Catalytic oligomerization of ethylene to higher linear alpha-olefins promoted by the cationic group 4 [(eta 5-Cp-(CMe2-bridge)-Ph)MII(ethylene)2]+ (M = Ti, Zr, Hf) active catalysts: a density functional investigation of the influence of the metal on the catalytic activity and selectivity

A detailed theoretical analysis is presented of the catalytic abilities of heavier group 4 (M = Zr, Hf) metals for linear ethylene oligomerization with the cationic [(eta(5)-C(5)H(4)-(CMe(2)-bridge)-C(6)H(5))M(IV)(CH(3))(2)](+) complex as precatalyst, employing a gradient-corrected DFT method. The parent Ti system has been reported as a highly selective catalyst for ethylene trimerization. The mechanism involving metallacycle intermediates, originally proposed by Briggs and Jolly, has been supported by the present study to be operative for the investigated class of group 4 catalysts. Metallacycle growth through bimolecular ethylene uptake and subsequent insertion is likely to occur at uniform rates for larger cycles that are furthermore comparable for Ti, Zr, and Hf catalysts. Ethylene insertion into the two smallest five- and seven-membered cycles is found to become accelerated for Zr and Hf catalysts, which is due to geometrical factors. In contrast, electronic effects act to raise the barrier for metallacycle decomposition, affording alpha-olefins upon descending group 4. This process is furthermore predicted to be kinetically more difficult for larger metallacycles. The oligomer distribution of the Zr-mediated reaction is likely to comprise predominantly 1-hexene together with 1-octene, while 1-butene and alpha-olefins of chain lengths C(10)-C(18) should occur only in negligible portions. A similar composition of alpha-olefins having C(6)-C(18) chain lengths is indicated for the Hf catalysts, but with long-chain oligomers and polymers as the prevalent fraction. Between the group 4 catalysts of the investigated type, the Zr system appears as the most promising candidate having catalytic potential for production of 1-octene, although not selectively. The influence of temperature to modulate the oligomer product composition has been evaluated.     

A sterically expanded "constrained geometry catalyst" for highly active olefin polymerization and copolymerization: an unyielding comonomer effect

The 14 A octamethyloctahydrodibenzofluorene moiety has been incorporated into a sterically expanded constrained geometry catalyst, Me2Si(eta1-C29H36)(eta1-N-tBu)ZrCl2.OEt2 (1). The solid-state structure suggests that the activated olefin polymerization catalyst is quite spatially accessible, rationalizing its extraordinary reactivity toward alpha-olefins. 1/MAO (MAO = methylaluminoxane) can be more reactive toward alpha-olefins than toward ethylene and exhibit activities that are linearly and continuously proportional to 4-methyl-1-pentene or 1-octene concentration in their copolymerizations with ethylene.     

用于乙烯齐聚高选择性制 1-辛烯反应的Cr(Ⅲ)基催化剂体系

将四元催化剂体系(乙酰丙酮铬-膦胺型配体-助催化剂甲基铝氧烷-促进剂六氯乙烷)用于乙烯齐聚制1-辛烯反应,考察了促进剂、助催化剂、Al/Cr摩尔比、反应温度和反应压力等对催化剂的活性和1-辛烯的选择性的影响.结果表明,该四元催化剂体系比三元催化剂体系(铬化合物-膦胺型配体-甲基铝氧烷)对乙烯齐聚反应具有更高的1-辛烯选择性.产物除有1-辛烯外,还有较大量的1-己烯、甲基环戊烷和亚甲基环戊烷.甲基铝氧烷是高选择性生成1-辛烯必不可少的助催化剂.作为促进剂的六氯乙烷可以使乙酰丙酮铬更有利于催化乙烯齐聚反应生成1-辛烯.     

