Direct in situ synthesis of cationic N-heterocyclic carbene iridium and rhodium complexes from neat ionic liquid: Application in catalytic dehydrogenation of cyclooctadiene

A direct synthetic route to cationic N-heterocyclic carbene (NHC) complexes of rhodium and iridium from neat dialkyl-imidazolium ionic liquids (ILs) has been found. The method uses complexes bearing basic anionic ligands, [M(COD)(PPh₃)X], X = OEt, MeCO₂, which react with the inactivated imidazolium cation in the absence of external bases yielding one M-NHC moiety and the free protonated base. This new one-pot synthesis leaving pure, catalytically active IL solutions is faster, cleaner and more efficient than traditional syntheses of such NHC complexes. The observed reactivity also gives insight into NHC incorporation of rhodium and iridium catalyzed reactions performed in common dialkyl-imidazolium ILs.The complexes synthesised in this manner are compared with their bis-phosphine analogues in terms of activity for catalytic dehydrogenation of 1,5-cyclooctadiene and 1,3-cyclooctadiene in neat [BMIM][NTf₂] as solvent. Even at high temperature, no ligand exchange reaction is observed with [(COD)M(PPh₃)₂] [NTf₂] catalysts. As expected, the yields of all the reactions were low, iridium was much more active in C-H activation than rhodium and the NHC ligands were more stable than triphenylphosphine. For all catalysts, the isomerisation of 1,5-cyclooctadiene is the major reaction. However, the phosphine-NHC complex of iridium seems to be more selective for dehydrogenation than its bis-phosphine counterpart, which is more active in transfer-hydrogenation and less stable under the applied conditions. Different reaction conditions were tried in order to optimise selectivity for dehydrogenation over isomerisation and transfer-hydrogenation. Surprisingly, with 1,3-cyclooctadiene as substrate selectivity for dehydrogenation is much higher than with 1,5-cyclooctadiene for all catalysts.     

Ruthenium-benzocrownether complexes: Synthesis, structures, catalysis and immobilisation in ionic liquids

A facile pathway to [RuCl₂(η⁶-benzocrownether)]₂ complexes is described and crystal structures of the complexes [RuCl₂(η⁶-benzo-15-crown-5)]₂ and [RuCl₂(η⁶-dibenzo-18-crown-6)]₂ are reported. The complexes were derivatised with (1S,2R)-2-amino-1,2-diphenylethanol and evaluated in the enantioselective transfer-hydrogenation of acetophenone. The effect of complexation of different alkaline metals (Na, K, Cs) within the crown on the selectivity and reaction rate was studied. Interaction of a sulfonated phosphine ligand with the crown was probed by NOESY-NMR and utilisation of the crownether to serve as an anchor for catalyst immobilisation was investigated.     

Iron-catalyzed intramolecular cyclotrimerization of triynes to annulated benzenes

An iron species derived from FeCl₂ or FeCl₃ by in situ reduction with zinc powder in the presence of imidazol-2-ylidene or bidentate nitrogen ligand could effectively catalyze intramolecular cycloisomerization of triynes to annulated benzenes. With a 2-iminomethylpyridine ligand, hydrates of FeCl₂ and FeCl₃ as well as their anhydrous ones could be used.     

Humic Acid Removal by Combining the Magnetic Property of Maghemite with the Adsorption Property of Nanosized Hydroxyapatite

Maghemite incorporated hydroxyapatite (HAP) nanocomposite was prepared by in situ precipitation of the calcium phosphate phase in an iron oxide colloidal suspension. The resultant nanocomposite was characterized by x-ray diffraction, Fourier transform infrared spectrometer, transmission electron microscope, N₂ adsorption analysis, and vibrating sample magnetometry. The potential of HAP/γ-Fe₂O₃ nanocomposite for HA adsorption from aqueous solution was evaluated by batch experiments and adsorption kinetic tests. HA adsorption amount on the adsorbent decreased with increasing solution pH and the presence of KNO₃ and alkali-earth metal ions resulted in enhanced HA adsorption. HA adsorption onto HAP/γ-Fe₂O₃ nanocomposite could be well described by Freundlich and Sips models, while HA adsorption process on the adsorbent obeyed pseudo-second-order kinetics and the adsorption rates decreased with increasing initial HA concentration. This study showed that the HAP/γ-Fe₂O₃ nanocomposite could be used as an efficient and magnetically separable adsorbent for the removal of HA from aqueous solution. Subsequent studies demonstrated that the HA-loaded HAP/γ-Fe₂O₃ nanocomposite could be further applied for the highly efficient adsorption of methylene blue (MB) and separated from the medium by a simple magnetic process.     

