Synthesis of atactic polypropylene: Propylene polymerization reactions with TiCl4–Al(C2H5)2Cl/Mg(C4H9)2 catalyst

The Ziegler catalyst, a combination of TiCl₄ and Al(C₂H₅)₂Cl, is a very poor catalyst for propylene polymerization. However, the addition of Mg(C₄H₉)₂ to the Ziegler catalyst at a [Mg]:[Al] molar ratio < 0.5 leads to the formation of a potent catalyst system for homopolymerization of propylene. Polymers produced with the TiCl₄–Al(C₂H₅)₂Cl/Mg(C₄H₉)₂ catalyst are mostly atactic and amorphous, their minor partially crystalline isotactic components constitute merely 5–10% of the combined polymer material. Principal advantages of the TiCl₄–Al(C₂H₅)₂Cl/Mg(C₄H₉)₂ catalyst for the manufacture of atactic PP include high activity, low cost, and the ease of use: the catalyst is prepared in situ from three commercially available components. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47692.     

The second life of Ziegler catalyst. Ethylene polymerization reactions with TiCl4–Al[C2H5]2Cl/Mg(C4H9)2 catalyst

The Ziegler catalyst, a combination of TiCl₄ and Al(C₂H₅)₂Cl, was widely used since 1950s for the commercial manufacture of linear polyethylene. We found that addition of Mg(C₄H₉)₂ to this catalyst at [Al]:[Mg]_molar > 2 leads to the formation of a very active catalyst system for homopolymerization of ethylene and for copolymerization of ethylene and 1-alkenes. The principal advantages of the ternary TiCl₄–Al(C₂H₅)₂Cl/Mg(C₄H₉)₂ catalyst are very high activity (six to seven times higher than the activity of the original Ziegler catalyst), low cost, and the ease of use: the catalyst is prepared in situ from three commercially available cheap compounds soluble in aliphatic and aromatic hydrocarbons. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47340.     

Synthesis and characterization of the first [Q]+[PhTeX4]− complex salt (Q=2-Br–C5NH5; Ph=C6H5; X=Br,I) exhibiting a polymeric chain structure

The reaction of diphenylditelluride with 2-bromopyridine in hydrobromide or hydroiodide acid affords the tetrahalophenyltellurate(IV) [2-Br–C₅NH₅][PhTeX₄] (X=Br and I). The structures of the two salts were characterised by single crystal X-ray diffractometry. The anionic units show a square pyramidal geometry about the tellurium atoms with the phenyl rings in the apical positions. Secondary, interanionic Te⋯X bonds as well as cation–anion H–X interactions hold the moieties in polymeric chains with an octahedral configuration about each tellurium center along the crystal lattice.     

Formation of Mg(OH)2 in Mg–Ni–Fe2O3 alloys prepared using reactive mechanical grinding

Nickel and purchased Fe₂O₃ or Fe₂O₃ synthesized by spray conversion were added to Mg via reactive mechanical grinding (mechanical grinding in H₂). Samples with compositions of 71.5 wt%Mg–23.5 wt%Ni–5 wt%Fe₂O₃ (purchased) and 71.5 wt%Mg–23.5 wt%Ni–5 wt%Fe₂O₃ (synthesized by spray conversion) were prepared, and the phase changes in the samples were examined using X-ray diffraction analysis following hydriding–dehydriding cycling, as well as following reactive mechanical grinding. Both samples contained an Mg(OH)₂ phase after hydriding–dehydriding cycling, as well as after reactive mechanical grinding. To the best of our knowledge, the formation of Mg(OH)₂ phase is not reported in Mg-Ni-Fe₂O₃ system hydrogen storage materials.     

XAFS characterization of the binuclear iron complex in overexchanged Fe/ZSM5 – structure and reactivity

We have characterized, with emphasis on XAFS spectroscopy, one of the most promising DeNOx catalysts, i.e., Fe/ZSM5 prepared through the FeCl₃sublimation technique. XAFS is a very useful tool for this purpose since it is element specific and can be used in situ, namely, in the presence of the reactants and at reaction temperature. In this communication it will be pointed out that the as-synthesized Fe/ZSM5 catalyst contains stable binuclear iron oxo/hydroxo-complexes. The reaction of these complexes with the probe molecule CO clearly shows that only one of the oxygen shells around iron changes while the iron contribution is not affected, the iron complex remaining binuclear. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of highly isotactic poly 1-hexene using Fe-doped Mg(OEt)2/TiCl4/ED Ziegler–Natta catalytic system