New processes for the selective production of 1-octene

Linear α-olefins, especially 1-hexene and 1-octene, are key components for the production of LLDPE and the demand for 1-hexene and 1-octene increased enormously in recent years. To meet this demand several processes were developed in the last decade to produce 1-hexene and 1-octene selectively. Here we review the new processes for 1-octene production based on homogeneous catalysts.Sasol's coal-based high temperature Fischer–Tropsch technology produces an Anderson–Schulz–Flory distribution of hydrocarbons with high α-olefin content and the desired alkenes, including 1-heptene and 1-octene, are separated by distillation. In this case, as in the SHOP process, 1-octene constitutes only a minor part of the total yield.Nowadays other technologies are being applied or considered for on-purpose 1-octene production: hydroformylation of 1-heptene, the telomerization of 1,3-butadiene, and ethene tetramerization.1-Heptene can be converted in three steps to 1-octene: (1) hydroformylation of 1-heptene to octanal, (2) hydrogenation of octanal to 1-octanol, and (3) dehydration of 1-octanol to 1-octene. This process was commercialized by Sasol.Dow commercialized a process based on butadiene. Telomerization of butadiene with methanol in the presence of a palladium catalyst yields 1-methoxy-2,7-octadiene, which is fully hydrogenated to 1-methoxyoctane in the next step. Subsequent cracking of 1-methoxyoctane gives 1-octene and methanol for recycle. Recently highly active and stable phosphine based systems were reported that show particularly good performance for the industrially attractive feedstock, the C₄ cut of the paraffin cracker.1-Hexene can be obtained by ethene trimerization by a family of catalysts based mainly on Cr. High selectivity to 1-hexene can be achieved thanks the propensity of the chromium based catalyst to form 7-membered ring metallacycles. Sasol has found catalyst systems that allow the formation of a 9-membered metallacycle in large proportion relative to 7-membered ring formation, yielding 1-octene.     

Homo-polymerization of alpha-olefins and co-polymerization of higher alpha-olefins with ethylene in the presence of CpTiCl2(OC6H4X-p)/MAO catalysts (X = CH3, Cl)

Cyclopentadienyl-titanium complexes containing -OC6H4X ligands (X = Cl,CH3) activated with methylaluminoxane (MAO) were used in the homo-polymerization of ethylene, propylene, 1-butene, 1-pentene, 1-butene, and 1-hexene, and also in co-polymerization of ethylene with the alpha-olefins mentioned. The -X substituents exhibit different electron donor-acceptor properties, which is described by Hammett's factor (sigma).The chlorine atom is electron acceptor, while the methyl group is electron donor. These catalysts allow the preparation of polyethylene in a good yield. Propylene in the presence of the catalysts mentioned dimerizes and oligomerizes to trimers and tetramers at 25 degrees C under normal pressure. If the propylene pressure was increased to 7 atmospheres,CpTiCl2(OC6H4CH3)/MAO catalyst at 25 degrees gave mixtures with different contents of propylene dimers, trimers and tetramers. At 70 degrees C we obtained only propylene trimer.Using the catalysts with a -OC(6)H(4)Cl ligand we obtained atactic polymers with M(w) 182,000 g/mol (at 25 degrees C) and 100,000 g/mol (at 70 degrees C). The superior activity of the CpTiCl2(OC6H4Cl)/MAO catalyst used in polymerization of propylene prompted us to check its activity in polymerization of higher alpha-olefins (1-butene, 1-pentene, 1-hexene)and in co-polymerization of these olefins with ethylene. However, when homo-polymerization was carried out in the presence of this catalyst no polymers were obtained. Gas chromatography analysis revealed the presence of dimers. The activity of the CpTiCl2(OC6H4Cl)/MAO catalyst in the co-polymerization of ethylene with higher alpha-olefins is limited by the length of the co-monomer carbon chain. Hence, the highest catalyst activities were observed in co-polymerization of ethylene with propylene (here a lower pressure of the reagents and shorter reaction time were applied to obtain catalytic activity similar to that for other co-monomers). For other co-monomers the activity of the catalyst decreases as follows: propylene >1-butene > 1-pentene > 1-hexene. In the case of co-polymerization of ethylene with propylene, besides an increase in catalytic activity, an increase in the average molecular weight M(w) of the polymer was observed. Other co- monomers used in this study caused a decrease of molecular weight. A significant increase in molecular weight distribution (M(w)/M(n)) evidences a great variety of polymer chains formed during the reaction.     

