Influence of acid–base properties of cobalt–molybdenum catalysts supported on magnesium orthophosphates in isomerization of 3,3-dimethylbut-1-ene

Synthesis and physico-chemical characterization of a pure magnesium phosphate (MgP) prepared by coprecipitation, and MgP modified by introduction of cobalt–molybdenum (4–12 wt.% of MoO₃ with the Co/Mo ratio fixed at 0.5) have been carried out. The structural properties of these catalysts were characterized by X-ray diffraction, their textural properties were determined by N₂ adsorption–desorption isotherms and the dispersion of cobalt–molybdenum was studied by XPS spectroscopy. Their acid properties have been investigated by in situ FT-IR spectroscopy of adsorbed molecules, often, 2,6-dimethylpyridine (pK_a = 6.7), pyridine (pK_a = 5.3). Co–Mo incorporation leads to a modification in the MgP acid–base properties, especially on the acid sites type and number. Thus, lower loading of cobalt–molybdenum species decreased the number of strong Lewis acid sites whereas higher loading increased it. It was found that Lewis acid sites on magnesium phosphates play an important role in the isomerization of 3,3-dimethylbut-1-ene.The 3,3-dimethylbut-1-ene (33DMB1) conversion increases with the reaction temperature from 493 to 653 K for MgP, but decreases after 573 K for MgP supported by Co–Mo. A linear relationship between both types of acid sites and conversion values was found. The deactivation of the catalysts appears at high reaction temperature (>573 K).     

Synthesis and characterization of thiosemicarbazone derivatives of 2-chloro-4-hydroxy-benzaldehyde and their rhenium(I) complexes

N-Thioamide thiosemicarbazone derived of 2-chloro-4-hydroxy-benzaldehyde (R = H, HL¹; R = Me, HL² and R = Ph, HL³) have been prepared and their reaction with fac-[ReX(CO)₃(CH₃CN)₂] (X = Br, Cl) in chloroform gave the adducts [ReX(CO)₃(HL)] (1a X = Cl, R = H; 1a′ X = Br, R = H; 1b X = Cl, R = CH₃; 1b′ X = Br, R = CH₃; 1c X = Cl, R = Ph; 1c′ X = Br, R = Ph) in good yield. Complexes 1a′ and 1b’ were also obtained by the reaction of HL¹ and HL³ with [ReBr(CO)₅] in toluene.All the compounds have been characterized by elemental analysis, mass spectrometry (FAB), IR and ¹H NMR spectroscopic methods. Moreover, the structures of HL², HL³ and 1a·H₂O were also established by X-ray diffraction. In 1a, the rhenium atom is coordinated by the sulphur and the azomethine nitrogen atoms, forming a five-membered chelate ring, as well as three carbonyl carbon and chloride atoms. The resulting coordination polyhedron can be described as a distorted octahedron.The study of the crystals obtained by slow evaporation of methanol and DMSO solutions of the adducts 1a′ and 1b, respectively, showed the formation of dimer structures based on rhenium(I) thiosemicarbazonates [Re₂(L¹)₂(CO)₆]·3H₂O (2a)·3H₂O and [Re₂(L²)₂(CO)₆]·(CH₃)₂SO (2b)·2(CH₃)₂SO. Amounts of these thiosemicarbazonate complexes [Re₂(L)₂(CO)₆] (2) were obtained by reaction of the corresponding free ligands with [ReCl(CO)₅] in dry toluene.In 2a·3H₂O and 2b·2(CH₃)₂SO the dimer structures are established by Re–S–Re bridges, where S is the thiolate sulphur from a N,S-bidentate thiosemicarbazonate ligand. In both structures the rhenium coordination sphere is similar; the dimers are in the same diamond Re₂S₂ face.     