In this article, polymerization of 1-hexene with FeCl_3-doped Mg(OET)₂/TiCl₄/electron donor (ED) catalytic system is presented. For this purpose, first a number of TiCl₄ catalysts supported on Mg(OEt)₂ and Fe-doped Mg(OEt)₂ supports were prepared with ethylbenzoate or dibutylphthalate as the internal EDs. After successive catalysts synthesis, they were employed in 1-hexene polymerization using cyclohexyl methyl dimethoxysilane as external ED as well as without it. The catalysts activity and molecular weight distribution (MWD) of poly 1-hexenes (PHs) were influenced strongly by both FeCl₃ doping and donor presence so that a remarkable increase in the catalyst activity was seen in doped catalysts. Deconvolution of MWD curves revealed that increase in the type of active centers by introducing FeCl₃ into the support should be responsible for the broadening of MWD of PHs. ¹³CNMR analysis indicated that while isotacticity does not change considerably by Fe doping, EDs increase its amount as high as 8–21%. Second, the stereoselective behavior of active Ti species in doped and undoped catalysts was fully explored by molecular modeling using density functional theory (DFT) method. Finally, with the aid of rheological measurements, the processability of polymers were evaluated and then the gel permeation chromatography (GPC) results were approved through the values obtained from model fitting as well as changes in moduli crossover modulus.     

Structure of a biologically active binuclear palladium complex in the compound bis(bis[(μ<Subscript>2</Subscript>-2-chloroethylammonium) (1,10-phenanthroline)-palladium(I)]) · octanitrates · dihydrates

The structure of a biologically active binuclear palladium complex, namely, [(1,10-phenanthroline) Pd(μ₂-2-chloroethylammonium) ₂ ⁴⁺ · 4NO ₃ ^? · H₂O, has been determined using X-ray diffraction analysis. The compound crystallizes in the monoclinic system, space group of symmetry Cc, with the unit cell parameters a = 24.527(3) Å, b = 13.097(1) Å, c = 22.651(3) Å, β = 104.23(1)°, V = 7052(2) ų, Z = 8, and ρ = 1.88 g/cm³. The final discrepancy factor is R1 = 0.0316 for 15581 symmetrically nonequivalent reflections with I ≥ 2σ(I), wR2 = 0.0513, and GooF = 1.047. The palladium atoms reside in the oxidation state of 1+, which is rarely encountered in organometallic compounds. The asymmetric part of the unit cell contains two chemically equivalent but crystallographically independent positively charged binuclear palladium complexes, eight NO ₃ ^? anions, and two water molecules. The π-π stacking interaction between the nearest 1,10-phenanthroline rings of the neighboring layers takes place. Moreover, the interlayer and intralayer interactions occur through electrostatic interaction forces and a complex three-dimensional system of hydrogen bonds, which are formed by water molecules and N ₃ ⁺ groups.     

The formation of [RuCl(p-cymene)(Me2HPz)(PPh2OR)]Cl (Me2HPz=3, 5-dimethylpyrazole; R=H,Me and p-Tol) complexes from the cleavage of the P–N bond of a P-coordinated P(Me2Pz)Ph2 ligand by ROH molecules in a ruthenium(II) complex. Crystal structure of [RuCl(p-cymene)(Me2HPz)(PPh2OH)]Cl

The complex [RuCl₂(p-cymene)]₂ reacts with 1-(3,5-dimethyl)pyrazolyldiphenylphosphine (P(Me₂Pz)Ph₂) to give the complex RuCl₂(p-cymene)(P(Me₂Pz)Ph₂). This compound reacts with ROH molecules (R=H, Me and p-Tol) to give [RuCl(p-cymene)(Me₂HPz)(PPh₂OR)]Cl (R=H, Me and p-Tol) complexes, which contain both Me₂HPz and PPh₂OR coordinated molecules.     