The influence of comonomer on ethylene/α-olefin copolymers prepared using [bis(N-(3-tert butylsalicylidene)anilinato)] titanium (IV) dichloride complex

We describe the synthesis of [bis(N-(3-tert-butylsalicylidene)anilinato)] titanium (IV) dichloride (Ti-FI complex) and examine the effects of comonomer (feed concentration and type) on its catalytic performance and properties of the resulting polymers. Ethylene/1-hexene and ethylene/1-octene copolymers were prepared through copolymerization using Ti-FI catalyst, activated by MAO cocatalyst at 323 K and 50 psi ethylene pressure at various initial comonomer concentrations. The obtained copolymers were characterized by DSC, GPC and 13C-NMR. The results indicate that Ti-FI complex performs as a high potential catalyst, as evidenced by high activity and high molecular weight and uniform molecular weight distribution of its products. Nevertheless, the bulky structure of FI catalyst seems to hinder the insertion of α-olefin comonomer, contributing to the pretty low comonomer incorporation into the polymer chain. The catalytic activity was enhanced with the comonomer feed concentration, but the molecular weight and melting temperature decreased. By comparison both sets of catalytic systems, namely ethylene/1-hexene and ethylene/1-octene copolymerization, the first one afforded better activity by reason of easier insertion of short chain comonomer. Although 1-hexene copolymers also exhibited higher molecular weight than 1-octene, no significant difference in both melting temperature and crystallinity can be noticed between these comonomers.     

乙烯选择性三聚/四聚铬系催化剂及其齐聚机理研究进展

线性α-烯烃是一类重要的有机化工原料和中间体,其下游市场包括聚乙烯、合成润滑油、表面活性剂等,其中C4~C8 组分的消费量占全球线性α-烯烃消费量的一半以上。采用1-己烯和1-辛烯作为共聚单体生产的线性低密度聚乙烯（LLDPE）和高密度聚乙烯（HDPE）产品具有优异的性能,被广泛用于薄膜、管材等领域。为了提高原子经济性,学术界和工业界一直致力于乙烯选择性三聚/四聚催化剂的设计与开发,而铬系催化剂是其中研究最广泛、最深入的体系。本文从配体、铬源、助催化剂、反应条件等方面综述了典型的铬系乙烯选择性三聚/四聚催化体系,包括雪佛龙菲利普斯乙烯三聚催化体系,Cr/PNP催化体系,以及其他N、P、Si配体等催化体系。在本文第二部分综述了乙烯选择性齐聚的相关机理提案,包括经典的Cossee-Arlman机理、单核金属环机理、双核金属环机理、双配位机理、及其他机理提案。     

ansa-Metallocene (R-Ph)2C(Cp)(Ind)MCl2 with electron withdrawing substituents on phenyl groups for olefin polymerization

The new ansa-complexes (R-Ph)₂C(Cp)(Ind)MCl₂ (R = CF₃, F, Cl; M = Ti, Zr or Hf) were synthesized from the reaction of dilithium salt of the corresponding ligands with appropriate group 4 metal halides. They were tested for ethylene homopolymerization and copolymerization in the presence of methylaluminoxane (MAO) at various ethylene pressures and temperatures. In the case of zirconocenes, complexes 2 (R = CF₃) and 8 (R = Cl) demonstrated much higher catalytic activity than complexes 10 (Ph₂C(Cp)(Ind)ZrCl₂) and 5 (R = F) in ethylene polymerization. The same trend was observed in titanocenes and hafnocenes. The electronic and geometric effects of substituents at the phenyl group on the polymerization activity were easily noticed. For the ethylene/1-hexene or 1-octene copolymerization, 2 also showed the highest catalytic activity, and the copolymers from complex 8 possessed the highest 1-hexene and 1-octene contents.     

