Aluminum Alkyls Research Articles

Hydrogenation of β-Keto Sulfones to β-Hydroxy Sulfones with Alkyl Aluminum Compounds: Structure of Intermediate Hydroalumination Products.

β-Hydroxy sulfones are important in organic synthesis. The simplest method of β-hydroxy sulfones synthesis is the hydrogenation of β-keto sulfones. Herein, we report the reducing properties of alkyl aluminum compounds R3Al (R = Et, i-Bu, n-Bu, t-Bu and n-Hex); i-Bu2AlH; Et2AlCl and EtAlCl2 in the hydrogenation of β-keto sulfones. The compounds i-Bu2AlH, i-Bu3Al and Et3Al are the at best reducing agents of β-keto sulfones to β-hydroxy sulfones. In reactions of β-keto sulfones with aluminum trialkyls, hydroalumination products with β-hydroxy sulfone ligands [R2AlOC(C6H5)CH2S(O)2(p-R1C6H4]n [where n = 1,2; 2aa: R = i-Bu, R1 = CH3; 2ab: R = i-Bu, R1 = Cl; 2ba: R = Et, R1 = CH3; 2bb: R = Et, R1 = Cl] and {[Et2AlOC(C6H5)CH2S(O)2(p-ClC6H4]∙Et3Al}n 3bb were obtained. These complexes in the solid state have a dimeric structure, while in solutions, they appear as equilibrium monomer–dimer mixtures. The hydrolysis of both the isolated 2aa, 2ab, 2ba, 2bb and 3bb and the postreaction mixtures quantitatively leads to pure racemic β-hydroxy sulfones. Hydroalumination reaction of β-keto sulfones with alkyl aluminum compounds and subsequent hydrolysis of the complexes is a simple and very efficient method of β-hydroxy sulfones synthesis.

Chiral Bis(oxazoline) Ligand‐Supported Alkyl Aluminum Cations

AbstractAlkyl aluminum cations have shown high Lewis acidity and capability of catalyzing challenging organic transformations, however, the related chiral catalyst is scarcely documented. Herein, we report the generation of a series of weakly solvated or Lewis base‐stabilized alkyl aluminum cationic complexes bearing chiral bis(oxazoline) ligands. The increase of steric hindrances at the ligand backbone and the aluminum center were found to significantly increase the complex stability. In the Gutmann–Beckett experiment and fluoride ion affinity calculation, these complexes display Lewis acidity greater than B(C6F5)3 and the reported tetra‐coordinate aluminum cation. Preliminary catalytic studies revealed that the aluminum cation catalysts can effectively promote hydroboration of ketone and hydrosilylation of un‐activated olefin, despite only poor ee values were obtained.

First example of cationic titanium (III) complexes with crown ether as catalysts for ethylene polymerization

Complex cations with a vacant coordination site are considered as the most plausible catalytically active centers of metallocene and post-metallocene polymerization catalysts. For the first time we demonstrated that cationic titanium (III) complexes stabilized with crown ether can be used as pre-catalysts for ethylene polymerization. In the presence of alkyl aluminum chlorides and MgBu2 as cocatalysts, these complexes catalyze ethylene polymerization to produce Ultra High Molecular Weight Polyethylene (UHMWPE) with productivity up to 4650 kgPE/mol Ti h⋅atm and molecular weight up to 1.8·106 Da. UHMWPE powders were processed by the solid-phase method with subsequent orientation drawing into high-strength (1.4–2.1 GPa) and high-modulus (91–118 GPa) films.

Improvement of catalytic activity for α‐diimine nickel complex with active sites stabilized by bulky boron counterions at elevated temperature