Synthesis of (NHC)Rh(cod)Cl and (NHC)RhCl(CO)2 complexes – Translation of the Rh- into the Ir-scale for the electronic properties of NHC ligands

Twenty-three different Rh complexes of the (NHC)RhCl(cod) and (NHC)RhCl(CO)₂ type were synthesized from [RhCl(cod)]₂. The electron donating nature of the NHC ligands was changed in a systematic manner. The redox potentials of the various (NHC)RhCl(cod) and the ν(CO) of the various (NHC)RhCl(CO)₂ were determined. A correlation of the Rh redox potentials and the Rh ν(CO), respectively, with the related data from analogous (NHC)IrCl(cod) and (NHC)IrCl(CO)₂ complexes established two linear relationships. The linear regression (R² = 0.993) of the Rh and the Ir redox potentials results in an equation for the redox potential transformation: E_1/2(Ir) = 1.016 · E_1/2(Rh) ? 0.076 V. The linear regression (R² = 0.97) of the Rh and Ir ν_av(CO) results in an equation for the ν_av(CO) transformation: ν_av(CO)Ir = 0.8695 · ν_av(CO)Rh + 250.7 cm^?1. In this manner the Rh and the Ir-scale for the determination of the electron donating properties of NHC ligands are unified.     

Diiron chelate complexes relevant to the active site of the iron-only hydrogenase

A novel unsymmetrically disubstituted propanedithiolate compound [Fe₂(CO)₄(κ²-dmpe)(μ-pdt)] (1) (pdt = SCH₂CH₂CH₂S, dmpe = Me₂PCH₂CH₂PMe₂) was synthesized by treatment of [Fe₂(CO)₆(μ-pdt)] with dmpe in refluxing THF. Compound 1 was characterized by single-crystal X-ray diffraction analysis. Protonation of 1 with HBF₄·Et₂O in CH₂Cl₂ gave at room temperature the μ-hydrido derivative [Fe₂(CO)₄(κ²-dmpe)(μ-pdt)(μ-H)](BF₄)] (2). At low temperature, ¹H and ³¹P–{¹H} NMR monitoring revealed the formation of a terminal hydride intermediate 3. Comparison of these results with those of a VT NMR study of the protonation of symmetrical compounds [Fe₂(CO)₄L₂(μ-pdt)] [L = PMe₃, P(OMe)₃] suggests that in disubstituted bimetallic complexes [Fe₂(CO)₄L₂(μ-pdt)], dissymmetry of the complex is required to observe terminal hydride species. Attempts to extend the series of chelate compounds [Fe₂(CO)₄(κ²-L₂)(μ-pdt)] by using arphos (arphos = Ph₂AsCH₂CH₂PPh₂) were unsuccessful. Only mono- and disubstituted derivatives [Fe₂(CO)_6−n(Ph₂AsCH₂CH₂PPh₂)_n(μ-pdt)] (n = 1, 4a; n = 2, 4b), featuring dangling arphos, were isolated under the same reaction conditions of formation of 1. Compound 4b was structurally characterized.     

Using pendant ferrocenyl group(s) as an intramolecular standard to probe the reduction of diiron hexacarbonyl model complexes for the sub-unit of [FeFe]-hydrogenase

The synthesis and characterisation of two diiron hexacarbonyl complexes [Fe₂(SXS)(CO)₆], 1 (SXS = ((^?SCH₂)₂C(CH₃)CH₂OCOFc, Fc = ferrocenyl group) and 2 (SXS = (^?SCH₂CH₂NHCOFc)₂), were described. By using intramolecularly integrated ferrocenyl group(s) in the complexes as an internal standard, the nature of two stepwise one-electron processes of the complexes coupled with a chemical reaction was clearly demonstrated. Examining how the reduction transformed into sole one-electron process with both increasing scanning rate under Ar/CO atmosphere and lowering temperature indicated conclusively that the reduction of both complexes couples to a chemical reaction which involves CO-loss.     

