Synthesis of multi-walled carbon nanotubes catalyzed by substituted ferrocenes

A range of substituted ferrocenes were used as catalysts for the synthesis of multi-walled carbon nanotubes (MWCNTs) and carbon fibers (CFs). These products were obtained in the temperature range 800-1000 °C, in a reducing atmosphere of 5% H₂ by pyrolysis of (CpR)(CpR′)Fe (R and R′ = H, Me, Et and COMe) in toluene solution. The effect of pyrolysis temperature (800-1000 °C), catalyst concentration (5 and 10 wt.% in toluene) and solution injection rate (0.2 and 0.8 ml/min) on the type and yield of carbonaceous product synthesized was investigated. Carbonaceous products formed include graphite film (mostly at high temperature; 900-1000 °C), carbon nanotubes and carbon fibers. The carbonaceous materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The ferrocene ring substituents influenced both the CNT diameter and the carbon product formed.     

Methyl abstraction kinetics of CpFe(CO)2Me using the benzyl radical clock

The rate constant for the methyl abstraction reaction of CpFe(CO)₂Me has been measured with the benzyl radical clock as (1.1 ± 0.2) × 10⁵ M⁻¹ s⁻¹ at room temperature. Time-resolved Fourier-transform Infrared (FTIR) absorption spectroscopy pointed towards the formation of the CpFe(CO)₂ radical upon benzyl abstraction. The main stable product has been established by a linear scan of the reaction mixture as Cp₂Fe₂(CO)₄ produced by the dimerization of the CpFe(CO)₂ radicals. The transition state structure for the abstraction process was also found at UB3LYP/6-311+G* level of theory to contain a planar CH₃ group.     

Photophysical properties and computational investigations of tricarbonylrhenium(I)[2-(4-methylpyridin-2-yl)benzo[d]-X-azole]L and tricarbonylrhenium(I)[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]L derivatives (X = N-CH3, O, or S; L = Cl, pyridine)

We report a combined experimental and computational study of new rhenium tricarbonyl complexes based on the bidentate heterocyclic N-N ligands 2-(4-methylpyridin-2-yl)benzo[d]-X-azole (X = N-CH₃, O, or S) and 2-(benzo[d]-X-azol-2-yl)-4-methylquinoline (X = N-CH₃, O, or S). Two sets of complexes are reported. Chloro complexes, described by the general formula Re(CO)₃[2-(4-methylpyridin-2-yl)benzo[d]-X-azole]Cl (X = N-CH₃, 1; X = O, 2; X = S, 3) and Re(CO)₃[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]Cl (X = N-CH₃, 4; X = O, 5; X = S, 6) were synthesized heating at reflux Re(CO)₅Cl with the appropriate N-N ligand in toluene. The corresponding pyridine set {Re(CO)₃[2-(4-methylpyridin-2-yl)benzo-X-azole]py}PF₆ (X = N-CH₃, 7; X = O, 8; X = S, 9) and {Re(CO)₃[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]py}PF₆ (X = N-CH₃, 10; X = O, 11; X = S, 12) was synthesized by halide abstraction with silver nitrate of 1-6 followed by heating in pyridine and isolated as their hexafluorophosphate salts. All complexes have been fully characterized by IR, NMR, electrochemical techniques and luminescence. The crystal structures of 1 and 7 were obtained by X-ray diffraction. DFT and time-dependent (TD) DFT calculations were carried out for investigating the effect of the organic ligand on the optical properties and electronic structure of the reported complexes.     

Organometallated Halonium Salts of the Type [{Cp(CO)2Fe}2X]SbY6 (X = Cl,Br, I; Y = F,Cl)

The reaction of CpFe(CO)₂X (X = Cl, Br, I) with SbY₅ (Y = F, Cl) in toluene leads to the cationic, halogen‐bridged compounds [{Cp(CO)₂Fe}₂X]SbY₆ ( 1 – 6 ). The halide of CpFe(CO)₂X is eliminated by the Lewis acid SbY₅, and the fragment “CpFe(CO)₂⁺” reacts with further CpFe(CO)₂X to form the halogen bridge between both the organometallic substituents. The exclusive formation of the counter anion SbY₆^– is caused by the oxidizing action of the antimony pentahalides, by which SbY₃ and the interhalogens XY are always obtained. The compounds have been characterized by their NMR‐, IR‐ and Mass spectra, the compounds 1 – 3 and 6 additionally by single crystal structure analyses. They show decreasing bond angles Fe–X–Fe following the range Cl → Br → I and the VSEPR concept; the two CpFe(CO)₂ groups are staggered with the dihedral angle Cp(centre)–Fe–Fe–Cp(centre) of about 160°.     

