Aluminum Alkyls Research Articles

β-Diketiminate aluminium complexes: synthesis, characterization and ring-opening polymerization of cyclic esters

A series of aluminium alkyl complexes (BDI)AlEt(2) (3a-m) bearing symmetrical or unsymmetrical beta-diketiminate ligand (BDI) frameworks were obtained from the reaction of triethyl aluminium and the corresponding beta-diketimine. The monomeric structure of the aluminium complex 3k was confirmed by an X-ray diffraction study, which shows that the aluminium center is coordinated by both of the nitrogen donors of the chelating diketiminate ligand and the two ethyl groups in a distorted tetrahedral geometry. Attempt to synthesize beta-diketiminate aluminium alkoxide complexes by the reactions of monochloride complex "(BDI-2a)AlMeCl" (4) with alkali salts of 2-propanol gave unexpectedly an aluminoxane [(BDI-2a)AlMe](2)(micro-O) (7) as characterized by X-ray diffraction methods. Complexes 3a-m and [(2,6-(i)Pr(2)C(6)H(3)NCMe)(2)HC]AlEt(2) (8) were found to catalyze the ring-opening polymerization (ROP) of epsilon-caprolactone with moderate activities. The steric and electronic characteristics of the ancillary ligands have a significant influence on the polymerization performance of the corresponding aluminium complexes. The introduction of electron-donating substituents at the para-positions of the aryl rings in the ligand resulted in an apparent decrease in catalytic activity. Complex 3h showed the highest activity among the investigated aluminium complexes due to the high electrophilicity of the metal center induced by the meta-trifluoromethyl substituents on the aryl rings. The increase of steric hindrance of the ligand by introducing ortho-substituents onto the phenyl moieties also resulted in a decrease in the catalytic activity. Although the viscosity average molecular weights (M(eta)) of the obtained poly(caprolactone)s increased with the enhancement of monomer conversion, the ROPs of epsilon-caprolactone initiated by complexes 3a-m and 8 were not well-controlled, as judged from the broad molecular weight distributions (PDI = 1.66-3.74, M(w)/M(n)) of the obtained polymers and the nonlinear relationship of molecular weight versus monomer conversion.

Zirconocene Immobilization and Activation on MgCl2-Based Supports: Factors Affecting Ethylene Polymerization Activity

The effect of cyclopentadienyl ring substitution on the immobilization and activation of zirconocenes on supports of type MgCl2/AlRn(OEt)3-n has been investigated. Comparison of the activity of immobilized zirconocenes (RCp)2ZrCl2 in ethylene polymerization, using simple aluminum alkyls such as AlEt3 or AliBu3 as a cocatalyst, revealed a remarkable effect of the substituent R in the cyclopentadienyl ring. Low activity (<300 kg/mol bar h) was obtained with R = H or Et, but longer alkyl substituents, notably n-Pr or n-Bu, gave more than an order of magnitude increase in activity. Zirconocenes with branched substituents (i-Pr, t-Bu) were less easily immobilized and gave relatively low activity, while the activities of zirconocenes of composition Cp(RCp)ZrCl2 (R = n-Pr, n-Bu, n-pentyl) were intermediate between those of Cp2ZrCl2 and (RCp)2ZrCl2. Experiments carried out under homogeneous conditions with aluminoxane cocatalysts indicated that the effect of cyclopentadienyl ring substitution can be related to di...

A Flat Model Approach to Tethered Bis(imino)pyridyl Iron Ethylene Polymerization Catalysts

AbstractA surface science model for a silica supported bis(imino)pyridyl iron complexes is applied to reveal the surface chemistry of these heterogeneous polymerization catalysts. The polymerization activity of these models and the molecular weight distribution of the resulting polymer are comparable to similar catalysts supported on amorphous silica. The catalyst deactivates partially during the first hour of ethylene polymerization. Based on photoelectron spectroscopy (XPS) we attribute this deactivation to iron extrusion by the aluminium alkyl activator.