Amine attack on coordinated alkenes: an interconversion from anti-Markovnikoff to Markovnikoff products

A sequence of alkene complexes of platinum, PtCl(2)(PPh(3))(alkene) (alkene = ethylene, propene, 1-butene, cis-2-butene, 1-hexene, 1-octene, and 1-decene), has been prepared. These complexes are characterized by NMR spectroscopy, including assignment of each proton, and X-ray crystal structures of the 1-propene and 1-hexene complexes. Each complex was reacted with diethylamine. For the 1-hexene, 1-octene, and 1-decene complexes, the amine displaces the alkene. For the smaller alkenes, the diethylamine nucleophilically attacks the coordinated alkene. For propene and 1-butene, the low-temperature addition leads to the anti-Markovnikoff nucleophilic attack, which slowly converts at room temperature to the Markovnikoff product. The transformation from anti-Markovnikoff to Markovnikoff addition occurs without diethylamine dissociation.     

Cobalt-catalyzed dimerization of alpha-olefins to give linear alpha-olefin products

[Cp*P(OMe)3CoCH2CH3]+ [BarF]-, generated by the addition of HBArF to Cp*P(OMe)3Co(ethene), catalyzes the oligomerization of 1-hexene to give dimers and trimers. When a deficit of the acid is used, linear alpha-olefin dimers are produced at the expense of trimeric products: e.g., 1-butene, 1-hexene, and 1-octene give 1-octene, 1-dodecene, and 1-hexadecene, respectively.     

新型均相铬系催化剂的制备与催化乙烯齐聚

合成了3种新型的N取代基中含有O/N杂原子的1,3,5-三氮杂环己烷[NNN]型配体,利用氢核磁共振谱(1H NMR)、碳核磁共振谱(13C NMR)及电子轰击质谱(EI-MS)等方法对其进行表征.将[NNN]型配体与Cr(Ⅲ)络合制备相应的均相铬催化剂,采用电喷雾质谱(ESI-MS)及元素分析分别对其进行表征.以甲基烷氧铝(MAO)为助催化剂,考察了反应温度、反应压力及铝铬摩尔比等因素对催化乙烯齐聚催化性能的影响.研究结果表明,在以甲苯为溶剂,反应温度50℃,反应压力0.8 MPa,铝铬摩尔比为500∶1,Cr浓度为2.0×10-4mol/L的反应条件下,取代基为3-二甲氨基丙基的均相铬催化剂的催化活性能够达到15.71×105g/(mol Cr·h),对1-己烯和1-辛烯的选择性达到91.02%,而取代基为3-乙氧基丙基的均相铬催化剂的催化活性比较低,为11.54×105g/(mol Cr·h),但对1-己烯和1-辛烯的选择性较高,达到93.05%.     

Selective ethylene oligomerization: Recent advances in chromium catalysis and mechanistic investigations

Selective production of linear α-olefins is of significant commercial interest. Recently discovered catalytic systems based on titanium, tantalum, and chromium show remarkable selectivity and productivity for the oligomerization of ethylene to 1-hexene or 1-octene. Chromium-based catalysts are the most selective and active and show the highest structural diversity. This paper discusses the most recent advances in chromium chemistry related to selective olefin oligomerization. Aspects regarding ligand design, catalyst generation, selectivity for different products, and reaction mechanism are presented. Isotopic labeling protocols designed to distinguish between various mechanisms of catalysis are reviewed.     

Copolymerization of ethylene α-olefin using MgCl2-ethanol adduct catalysts

The effects of the type and concentration of comonomers 1-hexene and 1-octene in the copolymerization of ethylene were investigated using pre polymerized Ziegler-Natta (catalyst a) and without pre polymerized (catalyst b) catalysts in the presence of hydrogen as a chain transfer agent. The properties of produced polymers were characterized by a set of techniques: (SEM), (EDX), (DSC), (GPC). TIBA and DEAC were used as co catalysts. The results of microscopic and SEM images showed the morphology and structure of catalysts (a) and (b) and the obtained spherical polymers. In the presence of 1-hexene, activity of catalyst (a) was at its maximum. The comonomer 1-octene at 32 mmol presented its activity (1.7 × 10³ g polymer/(g cat.h)) and after that, the activities decreased. Copolymerization of ethylene and 1-hexene by catalyst (b) showed higher activity (1.6 × 10³ g polymer/ polymer/(g cat.h)) at 40 mmol concentration of 1-hexene in comparison to catalyst (a).     

