Metal complexes in catalytic transformation of olefins. 7. Characteristics of active centers and the mechanism of dimerization of ethylene to butene-1 and polymerization of acetylene in the Ti(O-n-Bu)4-AlEt3 catalytic system in ethers

The formation and properties of active centers were studied in the dimerization of ethylene and polymerization of acetylene in the Ti(O-n-Bu)₄-AlEt₃ system, in heteroatomic solvents. The absence of ionic stages in the dimerization in dibutyl ether was established. Reaction of ethylene, acetylene (A), and phenylacetylene (PA) with the paramagnetic Ti(I) complex, producing butene-1 or polyacetylenes, a paramagnetic complex, and diamagnetic products, was established for the first time. The effect of such factors as T, [Ti]₀, Al/Ti, and M/Ti on consumption and accumulation kinetics of paramagnetic products was studied. Formation of a carbon-centered radical, produced by A or PA joining Ti(I) in the oxidation process, and whose further transformations cause derivation of all the above-mentioned products, was suggested. A probable mechanism was suggested for dimerization of ethylene to butene-1, with intermediate formation of titanacycles.Deceased.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1526–1535, July, 1992.     

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene,propylene homopolymerizations,and their copolymerization

A series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac‐Et(Ind)₂ZrCl₂/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2‐thiophenecarbonyl chloride to label a 2‐thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C^*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C^*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C^*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C^*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C^*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (k_p) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 867–875     

A theoretical study of catalytic hydration reactions of ethylene

The hydration reaction of ethylene, C₂H₄+H₂O → C₂H₅OH, catalyzed by oxoacids (H₃PO₄, H₂SO₄, and HClO₄) and metal cations (B³⁺, Al³⁺, Sc³⁺, Ga³⁺, La³⁺, Be²⁺, Mg²⁺, Ca²⁺, Zn²⁺, and Sr²⁺) are studied systematically by density functional theory with a BLYP functional. The reaction profiles of the main reaction and some side reactions, such as ester formation, dimerization of ethylene, and dehydrogenation of ethanol, have been determined with a variety of catalysts. In each case, the intermediate states, the transition states, and their energetics are calculated. Metal cations react more efficiently for the main reaction than oxoacids, but they also make the dehydrogenation reaction active. While the dimerization reaction is strongly affected by the acidity of the catalyst, both the acidity and basicity of the catalyst are important for the dehydrogenation reaction. Efficient formation of ethanol from ethylene over a catalyst is suggested. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1292–1304, 2000     

Synthesis of a new salphen‐type titanium complex and its application in ethylene polymerization and copolymerization

TiCl₂[salphen(di‐tBu)] was synthesized, characterized and employed as pre‐catalyst in ethylene homo‐ and copolymerization with propylene, 1‐octene and 10‐undecen‐1‐ol. X‐ray diffraction study on the titanium complex revealed a distorted octahedral coordination of the central metal with a trans‐Cl, cis‐O, cis‐N arrangement. The complex combined with MAO afforded moderate catalytic activities in ethylene polymerization. Furthermore the catalyst not only copolymerized ethylene with apolar monomer (propylene and 1‐octene), but also possessed significant capability of incorporation with polar monomer (10‐undecen‐1‐ol). Only single insertion of 1‐octene unit in ethylene‐co‐1‐octene polymer was detected by ¹³C NMR spectrum. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of new amphiphilic diblock copolymers containing poly(ethylene oxide) and poly(α‐olefin)

This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s‐PS), and elastomers, such as poly(ethylene‐co‐1‐octene) and poly(ethylene‐co‐styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ～270 °C to low glass‐transition temperature ～?60 °C. The chemistry involves two reaction steps, including the preparation of a borane group‐terminated polyolefin by the combination of a metallocene catalyst and a borane chain‐transfer agent as well as the interconversion of a borane terminal group to an anionic (? O^?K⁺) terminal group for the subsequent ring‐opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of α‐olefins to the ring‐opening polymerization of ethylene oxide. The well‐defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (M_w/M_n < 2.5), and absence of homopolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3416–3425, 2002     

Block copolymers prepared by emulsion polymerization with poly(ethylene oxide)–azo-initiators

Poly(ethylene oxide)-b-poly(styrene) block copolymers were prepared in the form of latex particles by emulsion polymerization of styrene with poly(ethylene glycol)–azo-initiators as well as with the redox initiation system poly(ethylene glycol)/Ce⁴⁺. The emulsion polymerization can be carried out in the absence of additional stabilizers if the chain length of the poly(ethylene glycol) is greater than 40. The latex particles as well as the copolymers were characterized by capillary hydrodynamic fractionation, ¹³C-nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy. By ¹³C-NMR spectroscopy a side reaction of the primary radicals arising from the azo-initiator was found which can contribute to the low efficiency of azo-initiators in emulsion polymerization.     