Facile Formation of Hexacyclic [Al3O2Cl] Aluminum and Alkoxide‐Bridged Titanium Complexes: Reactions of AlMe3 with [Ti(L)Cl2] [L = 2,2′‐Methylenebis(6‐tert‐butyl‐4‐methylphenolato)

AbstractThe titanium dichloride complex [(L)TiCl2] [L = 2,2′‐methylenebis(6‐tert‐butyl‐4‐methylphenolato)] (1) reacted with trimethylaluminum (AlMe3) in a 1:2 ratio to give a trimetallic aluminum complex of the composition [(L)(AlMe2)3(μ‐Cl)] (2) with a symmetric six‐membered ring [Al3(μ2‐O)2(μ2‐Cl)] and a four‐coordinate aluminum center in the solid state. The reaction of 1 equiv. AlMe3 gave [(L)TiMeCl] (3), which could absorb O2 gas to afford the oxygen‐insertion product [{(L)TiCl}2(μ‐OMe)2] (4) with a five‐coordinate metal center. Upon reaction of H2L with AlMe3, the binuclear, four‐coordinate adduct [{(L)AlMe}2] (5) was formed. Complex 4 supported on MgCl2 and activated with aluminum alkyls reveals high catalytic activity for ethylene polymerization to produce polymers with molecular weight distributions of ca. 3.1. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Investigations of the initial state polymerization of propylene with Ziegler–Natta catalysts in slurry

AbstractThe initial state polymerization of propylene with Ziegler–Natta catalysts has been investigated and discussed at very low polymerization yields under adiabatic industrial prepolymerization conditions in diluted slurry regarding the effects of significant process parameters like monomer pressure, aluminum alkyl, and donor kind and concentration including the morphology of the catalyst/polymer particles formed. A sharp temperature increase in the first minutes of the initial state polymerization is followed by a temperature maximum and a slow decrease. With cocatalyst triethyl aluminum (TEAL), high prepolymerization yields were already achieved at a molar ratio TEAL/Ti of 3.0, remaining about constant until ratios of at least 300. The external donor dicyclopentyl dimethoxy silane leads to higher polymerization yields than the donor cyclohexyl dimethoxymethyl silane in the initial state polymerization too; however, both show a remarkable decreasing effect on polymerization yield above a specific molar ratio donor/Ti obviously correlated with the bulkiness of the alkyl groups. The particle size of the catalyst and the catalyst/prepolymer particles is increasing with polymerization yield until about 22 g PP/g Cat with particles almost perfectly spherical. The particle size distribution is rather broad at lower prepolymerization stages but unifying with lower polymerization rates at higher polymerization times. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Biphasic ethylene polymerisation using ionic liquid over a titanocene catalyst activated by an alkyl aluminium compound

1- n-Butyl-3-methylimidazolium tetrachloroaluminate ([BMIM] +[AlCl 4] −) was applied to biphasic ionic liquid/hexane ethylene polymerisation as a medium of the Cp 2TiCl 2 titanocene catalyst activated by alkylaluminium compounds (MAO, AlEt 2Cl, AlEt 3). The best results were obtained using AlEt 2Cl. The results show that catalyst recycling, higher ethylene pressure, and greater Al/Ti molar ratio along with a greater volume of the ionic liquid phase enhance catalyst activity. The polyethylene gathered from the hexane phase is characterised primarily by its high purity. Its physical properties remain polyethylene obtained over a heterogeneous metallocene catalyst. Thus, biphasic ionic liquid polymerisation using a metallocene catalyst is possible and offers interesting technological implications.

Regularities of radiation-stimulated adsorption of n-hexane on an aluminum surface

IR reflection-absorption spectroscopy was used to examine the regularities of radiation-stimulated absorption of n-hexane on an aluminum surface. γ-Irradiation of an aluminum surface at room temperature produces sites capable of adsorbing n-hexane by the molecular and dissociative mechanisms. The kinetics of the adsorption of n-on aluminum γ-irradiated with doses of 5 to 25 Gy is indicative of activated dissociative chemisorption accompanied by the formation of aluminum alkyls and surface hydrides. A feasible mechanism for the process was proposed.

