Thermal oligomerization of isophthalonitrile catalyzed by o-carborane

The thermal reaction of equimolar quantities of isophthalonitrile and o-carborane has been shown to produce an adduct oligomer of isophthalonitrile. The structure was determined to involve condensation of three to five isophthalonitrile molecules to form a triazine-type system. This type of bonding gave rise to a trimer and pentamer. Further, the reaction was a homogeneous liquid phase reaction in which o-carborane is involved in a catalytic manner in the oligomerization. The overall reaction has first-order kinetics with an activation energy of 32.2 kcal/mole.     

Toward product control in ring‐opening oligomerization of 9H‐9‐borafluorenes

To get deep insights into the structure–reactivity relationship for ring‐opening oligomerization reactions toward targeted design of novel main‐chain boron‐containing materials, detailed DFT B97D/TZVP calculations are carried out to compare the ring‐opening oligomerization of both unsubstituted and tert‐butyl (tBu)‐substituted 9H?9‐borafluorenes. In contrast to substituent exchange between normal boranes, such reactions are initiated by substituent exchanges involving double B? C? B bridged intermediates. On tBu‐substitution, the B? C? B, and B? H? B bridged dimer intermediate is stabilized mainly due to enhanced barrier of 18.1 kcal/mol toward further trimerization channel and higher isomerization barrier of 22.5 kcal/mol toward the double B? H? B bridged dimer. In good agreement with available experiments, it is clearly shown that various product channels can be efficiently controlled by bulky substitution and by reaction temperatures, pointing out the way toward desired higher oligomers with improved thermal stability. © 2014 Wiley Periodicals, Inc.     

Kinetic features of cationic oligomerization of epoxides

The kinetic features of the cationic oligormerization of epoxides of various structures influenced by Lewis acids (BF₃OEt₂, SnCl₄) were investigated. It was shown that the systems studied could he divided into three groups, based on the nature of conversion-time kinetic curves of oligomerization: (1) (Epoxypropane-BF₃OEt₂, 3,4-epoxybutene-1-BF₃OEt₂) oligomerization stops before the monomer is exhausted completely. (2) (1-Chloro-2,3-epoxypropane-BF₃OEt₂ or SnCl₄, 2-methyl-2,3-epoxybutane-BF₃OEt₂) oligomerization can be carried out almost up to complete conversion of the monomer. The reaction rate, however, decreases more rapidly than that expected from the kinetics of monomer consumption. (3) (1-tert-Butylperoxy-2,3-epoxypropane-SnCI₄) oligomerization kinetics are described by a simple exponential function with regard to monomer concentration. Determination of the propagating species concentration in the systems studied suggests that the initiation of cationic oligornerization of epoxides with Lewis acids is an instantaneous process and the discrepancy observed is a result of the different nature of kinetics of the active site destruction. In the first group of systems the rapid destruction of the propagating species prevents the oligomerization to complete conversion. In the second group a somewhat lower rate of decrease in concentration of the propagating species with time is explained by their regeneration during the process. In the third system, which is a unique case, the concentration of the propagating species remains constant with time. It is assumed that these features are the result of the stability or pseudostability of the active sites which depends on the nature of the epoxide and initiator.     

Hyperbranched macromolecules bridged salicylaldimine cobalt complexes: synthesis,characterization and ethylene oligomerization studies

A series of novel 1.0 generation (1.0G) hyperbranched macromolecules bridged salicylaldimine cobalt complexes were synthesized in high yields. The compounds were characterized by fourier transform infrared (FT-IR) spectroscopy, ultraviolet (UV) visible spectroscopy, electrospray ionization mass spectrometry (ESI–MS), elemental analysis and thermal gravimetric analysis (TGA), as well as were investigated as precatalysts for the oligomerization of ethylene. Upon activation with methylaluminoxane (MAO) and diethylaluminumchloride (DEAC), the cobalt precatalysts showed moderate catalytic activities in the range of 10⁵ g/(mol Co h) in ethylene reactivity with the high selectivity for the butenes and high carbon number olefins products. The correlation between cobalt complexes and their catalytic activities and product distribution were investigated in detail under various reaction parameters. The research results showed that the catalytic activities of precatalysts increased with the increase of ethylene pressure and Al/Co molar ratio; however, the catalytic activities firstly increased and then decreased with the increase of reaction temperature. The highest activity of 2.54 × 10⁵ g/(mol Co h) and 50.18% selectivity of high number carbon olefins was obtained under the reaction temperature of 25 °C, ethylene pressure of 0.5 MPa, and Al/Co molar ratio of 1500. In addition, the nature of solvent and co-catalyst, as well as the structure of precatalysts, significantly affected both the activity and the product distribution of the resultant catalysts.     