Preparation of Well‐Defined Diblock Copolymers with Short Polypeptide Segments by Polymerization of N‐Carboxy Anhydrides

Summary: The ring‐opening polymerization of N‐carboxy anhydrides (NCA) of γ‐benzyl‐L ‐glutamate and β‐benzyl‐L ‐aspartate was studied in the presence of an ammonium chloride‐functionalized poly(ethylene oxide) macroinitiator, which possibly prevents side reactions such as NCA deprotonation. Although polymerization initiated by such macroinitiators was found to be quite slow, well‐defined conjugates of poly(ethylene oxide)‐block‐poly(γ‐benzyl‐L ‐glutamate) and poly(ethylene oxide)‐block‐poly(β‐benzyl‐L ‐aspartate) with polydispersity indexes as low as 1.05 were prepared. Moreover, the presence of ammonium chloride chain ends significantly prevented end‐group cyclization of poly(γ‐benzyl‐L ‐glutamate) after polymerization.

Gel permeation chromatograms recorded for the diblock copolymers of poly(ethylene oxide)‐block‐poly(γ‐benzyl‐L ‐glutamate) prepared by N‐carboxy anhydride polymerization initiated either by PEO‐NH₂ macroinitiator or PEO‐NHequation/tex2gif-stack-1.gifCl⁻ macroinitiator.     

Influences of steric bulkiness in hydrotris(pyrazolyl)borate ligands on ethylene polymerization reaction

Manganese(II) complex catalysts with hydrotris(pyrazolyl)borate ligands have been examined on their catalytic performance in ethylene polymerization and ethylene/1‐hexene copolymerization. The activities of [Mn(L6)(Cl)(NCMe)] ( 1 ) and [Mn(L10)(Cl)] ( 2 ) activated by Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] for ethylene polymerization go up to 326 and 11 kg mol (cat^?1) h^?1, respectively, (L6^? = hydrotris(3‐phenyl‐5‐methyl‐1‐pyrazolyl)borate anion, L10^? = hydrotris(3‐adamantyl‐5‐isopropyl‐1‐pyrazolyl)borate anion). In particular, for ethylene/1‐hexene copolymerization, complex 1 gives high‐molecular‐weight poly(ethylene‐co‐1‐hexene)s with the highest M_w of 439,000 in manganese olefin polymerization catalyst systems. Moreover, the 1‐hexene incorporation by complex 1 seems more efficient than that by [Mn(L3)(Cl)] ( 4 ) (L3^? = hydrotris(3‐tertiary butyl‐5‐isopropyl‐1‐pyrazolyl)borate anion). In this work, we demonstrated that the coordination geometry and coordination number are also important factors for ethylene polymerization reaction as well as steric hindrances and ligand frameworks in our manganese(II) catalysts. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5720–5727, 2009     

Sonochemical synthesis of methyl-4-(hetero)arylmethylene isoxazole-5(4H)-ones using SnII-montmorillonite

Tin exchanged montmorillonite K10 (Sn^II-Mont K10) was prepared by ion exchange between SnCl₂ and montmorillonite K10. The Sn^II-Mont K10 was characterized by X-ray diffraction, scanning electron microscope and energy-dispersive X-ray spectroscopy. The synthesized Sn^II-Mont K10 was used as a recoverable solid catalyst for synthesis of 3-methyl-4-arylmethylene isoxazole-5(4H)-ones via one-pot multicomponent cyclocondensation of hydroxylamine hydrochloride, ethyl acetoacetate and benzaldehyde derivatives in water under ultrasound irradiations. The yields of products were obtained 87–96%. The remarkable advantages of this method are a low-cost and eco-friendliness catalyst, rapid completion of the reactions, and avoidance of using organic solvents, excellent yield and mild conditions.     