Synthesis and structural characterization of two five coordinate aluminum alkyl and bis(trimethylsilyl)amino complexes bearing acyclic tetradentate Schiff bases

Two acyclic Schiff-base ligands, bis-5,5′-(1,3-propanediyldiimino)-2,2-dimethyl-4-hexene-3-one and bis-5,5′-(1,3-ethanediyldiimino)-2,2-dimethyl-4-hexene-3-one, were used to complex homoleptic triethylaluminum and tris[bis(trimethylsilyl)amino]aluminum, respectively. The acid–base reactions proceeded in excellent yields with elimination of ethane or bis(trimethylsilyl)amine during in situ deprotonation of the protio Schiff-base. The colorless aluminum complexes crystallized from n-pentane and were characterized by standard methods including single crystal X-ray diffraction. Polymerization of racemic lactide, with addition of alcohol, yielded PLA with narrow polydispersities but low molecular weights.

Synthesis, structural characterisation of new oligomeric alkyl aluminium (2,2′-methylene- p-chloro-bisphenoxides) and application as catalysts in polymerisation reactions involving cyclohexene oxide

The synthesis, spectroscopic characterisation and X-ray structure determination of the first aluminium para-chloro-bisphenoxides [Al 2(mbpcp) 2(C 2H 5) 2(THF) 2] and [Al 3(mbpcp) 2(C 2H 5) 5] (mbpcp = 2,2′-methylenebis(4-chlorophenol) are reported. 2,2′-Methylenebis(4-chlorophenol) was reacted with triethyl aluminium to yield under liberation of ethane, aluminium para-chloro-2,2′-methylene-bisphenoxides with different molecular complexities: a dinuclear and a trinuclear specie, both displaying two bridging bisphenoxide ligands. The nature of the solvent (coordinating or not) influences the aggregation degree of the final product. The use of a coordinating solvent like THF yields a dimeric structure with a bisphenol:metal ratio of 1 to 1 which displays a trigonal-bipyramidal coordination geometry around the aluminium atoms whereas using an apolar, weak-coordinating solvent like diethyl ether yields a trinuclear species with a bisphenol:metal ratio of 2 to 3, displaying aluminium atoms with both tetrahedral and trigonal-bipyramidal coordination geometries. These compounds were tested in preliminary screening tests as catalysts of the homopolymerisation of cyclohexene oxide (CHO) and copolymerisation of CHO with carbon dioxide. Both aluminium bisphenoxides are highly active in the ring opening polymerisation of CHO (RT, reaction time <5 min, M n ranging from 31 000 to 40 700 g/mol, polydispersities from 1.2 to 1.4). Both compound are also active in the copolymerisation of CHO with CO 2 although the carbonate amount remains low (75 bar, 90 °C, reaction time 8 h, M n ranging from 6800 to 15 200 g/mol, polydispersities from 1.9 to 2.5).

Surface modification of metallic Co nanoparticles

Monodisperse Co nanoparticles were synthesized by thermal decomposition in the presence of aluminium alkyls yielding air-stable Co nanoparticles after surface passivation. Several procedures for surface modification of these pre-stabilized, metallic Co nanoparticles are presented, including direct anchoring of surface-active functional groups and biocompatible dextran layers as well as silica and polymer coatings. As a result, individually coated nanoparticles as well as microspheres can be obtained.