Three α‐diimine Ni (II) catalysts (Cat.1, Cat.2 and Cat.3) were synthesized and investigated for ethylene polymerization using alkyl aluminum and organoboron compounds as binary cocatalyst. The effects of different alkyl aluminum and boron complexes on ethylene polymerization catalyzed by Cat.1, Cat.2, and Cat.3 were studied. The sodium tetrakis[3,5‐bis (trifluoromethyl)phenyl]borate (NaBArF) was found to have best promotion for the catalytic activity of Cat.1, compared to negative effect of dimethylanilinium tetrakis (pentafluorophenyl)borate (TTB) and trityl tetrakis (pentafluorophenyl)borate (AB). All the three catalysts showed higher catalytic activity when NaBArF was introduced into the catalytic system, especially for Cat.3 (increased by 41.3% at 70°C). There was still minor increase of the catalytic activity for Cat.2 which have much better thermostability than Cat.3. The charging sequence of NaBArF and the [B]/[Ni] ratio have significant effects on the catalytic activity. The better catalytic performance of Cat.1/AlEt2Cl/NaBArF could be explained by its ability to raise the number of active centers. Namely, the molar percentage of active centers of Cat.1/AlEt2Cl/NaBArF was still above 30%, which was 1.7 times that of Cat.1/AlEt2Cl even if polymerization ran up to 30 min based on 2‐thiophenecarbonyl chloride (TPCC) quench‐labeling method. Lower [Al]/[Ni] ratio but more active centers and longer active centers lifetime of this binary cocatalyst is promising for improving the activity of ethylene polymerization industrially at elevated temperature.

Effect of alkylaluminum structure and aggregation state on the micro-kinetics of ethylene polymerization catalyzed by α-diimine nickel complex

2-thiophenecarbonyl chloride (TPCC) quenching method was used into the study of alkylaluminum activation behavior on α-diimine nickel catalysts. The influence of alkylaluminum structure (AlEt2Cl, Al2Et3Cl3, AlEtCl2 and modified methylaluminoxane (MMAO)) and polymerization temperature on the kinetic factors (active center concentration [C*] and chain propagation rate constant kp) of ethylene polymerization catalyzed by the system was systematically studied. It was found that, compared with MMAO, alkyl aluminum chloride could better activate catalyst and produced more active centers in the polymerization system, but the value of kp was lower than MMAO. Unexpectedly, as the polymerization temperature increased, [C*] in the polymerization system with AlEtCl2 as cocatalyst gradually increased, and kp decreased. But the change of [C*] and kp of the polymerization system with MMAO as cocatalyst was opposite. It was proposed that cocatalyst is one of the factors affecting the thermal stability of catalyst.

Low-temperature ALD/MLD growth of alucone and zincone thin films from non-pyrophoric precursors.

The combined atomic/molecular layer deposition (ALD/MLD) technique is emerging as a state-of-the-art synthesis route for new metal-organic thin-film materials with a multitude of properties by combining those of the inorganic and the organic material. A major part of the studies so far reported have focused on aluminum or zinc alkyls, so-called alucone and zincone films, typically grown from trimethyl aluminum (TMA) or diethyl zinc (DEZ) as the metal-bearing precursor, and a simple aliphatic bi-functional alcohol molecule such as ethylene glycol (EG) as the organic precursor. However, these common precursors possess certain disadvantages: both TMA and DEZ are pyrophoric, DEZ being additionally thermally unstable, while EG has a strong tendency for various unideal reaction modes. Here we report novel ALD/MLD processes for alucone and zincone films based on non-pyrophoric bis-diisopropylamido-[3-(N,N-dimethylamino)propyl] aluminum(III) [Al(NiPr2)2(DMP)] and bis-3-(N,N-dimethylamino)propyl zinc(II) [Zn(DMP)2] precursors in combination with hydroquinone (HQ) as the organic precursor. We demonstrate that the [Al(NiPr2)2(DMP)] + HQ and [Zn(DMP)2] + HQ ALD/MLD processes work even at record low deposition temperatures (140 °C and 60 °C, respectively) yielding high-quality and relatively stable Al-HQ and Zn-HQ thin films with appreciably high growth rates (2.8 Å / cycle and 3.2 Å / cycle, respectively). Moreover, these ALD/MLD processes are compatible with the corresponding ALD processes, i.e. [Al(NiPr2)2(DMP)] + H2O and [Zn(DMP)2] + H2O, for the Al2O3 and ZnO films, thus opening up new horizons for the fabrication of novel metal-oxide : organic superlattice structures for e.g. flexible gas-barrier coatings or wearable thermoelectrics.

Aluminium alkyl complexes supported by imino-phosphanamide ligand as precursors for catalytic guanylation reactions of carbodiimides.