Diffusion of ethylene glycol accompanied by reactions in poly(ethylene terephthalate) melts

Diffusion coefficients of ethylene glycol (EG) have been measured in poly(ethylene terephthlate) (PET) melts by a quartz-spring sorption apparatus. A simple mathematical model was developed to investigate the sorption behavior accompanied by chemical reactions of EG and PET at high temperatures. Diffusion coefficients are deduced from experimental data for an asymptotically thin sample in order to minimize the effects of reactions. The diffusion coefficient of EG is strongly dependent on the vapor pressure of EG and temperature but not on the molecular weight of PET in this experimental range (degree of polymerization 80–120). The diffusion coefficient of EG in PET melt at 265°C is 2.58 × 10^?7 cm²/s at the limit of zero concentration of EG. The activation energy for diffusion is 38.4 kcal/gmol, and the heat of solution for sorption is ?44.9 kcal/gmol. The concentrations of the volatile materials resulting from reactions in PET-EG system were analyzed with gas chromatography. In addition, a fit of the current model to experimental data yields frequency factors for the polymerization reaction (k₁) and the acetaldehyde formation reaction (k₂) to be 5.84 × 10⁸ cm³/mol ? min and 3.90 × 10¹¹ min^?1, respectively.     

Novel titanium complexes bearing two chelating phenoxy‐imine ligands and their catalytic performance for ethylene polymerization

Three substituted salicylaldimine ligands ( 1a, 2a, 3a ) and their titanium complexes bis[N‐(5‐nitrosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 1 ), bis[N‐(5‐chlorosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 2 ) and bis[N‐(5‐bromosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 3 ) were synthesized and characterized by mass spectra, ¹H NMR and elemental analyses, as well as complex 1 by X‐ray structure analysis. In the presence of methylaluminoxane (MAO), 1, 2 and 3 are efficient catalysts for ethylene polymerization in toluene. Under the conditions of T = 60 °C, p = 0.2 MPa, and n(MAO)/n(cat) = 1500, the activities of 1–3 reached 4.55–8.80 × 10⁶ g of PE (mol of Ti h bar)^?1, which is much higher than that of the unsubstituted complex bis[N‐(salicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 4 ). The viscosity‐average molecular weight of polyethylene ranged from 24.8 × 10⁴ to 44.9 × 10⁴ g/mol for 1–3 and the molecular weight distribution M_w/M_n from 1.85 to 2.34. The effects of reaction conditions on the polymerization were examined in detail. The increase in ethylene pressure and rise in polymerization temperature are favorable for 1–3 /MAO to rise the catalytic activity and the molecular weight of polyethylene. Copyright © 2007 John Wiley & Sons, Ltd.     

Nickel-based ethylene oligomerization catalysts supported by PNSiP ligands

A series of nickel (II) complexes bearing silicon bridged diphosphines ligands (PNSiP) have been synthesized and characterized. All nickel precatalysts, activated with ethylaluminum dichloride (EtAlCl₂), exhibited moderate to high activities for ethylene dimerization to butylene. The in situ nickel precatalysts formed by mixing N-cyclopentyl-N-((diphenylphosphanyl)dimethylsilyl)-1,1-diphenylphosphanamine (L2) with NiBr₂(DME) showed high catalytic activity (2.40 × 10⁸ g/(mol_Ni·h)) and high product selectivity (88.6%) towards butene using methylcyclohexane as solvent at 1.0 MPa ethylene pressure and 45°C temperature, no polyethylene(PE) was observed. Ligand backbone tuning of PNSiP-based catalytic systems help in precise understanding of steric bulk variation effects on catalytic performance.     

Preparation and reactivity of metal-containing monomers

Homo- and copolymerization of vanadium-containing monomers (VCM) have been studied. Radical homopolymerization of VCM is accompanied by some side reactions, such as monomer disproportionation, copolymerization with ligandin situ, cyclopolymerization, V⁵⁺V⁴⁺ reduction,etc. These reactions complicate the interpretation of the results obtained. The character of radical copolymerization of VCM with styrene or acrylonitrile is preferably radical complex. Catalytic properties of vanadium-containing homo- and copolymers (in combination with organoaluminum compounds as cocatalysts) in Ziegler-Natta ethylene polymerization have been studied. It has been shown that the products inherit the properties of immobilized polymer catalysts.For Part 39, seeIzv. Akad. Nauk, Ser. Khim., 1994, 1047 [Russ. Chem. Bull., 1994, 43, 983 (Engl. Transl.)].Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2139–2144, December, 1994.     

