Addition Of Methylaluminoxane Research Articles

(Arylimido)niobium(V) Complexes Containing 2-Pyridylmethylanilido Ligand as Catalyst Precursors for Ethylene Dimerization That Proceeds via Cationic Nb(V) Species

(Arylimido)niobium(V) complexes containing 2-pyridylmethylanilido ligand Nb(NAr)X2(L) [L = 2-(2,6-Me2C6H3)NCH2(C5H4N); X = NMe2 (2a,b), OCH(CF3)2 (3a–c), Me (4a–c), CH2SiMe3 (5a); Ar = 2,6-Me2C6H3 (a), 2,6-iPr2C6H3 (b), 2-MeC6H4 (c)] have been prepared, and structures of 3a,b, 4b, and 5a were determined by X-ray crystallography. The dimethyl complexes (4a,b) exhibited catalytic activities for ethylene dimerization in the presence of methylaluminoxane (MAO), whereas the activity by 4c was negligible under the same conditions. Complex 4b showed the highest activity, and the activity at 50 °C was higher than those conducted at 25 and 80 °C. The major product was 1-butene, and 1-hexene was formed by subsequent reaction of ethylene with 1-butene accumulated in the reaction mixture. A first-order relationship between the activity [turnover frequency (TOF)] and ethylene pressure was observed, suggesting that the metal-alkyl species would play a role in this catalysis. The activities further increased remarkably upon addition of [Ph3C][B(C6F5)4] at 50 °C; TOF at the initial stage (5 min) of 2 100 000 h–1 (583 s–1) has been attained. Reactions of the dimethyl complexes (4a,b) with 1.0 equiv of [Ph3C][B(C6F5)4] in Et2O afforded [Nb(NAr)Me(L)]+[B(C6F5)4]−(Et2O)2 (6a,b), and the reaction of 6b with ethylene afforded 1-butene and 1-hexene even in the absence of MAO, clearly suggesting that the cationic species play a role in this catalysis. X-ray absorption near edge structure spectra of the catalyst solutions containing 4b (in toluene at 25 °C) and MAO (10 and 50 equiv) showed no significant differences in the pre-edge peak positions and intensities from that in the dimethyl complex (4b), strongly suggesting that both the oxidation states and the basic structures are maintained upon addition of MAO in these catalyst solutions.

Tailoring Hexagonal Gibbsite Single Crystal Nanoplatelets for Ethylene Polymerization and Nanocomposite Formation on MAO-Free Heterogeneous Bis(imino)pyridine Iron(II) Catalyst.

Ultrathin single crystal γ-Al(OH)3 (Gibbsite) nanoplatelets with average thickness <20 nm and length <800 nm, pretreated with trimethylaluminum (TMA), represent highly efficient activators and supports bis(imino)pyridine iron (II) (FeBIP) complex to produce high density polyethylene (HDPE) as well as gibbsite/HDPE nanocomposites in exceptionally high yields. Opposite to both methylaluminoxane (MAO)-activated homogeneous FeBIP catalyst and heterogenous silica-supported single site catalysts, no addition of MAO is required. At low TMA/Fe = 50 molar ratio, the superior catalyst activity (up to 6500 kg mol-1 h-1 bar-1 ) of FeBIP@TMA@Gibbsite is paralleled by controlled polyethylene particle growth without encountering reactor-fouling problems typical for homogeneous catalysts. TMA@Gibbsite is compared with other AlR3 @Gibbsite activators. The Al/Fe molar ratio governs catalyst activity as well as molar mass, molar mass distribution, and thermal properties of polyethylene. Moreover, hexagonal gibbsite nanoplatelets are uniformly dispersed in polyethylene to yield agglomerate-free polyethylene/gibbsite nanocomposites.

Synthesis and characterization of ethylene-propylene copolymer and polyethylene using α-diimine nickel catalysts

Nickel-based catalysts of dibromo[N,N′-bis(2,6-diisopropylphenyl)-2,3-butanediimine]nickel(II) (A) and dibromo[N,N′-(phenanthrene-9,10-diylidene)bis(2,6-diisopropylaniline)]nickel(II) (B) were synthesized under controlled conditions. The catalysts A, B and mixed of 1:1 weight ratio of them were used for ethylene-propylene (EP) copolymerization and ethylene polymerization. Methylaluminoxane (MAO) was used as a cocatalyst. The polymers were characterized by means of FT-IR, 1H NMR and DSC (Differential scanning calorimetry). In ethylene polymerization using mixed of 1:1 w/w of the catalysts A and B degree of branching polymer chain decreased with increasing monomer pressure while increased with enhancing polymerization temperature. In ethylene-propylene copolymerization using mixed of 1:1 w/w of A and B, the catalytic system showed the maximum activity at about [Al]/[Ni] = 2000:1 ratio and further addition of MAO did not affect the activity of the catalyst. Increasing the copolymerization temperature from 20 to 80 °C decreased the productivity of the catalytic system while increased the ethylene content of the copolymer. Decreasing relative pressure of P Pr /P Et from 9:1 to 1:1 increased the ethylene contents of the copolymers from 51 % to 72 % while decreased the viscosity average molecular weight (M v ) and glass transition temperature (T g ) of the products. A copolymer with more rubber-like behavior was obtained in relative pressure of P Pr /P Et (5:1) and total pressure of 5 bars.