The use of bis(diphenylphosphino)amines with N-aryl functionalities in selective ethylene tri- and tetramerisation

A systematic study was conducted on the Cr catalysed tri- and tetramerisation of ethylene using bis(diphenylphosphino)amine ligands with N-aryl functionality. This study revealed that the oligomerisation reaction product selectivity is primarily dependent on the structure and size of the N-aryl groups.

Addition of sufficient steric bulk to the N-phenyl group via ortho-alkyl substitution increased the combined 1-hexene and 1-octene selectivity (overall alpha selectivity) to above 82% at an overall 1-octene selectivity of 56%. The introduction of a single carbon spacer between the N-atom and the aryl-moiety, as well as the addition of branching on this carbon, resulted in further selectivity improvements, achieving an overall 1-octene selectivity of 64% and an overall alpha selectivity of 84%. This was obtained at catalyst productivities in excess of 1,000,000 g/g Cr/h.     

Mechanistic studies of olefin and alkyne trimerization with chromium catalysts: deuterium labeling and studies of regiochemistry using a model chromacyclopentane complex

A system for catalytic trimerization of ethylene utilizing chromium(III) precursors supported by diphosphine ligand PNP(O4) = (o-MeO-C6H4)2PN(Me)P(o-MeO-C6H4)2 has been investigated. The mechanism of the olefin trimerization reaction was examined using deuterium labeling and studies of reactions with alpha-olefins and internal olefins. A well-defined chromium precursor utilized in this studies is Cr(PNP(O4))(o,o'-biphenyldiyl)Br. A cationic species, obtained by halide abstraction with NaB[C6H3(CF3)2]4, is required for catalytic turnover to generate 1-hexene from ethylene. The initiation byproduct is vinylbiphenyl; this is formed even without activation by halide abstraction. Trimerization of 2-butyne is accomplished by the same cationic system but not by the neutral species. Catalytic trimerization, with various (PNP(O4))Cr precursors, of a 1:1 mixture of C2D4 and C2H4 gives isotopologs of 1-hexene without H/D scrambling (C6D12, C6D8H4, C6D4H8, and C6H12 in a 1:3:3:1 ratio). The lack of crossover supports a mechanism involving metallacyclic intermediates. Using a SHOP catalyst to perform the oligomerization of a 1:1 mixture of C2D4 and C2H4 leads to the generation of a broader distribution of 1-hexene isotopologs, consistent with a Cossee-type mechanism for 1-hexene formation. The ethylene trimerization reaction was further studied by the reaction of trans-, cis-, and gem-ethylene-d2 upon activation of Cr(PNP(O4))(o,o'-biphenyldiyl)Br with NaB[C6H3(CF3)2]4. The trimerization of cis- and trans-ethylene-d2 generates 1-hexene isotopomers having terminal CDH groups, with an isotope effect of 3.1(1) and 4.1(1), respectively. These results are consistent with reductive elimination of 1-hexene from a putative Cr(H)[(CH2)4CH=CH2] occurring much faster than a hydride 2,1-insertion or with concerted 1-hexene formation from a chromacycloheptane via a 3,7-H shift. The trimerization of gem-ethylene-d2 has an isotope effect of 1.3(1), consistent with irreversible formation of a chromacycloheptane intermediate on route to 1-hexene formation. Reactions of olefins with a model of a chromacyclopentane were investigated starting from Cr(PNP(O4))(o,o'-biphenyldiyl)Br. alpha-Olefins react with cationic biphenyldiyl chromium species to generate products from 1,2-insertion. A study of the reaction of 2-butenes indicated that beta-H elimination occurs preferentially from the ring CH rather than exo-CH bond in the metallacycloheptane intermediates. A study of cotrimerization of ethylene with propylene correlates with these findings of regioselectivity. Competition experiments with mixtures of two olefins indicate that the relative insertion rates generally decrease with increasing size of the olefins.     

Determination of reactivity ratios for ethylene/α-olefin copolymerization catalysed by the C2H4[Ind]2ZrCl2/methylaluminoxane system

The present study reports values of reactivity ratios for ethylene/1-hexene, ethylene/1-octene and ethylene/1-decene copolymerizations promoted by C₂H₄[Ind]₂ZrCl₂/MAO. The comonomer reactivities are markedly influenced by the number of carbon atoms of the α-olefin. The ethylene/1-decene copolymerization depends on the concentration of α-olefin in the feed.     