Binuclear titanium complexes coordinated by rigid p-phenylene linked bis-β-carbonylenamine: Synthesis,structure, ethylene polymerization and copolymerization with 1,5-hexadiene

Binuclear complexes for olefin polymerization have attracted great attention due to their unique catalytic properties compared with their mononuclear counterparts. Here a series of p-phenylene-bridgedbis-β-carbonylenamine ligands and their binuclear Ti complexes Ti ₂ L ¹ – Ti ₂ L ³ were prepared and characterized by ¹H NMR, ¹³C NMR, Fourier transform infrared spectroscopy, and elemental analysis. The binuclear complex Ti ₂ L ³ bearing an octylthio sidearm was further investigated by single-crystalX-ray diffraction, which revealed that the ligand was of β-imino enol form, with one titanium atom ligated with six other atoms, forming a deformed octahedral configuration. Furthermore, the ligand in Ti ₂ L ³ adopted a cis configuration, which was different from the trans configuration of its m-phenylene-bridged derivatives. These binuclear complexes ( Ti ₂ L ¹ – Ti ₂ L ³ ) could catalyze ethylene polymerization and copolymerization with 1,5-hexadiene(1,5-HD) efficiently under modified methylaluminoxane activation. Compared with the mononuclear complex TiL ⁵ , the binuclear catalysts were thermally more stable and showed higher activity for ethylene polymerization at higher temperatures. The activity of these titanium complexes for the copolymerization of ethylene with 1,5-HD were over 10⁶ g/mol Ti.h.atm, almost twice as high as for homopolymerization. Compared with the mononuclear analogue TiL ⁵ and the m-substituted binuclear derivative Ti ₂ L ⁴ , binuclear catalyst Ti ₂ L ² showed higher activity and insertion rate of the comonomer. The activity of Ti ₂ L ² was two to three times higher than that of TiL ⁵ and Ti ₂ L ⁴ , indicating that p-substituted binuclear catalysts generate clear bimetallic synergistic effect for the copolymerization of ethylene and 1,5-HD. Meanwhile, 1,5-HD takes 1,3-cyclopentyl form in the polymer by 1,3-insertion. The copolymer prepared by binuclear catalysts had higher molecular weight and wider molecular weight distribution than that prepared by the mononuclear catalyst.     

Block copolymerization initiated by Mn(III)-poly(ethylene glycol) redox system — general features and kinetics

The kinetics and mechanism of thermal polymerization of acrylonitrile initiated by Mn(III) pyrophosphate — poly(ethylene glycol) (PEG, molecular weight 6000) redox system in aqueous sulfuric acid medium was studied in the temperature range 30–60°C. The overall rates of polymerization and the disappearance of Mn³⁺ were determined. The polymerization was initiated by the organic free radical produced from the Mn³⁺-PEG reaction and the termination was by the metal ions. The rate of polymerization of acrylonitrile was found to be directly proportional to the square of the monomer concentration and first power of PEG concentration, and inversely proportional to the concentration of Mn³⁺. The rate of manganic ion disappearance was found to be directly proportional to manganic ion concentration and PEG concentration, and independent of the monomer concentration. Based on these observations, a plausible reaction scheme was suggested and suitable kinetic expressions were evaluated.     

Copolymerization of isoprene with ethylene catalyzed by cationic half‐sandwich fluorenyl scandium catalysts

Isoprene polymerization and copolymerization with ethylene can be carried out by using cationic half‐sandwich fluorenyl scandium catalysts in situ generated from half‐sandwich fluorenyl scandium dialkyl complexes Flu'Sc(CH₂SiMe₃)₂(THF)_n, activator, and AlⁱBu₃ under mild conditions. In the isoprene polymerization, all of these cationic half‐sandwich fluorenyl scandium catalysts exhibit high activities (up to 1.89 × 10⁷ g/mol_Sc h) and mainly cis?1,4 selectivities (up to 93%) under similar conditions. In contrast, these catalysts showed different activities and regio‐/stereoselectivities being significantly dependent on the substituents of the fluorenyl ligands in the copolymerization of isoprene with ethylene under an atmosphere of ethylene (1 atm) at room temperature, affording the random copolymers with a wide range of cis?1,4‐isoprene contents (IP content: 64 ? 97%, cis?1,4‐IP units: 65 ? 79%) or almost alternating copolymers containing mainly 3,4‐IP‐alt‐E or/and cis?1,4‐IP‐alt‐E sequences. Moreover, novel high performance polymers have been prepared via selective epoxidation of the vinyl groups of the 1,4‐isoprene units in the IP‐E copolymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2898–2907     