Halogenation of Lewis acid/base stabilised phosphanylboranes

The reaction pattern of the Lewis-acid/base stabilised phosphanylborane [(CO)₅W(H₂PBH₂ · NMe₃)] (1) with elemental halogens is comprehensively studied. The reaction with iodine and bromine leads to a selective halogenation at the tungstencarbonyl moiety under formation of [WX₂(CO)₄(H₂PBH₂ · NMe₃)] (X = I (2), Br (3)). Whereas 2 is a stable product the brominated compound 3 dimerises easily to [WBr₂(CO)₃(H₂PBH₂ · NMe₃)]₂ (4) under lost of CO. The CO elimination reaction of 3 is extensively studied. If 3 is reacted with [Et₄N][Br] the ionic compound [Et₄N][WBr₃(CO)₃(H₂PBH₂ · NMe₃)] (5) is formed. Otherwise, if 3 is combined with the donor ligand [H₂PBH₂ · NMe₃], the complex [WBr₂(CO)₃(H₂PBH₂ · NMe₃)₂] (6) is obtained. Compounds 2–6 are comprehensively characterised by X-ray diffraction analysis, NMR, and IR spectroscopy.     

Excess enthalpies of { ethyl tert -butylether + hexane + heptane,or octane } at the temperature 298.15 K

Excess molar enthalpies, measured at the temperature 298.15 K in a flow microcalorimeter, are reported for the ternary mixtures {x₁CH₃CH₂OC(CH₃)₃ + x₂CH₃(CH₂)₄CH₃ + (1  − x₁ − x₂)CH₃(CH₂)₅CH₃} and {x₁CH₃CH₂OC(CH₃)₃ + x₂CH₃(CH₂)₄CH₃ + (1  − x₁ − x₂)CH₃(CH₂)₆CH₃}. Smooth representations of the results are described and used to construct constant-enthalpy contours on Roozeboom diagrams. It is shown that useful estimates of the enthalpies of the ternary mixtures can be obtained from the Liebermann and Fried model, using only the physical properties of the components and their binary mixtures.     

Quaternary (liquid + liquid) equilibria for (water + 2-propanol + 1,1-dimethylethyl methyl ether + diisopropyl ether) at the temperature 298.15 K

(Liquid + liquid) equilibrium tie-lines were measured for one ternary system {x₁H₂O + x₂(CH₃)₂CHOH + (1 − x₁ − x₂)CH₃C(CH₃)₂OCH₃} and one quaternary system {x₁H₂O + x₂(CH₃)₂CHOH + x₃CH₃C(CH₃)₂OCH₃ + (1 − x₁ − x₂ − x₃)(CH₃)₂CHOCH(CH₃)₂} at T = 298.15 K and P^∘ = 101.3 kPa. The experimental (liquid + liquid) equilibrium results were satisfactorily correlated by modified and extended UNIQUAC models both with ternary and quaternary parameters in addition to binary ones.     

Near-infrared spectroscopy as an effective tool for monitoring the conformation of alkylammonium surfactants in montmorillonite interlayers

Application of near-infrared (NIR) spectroscopy to probing the arrangement of trimethylalkylammonium cations in montmorillonite interlayers has been demonstrated. Detailed analysis of the mid-IR (MIR) and NIR spectra of montmorillonite from Jelšový Potok (JP, Slovakia) saturated with surfactants with varying alkyl chain length (even numbers of carbon atoms from C6 to C18) was performed to show the advantages of the NIR region in characterizing surfactant conformations. The position of the ν_as(CH₂), (∼2930–2920 cm⁻¹), ν_s(CH₂) (∼2860–2850 cm⁻¹), 2ν_as(CH₂) (∼5810–5785 cm⁻¹), (ν + δ)_as(CH₂) (∼4340–4330 cm⁻¹) and (ν + δ)_s(CH₂) (∼4270–4250 cm⁻¹) signals was used as an indicator of the gauche/trans conformer ratio. For all bands, a shift toward lower wavenumber on increasing the alkyl chain length from 6 to 18 carbons suggests a transition from disordered liquid-like to more ordered solid-like structures of the surfactants. The magnitude of the shift was significantly higher for 2ν_as(CH₂) (28 cm⁻¹) than for ν_as(CH₂) (8 cm⁻¹) or ν_s(CH₂) (10 cm⁻¹), showing the NIR region to be a useful tool for examining this issue. Comparison of the IR spectra of crystalline alkylammonium salts and the corresponding organo-montmorillonites demonstrated a confining effect of montmorillonite layers on surfactant ordering. For each alkyl chain length the CH₂ bands of the organo-montmorillonites appeared at higher wavenumbers than for the unconfined surfactant, thus indicating a higher disorder of the alkyl chains. The wavenumber difference between corresponding samples was always higher in the NIR than in the MIR region. All these findings show NIR spectroscopy to be useful for conformational studies.     