Herein, we report the synthesis, characterisation, and application of three aluminium alkyl complexes, [κ2-{NHIRP(Ph)NDipp}AlMe2] (R = Dipp (2a), Mes (2b); tBu (2c), Dipp = 2,6-diisopropylphenyl, Mes = mesityl, and tBu = tert-butyl), supported by unsymmetrical imino-phosphanamide [NHIRP(Ph)NDipp]− [R = Dipp (1a), Mes (1b), tBu (1c)] ligands as molecular precursors for the catalytic synthesis of guanidines using carbodiimides and primary amines. All the imino-phosphanamide ligands 1a, 1b and 1c were prepared in good yield from the corresponding N-heterocyclic imine (NHI) with phenylchloro-2,6-diisopropylphenylphosphanamine, PhP(Cl)NHDipp. The aluminium alkyl complexes 2a, 2b and 2c were obtained in good yield upon completion of the reaction between trimethyl aluminium and the protic ligands 1a, 1b and 1c in a 1 : 1 molar ratio in toluene via the elimination of methane, respectively. The molecular structures of the protic ligands 1b and 1c and the aluminium complexes 2a, 2b and 2c were established via single-crystal X-ray diffraction analysis. Complexes 2a, 2b and 2c were tested as pre-catalysts for the hydroamination/guanylation reaction of carbodiimides with aryl amines to afford guanidines at ambient temperature. All the aluminium complexes exhibited a high conversion with 1.5 mol% catalyst loading and broad substrate scope with a wide functional group tolerance during the guanylation reaction. We also proposed the most plausible mechanism, involving the formation of catalytically active three-coordinate Al species as the active pre-catalyst.

Ethylene polymerization with a crystallographically well-defined metal–organic framework supported catalyst

Crystallographic characterization of a heterogeneous ethylene polymerization catalyst elucidates a chromium–carbon bond after alkyl aluminum activation and provides mechanistic insights.

Cationic polymerization of butadiene using alkyl aluminum compounds as co-initiators: an efficient approach toward solid polybutadienes

Solid, soluble in organic solvents polybutadienes with reduced unsaturation and high glass transition and softening points were synthesized for the first time.

A New Paradigm in Enantioselective Cobalt Catalysis: Cationic Cobalt(I) Catalysts for Heterodimerization, Cycloaddition, and Hydrofunctionalization Reactions of Olefins.

One of the major challenges facing organic synthesis in the 21st century is the utilization of abundantly available feedstock chemicals for fine chemical synthesis. Regio- and enantioselective union of easily accessible 1,3-dienes and other feedstocks like ethylene, alkyl acrylates, and aldehydes can provide valuable building blocks adorned with latent functionalities for further synthetic elaboration. Through an approach that relies on mechanistic insights and systematic examination of ligand and counterion effects, we developed an efficient cobalt-based catalytic system [(P∼P)CoX2/Me3Al] (P∼P = bisphosphine) to effect the first enantioselective heterodimerization of several types of 1,3-dienes with ethylene. In addition to simple cyclic and acyclic dienes, siloxy-1,3-dienes participate in this reaction, giving highly functionalized, nearly enantiopure silyl enolates, which can be used for subsequent C-C and C-X bond-forming reactions. As our understanding of the mechanism of this reaction improved, our attention was drawn to more challenging partners like alkyl acrylates (one of the largest volume feedstocks) as the olefin partners instead of ethylene. Prompted by the intrinsic limitations of using aluminum alkyls as the activators for this reaction, we explored the fundamental chemistry of the lesser known (P∼P)Co(I)X species and discovered that in the presence of halide sequestering agents, such as sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBARF) or (C6F5)3B, certain chiral bisphosphine complexes are superb catalysts for regio- and enantioselective heterodimerization of 1,3-dienes and alkyl acrylates. We have since found that these cationic Co(I) catalysts, most conveniently prepared in situ by reduction of the corresponding cobalt(II) halide complexes by zinc in the presence of NaBARF, promote enantioselective [2 + 2]-cycloaddition between alkynes and an astonishing variety of alkenyl derivatives to give highly functionalized cyclobutenes. In reactions between 1,3-enynes and ethylene, the [2 + 2]-cycloaddition between the alkyne and ethylene is followed by a 1,4-addition of ethylene in a tandem fashion to give nearly enantiopure cyclobutanes with an all-carbon quaternary center, giving a set of molecules that maps well into many medicinally relevant compounds. In another application, we find that the cationic Co(I)-catalysts promote highly selective hydroacylation and 1,2-hydroboration of prochiral 1,3-dienes. Further, we find that a cationic Co(I)-catalyst promotes cycloisomerization followed by hydroalkenylation of 1,6-enynes to produce highly functionalized carbo- and heterocyclic compounds. Surprisingly the regioselectivity of the alkene addition depends on whether it is a simple alkene or an acrylate, and the acrylate addition produces an uncommon Z-adduct. This Account will provide a summary of the enabling basic discoveries and the attendant developments that led to the unique cationic Co(I)-complexes as catalysts for disparate C-C and C-B bond-forming reactions. It is our hope that this Account will stimulate further work with these highly versatile catalysts which are derived from an earth-abundant metal.