Enantioselective total synthesis of pyrroloquinolone as a potent PDE5 inhibitor

A concise enantioselective strategy for the synthesis of key PDE5 inhibitor 2 was developed in 5 and 6 steps using asymmetric hydrogenation and one-pot chiral auxiliary approaches, respectively. The synthesis features the use of imine 6 obtained through Bischler-Napieralsky reaction from amide 5. Absolute R configuration was introduced in (+)-7 by asymmetric transfer-hydrogenation reaction with Ru(II) catalyst followed by establishing the tricyclic pyrroloquinalone core using the Winterfeldt oxidation. Another alternative synthetic approach for the introduction of chirality in the molecule employed imine 6 and chloroformates of different chiral auxiliaries, which achieved N-acyliminium ion intermediates that were reduced in situ using PdCl₂/Et₃SiH protocol. These synthetic routes were applied in the total synthesis of promising male erectile dysfunction (MED) PDE5 inhibitor 1.     

Preparation and characterization of thermally stable cellulose nanocrystals via a sustainable approach of FeCl<Subscript>3</Subscript>-catalyzed formic acid hydrolysis

Cellulose nanocrystals (CNCs) can be used as building blocks for the production of many renewable and sustainable nanomaterials. In this work, CNCs were produced from bleached eucalyptus kraft pulp with a high yield over 75 % via FeCl₃-catalyzed formic acid (FA) hydrolysis process. It was found that the particle size of resultant CNC products (F-CNC) decreased with the increase of FeCl₃ dosage in FA hydrolysis, and a maximum crystallinity index of about 75 % could be achieved when the dose of FeCl₃ was 0.015 M (i.e. about 7 % based on the weight of starting material). Thermogravimetric analyses revealed that F-CNC exhibited a much higher thermal stability (the decomposition temperature was over 260 °C) than S-CNC prepared by typical sulfuric acid hydrolysis. In the FeCl₃-catalyzed FA hydrolysis process, FA could be easily recovered and reused, and FeCl₃ could be transferred to Fe(OH)₃ as a high value-added product. Thus, the FeCl₃-catalyzed FA hydrolysis process could be sustainable and economically feasible. In addition, F-CNC could be well dispersed in DMSO and its dispersibility in water could be improved by a cationic surface modification.     

The Structure of the High Temperature Modification of Lithium Triflate (γ-LiSO3CF3)

The high temperature modification of lithium triflate (γ-LiSO₃CF₃) crystallises in the orthorhombic space group Cmca with the lattice parameters a = 6.3022(4), b = 8.6989(5), and c = 20.1262(14) Å (synchrotron powder diffraction data, T = 456 K). The crystal structure of γ-LiSO₃CF₃ is disordered, in the cationic as well as the anionic partial structure, and exhibits double layers of triflate anions with the lipophilic CF₃-groups facing each other. The lithium ions could not be located by the diffraction experiment due to their high mobility. The staggered triflate anion is twofold disorderd leading to two different positions on top of each other which are tilted to one another.     