Complexes in polymers II: FT-IR spectra,iodine oxidation,and photochemistry of [(η5-C5H)Fe(CO)2]2, [(η5-C5H5)Mo(CO)3]2 and Mn2(CO)10 in polystyrene,poly(methyl methacrylate) and polystyrene–polyacrylonitrile copolymer

The infrared spectra of [CpFe(CO)₂]₂, [CpMo(CO)₃]₂ and Mn₂(CO)₁₀ (Cp=η-C₅H₅) embedded in films of polystyrene (PS), poly(methyl methacrylate) (PMMA), and polystyrene-polyacrylonitrile (PS? AN), are comparable with those of the dimers in toluene, ethyl acetate and acetonitrile, respectively. Irradiation of the embedded dimers with UV light led to decomposition in PS and PMMA, while in PS? AN the complexes Cp₂Fe₂(CO)₃PS? AN and Mn₂(CO)₉PS? AN were formed, wherein a pendant nitrile group is coordinated to one of the metal atoms. Exposure of the embedded dimers to iodine vapour gave CpFe(CO)₂I, CpMo(CO)₃I and Mn(CO)₅I with the reaction being much slower in PMMA than in PS.     

Synthesis,characterization, electrochemical and photophysical properties of bimetallic complexes of rhenium(I) and osmium(II)

Monometallic and bimetallic diimine complexes of rhenium(I) and osmium(II), [(CO)₃(bpy)Re(4,4′-bpy)](PF₆) I, [(CO)₃(bpy)Re(4,4′-bpy)Re(bpy)(CO)₃](PF₆)₂II, [Cl(bpy)₂Os(4,4′-bpy)](PF₆) III and [Cl(bpy)₂Os(4,4′-bpy)Os(bpy)₂Cl](PF₆)₂IV, and a new heterobimetallic complex of rhenium(I) and osmium(II) [(CO)₃(bpy)Re(4,4′-bpy)Os(bpy)Cl](PF₆)₂V (bpy = 2,2′-bipyridine; 4,4′-bpy = 4,4′-bipyridine) have been synthesized and characterized by various spectral techniques. The photophysical properties of all the complexes have been studied and a comparison is made between the heterobimetallic and corresponding monometallic and homobimetallic complexes. Emission and transient absorption spectral studies reveal that excited state energy transfer from the rhenium(I) chromophore (∗Re) to osmium(II) takes place. The energy transfer rate constant is found to be 8.7 × 10⁷ s⁻¹.     

A stable carbonyl-pyrazine-metal(0) complex: Synthesis and characterization of cis-tetracarbonylpyrazinetrimethylphosphitetungsten(0)

Pentacarbonylpyrazinetungsten(0), (CO)₅W(pyz), is not stable in solution in polar solvents such as acetone or dichloromethane and undergoes conversion to a bimetallic complex, (CO)₅W(pyz)W(CO)₅ plus free pyrazine. These three species exist at equilibrium. Using the quantitative ¹H NMR spectroscopy, the equilibrium constant could be determined to be K_eq = (5.9 ± 0.8) × 10⁻² at 25 °C. Introducing a second pyrazine ligand into the molecule does not stabilize the complex, as cis-W(CO)₄(pyz)₂ was found to be less stable than W(CO)₅(pyz) and, therefore, could not be isolated. However, introducing trimethylphosphite as a donor ligand into the complex leads to the stabilization of the carbonyl-pyrazine-metal(0) complexes, as shown by the synthesis of cis-W(CO)₄[P(OCH₃)₃](pyz). This complex could be isolated from the reaction of the photogenerated W(CO)₄[P(OCH₃)₃](tetrahydrofuran) with trimethylphosphite upon mixing for 2 h at 10 °C in tetrahydrofuran and characterized by elemental analysis, IR, MS, ¹H, ¹³C, and ³¹P NMR spectroscopy.     