Synthesis, structural studies and reactivity of vanadium complexes with tridentate (OSO) ligand

The direct reaction between [VCl(3)(thf)3] or [VO(OEt)3] and 2,2'-thiobis{4-(1,1,3,3-tetramethyl-butyl)phenol (tbopH(2)) leads to the formation of [V(2)(micro-tbop-kappa(3)O,S,O)2Cl(2)(CH(3)CN)(2)] (1).4CH(3)CN or [V(2)(micro-OEt)2(O)2(tbop-kappa(3)O,S,O)2] (2), respectively, in high yield. Compounds 1 and 2 were characterized by chemical and physical techniques including X-ray crystallography and variable temperature magnetic susceptibility studies (J = -29.1 cm(-1)) for 1. Complexes 1 and 2 were supported on MgCl2 and when activated with aluminium alkyls, were found to effectively polymerize ethene to produce polyethylene with a narrow molecular weight distribution M(w)/M(n) approximately 3.

Synthesis and Reactivity of Pyrrolide-Diimine Complexes of Chromium

Lithium 2,5-bis{[(2,6-diisopropylphenyl)imino]methyl}pyrrol-1-ide (LiL) reacts with [CrCl3(thf)3] to yield the octahedral complex [(η2-L)CrCl2(thf)2] (1), in which only two of the three potential nitrogen donors are coordinated to chromium. In the presence of various alkyl aluminum cocatalysts, 1 catalyzes the polymerization of ethylene. Attempts to prepare alkyl derivatives of 1 were thwarted by an apparent disproportionation, yielding divalent [(η2-L)(η1-L)Cr(thf)] (2). The molecular structures of 1 and 2 have been determined by X-ray diffraction. The structure of 2 is unusual in that it features weak, but equivalent interactions of both imine groups of the η1-pyrrolide ligands with the chromium, giving rise to an approximately octahedral coordination geometry with two extremely long Cr-N distances.

Aluminum Alkyl Complexes Containing Bidentate, Mono‐ or di‐anionic Pyrrolyl Ligands: Intramolecular Elimination of Methane and 1‐Hexene Polymerization

AbstractA series of aluminum alkyl complexes were synthesized and their catalytic polymerization reactivity toward 1‐hexene was studied. Aluminum complexes, [C4H3N(CH2NHMe)‐2]AlR2 (1a, R = Me; 1b, R = Et), containing substituted pyrrolyl ligand can be prepared by reacting AlR3 with one equiv of C4H3NH(CH2NHMe)‐2 in diethyl ether at room temperature. Dimeric aluminum complexes, {[C4H3N‐(CH2NMe)‐2]AlR}2 (2a, R = Me; 2b, R = Et), can be obtained via metathesis by heating AlR3 and with one equiv of [C4H3NH(CH2NHMe)‐2] in toluene for 24 h or via intramolecular methane elimination by heating 1 and 2 at 90 °C in toluene. Complexes 1a, 1b, 2a, and 2b have been characterized by NMR spectroscopy and by X‐ray crystallography. Complexes 1a and 2a have shown moderate reactivity for 1‐hexene polymerization in the presence of MAO.

Reversible Chain Transfer between Organoyttrium Cations and Aluminum: Synthesis of Aluminum‐Terminated Polyethylene with Extremely Narrow Molecular‐Weight Distribution

Aminopyridinato-ligand-stabilized organoyttrium cations are accessible in very good yield through alkane elimination from trialkyl yttrium complexes with sterically demanding aminopyridines, followed by abstraction of one of the two alkyl functions using ammonium borates. At 80 degrees C and in the presence of small amounts of aluminum alkyl compounds, very high ethylene polymerization activities are observed if very bulky aminopyridinato ligands are used. During these polymerizations a reversible polyethylene chain transfer is observed between the organoyttrium cations and aluminum alkyls. The chain-transfer catalyst system described here is able to produce relatively long-chain (up to 4000 g mol-1) Al-terminated polyethylene with a molecular-weight distribution<1.1. In the synthesis of higher molecular PE a slight increase in polydispersity with increasing chain length (15,600 g mol-1, approximately 1.4) is observed owing to reduced reversibility caused by higher viscosity and precipitation of polymer chains (temperature of 80-100 degrees C).

