A Novel Method for Synthesis of ZSM‐5 Coatings on Monolithic Cordierite Substrate

ZSM‐5 coatings, have been synthesized onto a monolithic cordierite substrate by an environmental friendly and high coating selectivity method—Vapor Phase Transport (VPT). With this method, an aluminosilicate gel coated onto the monolithic cordierite substrate has been transformed into a ZSM‐5 layer under vapors of n‐butylamine and water, n‐Butylamine played a key role in the forming of ZSM‐5 layer on the cordierite substrate. The ZSM‐5/cordierite monolith composites prepared by this method were ion‐exchanged with Cu²⁺ and tested for the selective catalytic reduction of NO by propane. The deNO_x activities of Cu/ZSM‐5 monolith catalysts were not only dependent on the ion‐exchange methods, but also on the ZSM‐5 loading of the monolith catalysts. The best result was obtained over the Cu (B3)/ZSM‐5 monolith catalyst, which had a ZSM‐5 loading of about 13% and was prepared by a pressure exchange procedure. At a temperature of 723 K and a space velocity of 10,000 h^?1 (based on the monolith volume), 85% of NO conversion and 93% of C₃H₃ conversion were achieved over the Cu(B3)/ZSM‐5 monolith catalyst.     

Effect of Hydrohalogenation of Metal/Zeolite Catalysts for Cyclohexene Hydroconversion ‐Part 3‐ Pd/H‐ZSM‐5 Catalysts

Cyclohexene (CHE) hydroconversion was performed in a flow reactor at atmospheric pressure and temperatures of 50–400 °C using: Pd/H‐ZSM‐5, Pd/H‐ZSM‐5(HCl), and Pd/H‐ZSM‐5(HF) catalysts. These catalysts were characterized for acid site strength distribution via NH₃ TPD, Pd dispersion via H₂ chemisorption, TPR via reduction of the metal oxide in the catalysts and XRD for tracing crystallinity The hydroconversion steps proceeded as follows: CHE → Cyclohexane (CHA); CHE → Methylcyclopentenes (MCPEs) → Methylcyclopentane (MCPA); CHE → Cyclohexadienes (CHDEs) → Benzene → Alkylbenzenes; CHE and others → Hydrocrackedproducts. The overall hydroconversion of CHE was achieved in the catalyst order: Pd/H‐ZSM‐5 > Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). CHE hydrogenation step was the major reaction at low temperatures which significantly inhibited via HCl treatment, but slightly enhanced via HF treatment. At medium temperatures, on all catalysts, isomerisation to MCPEs and MCPA increase to a maximum then a decline with a further increase of temperature. The overall isomerisation of CHE was highest on the untreated catalyst. During the higher temperature range, dehydrogenation, alkylation and hydrocracking were increased with temperature. Dehydrogenation of CHE always yielded larger amounts of 1,3‐CHDE than 1,4‐CHDE. These cyclohexadienes were produced in the catalyst order: Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5. In general, benzene alkylation to toluene exceeded that of xylenes, indicating that the second methylation is more difficult than the first. However, the catalytic activities for benzene and toluene production were in the order: Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5(HF), whereas for xylenes production, Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). Intrapore diffusion plays an important role during the dehydrogenation reactions as well as during the interconversion of individual aromatic hydrocarbons.     

Effect of ketene additive and Si/Al ratio on the reaction of methanol over HZSM‐5 catalysts

The influence of ketene as possible intermediate for the reaction of methanol to aromatics was investigated over HZSM‐5 catalysts (Si/Al ratio of 15 and 9) using diketene‐acetone (2,2,6‐trimethyl‐4H‐1,3‐dioxin‐4‐one) as ketene precursor under atmospheric pressure at 300 °C. The physicochemical properties of HZSM‐5 catalysts were investigated by NH₃‐TPD, BET, XRD and ICP analysis. The distribution of products was measured by GC‐Mass spectrometer. These catalysts exhibit high reactivity and selectivity for the conversion of methanol and/or ketene to hydrocarbons (mostly high octane number xylenes, trimethylbenzenes, tetramethylbenzenes and ≤1.5% benzene). The conversion of neat diketene‐acetone over these catalysts produced aromatics compounds and significant amounts of oxygenated compounds (ketone, carboxylic acid, phenol, furan, pyran and others) depending on Si:Al ratio. These catalysts with high acid content produced small amount of saturated and unsaturated hydrocarbons without releasing significant amount of gas. The ketene and produced oxygenates from ketene appears to act as intermediates for the formation of aromatic compounds.     