On the Brink of Decomposition: Controlled Oxidation of a Substituted Arsanylborane as a Way to Labile Group 13-15-16 Compounds

The reactivity of the organic-substituted arsanylborane tBuAsHBH₂NMe₃ ( 1 ) towards different elemental chalcogenes as well as organic oxidants such as O-NMe_3, Me₃Si−O−O-SiMe₃, MesCNO and cyclohexenesulfide is reported. By the reaction of 1 with grey selenium, the selenium oxidation product tBuAs(Se)HBH₂NMe₃ ( 2 ) was obtained. For the oxidation with sulfur, the two products tBuAs(S)HBH₂NMe₃ ( 3 a ) and tBuAs(S)SHBH₂NMe₃ ( 3 b ) could be isolated as oils. The structural characterization of As(tBuAs(S)SHBH₂NMe₃)₃ ( 4 ) as well as corresponding DFT computations allow insights into the decomposition behavior of 3 a and 3 b in solution. For the reaction of MesCNO with 1 , the formation of an unusual As−H activation product Mes-C(NOH)-AstBu-BH₂NMe₃ ( 5 ) is observed. In the reaction with Me₃N−O, the first isolatable oxo-arsanylboranes tBuAs(O)HBH₂NMe₃ ( 6 a ) and tBuAs(O)OHBH₂NMe₃ ( 6 b ) are obtained, with 6 b also being accessible via the controlled reaction of 1 with air.     

Selective fabrication of porous iron oxides hollow spheres and nanofibers by electrospinning for photocatalytic water purification

Porous hematite (α-Fe₂O₃) hollow spheres and nanofibers could be obtained via electrospinning and subsequent thermal decomposition in air. The precursor could be fabricated by electrospinning using Fe(NO₃)₃ as the iron source and Polyvinylpyrrolidone (PVP) as a complexing reagent. Upon calcination, pure porous α-Fe₂O₃ hollow spheres and nanofibers could be obtained at 650 °C for 3 h. The novel hollow spheres have an abundantly porous structure as well as large surface areas. Benefitting from the special porous structure, narrow bandgap, and higher surface area, porous α-Fe₂O₃ hollow materials are used as visible-light-responsive photocatalysts. So we have investigated the visible light photodegradation behavior of porous hematite (α-Fe₂O₃) hollow spheres and nanofibers towards organic dyes, as Rhodamine B (RhB). The synergetic effects of higher surface area, pore structures promoted the photocatalytic efficiency for RhB degradation under visible light and contributed to achieving the enhanced and stable photocatalytic activity.     

Energy partitioning and reaction dynamics in the chemiluminescent channel of the reaction: HS + O3 → HSO* + O2

The title reaction forms electronically excited HSO(òA′) directly, with considerable vibrational and rotational excitation as well. The internal excitation of the HSO fragment is the maximum possible consistent with the concurrent formation of an O₂(¹Δ_g) molecule as the other reaction product. The observed vibrational excitation peaks in the υ′= 2 level of the υ₃ mode. No evidence about possible excitation of the other vibrational modes of HSO could be obtained.     

TG study on the chlorination of MoO2 by CCl4

Molybdenum-dioxide samples were produced by reduction of MoO₃ in flowing H₂. The chlorination kinetics of the pure crystalline MoO₂ and samples containing a mixture of Mo-oxides were studied by thermogravimetry, using gaseous CCl₄ as chlorinating agent. The initial samples and the chlorinated residues were investigated by XRD and BET methods, as well. The pure molybdenum-dioxide sample was remarkably less reactive than the partially reduced non-stoichiometric molybdenum-oxides or MoO₃. The characteristic sigmoid shape of the TG curves were explained by the difference in the reactivity of molybdenum-oxides and by the change of the specific surface area during chlorination. The observed reaction order ofn=0.5 suggests a fast, reversible dissociative adsorption of CCl₄ before the volatilization step. For samples of low specific surface area activation energies of 123 and 97 kJ·mol^?1 were obtained, and the kinetic curves could be well fitted by an Avrami-Erofeev equation. For sample of much higher specific surface area a diffusion controlled reaction (E _a=52 kJ·mol^?1) was supposed, and the kinetic model of contracting spheres could be applied.     