Study on the oligomerization of cyclopentadiene and dicyclopentadiene to tricyclopentadiene through diels-alder reaction

Summary The oligomerization of cyclopentadiene (CPD) and its dimer, dicyclopentadiene (DCPD), to tricyclopentadiene (TCPD) through Diels-Alder reaction at temperatures between 120 and 150°C was investigated. The results show that reaction temperature, pressure and solvent influence the product yield; at 150°C up to 50% yield of TCPD was obtained in the absence of solvents. The ratios of isomers A to B in the product can be adjusted by using different solvents. The kinetics indicate that the rate is more sensitive to the concentration of CPD than to that of DCPD.     

Cobalt complexes based on hyperbranched salicylaldimine ligands as catalyst precursors for ethylene oligomerization

Three hyperbranched salicylaldimine ligands with tetradecyl as core, with hexadecyl as core and with octadecyl as core were synthesized in good yields. These ligands were reacted with cobalt chloride hexahydrate to form three complexes ( C1 – C3 ). The compounds were characterized using Fourier transform infrared, ¹H NMR, mass and UV spectroscopies and thermogravimetric and differential thermal analyses. The catalytic properties of the hyperbranched cobalt complexes were evaluated for ethylene oligomerization. The effects of solvent and reaction parameters (Al/Co molar ratio, temperature and reaction pressure) on ethylene oligomerization were studied using the cobalt complex C3 as pre‐catalyst and methylaluminoxane (MAO) as co‐catalyst. Under these conditions ([Co] = 5 μmol, Al/Co = 500, 25 °C, 0.5 MPa ethylene, 30 min), the catalytic activity of complex C3 in toluene was 1.85 × 10⁵ g (mol Co)⁻¹ h⁻¹ and the selectivity for C₈₊ oligomers was 55.72%. The complex structure also had a significant influence on both the catalytic activity and selectivity. All three cobalt complexes, activated with MAO, showed moderate activities towards ethylene oligomerization and the activity of cobalt complex C1 was up to 1.99 × 10⁵ g (mol Co)⁻¹ h⁻¹. The kinds of metal center of complexes (cobalt complex C1 and nickel complex with tetradecyl as core) and their catalytic properties were investigated in detail under the same conditions.     

Prospects and crucial problems in oligomerization and polymerization with iron and cobalt complex catalysts

<正>The discovery of highly active 2,6-bis(imino)pyridyl iron and cobalt complexes provided a milestone of latetransition metal catalysts for ethylene oligomerization and polymerization with being currently investigated for the scale-up process.The crucial problems are remaining in the catalytic systems:the catalytic systems targeting ethylene polymerization produce more oligomers at elevated reaction temperatures,however,there is a recognizable amount of high-molecular-weight polyethylene remained in the modified catalytic system for the oligomerization process.Beyond the modification of bis(imino)pyridyl metal complexes,several alternative procatalysts' models have been developed in our group.This review highlighted the achievements in exploring new iron and cobalt complexes with tridentate NNN ligands as procatalysts for ethylene oligomerization and polymerization.     

Ethylene oligomerization by diimine iron(II) complexes/EAO

The catalytic properties of a series of Fe(II) diimine complexes (diimine=N,N′-o-phenylenebis(salicylideneaminato), N,N′-ethylenebis(salicylideneaminato), N,N′-o-phenylenebisbenzal, N,N′-ethylenebisbenzal) in combination with ethylaluminoxane (EAO) for ethylene oligomerization have been investigated. Treatment of the iron(II) complexes with EAO in toluene generates active catalytic systems in situ that oligomerize ethylene to low-carbon olefins. The effects of reaction temperature, ratios of Al/Fe and reaction periods on catalytic activity and product distribution have been studied. The activity of complex FeCl₂(PhCH=o-NC₆H₄N=CHPh) with EAO at 200°C is 1.35×10⁵ g oligomers/mol Fe·h, and the selectivity of C_4–10 olefins is 84.8%.     

