Chemistry of polybutadiene—iron carbonyl systems

The treatment of polybutadienes with iron carbonyls results in formation of polymers containing tricarbonyl(conjugated diene)iron units [C₈H₁₂Fe(CO)₃] and also results in geometrical isomerization of free double bonds. Heating of the iron carbonyl-containing polymers gives ferromagnetic products with enhanced thermal stability. The incorporation of iron carbonyl groups into the polymer is favored by basic solvents and high temperatures, the geometrical isomerization by acidic solvents and low temperatures. Steric factors are powerful in determining the rate of isomerization.     

An iron (II) guanidinate compound: Synthesis,characterization, thermal properties and its application as a CVD precursor for iron oxide film

An iron compound containing guanidinate ligand [Fe((SiMe₃)₂NC(ⁱPrN)₂)₂] was synthesized using a conventional lithium‐salt‐elimination reaction, and its chemical structure was characterized through elemental analysis, ¹H‐NMR and single‐crystal X‐ray diffraction, respectively. The thermal properties of the compound were examined through thermogravimetric analysis (TGA), and the TGA results demonstrated that the compound possessed sufficient volatility and suitable thermal stability for the CVD process. Moreover, the deposition experiments were conducted using the synthesized compound as a precursor and O₂ as an oxygen source to confirm its applicability as a CVD precursor, and α‐Fe₂O₃ films were successfully deposited at a relatively low deposition temperature (300°C).     

Synthesis and some properties of sulfur-containing iron tricarbonyl complexes

Synthesis of S₂Fe₂(CO)₆ and S₂Fe₃(CO)₉ by direct substitution of the carbonyl ligands in iron carbonyls with sulfur is described. The relative reactivities were determined for both iron carbonyls and organosulfur compounds in reactions of R₂S, R₂S₂ and RSH (R = alkyl, aryl) with Fe(CO)₅, Fe₂(CO)₉ and Fe₃(CO)₁₂. The properties of the [RSFe(CO)₃]₂ obtained are studied. New methods are found for their regeneration in the form of sulfides, disulfides and thiols.     

The formation of iron carbonyl radical anions in the reactions of iron carbonyls with trimethylamine N-oxide

The interaction of iron carbonyls, Fe(CO)₅, Fe₂(CO)₉ and Fe₃(CO)₁₂ with Me₃NO occurs according to a one-electron redox-disproportionation scheme giving rise to iron carbonyl radical anions: Fe₂(CO)₈^·− (1), Fe₃(CO)₁₂^·− (2), Fe₃(CO)₁₁^·− (3) and Fe₄(CO)₁₃^·− (4). The role of Me₃NO, inducing CO-substitution, consists of the generation of reactive 17-electron species with a labile coordination sphere in which the substitution for other ligands occurs, resulting from fast ligand and electron exchange in the confines of the ETC-reaction.     

Electron-impact studies of organometallic molecules—X. Some simple transition metal fluorocarbon complexes

The mass spectra of several fluoroalkyl, fluoroalkenyl and fluoroacyl complexes of manganese, rhenium, iron and ruthenium carbonyls are described. After loss of carbonyl groups, fluoroalkyl compounds eliminate an olefin, with formation of metal halide species. A trifluorovinyl complex shows a novel elimination of a carbon atom to give an ion postulated to be a difluorocarbene-metal fluoride; the occurrence of difluorocarbene-metal ions in the spectra of some related complexes is also discussed. The spectra of the acyl complexes show little evidence of elimination of the acyl carbonyl group; the major process is fission of the CO? R_f bond with loss of a fluoroalkyl radical and formation of the cationic metal carbonyl, e.g. π-C₅H₅M(CO)₃⁺ (M ? Fe or Ru). The relevance of thermal or photochemical model reactions to processes occurring in the mass spectrometer is discussed.     

Mono-substitution of iron pentacarbonyl metal hydride: facilitation

Controlling the degree of substitution of iron pentacarbonyl with neutral ligands has usually been difficult. Conditions are reported whereby considerable control may be exercised over the substitution of iron pentacarbonyl; with PPh₃ the ratio of mono-/disubstitution may be varied over a range of 50. The substituted iron carbonyl complexes were obtained by treating iron pentacarbonyl with lithium aluminum hydride or sodium borohydride in refluxing THF in the presence of a variety of neutral ligands. The method is particularly useful for a simple high yield synthesis for monosubstituted iron carbonyls.     