Synthesis, Characterization of Rare‐Earth Metal Chlorides Bearing Indolyl‐Based NCN Pincer Ligand and Their Catalytic Activity toward 1,4‐cis Polymerization of Isoprene

Main observation and conclusionA novel indolyl‐based NCN pincer ligand precursor HL (HL = (1‐(2‐(CH2)4NCH2CH2)‐3‐(2,6‐iPr2C6H3N=CH)C8H5N)) was rationally and precisely designed, and successfully prepared in a high yield. Lithiation of HL with nBuLi in n‐hexane, followed by treatment with RECl3 in THF led to the isolation of rare‐earth metal chlorides in monomeric form (κ3‐L)RECl2(THF) (RE = Sc(2), Yb(3)), and dimeric form [(κ3‐L)RECl(THF)(μ‐Cl)]2 (RE = Er(4), Y(5)) bearing the novel indolyl‐based NCN pincer ligand in designed pincer ligation depending on different metal ionic radii; and the chloride bridged rare‐earth metal and lithium mixed complexes in form (κ2‐L)2RE(μ‐Cl)2Li(THF)2 (RE = Y(6), Dy(7). All complexes were fully characterized and their structures were determined. The diamagnetic complexes 2, 5 and 6 were furtherly characterized by the NMR spectroscopic method. The catalytic activity studies revealed that the central metal ions, borates, aluminum alkyls, and ligation of the central metal ions have influences on catalytic activity, and regio‐ and stereoselectivity for the polymerization of isoprene. With cooperation of the cocatalysts, the pincer‐type yttrium chloride 5 initiated the isoprene polymerization with a high activity producing polymers with high regio‐ and stereoselectivity (1,4‐cis polymers up to 99.6%), and the Mn as high as 8.76 × 105.

Al-alkyls as acceptor dopant precursors for atomic-scale devices

Atomically precise ultradoping of silicon is possible with atomic resists, area-selective surface chemistry, and a limited set of hydride and halide precursor molecules, in a process known as atomic precision advanced manufacturing (APAM). It is desirable to expand this set of precursors to include dopants with organic functional groups and here we consider aluminium alkyls, to expand the applicability of APAM. We explore the impurity content and selectivity that results from using trimethyl aluminium and triethyl aluminium precursors on Si(001) to ultradope with aluminium through a hydrogen mask. Comparison of the methylated and ethylated precursors helps us understand the impact of hydrocarbon ligand selection on incorporation surface chemistry. Combining scanning tunneling microscopy and density functional theory calculations, we assess the limitations of both classes of precursor and extract general principles relevant to each.

Mechanistic study of vanadium-modified and sulfation-modified Phillips catalyst

• Differed from “naked” chromium center, two reduction routes with methyl formate derivant attaching on chromium center are put forward. • Compared with traditional Phillips catalyst, vanadium-modified Phillips catalyst is more exergonic during reduction process. • Alkylation with assistance of cocatalyst is meaningful to Phillips catalyst and assistance of TiBA with larger steric hindrance shows lower Gibbs free energy than dimeric TMA, which is in accordance with experimental evidences. • The addition of sulfur atom directly bonding with chromium center reduces energy barrier of chain propagation significantly. Phillips catalyst is one of the most significant industrial catalyst for polyolefin. Various modified methods have been developed to promote the polymerization activity and regulate properties of polyolefin, including vanadium-modification, sulfation-modification, etc. Vanadium-modified Phillips catalyst can produce bimodal polyethylene with sectional ultra-high molecular weight polyethylene to improve the mechanical property. Compared with traditional Phillips catalyst, sulfation-modified Phillips catalyst exhibits higher polymerization activity and wider molecular weight distribution. However, lack of knowledge still puzzles researchers in reduction, alkylation and modification for Phillips catalyst. In addition, complex chemical surrounding for heterogeneous catalyst is still a big challenge to carry out explicit analysis of this catalyst. In this work, fundamental insight into two modified methods towards Phillips catalyst has been garnered. The possible active metal centers existing on the surface of silica support and feasible precursors with reductant attaching on the chromium center were investigated. Moreover, based on two alkylation precursors with assistance of different alkyl aluminum, we proposed a probable six-membered ring mechanism through the Tischenko reaction with formation of methyl formate derivant. Interestingly, the addition of sulfur atom reduces energy barrier of chain propagation significantly. These results account for the advantages of vanadium-modification, sulfation-modification and cocatalyst for traditional Phillips catalyst.