A Symmetric Co(N5)2(H2O)4⋅4 H2O High‐Nitrogen Compound Formed by Cobalt(II) Cation Trapping of a Cyclo‐N5− Anion

The reactions of (N₅)₆(H₃O)₃(NH₄)₄Cl with Co(NO₃)₂⋅6 H₂O at room temperature yielded Co(N₅)₂(H₂O)₄⋅4 H₂O as an air‐stable orange metal complex. The structure, as determined by single‐crystal X‐ray diffraction, has two planar cyclo‐N₅⁻ rings and four bound water molecules symmetrically positioned around the central metal ion. Thermal analysis demonstrated the explosive properties of the material.     

Chromium complexes based on thiophene–imine ligands for ethylene oligomerization

A new set of Cr(III) complexes, {L}CrCl₃(THF), based on thiophene–imine ( 2a , L = PhOC₆H₄(N═CH)‐2‐SC₄H₃; 2b , L = PhOC₂H₄(N═CH)‐2‐SC₄H₃; 2c , L = Ph(NH)C₂H₄(N═CH)‐2‐SC₄H₃; 2d , L = PhOC₆H₄(N═CH)‐2‐SC₄H₂‐5‐Ph; 2e , L = Ph(NH)C₂H₄(N═CH)‐2‐SC₄H₂‐5‐Ph) have been prepared and characterized using elemental analysis and infrared spectroscopy. Upon activation with methylaluminoxane, all the chromium complexes generated active systems affording a nonselective distribution of α‐olefins with turnover frequencies in the range 9500–93 500 (mol ethylene) (mol Cr)^?1 h^?1, and producing mostly oligomers (95.0–99.3 wt% of total products). Small amounts of polymer were produced in these oligomerization reactions (0.8–8.2 wt%). The catalytic activities were quite sensitive to the ligand environment. Moreover, the effects of oligomerization parameters (temperature, [Al]/[Cr] molar ratio, time) on the activity and on the product distribution were examined.     

Epoxidation of cyclohexene with H2O2 over efficient water‐tolerant heterogeneous catalysts composed of mono‐substituted phosphotungstic acid on co‐functionalized SBA‐15

A series of Keggin‐type heteropolyacid‐based heterogeneous catalysts (Co‐/Fe‐/Cu‐POM‐octyl‐NH₃‐SBA‐15) were synthesized via immobilized transition metal mono‐ substituted phosphotungstic acids (Co‐/Fe‐/Cu‐POM) on octyl‐amino‐co‐functionalized mesoporous silica SBA‐15 (octyl‐NH₂‐SBA‐15). Characterization results indicated that Co‐/Fe‐/Cu‐POM units were highly dispersed in mesochannels of SBA‐15, and both types of Brønsted and Lewis acid sites existed in Co‐/Fe‐/Cu‐POM‐octyl‐NH₃‐SBA‐15 catalysts. Co‐POM‐octyl‐NH₃‐SBA‐15 catalyst showed excellent catalytic performance in H₂O₂‐mediated cyclohexene epoxidation with 83.8% of cyclohexene conversion, 92.8% of cyclohexene oxide selectivity, and 98/2 of epoxidation/allylic oxidation selectivity. The order of catalytic activity was Co‐POM‐octyl‐NH₃‐SBA‐15 > Fe‐POM‐octyl‐NH₃‐SBA‐15 > Cu‐POM‐octyl‐NH₃‐SBA‐15. In order to obtain insights into the role of ‐octyl moieties during catalysis, an octyl‐free catalyst (Co‐POM‐NH₃‐SBA‐15) was also synthesized. In comparison with Co‐POM‐NH₃‐SBA‐15, Co‐POM‐octyl‐NH₃‐SBA‐15 showed enhanced catalytic properties (viz. activity and selectivity) in cyclohexene epoxidation. Strong chemical bonding between ‐NH₃⁺ anchored on the surface of SBA‐15 and heteropolyanions resulted in excellent stability of Co‐POM‐octyl‐NH₃‐SBA‐15 catalyst, and it could be reused six times without considerable loss of activity.     