Mechanism of Exciplex Decay: The Quantum Yields and the Rate Constants of Radical Ion Formation from Exciplexes with Partial Charge Transfer

The dynamics of exciplex and radical ion formation was studied in donor–acceptor systems with G ^* _et > –0.1 eV. It was shown that the quenching of excited singlet states of aromatic molecules by electron donors in polar solvents led to the formation of radical ions via exciplex dissociation resulting to complete charge separation. Intersystem crossing and internal conversion into the ground state (back electron transfer) compete with this process. The quantum yields and the rate constants of the radical ion formation were measured.     

Anti-oxidant and pro-oxidant reactivities of copper(II), manganese(II) and iron(III) 3,5-di-<Emphasis Type="Italic">i</Emphasis>-propylsalicylate chelates during peroxidation of alkylbenzenes

Bioactive copper(II), iron(III), and manganese(II) 3,5-di-i-propylsalicylate (3,5-DIPS) chelates were investigated in order to determine their ability to inhibit the free radical initiated chain reactions leading to the peroxidation of isopropylbenzene (i-PrPh) and ethylbenzene (EtPh). Quantitative kinetic studies of these chelates established the following order of anti-oxidant reactivities: manganese(II)-(3,5-DIPS)₂>iron(III)(3,5-DIPS)₃>copper(II)₂(3,5-DIPS)₄> > 3,5-DIPS acid. The mechanism of anti-oxidant reactivity of these three chelates is established as being due, in part, to their chain-breaking capacity resulting from the chemical reduction of the generated peroxyl radical to yield alkybenzenelhydroperoxides via reaction of the 3,5-DIPS ligand with the peroxyl radical. In the case of manganese(II)3,5-di-i-propylsalicylate, the central metalloelement also interacts with the peroxyl radical. The manganese(II)-(3,5-DIPS)₂ and copper(II)₂(3,5-DIPS)₄ chelates were also found to exhibit alkylhydroperoxide pro-oxidative reactivity leading to the formation of the alkylbenzeneperoxyl radical. In addition, the manganese(II) atom underwent oxidation to manganese(III) with the formation of the alkylbenzenehydroperoxide or superoxide with air oxygen oxidation. Amyl acetate and dipropylamine (n-Pr₂NH) were added to the reaction mixture to model the biochemical presence of ester or amine cellular components. Addition of amyl acetate to the reaction mixture increased the anti-oxidant reactivity of manganese(II)-(3,5-DIPS)₂ while decreasing its pro-oxidant reactivity. The weaker anti-oxidant reactivites of iron(III)(3,5-DIPS)₃ and copper(II)₂(3,5-DIPS)₄ were less affected by the addition of amyl acetate and the pro-oxidant reactivity of copper(II)₂(3,5-DIPS)₄ was not changed by the addition of amyl acetate, while the pro-oxidant property of iron(III)(3,5-DIPS)₃ was eliminated. In contrast to 2,6-di-t-butyl-4-methylphenol, butylated hydroxy toluene (BHT), anti-oxidant reactivities of copper(II), iron(III), and manganese(II) 3,5-DIPS chelates were dramatically enhanced by the addition of n-Pr₂NH to the reaction mixture. It is concluded that all three metalloelement chelates react with and remove alkylbenzeneperoxyl radicals and the hydroperoxyl radical. The manganese(II)-(3,5-DIPS)₂ and copper(II)₂(3,5-DIPS)₄ chelates may also be useful in removing hydroperoxides in vivo. These reactivities, in addition to their established superoxide dismutase (SOD)-mimetic and catalase-mimetic reactivities, are suggested to possibly permit anti-oxidant and pro-oxidant reactivities in aqueous and organic cellular compartments.     