The quest for magnets composed of vanadium and 1,4-benzoquinones

The reaction of V^o(CO)₆ and representative quinones, A (A = benzoquinone, chloranil, 2,3-dicyano-1,4-naphthoquinone, and dihydroxy-1,4-benzoquinone), form materials of V(A)₂ · zCH₂Cl₂ (z < 0.1) composition, which exhibits antiferromagnetic coupling and do not magnetically order above 5 K.     

Some aspects of metal-support strong interactions in Rh/Al2O3 catalyst under oxidising and reducing conditions

The aim of the Letter is to elucidate the nature of metal-support interaction in the 2 wt% Rh/Al₂O₃ catalyst obtained by annealing Rh–O–Al xerogel at 1113 K in air.XPS, HRTEM, and XRD results reveal that during the Rh–O–Al xerogel annealing in air, rhodium incorporates into forming alumina, which results mostly in Rh⁴⁺/δ-Al₂O₃ solid solution formation.However, in the course of the catalyst reduction at 773 with H₂ and at 823 K with CH₄ the Rh⁴⁺/δ-Al₂O₃ solid solution transforms into Rh–Al alloy. The islands of rhodium form on the surface of the Rh–Al alloy nanocrystallites if the reduction is slow enough.     

Dinuclear ruthenium(I) complexes of the type [Ru2(CO)4L2] with carboxylate or 2-pyridonate ligands: Evaluation as catalysts for olefin cyclopropanation with diazoacetates

Dinuclear ruthenium(I,I) carboxylate complexes [Ru₂(CO)₄(μ-OOCR)₂]_n (R = CH₃ (1a), C₃H₇ (1b), H (1c), CF₃ (1d)) and 2-pyridonate complex [Ru₂(CO)₄(μ-2-pyridonate)₂]_n (3) catalyze efficiently the cyclopropanation of alkenes with methyl diazoacetate. High yields are obtained with terminal nucleophilic alkenes (styrene, ethyl vinyl ether, α-methylstyrene), medium yields with 1-hexene, cyclohexene, 4,5-dihydrofuran and 2-methyl-2-butene. The E-selectivity of the cyclopropanes obtained from the monosubstituted alkenes and the cycloalkenes decreases in the order 1b > 1a > 1d > 1c. The cyclopropanation of 2-methyl-2-butene is highly syn-selective. Several complexes of the type [Ru₂(CO)₄(μ-L¹)₂]₂ (4) and (5), [Ru₂(CO)₄(μ-L¹)₂L²] (L² = CH₃OH, PPh₃) (6)–(9) and [Ru₂(CO)₄(CH₃CN)₂(μ-L¹)₂] (10) and (11), where L¹ is a 6-chloro- or 6-bromo-2-pyridonate ligand, are also efficient catalysts. Compared with catalyst 3, a halogen substituent at the pyridonate ligand affects the diastereoselectivity of cyclopropanation only slightly.     

Density functional theory investigation of the photodissociation channels of acetophenone

The photodissociations of acetophenone (C₆H₅COCH₃) have been investigated by density functional theory (DFT) approach. The experimentally observed three photodissociation channels were clarified from the theoretical calculations on the related reactants, transition states (TSs), and products. Two of the three channels, C₆H₅COCH₃ → C₆H₅CO + CH₃ and C₆H₅COCH₃ → C₆H₅ + CH₃CO, were assigned to Norrish I reactions on the potential energy surfaces (PESs) of the lowest triplet state (T₁). And, the first one is more favorable for lower barrier. The subsequent decompositions, C₆H₅CO → C₆H₅ + CO and CH₃CO → CH₃ + CO, were also studied by the similar calculations as above. The third photodissociation channel, C₆H₅COCH₃ → C₆H₅CH₃ + CO, has been documented on the PESs of the ground state (S₀). The third one played a minor role in the photodissociations of C₆H₅COCH₃ for much higher barrier than the first two.     