Surface engineering of Co and FeCo nanoparticles for biomedical application

Monodisperse Co, Fe, and FeCo nanoparticles are prepared via thermal decomposition ofmetal carbonyls in the presence of aluminium alkyls, yielding air-stable magnetic metalnanoparticles after surface passivation. The particles are characterized by electronmicroscopy (SEM, TEM, ESI), electron spectroscopy (MIES, UPS, and XPS) and x-rayabsorption spectroscopy (EXAFS). The particles are peptized by surfactants to form stablemagnetic fluids in various organic media and water, exhibiting a high volume concentrationand a high saturation magnetization. In view of potential biomedical applications of theparticles, several procedures for surface modification are presented, includingpeptization by functional organic molecules, silanization, and in situ polymerization.

Investigation of ion pair formation in the triphenylmethyl chloride–trimethyl aluminium system, as a model for the activation of olefin polymerization catalyst

Triphenylmethyl chloride (“trityl chloride”, Ph 3CCl) will transfer chloride ions to aluminium alkyls and methylaluminoxane and it is thereby converted into 1,1,1-triphenylethane (“trityl methyl” Ph 3CMe) and the triphenylcarbonium ion (“trityl ion”, Ph 3C +). IR spectra of these trityl species have been recorded. Assignments are supported by quantum chemical calculations, leading to significant revisions for some of the modes that are most influenced by reactions. A bright yellow colour shown to be due to the trityl cation, makes trityl chloride a useful indicator for ion pair formation. Trimethyl aluminium (TMA) is chlorinated by trityl chloride and forms dimethyl aluminium chloride (DMAC). DMAC will form a stable ion pair with trityl chloride, probably by forming the anion Al 2Cl 3Me 4 −. Large excess of trityl chloride causes the formation of AlCl 4 −, and probably AlCl 3Me − and AlCl 2Me 2 − anions. It appears that methyl aluminium chloride anions are formed if, and only if, the anions have at least three chlorine atoms, possibly because of the need to dissipate the negative charge enough to keep the anion dissolved in the hydrocarbon solvent. Methylaluminoxane (MAO) also forms ion pair with trityl chloride, although to lesser extent and less persistent.

Sterically Hindered Aluminum Alkyls: Weakly Interacting Scavenging Agents of Use in Olefin Polymerization

Sterically hindered aluminum methyl compounds derived from reaction of hindered phenols with AlMe3 (i.e., MeAl(BHT)2 and MeAl(BHT*)2; BHT = 2,6-di-tert-butyl-4-methylphenoxide; BHT* = 2,4,6-tri-tert-butylphenoxide) are useful scavenging agents in olefin polymerization using metallocene catalysts. They do not, or only slowly, react with activators such as B(C6F5)3 or [Ph3C][B(C6F5)4] at 25 °C, nor do they coordinate to or react with metallocenium ion-pairs derived from metallocene dialkyls and these activators. A mixture of AlMe3 and a large excess of MeAl(BHT)2 proves advantageous for catalysts that are susceptible to reaction with BHT-H, the hydrolysis product of MeAl(BHT)2. Ethylene polymerization experiments establish that the activity of [Cp2ZrMe][MeB(C6F5)3] is only slightly inhibited by AlMe3 in the presence of a significant excess of MeAl(BHT)2. Spectroscopic studies have revealed that AlMe3 is in equilibrium with MeAl(BHT)2, forming Me2Al(BHT). At low temperature using 13C NMR spectroscopy, a 1:1 ...

Synthesis, Characterization, and Polymerization Activity of the Scandium Half‐Sandwich Complex [Sc(η5‐C5Me4{SiMe2(C6F5)})(CH2SiMe3)2(THF)

AbstractThe scandium half‐sandwich (bis)alkyl complex [Sc(η5‐C5Me4{SiMe2(C6F5)})(CH2SiMe3)2(THF)] has been prepared by σ‐bond metathesis between [Sc(CH2SiMe3)3(THF)2] and C5Me4H{SiMe2(C6F5)}. Structural characterization by single crystal X‐ray diffraction revealed the typical piano‐stool geometry for this type of complex. The addition of [Ph3C][B(C6F5)4] resulted in the formation of a half‐sandwich alkyl cation which is an efficient catalyst for the syndiospecific polymerization of styrene in the presence of aluminium alkyls.