A complete series of tricarbonylhalidorhenium(I) complexes (abpy)Re(CO)3(Hal), Hal = F, Cl, Br, I; abpy = 2,2′-azobispyridine: Structures, spectroelectrochemistry and EPR of reduced forms

For the first time a complete set of tricarbonylhalidorhenium(I) complexes (Hal = F, Cl, Br, I) has been studied in a systematical fashion by example of (abpy)Re(CO)₃(Hal), abpy = 2,2′-azobispyridine. Crystal structures of chloride, bromide and iodide analogues are now available, showing increasing planarization of the abpy ligand in that order. Cyclic voltammetry, EPR, IR and UV/Vis spectroelectrochemistry of the reduced forms [(abpy)Re(CO)₃(Hal)]⁻ illustrate that the four halide complexes differ only partially in their properties. The strongest deviations are observed for [(abpy)Re(CO)₃F]⁻ which is distinguished by the widest electrochemical potential range but most pronounced chemical lability. In the EPR spectrum the fluoride exhibits the highest isotropic g value (2.0085) and the lowest rhenium coupling constant, which is of the same magnitude (2 mT) as the detectable ¹⁹F hyperfine splitting.     

Coordination and reactivity of white phosphorus and tetraphosphorus trisulphide in the presence of the fragment CpFe(dppe) [dppe = 1,2-bis(diphenylphosphino)ethane]

The reaction of [CpFe(dppe)Cl] (1) [dppe = 1,2-bis(diphenylphosphino)ethane] with one equivalent of P₄ or P₄S₃ in the presence of a chloride scavenger, TlPF₆ or AgOTf (OTf = triflate, OSO₂CF₃), affords the complexes [CpFe(dppe)(η¹-P₄)]PF₆ (2) and [CpFe(dppe)(η¹-P_basal-P₄S₃)]OTf (3) which contain the tetrahedral P₄ and the mixed P₄S₃ cage molecule η¹-bound to the metal. Both P₄ and P₄S₃ yield furthermore the dimetal compounds [{CpFe(dppe)}₂(μ,η^1:1-P₄)](PF₆)₂ (4) and [{CpFe(dppe)}₂(μ,η^1:1-P_apical-P_basal-P₄S₃)](OTf)₂ (5), which contain the tetrahedral P₄ or the mixed-cage P₄S₃ molecule tethering two ruthenium fragments via two phosphorus atoms. All the compounds have been characterized by elemental analyses and NMR measurements. The crystal structure of 4 has been determined by X-ray diffraction methods. The complexes readily react with excess water under mild reaction conditions and the outcoming products have been identified.     

Rhodium(I) complexes with 1′-(diphenylphosphino)ferrocenecarboxylic acid as active and recyclable catalysts for 1-hexene hydroformylation

The rhodium complex trans-[Rh(CO)(Hdpf-κP)(dpf-κ²O,P)] (1), (Hdpf = 1′-(diphenylphosphino)ferrocenecarboxylic acid) was used as an efficient and recyclable catalyst for 1-hexene hydroformylation producing ca. 80% of aldehydes at 10 atm CO/H₂ and 80 °C. After the reaction, unchanged complex 1 was separated from the reaction mixture and used again three times with the same catalytic activity. The effect of modifying ligands, phosphines and phosphites, on the reactivity of 1 was investigated. The active catalytic systems containing 1 or trans-[Rh(CO)(L)(dpf-κ²O,P)] (2) were formed in situ from acetylacetonato rhodium(I) precursors [Rh(CO)₂(acac)] (3) or [RhL(CO)(acac)] (4) and Hdpf or Medpf (L = phosphine, Medpf = methyl ester of Hdpf).     

Synthesis of copper(I) bis(3,5-dimethylpyrazolyl)methane olefin complexes and their reactivity towards carbon monoxide

The chemistry of bis(3,5-dimethylpyrazolyl)methane complexes of copper(I) has been investigated and a dinuclear copper(I) derivative of formula {Cu₂[μ-CH₂(3,5-Me₂Pz)₂]₂}(TfO)₂ [TfO = trifluoromethanesulphonate anion, ], characterized by an uncommon bridging coordination of the bis(pyrazolyl)methane ligands, has been isolated and characterized by X-ray diffraction methods. Moreover, new olefin derivatives of general formula [Cu[CH₂(3,5-Me₂Pz)₂](olefin)]TfO have been prepared (olefin: coe = cyclooctene, van = 4-vinylanisole, nbe = norbornene), their carbonylation reactions, {Cu[CH₂(3,5-Me₂Pz)₂](olefin)}TfO + CO ? {Cu[CH₂(3,5-Me₂Pz)₂](CO)}TfO + olefin, have been studied gas volumetrically and the thermodynamical parameters of the equilibria for the displacement of the coordinated olefin by carbon monoxide have been determined.     