Dissociation of the diphenylnitrile imine radical cation into benzonitrile and [phenylnitrene]+˙

The collision induced dissociation/mass analysed ion kinetic energy mass spectra of 2,5-diphenyltetrazole demonstrate the decay sequence [diphenyltetrazole]^+˙→ [diphenylnitrile imine]^+˙→ m/z 91. The m/z 91 ion was shown to be identical to the ion formed by loss of N₂ from the phenyl azide radical cation, thus suggesting the phenylnitrene structure for the m/z 91 ion.     

AGET ATRP of water‐soluble PEGMA: Fast living radical polymerization mediated by iron catalyst

In this work, living radical polymerizations of a water‐soluble monomer poly(ethylene glycol) monomethyl ether methacylate (PEGMA) in bulk with low‐toxic iron catalyst system, including iron chloride hexahydrate and triphenylphosphine, were carried out successfully. Effect of reaction temperature and catalyst concentration on the polymerization of PEGMA was investigated. The polymerization kinetics showed the features of “living”/controlled radical polymerization. For example, M_n,GPC values of the resultant polymers increased linearly with monomer conversion. A faster polymerization of PEGMA could be obtained in the presence of a reducing agent Fe(0) wire or ascorbic acid. In the case of Fe(0) wire as the reducing agent, a monomer conversion of 80% was obtained in 80 min of reaction time at 90 °C, yielding a water‐soluble poly(PEGMA) with M_n = 65,500 g mol^?1 and M_w/M_n = 1.39. The features of “living”/controlled radical polymerization of PEGMA were verified by analysis of chain‐end and chain‐extension experiments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

In situ characterization of an iron catalyst by potassium ion desorption and electron emission measurements

The surface conditions of an industrial iron catalyst were monitoredin situ by work function measurements and measurements of thermal desorption of potassium ions. Changes in activation energy for potassium ion desorption and in work function values during catalyst activation and deactivation are discussed in terms of the potassium coverage and chemical composition of the catalyst surface.     

Physicochemical and functional peculiarities of metal oxide whiskers

Practical aspects of preparation and prospects for practical use of a series of the metal oxide whiskers were studied. The procedures for the synthesis were proposed, and the phase composition, micromorphology, and electrochemical and sensor characteristics of the macroscopic (up to 5–10 mm long) whiskers in the Ba-V-O, Ba-Mn-O, and Sn-O systems were analyzed. The electroconducting BaV₈O_21-δ whiskers were prepared by the hydrothermal treatment. These whiskers possess stable electrochemical characteristics appropriate for the development of novel secondary current sources. The protonated form of the Ba₆Mn₂₄O₄₈ whiskers produced by the isothermal vaporization of chloride fluxes is a mixed conductor with the proton and electron conductivity at a level of mS units at 25 °C. A new procedure by the thermal disproportionation of tin(ii) oxide under nitrogen was proposed for the growth of SnO₂ whiskers of various morphology. The produced whiskers have substantial sensor sensitivity toward a series of toxic components of the gaseous medium, such as nitrogen dioxide. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1023–1034, May, 2008.     

Prototropic rearrangements of unsaturated hydrocarbons promoted by iron carbonyls

Results from the thermal and photochemical reactions of $\text{cis}$-1,3-pentadiene and 4-methyl-1,3-pentadiene with iron pentacarbonyl are described together with those obtained from the thermolysis and photolysis of their η²-iron tetracarbonyl and η⁴-iron tricarbonyl complexes. Consideration of these results, and some recent related work of others, allows a new reaction path to be formulated for alkene and diene isomerizations promoted by iron carbonyls.     

Interaction between peroxide ion and phenol group which are coordinated to the same iron(III) ion