Synthesis, characterization, and spectroscopic studies of palladium(II) and silver(I) complexes of 4-methoxybenzoylmethylenetriphenylphosphorane and 4-fluorobenzoylmethylenetriphenylphosphorane

The reactions of 4-methoxybenzoylmethylenetriphenylphosphorane ylide (MOBPPY), {(Ph)₃PCHCOC₆H₄OMe}, and 4-flourobenzoylmethylenetriphenylphosphorane ylide (FBPPY) with [Pd(C₆H₄CH₂NH₂-κ²-C-N)ClL] (L = Py, 3-MePy, 4-MePy, or PPh₃), in equimolar ratios in CH₂Cl₂ yield [Pd(C₆H₄CH₂NH₂-κ²-C-N)L (Ye)]TfO [(L = PPh₃, Ye = MOBPPY; L = PPh₃, Ye = FBPPY; L = Py, Ye = MOBPPY; or L = 3-MePy, Ye = MOBPPY]. The reaction of MOBPPY with AgOTf (OTf = CF₃SO₃) in molar ratios (2:1) using dry acetone as solvent gives [Ag(MOBPPY)₂]OTf.     

Phosphatation of Zeolite H‐ZSM‐5: A Combined Microscopy and Spectroscopy Study

A variety of phosphated zeolite H‐ZSM‐5 samples are investigated by using a combination of Fourier transfer infrared (FTIR) spectroscopy, single pulse ²⁷Al, ²⁹Si, ³¹P, ¹H‐³¹P cross polarization (CP), ²⁷Al‐³¹P CP, and ²⁷Al 3Q magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, scanning transmission X‐ray microscopy (STXM) and N₂ physisorption. This approach leads to insights into the physicochemical processes that take place during phosphatation. Direct phosphatation of H‐ZSM‐5 promotes zeolite aggregation, as phosphorus does not penetrate deep into the zeolite material and is mostly found on and close to the outer surface of the zeolite, acting as a glue. Phosphatation of pre‐steamed H‐ZSM‐5 gives rise to the formation of a crystalline tridymite AlPO₄ phase, which is found in the mesopores of dealuminated H‐ZSM‐5. Framework aluminum species interacting with phosphorus are not affected by hydrothermal treatment. Dealuminated H‐ZSM‐5, containing AlPO₄, retains relatively more framework Al atoms and acid sites during hydrothermal treatment than directly phosphated H‐ZSM‐5.     

Eco-friendly non-acid intercalation and exfoliation of graphite to graphene nanosheets in the binary-peroxidant system for EMI shielding

The development of the preparation strategy for high-quality and large-size graphene via eco-friendly routes is still a challenging issue. Herein, we have successfully developed a novel route to chemically exfoliate natural graphite into high-quality and large-size graphene in a binary-peroxidant system. This system is composed of urea peroxide (CO(NH₂)₂⋅H₂O₂) and hydrogen peroxide (H₂O₂), where CO(NH₂)₂⋅H₂O₂ is used in preparing graphene for the first time. Benefiting from the complete decomposition of CO(NH₂)₂⋅H₂O₂ and H₂O₂ into gaseous species under microwave (MW) irradiation, no water-washing and effluent-treatment are needed in this chemical exfoliation procedure, thus the preparation of graphene in an eco-friendly way is realized. The resultant graphene behaves a large-size, high-quality and few-layer feature with a yield of ~100%. Then 4 µm-thick ultrathin graphene paper fabricated from the as-exfoliated graphene is used as an electromagnetic interference (EMI) shielding material. And its absolute effectiveness of EMI shielding (SSE/t) is up to 34,176.9 dB cm²/g, which is, to the best of our knowledge, among the highest values so far reported for typical EMI shielding materials. The EMI shielding performance demonstrates a great application potential of graphene paper in meeting the ever-increasingly EMI shielding demands in miniaturized electronic devices.     