Structure and reactivity of derivatives of dihalogenomethyl indium(III) halides, X2InCHX2 (X = Cl, Br, I)

The reactions of indium monohalides, InX with haloforms, CHX₃, in 1,4-dioxane (diox), produce the dioxane adducts of dihalogeno-dihalogenomethyl-indium(III), X₂In(diox)_nCHX₂ (X = Cl, Br, n = 1; X = I, n = 2) compounds. The ionic derivative [(C₂H₅)₄N] [Cl₃InCHCl₂] was prepared and its crystal structure determined by X-ray means. The reactions of the X₂In(diox)_nCHX₂ compounds are significantly different from those of the related X₂InCH₂X compounds. The dihalogenomethyl derivatives react with strong electrophiles suggesting dihalogenomethyl substituents of mild nucleophilic character, while the carbon atoms in the halogenomethyl derivatives are electrophilic.     

Synthesis and structures of CpFe(CO)2(κE-ECS2Ph) and [CpFe(CO)(κS,E-ECS2Ph)] (E = S,Se)

The iron trithiocarbonato complex CpFe(CO)₂(κS-SCS₂Ph) (1a) and its selenodithiocarbonato analogue CpFe(CO)₂(κSe-SeCS₂Ph) (1b) were generated by room temperature reactions of (μ-E_x)[CpFe(CO)₂]₂ (E = S; x = 2, 3. E = Se; x = 1) with PhSC(S)Cl. These compounds can be converted into the complexes CpFe(CO)(κ²S,E-ECS₂Ph) [E = S (2a), Se (2b)], in which the trithiocarbonato or the selenodithiocarbonato ligand is bonded to the iron in a chelate form, under photolytic conditions. The composition and structure of all products have been verified by elemental analyses, IR and ¹H NMR spectroscopies. The crystal structures for compounds 1a, 1b, and 2b show a three-legged piano-stool configuration at Fe in each complex. The spectroscopic and structural data in this work are commensurate with the electronic factor of the S- and Se-donor ligands.     

ACETYL TRANSFER BETWEEN MANGANESE AND IRON COMPLEXES: REACTION OF ACETYLPENTACARBONYLMANGANESE WITH DICARBONYLCYCLOPENTADIENYLIRON(0)

Abstract

Reaction of Mn(CO)₅(C(O)Me) with CpFe(CO)₂ ^? results in CpFe(CO)₂Me, Cp₂Fe₂(CO)₄ and Mn(CO)₅ ^? in less than five minutes at room temperature. Labeling the carbonyl of the acetyl puts the label only on a carbonyl of the CpFe(CO)₂Me. Thus the acetyl is transferred from the manganese to the iron as a group, before CO dissociation leads to the methyl product. CO dissociation from CpFe(CO)₂(C(O)Me) does not occur under the experimental conditions. A scheme is suggested to accommodate these observations.     

The effect of arylferrocene ring substituents on the synthesis of multi-walled carbon nanotubes

The synthesis of shaped carbon nanomaterials (SCNMs) such as carbon nanotubes (CNTs), amorphous carbon, carbon fibres (CFs) and carbon spheres (CSs) was achieved using para-substituted arylferrocenes, FcPhX (X = H, OH, Br, COCH₃) or a mixture of ferrocene (FcH) and substituted benzenes (PhX; X = H, OH, Br, COCH₃). The reactions were carried out by an injection chemical vapour deposition (CVD) method using toluene solutions (carrier gas: 5% H₂ in Ar at a flow rate of 100 ml/min) in the temperature range of 800-1000 °C. In most instances multi-walled CNTs (MWCNTs) were produced. Variations in the concentrations of precursor catalysts, the injection rate and temperature affected the type, distribution and dimensions of the SCNMs produced. The overall finding is that the presence of Br and O in these studies significantly reduces CNT growth. A comparative study on the effect of FcPhX versus FcH/PhX mixtures was investigated. The SCNMs were characterized by transmission electron microscopy (TEM), Raman spectroscopy and thermal gravimetric analysis (TGA).     

Theoretical Study of the Solvent Effect on the Electronic and Vibrational Properties of [CpFe(CO)<Subscript>2</Subscript>(NCS)] and [CpFe(CO)<Subscript>2</Subscript>(SCN)] Linkage Isomers

The present study illustrates the stability of [CpFe(CO)₂(NCS)] and [CpFe(CO)₂(SCN)] linkage isomers by the use of MPW1PW91 quantum method in the gas and solution phases. Our results reveal that the [CpFe(CO)₂(NCS)] isomer is more stable than the [CpFe(CO)₂(SCN)] isomer. Based on the polarizable continuum model, the effect of the solvent polarity on the stability, structural parameters, frontier orbital energies, and vibrational modes of carbonyl ligands (ν_CO) of these linkage complexes is explored. The molecular orbital analysis suggests that the major contributions to HOMO and LUMO arise from the ambidentate ligand and Fe in two isomers, respectively. In addition, the bonding interaction between the CpFe(CO)₂ fragment and the ambidentate ligand is studied by means of the energy decomposition analysis. The back-bonding effect in Fe–CO bonds is revealed in the calculation of the quadrupole polarization of the carbon atom by the QTAIM analysis. The character of Fe–N and Fe–S bonds in these complexes is analyzed by the natural bond orbital analysis.     