Hyperbranched bisphosphinoamine ligands: synthesis,characterization and application in ethylene oligomerization

Two hyperbranched bisphosphinoamine (PNP) ligands and chromium complexes were synthesized in good yield with 1.0 generation (1.0 G) hyperbranched macromolecules, chlorodiphenylphosphine (Ph₂PCl) and CrCl₃(THF)₃ as raw materials. The hyperbranched PNP ligands and chromium complexes were characterized by FT-IR, ¹H NMR, ³¹P NMR, UV and ESI-MS. Comparing with the chromium complexes, the hyperbranched PNP ligands, in combination with Cr(III), and activation by methylaluminoxane (MAO) in situ generated species with better catalytic performance for ethylene oligomerization. The effect of solvent, chromium source, ligand/Cr molar ratio, reaction temperature, Al/Cr molar ratio and reaction pressure on the catalytic activity and product selectivity were studied. The results showed that with increase of ligand/Cr molar ratio, reaction temperature and Al/Cr molar ratio, the catalytic activity increased at first and then decreased. However, the catalytic activity continuously increased with increase of reaction pressure. Under the optimized conditions, the catalytic system of hyperbranched PNP/Cr(III)/MAO led to catalytic activity of 2.68 × 10⁵ g/(mol Cr·h) and 37.71% selectivity for C₆ and C₈.     

Selective ethylene oligomerization bearing hyperbranched bispyridylamine chromium catalyst

Two new hyperbranched bispyridylamine ligands and multinuclear chromium complexes were synthesized with 1.0?G hyperbranched macromolecules, 2-chloropyridine, 2-chloro-4-methylpyridine and CrCl₃(THF)₃ as raw materials. The structures of hyperbranched ligands and chromium complexes were characterized by UV, FT-IR, ¹H NMR, ESI-MS, and elemental analysis. These hyperbranched chromium complexes were evaluated as catalyst precursors by using MAO as activator in the oligomerization of ethylene. Effects of reaction temperature, reaction pressure, Al/Cr molar ratio, concentration of catalyst, solvent, and the structure of catalysts on the catalytic activity and product selectivity were investigated. The oligomerization results showed that with increase of reaction temperature, reaction pressure, and Al/Cr molar ratio, the catalytic activity increased and then decreased; the catalytic activity continuously decreased as the amount of catalyst increased. The products were mainly based on C₆ and C₈. Under optimized conditions, the catalytic system of hyperbranched NNN/Cr(III)/MAO led to activity of 1.26?×?10⁵ g/(mol·Cr·h) and 63.34% selectivity for C₆ and C₈.     

Kinetics of alpha‐methylstyrene oligomerization by catalytic chain transfer

Alpha‐methylstyrene (AMS) can be effectively dimerized by a free‐radical mechanism mediated by the catalytic chain transfer (CCT). Above the ceiling temperature of AMS, 61 °C, the dimer may become almost an exclusive product with only a small percentage of impurity of AMS trimer and tetramer. Kinetics of the AMS oligomerization has two characteristic features. First, the rate of the oligomerization increases with concentration of the CCT catalyst. Second, conversion reaches a plateau at 60–70%. A kinetic scheme explained both effects. Besides AMS, para‐ and methasubstituted AMS can also be dimerized. Orthosubstituted AMS's do not oligomerize. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1366–1376, 2002     

Kinetics and mechanism of the shock induced thermal decomposition of n-propylsilane

The kinetics and mechanism of the thermal decomposition of n-propylsilane have been studied by the single pulse shock tube-comparative rate technique at pressures around 4700 torr between 1095–1240 K. The primary dissociation processes are 1,1 and 1,2 H₂ elimination with ø_1,1 ? 0.75 and ø_1,2 ? 0.25, respectively. Subsequent decompositions of the primary process product, n-propylsilylene, to propylene and ethylene is complete even in the presence of excess butadiene. Possible mechanistic paths for these decompositions are discussed and an activation energy range of 30 ± 4 kcal is established for both processes. Induced decomposition via silylene chains accounts for 36–46% of the overall reaction in the uninhibited decomposition of n-propylsilane. The silylene chains are quenched in excess butadiene, and studies under maximum inhibition give overall decomposition kinetics of, log k(nPrSiD₃, s^?1) = 15.26–65,300 ± 1950 cal/2.303. Computer modeling results of the overall reaction both in the absence and presence of butadiene are also presented and shown to be in acceptable agreement with the experimental observations.     

