC catalyzed reactions of VCP aroused strong interest in many laboratories and new catalysts were used for an extended range of VCPs, including those with electron-withdrawing sub- stituents, cyclopropyl-substituted 1,3-dienes and acetylenes. The principal objective of this review is to consider and systematize the reported information on stoichio-

An Efficient Route for the Synthesis of a Tin(II) Substituted Carbodiimide from a Diazo Compound

The reaction of beta-diketiminate substituted tin(II) chloride, LSnCl (1; L = HC{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)), with the lithium salt of trimethylsilyl diazomethane (LiC(N(2))SiMe(3)) is described. In the course of the reaction, the exclusive formation of tin(II) substituted carbodiimide LSnNCNSiMe(3) (2) is observed in good yield. This reaction occurs at room temperature without any side products. Furthermore, we reacted diiron nonacarbonyl, Fe(2)(CO)(9), with compound 2 to confirm the carbodiimide skeleton (N=C=N) without rearrangement. The latter reaction leads to the tin(II) coordinate iron carbonyl complex LSnNCNSiMe(3)Fe(CO)(4) (3). Compounds 2 and 3 were investigated by microanalysis and multinuclear NMR spectroscopy and were further characterized by X-ray structural analysis.

Preparation of iron carbonyl complexes of germanium(II) and tin(II) each with a terminal fluorine atom

The reaction of β-diketiminate substituted germanium(II) and tin(II) fluorides (LGeF ( 1) and LSnF ( 2)) (L = CH{(CMe) 2(2,6- iPr 2C 6H 3N) 2}) with diiron nonacarbonyl, Fe 2(CO) 9 at room temperature, leads to the iron carbonyl complexes of germanium(II) LGeFFe(CO) 4 ( 3) and tin(II) LSnFFe(CO) 4 ( 4), respectively. Compounds 3 and 4 were characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Furthermore, both complexes ( 3 and 4) were investigated by X-ray structural analysis which shows that both compounds are monomeric in the solid state containing terminal fluorine atoms.