Aluminium complexes supported by a thioether-bridged salen ligand: synthesis, characterization and application in ε-caprolactone homopolymerization and copolymerization with L-lactide

Several aluminium alkyl and alkyloxide complexes supported by a thioether-bridged salen ligand were synthesized by the protonolysis reaction. Reactions of N,N’-bis(3,5-di-tert-butylsalicylidene)-2,2’-diaminophenylsulfide (H2L) with one or two equivalents of AlMe3 in toluene at 100 °C afforded the corresponding mono- and binuclear aluminium methyl complexes LAlMe (1) and L(AlMe2)2 (2). Treatment of the in situ generated complex 1 with one equivalent of ROH (R = PhCH2, iPr, CH3OCH2CH2) produced the desired aluminium alkyloxide complexes LAlOCH2Ph (3), LAl(OiPr) (4) and LAlO(CH2)2OCH3 (5). All the molecular structures were established by single crystal X-ray diffraction studies. It was found that aluminium alkyloxide complexes 3-5 showed higher catalytic activity for the homopolymerization of ε-caprolactone (ε-CL) than corresponding aluminium methyl complexes 1 and 2. Furthermore, these alkyloxide complexes were also efficient initiators for the copolymerization of L-lactide and ε-CL to give practically random copolymers.

Aluminum Amidinates: Insights into Alkyne Hydroboration.

The mechanism of the aluminum-mediated hydroboration of terminal alkynes was investigated using a series of novel aluminum amidinate hydride and alkyl complexes bearing symmetric and asymmetric ligands. The new aluminum complexes were fully characterized and found to facilitate the formation of the (E)-vinylboronate hydroboration product, with rates and orders of reaction linked to complex size and stability. Kinetic analysis and stoichiometric reactions were used to elucidate the mechanism, which we propose to proceed via the initial formation of an Al-borane adduct. Additionally, the most unstable complex was found to promote decomposition of the pinacolborane substrate to borane (BH3), which can then proceed to catalyze the reaction. This mechanism is in contrast to previously reported aluminum hydride-catalyzed hydroboration reactions, which are proposed to proceed via the initial formation of an aluminum acetylide, or by hydroalumination to form a vinylboronate ester as the first step in the catalytic cycle.

The Effect of Titanium Tetra-Butoxide Catalyst on the Olefin Polymerization.

The purpose of this study was to assess the ability of titanium Ti(IV) alkyloxy compounds supported by organic polymer polyvinyl chloride (PVC) to polymerize ethylene by feeding triethylaluminium (TEA) as a cocatalyst. Additionally, the impacts of the molar ratio of [Al]/[Ti] on the catalytic activities in ethylene’s polymerization and of the comonomer through utilization of diverse quantities of comonomers on a similar or identical activity were studied. The optimal molar ratio of [Al]/[Ti] was 773:1, and the prepared catalyst had an initial activity of up to 2.3 kg PE/mol Ti. h. when the copolymer was incorporated with 64 mmol of 1-octene. The average molecular weight (Mw) of the copolymer produced with the catalysts was between 97 kg/mol and 326 kg/mol. A significant decrease in the Mw was observed, and PDI broadened with increasing concentration of 1-hexene because of the comonomer’s stronger chain transfer capacity. The quick deactivation of titanium butoxide Ti(OBu)4 on the polymers was found to be associated with increasing oxidation when supported by the catalyst. The presence of Ti(III) after reduction with the aluminum alkyls cleaves the carbon-chlorine bonds of the polymer, producing an inactive polymeric Ti(IV) complex. The results show that synergistic effects play an important role in enhancing the observed rate of reaction, as illustrated by evidence from scanning electron microscopy (SEM). The diffusion of cocatalysts within catalytic precursor particles may also explain the progression of cobweb structures in the polymer particles.