Synthesis,characterization, and ethylene oligomerization of three novel dendritic nickel catalysts

Three dendritic nickel complexes C1–C3 were synthesized from three poly(amido amine) dendrimers, salicylic aldehyde and nickel chloride hexahydrate via Schiff base condensation reaction and coordination reaction. The structures of the dendritic ligands and nickel complexes were characterized by FT-IR, UV, ¹H NMR, ESI–MS, and elemental analysis. When activated with aluminum co-catalysts, three complexes C1–C3 were able to catalyze ethylene oligomerization. The catalytic activities and the product distribution of complexes C1–C3 were depended on the reaction parameter, co-catalyst, solvent, and the structure of the pre-catalyst. When using ethyl aluminum sesquichloride (EASC) as co-catalyst in toluene, the catalytic activity of complex C3 containing the longest bridging methylene groups reached the highest value of 1.63 × 10⁶ g·(mol Ni·h)^?1 with 69.15% C₁₁ in the product at 30 min, 25 °C, 0.5 MPa, and Al/Ni ratio of 900.     

一种新型双亚胺吡啶铁系催化剂的乙烯低聚研究

线性α 烯烃广泛地应用于洗涤剂、增塑剂、润滑油等精细化学品的合成以及作为共单体制备线性低密度聚乙烯 (ＬＬＤＰＥ) .目前工业上主要是应用ＳＨＯＰ法[1] 、Ｃｈｅｖｒｏｎ工艺和Ａｍｏｃｏ工艺[2 ] 通过乙烯低聚制备 .近些年发展起来的新型高活性后过渡金属乙烯低聚催化剂能够高选择性地制备线性α 烯烃[3 ,4] .Ｂｒｏｏｋｈａｒｔ等[4] 的研究表明 ,对于双亚胺吡啶铁系乙烯聚合催化剂而言 ,配体上苯基的邻位取代基位阻减小可以实现乙烯低聚 ,并具有高活性、高选择性以及理想的低聚产物分布 .本文的工作是从配体的空间位阻效应对催化剂…     

Organometallic Aspects of the Fischer-Tropsch Synthesis

The Fischer-Tropsch Synthesis counts among the industrial-scale processes having a versatile and broad product range, and has for decades offered the most attractive possibility for the use of coal as a source of heating oil and fuels. This conceivably simple reaction, the catalytic hydrogenation of carbon monoxide, generally leads to simple hydrocarbons as well (i.e. short chain olefins) that have been sought as chemical feedstocks since the oil crisis of the seventies, but fails to provide the large-scale, economic process required, due in large part to the minimal selectivity of traditional Fischer-Tropsch processes. In an effort to solve this problem current research in this sector is concerned not only with the optimization of old and the development of new catalytic systems, but also increasingly with the elucidation of numerous relevant reaction mechanisms. This article will discuss, from the viewpoint of an organometallic chemist, the significance of typical model reactions, both with regard to some fundamental aspects of synthesis gas chemistry, and in comparison with previous views concerning the mechanism of the Fischer-Tropsch Synthesis. The importance of various unique classes of complexes that have been studied in the context of Fischer-Tropsch chemistry is also evaluated with regard to their importance in the synthesis of hydrocarbons from carbon monoxide and hydrogen. It emerges that the primary steps of the reductive oligomerization of carbon monoxide are best described by the carbide/methylene mechanism, as originally proposed by Hans Fischer and Franz Tropsch.     

Synthesis of an inorganic-organic polymer blend from orthoboric acid and caprolactam

The possibility of modifying boron polyoxide with an oligomeric amide upon thermal dehydration of orthoboric acid and oligomerization of caprolactam in a common melt is shown. The products obtained after thermal pretreatment of the initial blend containing 30 wt % caprolactam are investigated. It is shown that the main processes at T < 200°C are dehydration of orthoboric acid and hydrolysis of caprolactam with the formation of ε-aminocaproic acid. At temperatures of 225–260°C, the predominant process is the formation of boron polyoxide and a caprolactam-based oligomeric product. The data of ¹¹B NMR spectroscopy show that the chemical transformations of caprolactam occur against the background of the N:B donor-acceptor interaction. The two-dimensional [¹¹B-¹H] heteronuclear correlation spectrum indicates that the systems obtained upon thermal treatment are solid solutions.     