Synthesis of ZrB2–SiC–ZrC nanocomposite by spark plasma in ZrSiO4/B2O3/C/Mg system

A novel reduction process by spark plasma is proposed for the synthesis of homogeneous intermixed ZrB₂–SiC–ZrC nanostructure powder using ZrSiO₄, B₂O_3, C and Mg as starting materials. In the present research, the reaction mechanisms were investigated by the displacement–temperature–time (DTT), the displacement rate–temperature and the displacement rate–time diagrams which were obtained during spark plasma cycles. The synthesis process of the composite was completed after 15 min at temperature of 400 °C. The total shrinkage of 5.5 mm was observed due to the rearrangement and reaction phenomenon. The main shrinkage occurs within a period of less than 1 min at 400 °C similar to the self propagating high temperature synthesis. Finally using Rietveld method, the mean crystallites sizes of about 26, 25 and 22 nm were calculated for ZrB₂, SiC and ZrC phases, respectively.     

Formation mechanism of whiskers in Al–MgAl2O4–MgO refractories at 1400 °C under N2 atmosphere

Al–MgAl₂O₄–MgO refractories were prepared using fused magnesia, metal Al, fused spinel and sintered high purity magnesia as raw materials. The phase composition and microstructure of Al–MgAl₂O₄–MgO refractories treated at 1400 °C under N₂ atmosphere were investigated by means of XRD, SEM and EDS. The results showed that magnesia (MgO) whiskers and MgAlON whiskers were formed on the surface and in the inner area of the Al–MgAl₂O₄–MgO refractories, respectively. The MgO whiskers grew preferentially along the axial direction, forming cylindrical shape MgO whiskers. Then the cylindrical MgO whiskers further absorbed Mg(g) and O₂(g), and grew along the radial direction to form the square columnar shape MgO whiskers. The MgAlON whiskers firstly grew in one-dimensional direction, forming whisker shape MgAlON, then some whisker shape MgAlON gradually developed and grew into two-dimensional flake shape MgAlON. The sintering and thermal shock resistance was significantly improved by the whiskers. The growth process of magnesia whiskers and MgAlON whiskers were dominated by a vapor-solid (VS) mechanism.     

Combustion synthesis and electrophysical properties of hollandites of the system K2O–MeO–TiO2 (Me = Mg,Ni, Cu)

Hollandite-based ceramics are mainly produced by the traditional solid-phase method. However, the use of “wet” chemistry can improve its morphological characteristics, increase porosity, etc., as well as change the electrophysical properties. In this study complex oxides with hollandite-type structure in the system K₂O–MeO–TiO₂ (Me = Mg, Ni, Cu) were synthesized by combustion of citrate–nitrate compositions (a special case of the sol–gel method). The structure of obtained material was studied using the XRD and SEM analysis. While studying the electrophysical properties, it was found that in a stream of hydrogen, the electrical conductivity of hollandites with magnesium and nickel increases significantly (by 2–3 orders of magnitude) over the entire studied temperature range. Thus, ceramics based on these hollandites can be used to create hydrogen sensors.     

Ca(BH4)2 as a simple tool for the preparation of thorium and uranium metallocene borohydride complexes: First synthesis and crystal structure of (C5Me5)2Th(η3-H3BH)2

Calcium borohydride allows for the high-yielding synthesis of (C₅Me₅)₂An(η³-H₃BH)₂ (An = Th, U) by reaction with (C₅Me₅)₂AnCl₂ (An = Th, U). While a preparative synthesis of (C₅Me₅)₂U(η³-H₃BH)₂ has been previously reported in the literature using K(C₅Me₅) and U(BH₄)₄, the use of Ca(BH₄)₂ is higher yielding and mild. Full characterization of the novel compound (C₅Me₅)₂Th(η³-H₃BH)₂ is presented.     

Insights in the sol–gel processing of Pb(Mg1/3Nb2/3)O3. The synthesis and crown structure of a new lead magnesium cluster: Pb6Mg12(μ-OAc)6(μ2,η2-OAc)18(μ3,η2-OC2H4OPri)12

The synthesis and molecular structure of a Pb–Mg bimetallic acetatoalkoxide (Pb₆Mg₁₂(μ-OAc)₆(μ₂,η²-OAc)₁₈(μ₃,η²-OC₂H₄OPrⁱ)₁₂, space group R-3, a=b=30.032(2), c=18.855(2) Å, α=β=90°, γ=120°) are discussed in this article. This compound was isolated as an intermediate during the elaboration of Pb(Mg_1/3Nb_2/3)O₃ (PMN) using sol–gel process. It results from the reaction of a bimetallic Mg/Nb species with lead acetate in 2-isopropoxyethanol.     