Density functional theory study on structural isomers and bonding of model complexes M(CO)5(BH3 · PH3) (M = Cr, Mo, W) and W(CO)5(BH3 · AH3) (A = N, P, As, Sb)

The influence of group 15 various substituents and effect of metal centers on metal-borane interactions and structural isomers of transition metal-borane complexes W(CO)₅(BH₃ · AH₃) and M(CO)₅(BH₃ · PH₃) (A = N, P, As, and Sb; M = Cr, Mo, and W), were investigated by pure density functional theory at BP86 level. The following results were observed: (a) the ground state is monodentate, η¹, with C₁ point group; (b) in all complexes, the η¹ isomer with C_S symmetry on potential energy surface is the transition state for oscillating borane; (c) the η² isomer is the transition state for the hydrogens interchange mechanism; (d) in W(CO)₅(BH₃ · AH₃), the degree of pyramidalization at boron, interaction energy as well as charge transfer between metal and boron moieties, energy barrier for interchanging hydrogens, and diffuseness of A increase along the series A = Sb < As < P < N; (e) in M(CO)₅(BH₃ · PH₃), interaction energy is ordered as M = W > Cr > Mo, while energy barrier for interchanging hydrogens decreases in the order of M = Cr > W > Mo.     

Synthesis and properties of palladium(I) carbonyl chlorides

Palladium(I) carbonyl chloride (PdCOCl) _n has been synthesized by the effect of CO on PdCl₂ in the presence of trace water. Anionic palladium(I) carbonyl chloride has been synthesized during treatment of ethanol-based or acetone-based solutions of H₂PdCI₄ containing small amounts of water; it has been isolated from the solution as the salt Cs₂[Pd₂(CO)₂Cl₄]. IR-spectra, X-ray diffraction patterns, and thermogravimetry data on synthesized palladium(I) carbonyl complexes are presented.     

Backbone modified small bite-angle diphosphines: Synthesis and molecular structures of [M(CO)4{X2PC(RR)PX2}] (M = Mo, W; X = Ph, Cy; R = H, Me, Et, Pr, allyl, R = Me, allyl)

A range of new small bite-angle diphosphine complexes, [M(CO)₄{X₂PC(R¹R²)PX₂}] (M = Mo, W; X = Ph, Cy; R¹ = H, Me, Et, Pr, allyl, R² = Me, allyl), have been prepared via elaboration of the methylene backbones in [M(CO)₄(X₂PCH₂PX₂)] as a result of successive deprotonation and alkyl halide addition. When X = Ph it proved possible to replace both methylene protons but for X = Cy only one substitution proved possible. This is likely due to the electron-releasing nature of the cyclohexyl groups but may also be due to steric constraints. Attempts to prepare the bis(allyl) substituted complex [Mo(CO)₄{Ph₂PC(allyl)₂PPh₂}] were only moderately successful. The crystal structures of nine of these complexes are presented.     

Austauschreaktionen an komplexgebundenen liganden von elementen der IV. Hauptgruppe : III. Darstellung von halogen-, pseudohalogen- und hydridokomplexen des typs π-C5H5Fe(CO)2SiX3

The complexes CpFe(CO)₂SiBr₃, CpFe(CO)₂SiI₃, CpFe(CO)₂SiBr₂(OMe), and CpFe(CO)₂SiI(NH-cyclo-C₆H₁₁)₂ are prepared by the reaction of CpFe(CO)₂SiR₃ (R = OMe, NH-cyclo-C₆H₁₁) with HBr, HI and CH₃I. Treating CpFe(CO)₂SiCl₃ with a large excess of NaN₃, KOCN or KSCN yields the first tri-pseudohalogensilyl—transition-metal-complexes. The compounds are characterized by IR and mass spectra. A new method of preparation of the already known complex CpFe(CO)₂SiH₃ is described starting from CpFe(CO)₂SiCl₃ and LiAlH₄.