BUTADIENE RUBBER: SYNTHESIS, MICROSTRUCTURE, AND ROLE OF CATALYSTS

ABSTRACTButadiene rubber (BR) is one of the most useful and second most produced rubber worldwide. Polymerization of 1,3-butadiene (BD) is a highly stereospecific reaction that offers a wide variety of BR with different microstructures and influences the fundamental properties of the rubber. Since the first successful polymerization of conjugated diene using the Ziegler–Natta–based catalyst (TiCl4 or TiCl3 with aluminum alkyls) in 1954, the research on producing synthetic rubber with an appropriate catalyst system has been accelerated. Subsequently, various research groups are actively engaged in designing active catalyst systems based on a suitable combination of transition metal complexes with alkyl-aluminum and successfully using them in BD polymerization. Although various scientific inventions have proven their significance for the production of high-quality BR, with the rising demands in improving the quality of the product, research on developing new catalyst systems with enhanced catalytic activity and high stereoselectivity is still in progress. The present review focuses on the synthesis of BR using various transition metal catalysts and discusses their microstructures. The catalysts based on new-generation metal complexes with phosphorus, nitrogen, and oxygen donor ligands (e.g., phosphines, imines, 1,10-phenanthroline, and imino-pyridines) have been introduced. The role that catalysts play in the production of BR with different microstructures (i.e., high-cis, high-trans or low-cis, low-trans polybutadiene) has also been described. The combination of catalyst (transition metal complex) and suitable co-catalyst (alkyl-aluminum) is the major factor influencing the reaction and microstructure of the resulting polymer. This report focuses on the effect of transition metal catalysts (i.e., lithium [Li], titanium [Ti], zirconium [Zr], iron [Fe], cobalt [Co], nickel [Ni], and neodymium [Nd]) on the activity and stereoselectivity of polymers such as 1,4-cis-, 1,4-trans-, and 1,2-vinyl-polybutadiene.

Study on the Structure, Thermodynamic property, and Fluorescence of Pyridin‐2‐ylmethyl‐tert‐butylamine Dimethyl aluminum complex

AbstractPyridin‐2‐ylmethyl‐tert‐butylamine dimethyl aluminum complex with a planar five‐membered ring was synthesized and characterized by elemental analysis, UV‐Vis spectra, TG/DSC, 1H NMR, and 13C NMR. Through single‐crystal diffraction, it is proved that the structure of the alkyl aluminum complex is a planar five‐membered ring. By comparison the crystal data of 11 kinds of five‐membered ring dialkyl aluminum complexes, we found that the planar five‐membered ring dialkyl aluminum is formed when there is at least one unequal sp2 hybrid nitrogen in the ligand. TG/DSC study of the compound′s thermodynamic properties showed the thermal decomposition temperature of complex 7 was determined to be 210 °C. The rigid plane structure of the product was proved by fluorescence analysis. When the excitation wavelength was 380 nm, the emission wavelength was 478 nm.

Investigations on the Ethylene Polymerization with Bisarylimine Pyridine Iron (BIP) Catalysts

The kinetics and terminations of ethylene polymerization, mediated by five bisarylimine pyridine (BIP) iron dichloride precatalysts, and activated by large amounts of methyl aluminoxane (MAO) was studied. Narrow distributed paraffins from initially formed aluminum polymeryls and broader distributed 1-polyolefins and (bimodal) mixtures, thereof, were obtained after acidic workup. The main pathway of olefin formation is beta-hydrogen transfer to ethylene. The rate of polymerization in the initial phase is inversely proportional to the co-catalyst concentration for all pre-catalysts; a first-order dependence was found on ethylene and catalyst concentrations. The inhibition by aluminum alkyls is released to some extent in a second phase, which arises after the original methyl groups are transformed into n-alkyl entities and the aluminum polymeryls partly precipitate in the toluene medium. The catalysis is interpretable in a mechanism, wherein, the relative rate of chain shuttling, beta-hydrogen transfer and insertion of ethylene are determining the outcome. Beta-hydrogen transfer enables catalyst mobility, which leads to a (degenerate) chain growth of already precipitated aluminum alkyls. Stronger Lewis acidic centers of the single site catalysts, and those with smaller ligands, are more prone to yield 1-olefins and to undergo a faster reversible alkyl exchange between aluminum and iron.

Selective dimerisation of 1-hexene mediated by aluminium alkyl chloride-activated tungsten imido complexes

Tungsten imido complexes, in combination with EtAlCl2, were found to be efficient pro-catalysts for selective dimerization of 1-hexene to methyl-branched dodecenes, products that can be used for the production of jet and diesel engine fuels.