Synthesis of polyethylene with bimodal molecular weight distribution by supported iron‐based catalyst

Through immobilization of two iron‐based complexes, [((2,6‐MePh)N = C(Me))₂C₅H₃N]FeCl₂ ( 1 ) and [((2,6‐iPrPh)N = C(Me))₂C₅H₃N]FeCl₂ ( 2 ), on SiO₂ pretreated with tetraethylaluminoxane (TEAO), two supported iron‐based catalysts, 1 /TEAO/SiO₂ ( 3 ) and 2 /TEAO/SiO₂ ( 4 ), were prepared. These two supported catalysts 3 and 4 could be used to catalyze ethylene polymerization with moderate polymerization activity and prepare linear high‐density polyethylene with bimodal molecular weight distribution (MWD). It was demonstrated that immobilization of catalyst could significantly improve molecular weight (MW) of high‐MW fraction of the resultant polyethylene, as well as maintain bimodal MWD of polyethylene produced by the corresponding homogeneous catalysts. Such bimodal MWD of polyethylene produced by supported iron‐based catalysts could be well tailored by varying polymerization conditions, such as ethylene pressure and molar ratio of Al to Fe. It has been proven that TEAO is an efficient activator for both homogeneous and heterogeneous iron‐based catalysts for producing polyethylene with bimodal MWD. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5662–5669, 2004     

Kinetics of the uptake of SO2 on mineral oxides: Improved initial uptake coefficients at 298 K from pulsed Knudsen cell experiments

The uptake of SO₂ on γ‐Fe₂O₃, γ‐Al₂O₃, and Saharan dust has been studied at T = 298 K using a Knudsen cell reactor operated in a steady‐state as well as in a pulsed mode. The initial uptake coefficients determined in the steady‐state mode have been found to be affected by surface saturation as well as bulk diffusion of SO₂ resulting in an apparent dependence of the initial uptake coefficients on the sample mass of the mineral oxides. However, by operating the Knudsen cell in the pulsed mode with shorter response time, these effects could be suppressed. Initial uptake coefficients of γ_ini (Fe₂O₃) = (8.8 ± 0.4) × 10^?2, γ_ini (Al₂O₃) = (7.4 ± 0.9) × 10^?3, and γ_ini (Saharan dust) = (7.6 ± 0.5) × 10^?2 were derived. This suggests that Fe₂O₃ is an important component in determining the reactivity of mineral dusts. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 242–249, 2006     

Benzyltributylammonium periodate as a novel and safe oxygen source for Mn-porphyrin catalyzed practical and highly selective oxygenation of hydrocarbons

Benzyltributylammonium periodate (BzBu₃NIO₄) was prepared easily in high yield in neat water. The compound crystallized with two cations and two anions per asymmetric unit and a space group of Pna2₁ was determined by single-crystal X-ray diffraction. It was used practically in the clean and selective epoxidation of olefins and oxygenation of saturated hydrocarbons catalyzed by manganese (III) porphyrins in water/ethanol as a green media. The catalyst could be reused without noticeable loss of activity, and the oxidant’s by-product (BzBu₃NIO₃) could also be reused. The efficiency of the oxidation system depends critically upon the steric hindrances and electronic structures of both the nitrogen donors and Mn-catalysts. Some evidences suggest the involvement of a high valent Mn-oxo species as well as a six-coordinate [(L)(Por)Mn-OIO₃] complex in the oxidation reactions.     

Ionic liquid immobilization on carbon nanofibers and zeolites: Catalyst design for the liquid-phase toluene chlorination

The environmental-friendly chlorination reaction of toluene by trichloroisocyanuric acid (TCCA, C₃N₃O₃Cl₃) was investigated applying immobilized ionic liquids (ILs) on different supports. Ionic liquids were grafted either on carbon nanofibers (CNF) or encapsulated in zeolites. Their influence on the chlorination activity as well as on the selectivity in different chlorinated products was studied. An unusually high selectivity toward meta-chlorotoluene was achieved, up to 36%. Hence, the selectivity could be tuned to produce either expected ortho-/para-chlorotoluene or meta-chlorotoluene with a proper support choice.     