Palladium and platinum complexes with planar chiral 1,2-disubstituted ferrocenes containing phosphine and thioether donor groups

Three palladium(II) complexes and four platinum(II) complexes having general formula CpFe{1,2-C₅H₃(PPh₂)(CH₂SR)}MCl₂ (M = Pd, R = Ph, Et and tBu; M = Pt, R = Ph, Et, tBu and Cy) have been synthesized by reaction of the corresponding CpFe{1,2-C₅H₃(PPh₂)(CH₂SR)} ligands with PdCl₂(CH₃CN)₂ or PtCl₂(CH₃CN)₂. These complexes have been fully characterized in solution and in solid state. In all cases, monomeric square planar complexes were obtained as pure diastereoisomers.     

Vibrational spectroscopic study of syngenite formed during the treatment of liquid manure with sulphuric acid

Syngenite (K₂Ca(SO₄)₂·H₂O), formed during treatment of manure with sulphuric acid, was studied by infrared, near-infrared (NIR) and Raman spectroscopy. C_s site symmetry was determined for the two sulphate groups in syngenite (P2₁/m), so all bands are both infrared and Raman active. The split ν₁ (two Raman+two infrared bands) was observed at 981 and 1000 cm⁻¹. The split ν₂ (four Raman+four infrared bands) was observed in the Raman spectrum at 424, 441, 471 and 491 cm⁻¹. In the infrared spectrum, only one band was observed at 439 cm⁻¹. From the split ν₃ (six Raman+six infrared) bands three 298 K Raman bands were observed at 1117, 1138 and 1166 cm⁻¹. Cooling to 77 K resulted in four bands at 1119, 1136, 1144 and 1167 cm⁻¹. In the infrared spectrum, five bands were observed at 1110, 1125, 1136, 1148 and 1193 cm⁻¹. From the split ν₄ (six infrared+six Raman bands) four bands were observed in the infrared spectrum at 604, 617, 644 and 657 cm⁻¹. The 298 K Raman spectrum showed one band at 641 cm⁻¹, while at 77 K four bands were observed at 607, 621, 634 and 643 cm⁻¹. Crystal water is observed in the infrared spectrum by the OH-liberation mode at 754 cm⁻¹, OH-bending mode at 1631 cm⁻¹, OH-stretching modes at 3248 (symmetric) and 3377 cm⁻¹ (antisymmetric) and a combination band at 3510 cm⁻¹ of the H-bonded OH-mode plus the OH-stretching mode. The near-infrared spectrum gave information about the crystal water resulting in overtone and combination bands of OH-liberation, OH-bending and OH-stretching modes.     

The reactions of Rh2(CO)4Cl2 with 1,5-cyclooctadiene and tetramethylallene. A combined in-situ vibrational spectroscopies, spectral reconstruction and DFT study

Reactions of Rh₂(CO)₄Cl₂ with 1,5-cyclooctadiene (COD) and tetramethylallene (TMA) were performed separately in anhydrous hexane under argon atmosphere. Multiple perturbations of Rh₂(CO)₄Cl₂, COD and TMA were also performed during the reactions. These two reactions were monitored by in-situ FTIR (FIR and MIR) and/or Raman spectroscopies and the collected spectra were further analyzed with BTEM family of algorithms. DFT calculations were performed to identify the organometallic species present. The known diene complex Rh₂(CO)₂Cl₂(η⁴-C₈H₁₂) and a new allene complex Rh₂(CO)₃Cl₂(η²-C₇H₁₂) were formed as the two primary organo-rhodium products. Their pure component spectra were reconstructed in the three characteristic regions of 200-680, 800-1360, and 1500-2200 cm⁻¹. Their relative concentrations were also obtained by the least square fitting of the carbonyl region 1500-2200 cm⁻¹. The present contribution shows the usefulness of combining in-situ spectroscopic measurements, BTEM analysis and DFT spectral prediction in order to analyze organometallic reactions at high dilution and identify the reaction products.     