Role of the Metal Oxidation State in the SNS−Cr Catalyst for Ethylene Trimerization: Isolation of Di- and Trivalent Cationic Intermediates

The reaction of the highly selective [CySCH2CH2N(H)CH2CH2SCy]CrCl3 catalyst precursor with alkyl aluminum activators was examined with the aim of isolating reactive intermediates. Reaction with Me3Al afforded a cationic trivalent chromium alkyl species {[CySCH2CH2N(H)CH2CH2SCy]CrMe(mu-Cl)}2{(AlMe3)2(m-Cl}2.(C7H8)2 (1a). Although it was not possible to obtain crystalline samples of sufficient quality from the reaction with MAO (the most preferred activator), the near-to-identical EPR spectra indicated a very close structural similarity with 1a. Ethylene oligomerization tests clearly revealed that 1 and other cationic trivalent dimeric complexes {[CySCH2CH2N(H)CH2CH2SCy] CrCl(mu-Cl)}2{AlCl4}2.(C7H8)1.5 (2), monomeric [(CySCH2CH2N(H)CH2CH2SCy)CrCl2 (THF)][AlCl4] (3), and {[CySCH2CH2N(H)CH2CH2SCy]Cr(eta2-AlCl4)}{Al2Cl7} (4) adducts display the same catalyst selectivity as the [CySCH2CH2N(H)CH2CH2SCy]CrCl3 complex and, therefore, are probably all precursors to the same catalytically active species. 2, 3, and 4 were obtained upon treatment of [CySCH2CH2N(H)CH2CH2SCy] CrCl3 with different stoichiometric ratios of AlCl3.. When i-BAO activator was used, reduction of the metal center occurred readily, affording {([CySCH2CH2N(H)CH2CH2S Cy]Cr)(mu-Cl)]2}{(i-Bu)2AlCl2}2 (5). 5 is also a selective catalyst, thus indicating that trivalent species are most probably precursors to a divalent catalytically active complex. Reaction of CrCl2(THF)2 with the ligand afforded the labile divalent adduct [CySCH2CH2N(H)CH2CH2SCy]CrCl2(THF) (6), also catalytically active and selective. Instead, deprotonation of the ligand with n-BuLi followed by reaction with CrCl2(THF)2 gave the dinuclear complex [(mu-CySCH2CH2NCH2CH2SCy)CrCl]2 (7), which did not produce oligomers.

Notable Effects of Aluminum Alkyls and Solvents for Highly Efficient Ethylene (Co)polymerizations Catalyzed by (Arylimido)- (aryloxo)vanadium Complexes

The effects of both Al cocatalyst and solvent on catalytic activity in the ethylene polymerization by the (arylmido)(aryloxo)vanadium(V) complex, VCl2(N-2,6-Me 2 C 6 H 3 )(O-2,6-Me 2 C 6 H 3 ) (1), have been explored in detail. The activity of 5.84 × 10 5 kgPE/molV-h (TOF 2.08 × 10 7 h -1 ) has been achieved by 1/EtAlCl 2 catalyst in CH 2 Cl 2 at 0°C, and the activity in toluene increased in the order: i-Bu 2 AlCl > EtAlCl 2 > Me 2 AlCl > Et 2 AlCl > Et 2 Al(OEt), AlEt 3 , AlMe 3 (negligible activities). Both aluminum alkyl cocatalyst and solvent also affected the catalytic activity and the norbornene (NBE) incorporation in the ethylene/NBE copolymerization using complex 1, whereas the NBE contents were not strongly affected by the kind of aryl oxide ligand in VCl2(N-2,6-Me 2 C 6 H 3 )(OAr) [OAr=O-2,6-Me 2 C 6 H 3 (1), O-2,6-i-Pr 2 C 6 H 3 (2), O-2,6-Ph 2 C 6 H 3 (3)].