Mechanistic investigations of the ethylene tetramerisation reaction

The unprecedented selective tetramerisation of ethylene to 1-octene was recently reported. In the present study various mechanistic aspects of this novel transformation were investigated. The unusually high 1-octene selectivity in chromium-catalyzed ethylene tetramerisation reactions is caused by the unique extended metallacyclic mechanism in operation. Both 1-octene and higher 1-alkenes are formed by further ethylene insertion into a metallacycloheptane intermediate, whereas 1-hexene is formed by elimination from this species as in other reported trimerisation reactions. This is supported by deuterium labeling studies, analysis of the molar distribution of 1-alkene products, and identification of secondary co-oligomerization reaction products. In addition, the formation of two C6 cyclic products, methylenecyclopentane and methylcyclopentane, is discussed, and a bimetallic disproportionation mechanism to account for the available data is proposed.     

DEPENDENCE OF THE DISTRIBUTION OF ACTIVE CENTERS ON MONOMER IN SUPPORTED ZIEGLER-NATTA CATALYSTS

Distribution of active centers(ACD)of ethylene or 1-hexene homopolymerization and ethylene-1-hexene copolymerization with a MgCl_2/TiCl_4 type Z-N catalyst were studied by deconvolution of the polymer molecular weight distribution into multiple Flory components.Each Flory component is thought to be formed by a certain type of active center. ACD of ethylene-1-hexene copolymer with very low 1-hexene incorporation was compared with that of ethylene homopolymer to see the effect of introducingα-olefin on eth...     

15个乙烯—乙烯基化合物共聚物的取代基参数

本文应用取代基参数（ＳＣＳ）方法处理了１５个ＥＶ共聚物的＾１３ＣＮＭＲ谱，它们是：（１）乙烯α－烯烃共聚物，即乙烯－丙烯共聚物，乙烯－丁烯－１共聚物，乙烯４－甲基－１－戊烯共聚物，乙烯－己烯－１共聚物和乙烯－辛烯－１共聚物；（２）乙烯－含氧乙烯共聚物，即乙烯－甲基丙烯酸Ｎ，Ｎ－二甲基胺乙酯共聚物，乙烯－丙烯酸甲酯共聚物，乙烯－丙烯酸共聚物，乙烯－乙酸乙烯酯，乙烯－乙烯醇，乙烯－一氧化碳共聚物（ＥＣ     

Heterogeneous Copolymerization of Ethylene and α-olefins Using Aluminohydride-Zirconocene/SiO2/MAO by High-Throughput Screening

Copolymerizations of ethylene and α-olefins (1-hexene and 1-octene) using a supported catalyst derived from the activation of a zirconocene aluminohydride complex with PMAO and MMAO are reported. The supported (nBu-Cp₂ZrH₃AlH₂)/SiO₂/MAO system was evaluated by high-throughput techniques, in order to find approaches to the optimal copolymerization conditions. The polymerization reactions were carried out in a parallel polymerization reactors system (PPR) by Symyx Technologies, Inc. The screening of the activity of the supported system and the molecular weight (MW) of the polymers and copolymers obtained in the PPR, allowed us to optimize copolymerization conditions, like hydrogen (H₂) addition to control MW and molecular weight distribution (MWD), polymerization temperature, cocatalyst ratio, and solvent type. The copolymerization reactions were scaled-up in order to validate the performance of the catalytic system at higher polymerization scales, according to the results obtained in the combinatorial phase. The scaled-up copolymerizations of ethylene with 1-hexene and 1-octene, showed high activities and MW, and low comonomer incorporation (from 0.3 to 1.3 mol-%, determined by ¹³C NMR). However, the crystallinity (X_c), thermal properties (T_c and T_m) and densities of the polyethylenes obtained with the supported (nBu-Cp₂ZrH₃AlH₂)/SiO₂/MAO system, were significantly modified, approaching those of metallocene linear low-density polyethylenes (mLLDPE).