Catalytic Performance of Modified HMCM‐22 Catalysts in Xylene Isomerization

HMCM‐22 catalysts modified with La₂O₃ (5% La) and MgO (≈0.87% Mg) were prepared respectively by impregnation method, and were characterized by scanning electron microscopy, X‐ray diffraction, N₂ physical adsorption‐desorption and temperature‐programmed desorption of NH₃. The effect of supported metallic oxides (La₂O₃, MgO) on catalytic performance in xylene isomerization of C8 aromatics (ethylbenzene, m‐xylene and o‐xylene) was investigated in detail. The experimental results showed that 5% La/HMCM‐22 catalyst had higher isomerization activity and stronger shape‐selectivity than 0.87% Mg/HMCM‐22 catalyst, owing to its more acid sites and smaller pore size. And the loading amount of La was optimized to be about 7%. Moreover, supporting metal over 7% La/HMCM‐22, respectively with 0.3% Pt, 3% Ni and 3% Mo, was carried out to prepare bifunctional isomerization catalysts. In comparison, 3% Mo/7% La/HMCM‐22 showed the best catalytic performance with both high activity and high selectivity, with the low hydrocracking of m‐xylene and o‐xylene. Besides, the optimal reaction conditions were found: 340°C, 1.5 MPa H₂, WHSV 4 h^?1 and H₂/C8 4 mol/mol. Under the above conditions, ethylbenzene conversion was up to 20%, para‐selectivity was over 23% with low xylene loss of 2.9%.     

Influence of Metallic Modification on Ethylbenzene Dealkylation over ZSM‐5 Zeolites

A series of metal‐modified HZSM‐5 catalysts were prepared by impregnation and were used for ethylbenzene dealkylation of the mixed C8 aromatics (ethylbenzene, m‐xylene and o‐xylene). The effects of different supported metals (Pt, Pd, Ni, Mo) on catalytic performance, including reaction conditions, were investigated. The physicochemical properties of catalysts were characterized by means of XRD, BET, TEM and NH₃‐TPD. Experimental results showed that metallic modification obviously increased the ethylbenzene conversion and reduced the coke deposition, greatly improving the catalyst stability. The distinction of ethylbenzene conversion depended on the interaction between hydrogenation reactivity and acidic cracking of bifunctional metal‐modified zeolites. Compared with Pt and Ni, Pd and Mo were easier to disperse into HZSM‐5 micropores during loading metals. The acidic density of different metal‐modified HZSM‐5 declined in the following order: HZSM‐5>Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. The activity of ethylene hydrogenation decreased with Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. In comparison, Pd/HZSM‐5 showed the best catalytic performance with both high activity and high selectivity, with less cracking loss of m‐xylene and o‐xylene. Moreover, the following reaction conditions were found to be preferable for ethylbenzene dealkylation over Pd/HZSM‐5: 340°C, 1.5 MPa H₂, WHSV 4 h^?1, H₂/C8 4 mol/mol.     

Monophosphine‐substituted diiron azadithiolate complexes: New syntheses,characterization and electrochemical properties