We have prepared several new iron(III) complexes with ligands which contain a phenol group; these are tetradentate [(X-phpy)H, X and H(phpy) represent the substituents on the phenol ring and N,N-bis(2-pyridylmethyl)-N-(2-hydroxybenzyl)amine, respectively] and pentadentate ligands [(R-enph-X)H; R=ethyl(Et) or methyl(Me) derivative and H(Me-enph) denotes N,N-bis(2-pyridylmethyl)-N″-methyl-N″-(2″-hydroxyl-benzylamine)ethylenediamine] and have determined the crystal structures of Fe(phpy)Cl₂, Fe(5-NO₂-phpy)Cl₂, and Fe(Me-enph)ClPF₆, which are of a mononuclear six-coordinate iron(III) complex with coordination of one or two chloride ion(s). These compounds are highly colored (dark violet) due to the coordination of phenol group to an iron(III) atom. When hydrogen peroxide was added to the solution of the iron(III) complex, a color change occurs with bleaching of the violet color, indicating that oxidative degradation of the phenol moiety occurred in the ligand system. The bleaching of the violet color was also observed by the addition of t-butylhydroperoxide. The rate of the disappearance of the violet color is highly dependent on the substituent on the phenol ring; introduction of an electron-withdrawing group in the phenol ring decreases the rate of bleaching, suggesting that disappearance of the violet band should be due to a chemical reaction between the phenol group and a peroxide adduct of the iron(III) species with an η¹-coordination mode and that in this reaction the peroxide adduct acts as an electrophile towards phenol ring. The intramolecular interaction between the phenol moiety and an iron(III)-peroxide adduct may induce activation of the peroxide ion, and this was supported by several facts that the solution containing an iron(III) complex and hydrogen peroxide exhibits high activities for degradation of nucleosides and albumin.     

Decomposition of Picolyl Radicals at High Temperature: A Mass Selective Threshold Photoelectron Spectroscopy Study

The reaction products of the picolyl radicals at high temperature were characterized by mass-selective threshold photoelectron spectroscopy in the gas phase. Aminomethylpyridines were pyrolyzed to initially produce picolyl radicals (m/z=92). At higher temperatures further thermal reaction products are generated in the pyrolysis reactor. All compounds were identified by mass-selected threshold photoelectron spectroscopy and several hitherto unexplored reactive molecules were characterized. The mechanism for several dissociation pathways was outlined in computations. The spectrum of m/z=91, resulting from hydrogen loss of picolyl, shows four isomers, two ethynyl pyrroles with adiabatic ionization energies (IE_ad) of 7.99 eV (2-ethynyl-1H-pyrrole) and 8.12 eV (3-ethynyl-1H-pyrrole), and two cyclopentadiene carbonitriles with IE′s of 9.14 eV (cyclopenta-1,3-diene-1-carbonitrile) and 9.25 eV (cyclopenta-1,4-diene-1-carbonitrile). A second consecutive hydrogen loss forms the cyanocyclopentadienyl radical with IE′s of 9.07 eV (T₀) and 9.21 eV (S₁). This compound dissociates further to acetylene and the cyanopropynyl radical (IE=9.35 eV). Furthermore, the cyclopentadienyl radical, penta-1,3-diyne, cyclopentadiene and propargyl were identified in the spectra. Computations indicate that dissociation of picolyl proceeds initially via a resonance-stabilized seven-membered ring.     

Single and double hydrogen migration in the fragmentation of 3-methyl-2-butyl trifluoroacetate

Three of the main oxygen-containing fragments resulting from 3-methyl-2-butyl trifluoroacetate (11) had been identified previously as the 1-triflnoroacetoxyethyl cation (m/z 141, 12, product of simple cleavage), and the products of single (m/z 142) and double hydrogen transfer (m/z 143, protonated ethyl trifluoroacetate). Collisionally activated dissociation of m/z 142 and the isotopomers resulting from 11-2-d, 11-1-d₃, 11-5,6-d₆, and 11-¹⁸O₂ has established that m/z 142 is the oxygen protonated 1-trifluoroacetoxyethyl free radical (17) formed by hydrogen shift irom a γ-methyl group to oxygen in the molecular ion, rather than in a complex (18) between 12 and the 2-propyl free radical, as expected based on a mechanistic model existing in the literature. The second hydrogen transferred originates in the other γ-methyl group; its migration may occur, but does not have to, in the complex between 17 and a molecule of propene, prior to dissociation of the two fragments. Collision-activated dissociation has now shown that the m/z 140 ion observed in the spectrum is the molecular ion of vinyl trifluoroacetate, possibly formed by a hydrogen transfer from 12 to the 2-propyl radical in the complex 18. The hydrogen migration to oxygen exhibits no isotope effect, whereas the transfers to carbon atoms exhibit small primary and α secondary kinetic isotope effects. Exclusive migration of the tertiary hydrogen from C(3) occurs in the formation of 2-methylbutene cation radical (m/z 70) from the molecular ion. The hydrocarbon ion fragments and the heteroatom-containing fragments are formed from 11 by disjoint pathways.     