Carbonyl and nitrosyl diruthenium compounds: Crystal structure of [Ru2(O2CMe)(DPhF)3(CO)]BF4 · CH2Cl2 and its isomorphous nitrosyl analogue

The reaction of [Ru₂(O₂CMe)(DPhF)₃(H₂O)]BF₄ (DPhF = N,N′-diphenylformamidinate) with CO gas leads to [Ru₂(O₂CMe)(DPhF)₃(CO)]BF₄ (1), that is the first isolated carbonyl complex containing the Ru₂⁵⁺ unit. The nitrosyl analogue [Ru₂(O₂CMe)(DPhF)₃(NO)]BF₄ (2) is prepared by reaction of Ru₂Cl(O₂CMe)(DPhF)₃ with NOBF₄. However, the attempts to obtain the cyanide derivative by reaction of Ru₂Cl(O₂CMe)(DPhF)₃ or [Ru₂(O₂CMe)(DPhF)₃(H₂O)]BF₄ with NaCN were unsuccessful. The structure of compounds 1 · CH₂Cl₂ and 2 · CH₂Cl₂ are described. Both compounds are isomorphous. The magnetic measurements at variable temperature demonstrate that 1 is paramagnetic with one unpaired electron in all range of temperature, in contrast to the three unpaired electrons usually present in Ru₂⁵⁺ complexes. The analogous nitrosyl compound 2 is diamagnetic.     

Synthesis and structure of a dmpe-substituted dinuclear complex bridged by a substituent-free gallium atom: Electronic effect of metal fragment on the iron–gallium bonding

A dinuclear complex bridged by a substituent-free gallium atom, Cp¹(dmpe)Fe–Ga–Fe(CO)₄ (1b: Cp¹ = η-C₅Me₅, dmpe = Me₂PCH₂CH₂PMe₂), was synthesized by the reaction of Cp¹Fe(dmpe)GaCl₂ with K₂[Fe(CO)₄]. Crystal structure analysis of complex 1b showed that the geometry around the gallium atom is essentially linear and the two Fe–Ga bonds are significantly shorter than those of usual single bonds, indicating the multiple bonding character of the Fe–Ga bonds. Comparison of the structure and IR data of 1b and those of Cp¹(dppe)Fe–Ga–Fe(CO)₄ (1a: dppe = Ph₂PCH₂CH₂PPh₂) revealed that the Fe–Ga bond is sensitive to the electronic character of the metal fragment. The Fe–Ga bond is shortened upon introducing a more π-basic metal fragment.     

Gas sensing selectivity of hexagonal and monoclinic WO3 to H2S

Hexagonal and monoclinic tungsten oxide (h- and m-WO₃) samples were produced by annealing hexagonal ammonium tungsten bronze, (NH₄)_0.07(NH₃)_0.04(H₂O)_0.09WO_2.95 at 470 and at 600 °C, respectively. Their structure, composition and morphology were analyzed by XRD, Raman, XPS, ¹H-MAS NMR and SEM. In order to study the effect of crystal structure on the gas sensitivity of tungsten oxides, h- and m-WO₃ were tested as gas sensors to CH₄, CO, H₂, NO and H₂S (1000 and 10 ppm) at 200 °C. Monoclinic WO₃ responded to all gases, but its gas sensing signal was two magnitudes greater to 10 ppm H₂S than to other gases, and it also detected H₂S even at 25 °C. Hexagonal WO₃ responded only to 10 ppm H₂S. Its sensitivity was smaller compared to m-WO₃, however, the response time of h-WO₃ was significantly faster. The gas sensing tests showed that while m-WO₃ had relative selectivity to H₂S in the presence CH₄, CO, H₂, NO; h-WO₃ had absolute selectivity to H₂S in the presence these gases.