Heptane-soluble homogeneous zirconocene catalyst: Synthesis of a single diastereomer,polymerization catalysis,and effect of silica supports

Bis(1-indenyl)-di[1′S, 2′R, 5′S)-methoxy]silane ( 1 ) was converted into a mixture of corresponding ansa-diastereomeric zirconocenes. Further purification afforded a single dia-stereomer, di[(1′S, 2′R, 5′S)-methoxy] silylene-bis[η⁵-1(R, R)-(+)-indenyl] dichlorozirconium ( 2 ), which is optically active and hydrocarbon soluble. Extremely rapid ethylene, propylene, and ethylene-hexene polymerizations were observed both in toluene and n-heptane solutions; for instance, at 50°C, activity for ethylene polymerization reaches ～ 1.5×10¹⁰ (g of PE/((mol of Zr) · [C₂H₄] · h). The “bare” zirconocenium ion generated from 2/TIBA/Ph₃CB(C₆F₅)₄ exhibits unusual polymerization behaviors; the polymerization activity increases monotonically with temperature of polymerization (T_p) up to a conventional polymerization condition (50–70°C), and the ¹³C NMR study shows that the isotactic poly-propylene obtained has fairly high [mmmm] methyl pentad distributions at high T_p (?25°C with [mmmm] ～ 0.93–0.75) and a perfect stereoregularity at low T_p (?0°C with [mmmm] > 0.99). The catalyst precursors 2 and Et(Ind)₂ZrCl₂ ( 3 ) supported on silica by different approaches produced poly(olefins) of different molecular weights and stereoregularities, and a methylaluminokane and Ph₃CB(C₆F₅)₄ free silica-supported zirconocene system was found to be activated by triisobutylaluminum. © 1995 John Wiley & Sons, Inc.     

Ethylene polymerization reactions with Ziegler–Natta catalysts. III. Chain-end structures and polymerization mechanism

Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit a number of features that differentiate them from polymerization reactions of α olefins: (1) a relatively low ethylene reactivity, (2) markedly higher polymerization rates in the presence of α olefins, (3) a high reaction order with respect to ethylene concentration, and (4) a strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions¹ provided the basis for a new kinetic scheme that postulates the equilibrium formation of Ti C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts several new features of ethylene polymerization reactions, one being that chain initiation via insertion of any α-olefin molecule into the Ti H bond should proceed with an increased probability compared to that via ethylene insertion into the same bond. As a result, a significant fraction of ethylene/α-olefin copolymer chains should contain α-olefin units as the starting units. This article provides experimental data supporting this prediction on the basis of both a detailed structural analysis of co-oligomers formed in ethylene/1-pentene and ethylene/4-methyl-1-pentene copolymerization reactions and a spectroscopic analysis of chain ends in the copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4281–4294, 1999     

Silane‐bridged diphosphine ligand for palladium‐catalyzed ethylene oligomerization

In this study, bis(diphenylphosphinemethyl)dimethyl silane ( L1 ) and its palladium(II) halide complex, L1 /PdCl₂ ( C1 ), were synthesized and characterized. Single‐crystal X‐ray analysis of the complex revealed bidentate coordination at the Pd center. In combination with methylaluminoxane (MAO) as co‐catalyst, C1 exhibited excellent catalytic activity and selectivity for ethylene dimerization toward butene. The maximum catalytic activity obtained from the C1 /MAO system for ethylene dimerization to yield butenes was 7.33 × 10⁵ g/(mol_Pd · h). The selectivity toward butene remained stable and high (> 96%) over the various conditions.     

茂－茚锆金属络合物催化乙烯/1－己烯共聚和丙稀均聚研究

Complexes （R^1Cp）（R^2Ind）ZrCl2, the catalysts previously reported active for ethylene polymerization showed high activity in ethylene/1-hexene copolymerization and propylene polymerization in the presence of MAO. The content of 1-hexene in copolymers ranged from 1.2% to 3.2%. In propylene polymerization the complex 1 showed the highest activity, up to 1.2×10^6 g of polypropylene per mol of catalyst per hour. Based on the analysis of NMR spectral data, the relationships between complex structures and polymerization results were explored.