Investigating the synthesis and properties of diiron azadithiolate complexes is one of the key topics for mimicking the active site of [FeFe]‐hydrogenases, which might be very useful for the design of new efficient catalysts for hydrogen production and the development of a future hydrogen economy. A series of new phosphine‐substituted diiron azadithiolate complexes as models for the active site of [FeFe]‐hydrogenases are described. A novel and efficient way was firstly established for the preparation of phosphine‐substituted diiron azadithiolate complexes. The reaction of Fe₂(μ‐SH)₂(CO)₆ and phosphine ligands L affords the intermediate Fe₂(μ‐SH)₂(CO)₅L ( A ). The intermediate reacts in situ with a premixed solution of paraformaldehyde and ammonium carbonate to produce the target phosphine‐substituted diiron azadithiolate complexes Fe₂[(μ‐SCH₂)₂NH](CO)₅L ( 1a – 1f ) (L = P(C₆H₄–4‐CH₃)₃, P(C₆H₄–3‐CH₃)₃, P(C₆H₄–4‐F)₃, P(C₆H₄–3‐F)₃, P(2‐C₄H₃O)₃, PPh₂(OCH₂CH₃)). Furthermore, reactions of the intermediate A with I‐4‐C₆H₄N(CH₂Cl)₂ in the presence of Et₃N give the phosphine‐substituted diiron azadithiolate complexes Fe₂[(μ‐SCH₂)₂NC₆H₄–4‐I](CO)₅L ( 2a – 2e ) (L = P(C₆H₄–4‐CH₃)₃, P(C₆H₄–3‐CH₃)₃, P(C₆H₄–4‐F)₃, P(C₆H₄–3‐F)₃, P(2‐C₄H₃O)₃). All the complexes were fully characterized using elemental analysis, IR and NMR spectroscopies and, particularly for 1a , 1c – 1e , 2a and 2c , single‐crystal X‐ray diffraction analysis. In addition, complexes 1a – 1f and 2a – 2e were found to be catalysts for H₂ production under electrochemical conditions. Density functional theory calculations were performed for the reactions of Fe₂(μ‐SH)₂(CO)₆ + P(C₆H₄–4‐CH₃)₃.     

Theoretical study of the adsorption of ethylene on alkali‐exchanged zeolites

The structures of alkali‐exchanged faujasite (X–FAU, X = Li⁺ or Na⁺ ion) and ZSM‐5 (Li–ZSM‐5) zeolites and their interactions with ethylene have been investigated by means of quantum cluster and embedded cluster approaches at the B3LYP/6‐31G(d, p) level of theory. Inclusion of the Madelung potential from the zeolite framework has a significant effect on the structure and interaction energies of the adsorption complexes and leads to differentiation of different types of zeolites (ZSM‐5 and FAU) that cannot be drawn from a typical quantum cluster model, H₃SiO(X)Al(OH)₂OSiH₃. The Li–ZSM‐5 zeolite is predicted to have a higher Lewis acidity and thus higher ethylene adsorption energy than the Li–FAU zeolites (16.4 vs. 14.4 kcal/mol), in good agreement with the known acidity trend of these two zeolites. On the other hand, the cluster models give virtually the same adsorption energies for both zeolite complexes (8.9 vs. 9.1 kcal/mol). For the larger cation‐exchanged Na–FAU complex, the adsorption energy (11.6 kcal/mol) is predicted to be lower than that of Li–FAU zeolites, which compares well with the experimental estimate of about 9.6 kcal/mol for ethylene adsorption on a less acidic Na–X zeolite. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 333–340, 2003     

Reversible Ammonium Ion Intercalation/de-intercalation with Crystal Water Promotion Effect in Layered VOPO4⋅2 H2O**

The non-metal NH₄⁺ carrier has attracted tremendous interests for aqueous energy storage owing to its light molar mass and fast diffusion in aqueous electrolytes. Previous study inferred that NH₄⁺ ion storage in layered VOPO₄⋅2 H₂O is impossible due to the removal of NH₄⁺ from NH₄VOPO₄ leads to a phase change inevitably. Herein, we update this cognition and demonstrated highly reversible intercalation/de-intercalation behavior of NH₄⁺ in layered VOPO₄⋅2 H₂O host. Satisfactory specific capacity of 154.6 mAh g⁻¹ at 0.1 A g⁻¹ and very stable discharge potential plateau at 0.4 V based on reference electrode was achieved in VOPO₄⋅2 H₂O. A rocking-chair ammonium-ion full cell with the VOPO₄⋅2 H₂O//2.0 M NH₄OTf//PTCDI configuration exhibited a specific capacity of 55 mAh g⁻¹, an average operating voltage of about 1.0 V and excellent long-term cycling stability over 500 cycles with a coulombic efficiency of ≈99 %. Theoretical DFT calculations suggest a unique crystal water substitution process by ammonium ion during the intercalation process. Our results provide new insight into the intercalation/de-intercalation of NH₄⁺ ions in layered hydrated phosphates through crystal water enhancement effect.     