Syndiospecific styrene polymerization by (tert-BuC5H4)TiCl2(O-2,6-iPr2C6H3) – borate catalyst system

(^tBuC₅H₄)TiCl₂(O-2,6-ⁱPr₂C₆H₃) (2) exhibited relatively high catalytic activity for syndiospecific polymerization of styrene at 25 °C if both [PhMe₂NH]B(C₆F₅)₄ and a mixture of AlⁱBu₃/Al(n-C₈H₁₇)₃ were used as the cocatalyst. Effects of both organoaluminum and organoboron compounds were explored, and the effect of cocatalyst was different from that observed in 1-hexene polymerization catalyzed by Cp*TiCl₂(O-2,6-ⁱPr₂C₆H₃) (1). Resultant syndiotactic polystyrene possessed narrow molecular weight distribution under the optimized conditions, and the M_w values were unchanged during the time course.     

Substitution of chlorides by l-methionine in the dinuclear [Pt2(8NNpy)Cl4] complex in DMF–water solution

Reaction between dinuclear [Pt₂(8NNpy)Cl₄] complex and l-methionine (Met) has been studied spectrophotometrically in DMF–water (1:1 by volume) medium (DMF = N,N-dimethylformamide). Such medium results from the complex insolubility at purely aqueous solutions. Only one step of the reaction can be observed in an hour-timescale. Rate constants for the reversible first step of the reaction (k₁ (forward) and k₂[Cl⁻] (backward)) and activation parameters have been determined. A negative ΔS^≠ confirms the associative character of the process. The results show a huge influence of the incoming nucleophile size and structure on the reaction rate. A qualitative extrapolation of the results into ‘pure’ aqueous conditions suggests that the chlorides in the complex can be substituted at aqueous medium faster than in the case of cisplatin, which results from the presence of the π-acceptor ligands in the coordination sphere of [Pt₂(8NNpy)Cl₄] complex.     

Theoretical study of the reactive intermediate Si2Me4[(η5-C5H4) Fe(CO)2] 2 2−

In two previous papers (Kinget al., J. Organomet. Chem. 19, 327, 1969; Pannellet al., Organometallics 9, 859, 1990), the synthesis and X-ray structure of the two tetramethyl disilyl complexes [(η⁵-C₅H₅) Fe(CO)₂]₂Si₂Me₄ (I) and Si₂Me₄[(η⁵-C₅H₄) Fe(CO)₂CH₃]₂ (II) were reported. ComplexII is obtained fromI [2]. However, attempts to form other derivatives fromI have generally failed. In the chemical process to getII fromI, an intermediate complex, Si₂Me₄[(η⁵-C₅H₄) Fe(CO)₂] ₂ ^2? (III), is probably formed. This is similar to complexII without the two methyl groups bonded to the Fe atoms. Therefore, a theoretical study that may shed some light on the intermediate structure, stability, and reactivity is justified. We have developed theoretical studies consisting of extended Huckel electronic structure calculations on the simulated intermediate geometry. The results obtained from these calculations suggest that it might be stable enough to form during reactions of complexI. The more reactive sites, which suggest reaction alternatives, are pointed out.     

Semi-rigid N-para-ferrocenyl(benzoyl)amino-acid esters for biomaterials: synthesis and characterization of Fc-C6H4CONHCH(R)CO2Me where Fc = (η5-C5H5)Fe(η5-C5H4) and R=H,CH3,CH2CH(CH3)2,CH2C6H5 and the X-ray crystal structures of Fc-C6H4CO2Me and the l-alanine derivative Fc-C6H4CONHCH(CH3)CO2Me

A series of N-para-(ferrocenyl)benzoyl amino-acid esters, para-Fc(C₆H₄)CONHCH(R)CO₂CH₃ {Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄); R = H, CH₃, CH₂CH(CH₃)₂, CH₂C₆H₅}, 3–6 have been prepared by coupling para-(ferrocenyl)benzoic acid to the amino-acid esters (gly, l-Ala, l-Leu, l-Phe) using the standard 1,3-dicyclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBt) protocol. The compounds were fully characterized by a range of spectroscopic techniques including FAB-MS. The X-ray crystal structures of the parent para-(ferrocenyl)benzoyl methyl ester, Fc-C₆H₄CO₂Me, 1 and a chiral derivative N-{para-(ferrocenyl)benzoyl}-l-alanine methyl ester, Fc-C₆H₄CONHCH(CH₃)CO₂Me, 4 have been determined.