Reactions of diazoles with manganese and iron carbonyls

The compounds of two types were isolated in the reactions of dimanganese decacarbonyl with diazoles. The compounds with an unaltered oxidation state of the metal were formed as a result of nucleophilic substitution of a carbonyl ligand of Mn₂(CO)₁₀. The compounds with an altered oxidation state of the central atom were produced in redox-transformations of Mn₂(CO)₁₀. The substances were characterized by the data of mass-, IR-, ¹H-NMR-spectra. The EPR-data were obtained for paramagnetic Mn²⁺ salts. The reactions of Mn₂(CO)₁₀ with diazoles are compared with those of iron carbonyls.     

Effect of hydrogen gas impurities on the hydrogen dissociation on iron surface

A small addition of oxygen to hydrogen gas is known to mitigate the hydrogen embrittlement (HE) of steels. As atomic hydrogen dissolution in steels is responsible for embrittlement, catalysis of molecular hydrogen dissociation by the steel surface is an essential step in the embrittlement process. The most probable role of oxygen in mitigating HE is to inhibit the reactions between molecular hydrogen and the steel surface. To elucidate the mechanism of such surface reaction of hydrogen with the steel in the presence of oxygen, hydrogen, and oxygen adsorption, dissociation, and coadsorption on the Fe(100) surface were investigated using density functional theory. The results show that traces of O₂ would successfully compete with H₂ for surface adsorption sites due to the grater attractive force acting on the O₂ molecule compared to H₂. The H₂ dissociation would be hindered on iron surfaces with predissociated oxygen. Prompted by the notable results for H₂ + O₂, other practical systems were considered, that is, H₂ + CO and CH₄. Calculations were performed for the CO chemisorption and H₂ dissociation on iron surface with predissociated CO, as well as, CH₄ surface dissociation. The results indicate that CO inhibition of H₂ dissociation proceeds via similar mechanism to O₂ induced inhibition, whereas CH₄ traces in the H₂ gas have no effect on H₂ dissociation. © 2014 Wiley Periodicals, Inc.     

Hypervalent radical formation probed by electron transfer dissociation of zwitterionic tryptophan and tryptophan‐containing dipeptides complexed with Ca2+ and 18‐crown‐6 in the gas phase

The relationship between peptide structure and electron transfer dissociation (ETD) is important for structural analysis by mass spectrometry. In the present study, the formation, structure and reactivity of the reaction intermediate in the ETD process were examined using a quadrupole ion trap mass spectrometer equipped with an electrospray ionization source. ETD product ions of zwitterionic tryptophan (Trp) and Trp‐containing dipeptides (Trp‐Gly and Gly‐Trp) were detected without reionization using non‐covalent analyte complexes with Ca²⁺ and 18‐crown‐6 (18C6). In the collision‐induced dissociation, NH₃ loss was the main dissociation pathway, and loss related to the dissociation of the carboxyl group was not observed. This indicated that Trp and its dipeptides on Ca²⁺(18C6) adopted a zwitterionic structure with an NH₃⁺ group and bonded to Ca²⁺(18C6) through the COO^? group. Hydrogen atom loss observed in the ETD spectra indicated that intermolecular electron transfer from a molecular anion to the NH₃⁺ group formed a hypervalent ammonium radical, R‐NH₃, as a reaction intermediate, which was unstable and dissociated rapidly through N–H bond cleavage. In addition, N–C_α bond cleavage forming the z₁ ion was observed in the ETD spectra of Trp‐GlyCa²⁺(18C6) and Gly‐TrpCa²⁺(18C6). This dissociation was induced by transfer of a hydrogen atom in the cluster formed via an N–H bond cleavage of the hypervalent ammonium radical and was in competition with the hydrogen atom loss. The results showed that a hypervalent radical intermediate, forming a delocalized hydrogen atom, contributes to the backbone cleavages of peptides in ETD. Copyright © 2015 John Wiley & Sons, Ltd.