Formation of Mesopores in USY Zeolites: A Case Revisited

Steaming of NH₄Y zeolite at 723 K and 873 K is accompanied by the formation of extra‐framework amorphous aluminosilicate and silica gel in addition to earlier observed extra‐framework aluminum species. Their occurrence is directly associated with the formation of mesopores. Bulk (intracrystalline) mesopores occur inside the crystallite nuclei and surface (intercrystalline) mesopores are located nearby the crystallite surface. Corrosion of the zeolite framework results in a loss of crystallinity and, consequently, decreased catalytic activity of the USY catalysts synthesized. Analysis of the reasons of mesopore formation may help to reduce these disadvantages.     

Screening heterogeneous catalysts for the pyrolysis of lignin

The pyrolytic conversion of pure lignin at 600 °C in flowing helium over five catalysts is described and compared to the control bed material, sand. Product distribution as char, liquid, and gas are described as well as the composition of the liquid and gas fractions. The catalysts examined were HZSM-5, KZSM-5, Al-MCM-41, solid phosphoric acid, and a hydrotreating catalyst, (Co/Mo/Al₂O₃). The sand yielded a liquid phase that was 97% oxygenated aromatics and a gas phase that was CO (18 vol%), CO₂ (16 vol%), and CH₄ (12 vol%). HZSM-5 was the best catalyst for producing a deoxygenated liquid fraction yielded almost equal amounts of simple aromatics (46.7%) and naphthalenic ring compounds (46.2%). The gas phase over this catalyst consisted of CO (22 vol%), CO₂ (14 vol%), H₂ (12 vol%), and CH₄ (10 vol%). The Co/Mo/Al₂O₃ hydrotreating catalyst yielded a liquid consisting of 21% aromatics, 4% naphthalenics, and 75% oxygenated aromatics and a gas phase that was rich in hydrogen: H₂ (18 vol%), CO₂ (16 vol%), CO (12 vol%), and CH₄ (8 vol%).     

A Comparison of NO Reduction Over Mn–Cu/ZSM5 and Mn–Cu/MWCNTs Catalysts Assisted by Plasma at Ambient Temperature

Manganese–copper bimetal oxide catalysts supported on ZSM5 and acid-treated multi-walled carbon nanotubes (MWCNTs) were produced by incipient wetness impregnation for selective catalytic reduction of NO with dielectric barrier discharge plasma. Plasma can activate molecules even at ambient temperature, generating active oxygen species such as O, O₃, and HO₂ radicals, which can oxidize NO to NO₂ effectively. The SCR activity of Mn–Cu/MWCNTs was studied and compared to that of the Mn–Cu/ZSM5. The obtained samples were characterized by XRD, SEM, TEM, ICP, H₂-TPR, Raman spectroscopy, and XPS. The results show that Mn–Cu/MWCNTs catalyst possesses NO removal activity superior to that of the Mn–Cu/ZSM5 catalyst. MWCNTs-based catalyst attains NO removal efficiency of 88% at 480 J/L, while the ZSM5-supported catalyst achieves NO removal efficiency of 82% at the same energy density. The oxygen content increased from 3.33 to 19.07% on the nanotube surface after introducing Mn and Cu, which almost remained unchanged on ZSM5. The oxygen-containing functionalities are important for NO_x adsorption and removal. Moreover, the characterization revealed that CuO is the main phase of copper oxide, but copper dispersion decreases on Mn–Cu/ZSM5 surface because of the formation of copper dimer species. The manganese is well-dispersed on the catalysts, MnO₂ and Mn₂O₃ contents of Mn–Cu/MWCNTs are larger than that of Mn–Cu/ZSM5, MnO₂ is the predominant phase of manganese oxide.     