Oligomerization of vinyl monomers 18. Stereochemistry of anionic oligomerization of 4-vinylpyridine

Oligomers of 4-vinylpyridine were prepared by reaction in vacuo of 4-vinylpyridine with lithio-4-ethylpyridine at ?78°C, followed by reaction with CH₃I(¹³CH₃I) or CH₃OH. The stereochemistry was studied by NMR and GC. Methylation and the addition of 4-vinylpyridine occurred in a stereochemically nonselective manner. The data also indicated that in contrast to the oligomerization of 2-vinylpyridine the stereoisomeric meso and racemic 4-pyridyl carbanions propagated with equal reaction rates. The stereochemistry was readily explained by an absence of coordination of the Li ion by the nitrogen of the penultimate pyridine ring observed in the corresponding oligomerization of 2-vinylpyridine.     

Synthesis of short straight-chain alkylamine based hyperbranched nickel complexes and their catalytic performance of ethylene oligomerization

Short straight-chain alkylamine based hyperbranched molecules and their corresponding salicylaldimine nickel complexes have been synthesized in high yield and characterized by FTIR, ¹H-NMR and mass spectrometry. The optimal reaction parameters were determined under the catalytic system of methylaluminoxane (MAO) as co-catalyst and toluene as solvent. Under these conditions, the effect of catalyst structure, solvent and co-catalyst were determined. Upon activation of MAO in toluene, ethylene oligomerization products were homogeneous distribution of butene, hexene and octene with trace higher olefin. The same catalytic system under cyclohexane and methyl cyclohexane as solvent, however, produced majority of butene. Under the activation of EtAlCl₂, Et₂AlCl and EASC as co-catalyst in toluene, ethylene oligomerization reaction was tandem with Friedel-Crafts reaction in catalytic system.     

Influence of the ligand structure on the properties of bidentate salicylaldimine nickel(II) complexes in ethylene oligomerization

Three nickel(II) complexes (C1–C3) bearing diamine-bridged 4-hydroxysalicylaldehyde ligands (L1–L3) were successfully synthesized, and all the compounds were characterized by physicochemical and spectroscopic methods. The influence of the oligomerization parameters on the catalytic properties of complex C2 was systematically investigated. The results showed that oligomerization parameters played an important role in the catalytic properties and the catalytic activity was 19.90?×?10⁴ g/(mol·Ni·h) and the selectivity of C₈₊ olefins was 60.25% when the precatalyst dosage was 5 μmol, the Al/Ni molar ratio was 500, the temperature was 25 °C, the reaction time was 30 min and the pressure of ethylene was 0.7 MPa. Complexes C1–C3 with different lengths of the bridged group were evaluated for ethylene oligomerization, and the results showed that the length of the alkyl chain in the ligand had little influence on the catalytic properties. Complex C4 based on ethanediamine-bridged salicylaldimine and C5 based on the hyperbranched salicylaldimine in our previous work were also investigated to study the influence of the ligand structure on the catalytic properties. The catalytic activity [31.80?×?10⁴ g/(mol·Ni·h)] and the content of the low-carbon oligomers (70.16%) for complex C4 were higher than complex C2 with hydroxyl substituent in benzene ring. The catalytic activity and the content of the low carbon oligomers for complex C5 were far higher than other four complexes.

     

Study of ethylene oligomerization

A study was made of the oligomerization of ethylene, initiated by the thermal decomposition of azoethane and azo-isopropane at low temperatures, where the polymerization equilibria are shifted somewhat in the direction of the formation of products with longer carbon chains. The findings supported the picture acquired from a study of the propionaldehyde–ethylene system. Also under these conditions the oligomerization proceeds via addition between the ethylene and radicals, followed by isomerization and decomposition of the longer radicals, with a tendency to yield propylene and longer olefins. At the lower temperatures the decomposition of radicals with shorter carbon chain becomes less important in comparison with their addition reactions and, in spite of the otherwise identical mechanism, this leads to a different product distribution.