Influence of H2O on alternating copolymerization with the EtnAlCl3-n-VOCl3 catalyst system

The effect of the catalytic amount of H₂O was investigated with the Et_nAlCl_3-n-VOCl₃ catalyst system on the alternating copolymerization of acrylic monomers with diolefins and styrene. The presence of the catalytic amount of H₂O produced an improvement in the yield and in the molecular weight as well as the structure of copolymer with the Et_nAlCl_3-n-VOCl₃ catalyst system. The efficiency of the aluminum components in the Et_nAlCl_3-n-VOCl₃ system appears with AlEt₃ and especially with Et_1.5AlCl_1.5. The catalytic activity was found to depend upon the H₂O Et_nAlCl_3-n molar ratio and was also affected by the order of mixing of the catalyst components and the monomers. Effective catalyst could be prepared when the catalyst components (except VOCl₃) were premixed without presence of monomers. The possible catalytic behavior of H₂O was discussed.     

1,3-Dipolar cycloaddition of chalcones and arylidene-1,3-dicarbonyls with diazosulfone for the regioselective synthesis of functionalized pyrazoles and pyrazolines

A convenient method for the synthesis of 3-acylpyrazoles and pyrazole-3-carboxylates using diazosulfone as a reactive 1,3-dipole and a diazomethane equivalent is reported here. Chalcones, arylidenemalonates and other arylidene-1,3-dicarbonyls performed well as the dipolarophiles in the reaction with the diazosulfone which took place under simple base mediated conditions (Cs₂CO₃ or NaOEt in EtOH). In few cases, the initial cycloadducts, the intermediate pyrazoline derivatives, could also be isolated and characterized. The pyrazoline derivatives undergo an alkoxide mediated 1,4-elimination, viz. decarboxylation-detosylation to afford the pyrazole derivatives.     

The effects of strain and charge doping on the electronic properties of graphitic C3N5

Inspired by the successful synthesis of a new graphitic C₃N₅ (termed as g-C₃N₅), we systematically investigate its geometry and electronic properties. The layered g-C₃N₅ has a nanopore diameter of 13.8 Å. It is a direct semiconductor with a band gap of 0.53 eV. The influence of strains on the electronic properties is considered. When applying uniaxial or biaxial compressive strain, the band gap can decrease until zero, resulting in a semiconductor-to-metal transition. The effects of charge doping on the electronic properties are also studied. With the increase of negative charge doping, the band gap becomes narrow until zero, indicating that a semiconductor-to-metal transition occurs as well. In addition, the electronic properties of g-C₃N₅ can be tuned by both strain and charge doping. Thus, we provide a fundamental understanding of g-C₃N₅, and its semiconductor-to-metal transition could be possibly experimentally approached by strain and charge doping, extending the electronic usage of g-C₃N₅.     

Sensing the Molecular Structures of Hexan-2-one by Internal Rotation and Microwave Spectroscopy

Using two molecular jet Fourier transform spectrometers, the microwave spectrum of hexan-2-one, also called methyl n-butyl ketone, was recorded in the frequency range from 2 to 40 GHz. Three conformers were assigned and fine splittings caused by the internal rotations of the two terminal methyl groups were analyzed. For the acetyl methyl group CH₃ COC₃H₆CH₃, the torsional barrier is 186.9198(50) cm⁻¹, 233.5913(97) cm⁻¹, and 182.2481(25) cm⁻¹ for the three observed conformers, respectively. The value of this parameter could be linked to the structure of the individual conformer, which enabled us to create a rule for predicting the barrier height of the acetyl methyl torsion in ketones. The very small splittings arising from the internal rotation of the butyl methyl group CH₃COC₃H₆ CH₃ could be resolved as well, yielding the respective torsional barriers of 979.99(88) cm⁻¹, 1016.30(77) cm⁻¹, and 961.9(32) cm⁻¹.     

表面活性剂模板在空气-水界面ZrO2薄膜中的稳定性

采用模板——十二烷基苯磺酸(DBS-H)在空气-水界面组装ZrO₂薄膜，研究了DBS-H在ZrO₂自组装薄膜中的水溶性、化学稳定性、热稳定性和光化学稳定性。模板的各类稳定性将直接控制ZrO₂薄膜结构，主要表现在层间距变化上。从模板与Na₂SiO₃反应的研究中获得了一种制备ZrO₂ / SiO₂复合氧化物薄膜的新方法，并推测出该复合薄膜的结构。