Preparation of new dinuclear half-titanocene complexes with ortho- and meta-xylene linkages and investigation of styrene polymerization

Half-titanocene is well-known as an excellent catalyst for the preparation of SPS (syndiotactic polystyrene) when activated with methylaluminoxane (MAO). Dinuclear half-sandwich complexes of titanium bearing a xylene bridge, (TiCl₂L)₂{(μ-η⁵, η⁵-C₅H₄-ortho-(CH₂–C₆H₄–CH₂)C₅H₄}, (4 (L = Cl), 7 (L = O-2,6-iPr₂C₆H₃)) and (TiCl₂L)₂{(μ-η⁵, η⁵-C₅H₄-meta-(CH₂–C₆H₄–CH₂)C₅H₄} (5 (L = Cl), 8(L = O-2,6-iPr₂C₆H₃)), have been successfully synthesized and introduced for styrene polymerization. The catalysts were characterized by ¹H- and ¹³C NMR, and elemental analysis. These catalysts were found to be effective in forming SPS in combination with MAO. The activities of the catalysts with rigid ortho- and meta-xylene bridges were higher than those of catalysts with flexible pentamethylene bridges. The catalytic activity of four dinuclear half-titanocenes increased in the order of 4 < 5 < 7 < 8. This result displays that the meta-xylene bridged catalyst is more active than the ortho-xylene bridged and that the aryloxo group at the titanium center is more effective at promoting catalyst activity compared to the chloride group at the titanium center. Temperature and ratio of [Al]:[Ti] had significant effects on catalytic activity. Polymerizations were conducted at three different temperatures (25, 40, and 70 °C) with variation in the [Al]:[Ti] ratio from 2000 to 4000. It was observed that activity of the catalysts increased with increasing temperature, as well as higher [Al]:[Ti]. Different xylene linkage patterns (ortho and meta) were recognized to be a principal factor leading to the characteristics of the dinuclear catalyst due to its different spatial arrangement, causing dissimilar intramolecular interactions between the two active sites.     

Ruthenium bidentate phosphine complexes for the coordination and catalytic dehydrogenation of amine- and phosphine-boranes

Addition of the amine–boranes H₃B ? NH₂tBu, H₃B ? NHMe₂ and H₃B ? NH₃ to the cationic ruthenium fragment [Ru(xantphos)(PPh₃)(OH₂)H][BAr^F₄] ( 2 ; xantphos=4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene; BAr^F₄=[B{3,5‐(CF₃)₂C₆H₃}₄]^?) affords the η¹‐B? H bound amine–borane complexes [Ru(xantphos)(PPh₃)(H₃B ? NH₂tBu)H][BAr^F₄] ( 5 ), [Ru(xantphos)(PPh₃)(H₃B ? NHMe₂)H][BAr^F₄] ( 6 ) and [Ru(xantphos)(PPh₃)(H₃B ? NH₃)H][BAr^F₄] ( 7 ). The X‐ray crystal structures of 5 and 7 have been determined with [BAr^F₄] and [BPh₄] anions, respectively. Treatment of 2 with H₃B ? PHPh₂ resulted in quite different behaviour, with cleavage of the B? P interaction taking place to generate the structurally characterised bis‐secondary phosphine complex [Ru(xantphos)(PHPh₂)₂H][BPh₄] ( 9 ). The xantphos complexes 2 , 5 and 9 proved to be poor precursors for the catalytic dehydrogenation of H₃B ? NHMe₂. While the dppf species (dppf=1,1′‐bis(diphenylphosphino)ferrocene) [Ru(dppf)(PPh₃)HCl] ( 3 ) and [Ru(dppf)(η⁶‐C₆H₅PPh₂)H][BAr^F₄] ( 4 ) showed better, but still moderate activity, the agostic‐stabilised N‐heterocyclic carbene derivative [Ru(dppf)(ICy)HCl] ( 12 ; ICy=1,3‐dicyclohexylimidazol‐2‐ylidene) proved to be the most efficient catalyst with a turnover number of 76 h^?1 at room temperature.