Ethylene polymerization using fluorinated FI Zr-based catalyst

A fluorinated FI Zr-based catalyst of bis[N-(3,5-dicumylsalicylidene)-2′,6′-flouroanilinato]zirconium(IV) dichloride was prepared and used for polymerization of ethylene. It was revealed that ortho-F-substituted phenyl ring on the N electronically plays a key role in the suppression of chain transfer reactions especially β-hydride transfer which resulted in an increase in the molecular weight of the obtained polymer and moderation of the catalyst activity as well. Methylaluminoxane (MAO) and triisobuthylaluminum (TIBA) were used as a cocatalyst and a scavenger, respectively. The catalyst showed the maximum activity at about [Al]:[Zr] = 32000:1 M ratio and further addition of MAO did not affect the activity of the catalyst. Ortho-F not only impressed the activity, but also reduced the [Al]:[Zr] molar ratio needed to reach the highest activity in comparison with the similar non-fluorinated FI catalysts. The highest activity of the prepared catalyst was obtained at 35 °C. At the monomer pressure of 3 bars polyethylene was obtained with the viscosity average molecular weight (M v) of 1.3 × 106 indicating the dramatic effect of ortho-F substitution on the polymerization mechanism. The polymerization was carried out using different amounts of hydrogen. Neither the activity of the catalyst nor the viscosity average molecular weight (M v) of the obtained polymer was sensitive to the hydrogen concentration. However, higher amount of hydrogen could slightly increase the activity of the catalyst.

Study of activation process and active site of co‐based catalyst for 1, 3‐butadiene polymerization using X‐ray absorption spectroscopy and DFT calculations

AbstractActivation process and active site of Co‐based Ziegler‐Natta catalysts were studied by using synchrotron X‐ray absorption spectroscopic technique and an optimum model of the cobalt active site was proposed with density functional theory (DFT) calculations. In the X‐ray absorption near edge structure (XANES) spectrum of Co(2‐ethylhexanoate)2, the preedge peak, 1s → 3d transition at 7707.8 eV and the K‐edge peak, 1s → 4p transition at 7719.2 eV were observed. Both the intense K‐edge and the weak preedge peaks indicate that Co(2‐ethylhexanoate)2 possesses high Oh symmetry and the cobalt exists in a divalent state. Upon addition of methylaluminoxane (MAO), some changes in peak positions and intensities were observed. The preedge peak was a little shifted to 7708.2 eV with increased intensity, and the K‐edge peak was shifted to a lower energy, 7717.2 eV with decreased intensity. This indicates that the oxidation state of cobalt still mainly remained +2 and the coordination geometry was altered from Oh to Td resulting from Co 3d and 4p orbital mixing with a loss of Oh symmetry. In the XANES spectrum of a mixture of Co(2‐ethylhexanoate)2, MAO and t‐BuCl, the K‐edge peak at 7715.7 eV was observed. The orbital mixing of 4p cobalt and 2p chlorine orbitals results in a low energy transition. In 1,3‐butadiene polymerization, this is attributable to the coordination of chlorine to cobalt, which is believed to facilitate cis‐configuration and increasing reactivity. B(C6F5)3 was employed as Lewis acid, but no significant interaction with cobalt was found in the XANES spectrum of a mixture of Co(2‐ethylhexanoate)2, Al(iBu) and B(C6F5)3, which is similar to the XANES of a mixture of Co(2‐ethylhexanoate)2 and Al(iBu)3. B(C6F5)3 as Lewis acid does not greatly disturb the coordination symmetry of cobalt nor influence the oxidation state. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Demonstration of Promoted Zinc Schlenk Equilibria, their Equilibrium Values and Derived Reactivity

The presence of promoted Schlenk equilibria for organozinc halide species has been explicitly demonstrated by 13C NMR studies. Thus, addition of methylaluminoxane (MeAlO)n, MAO, to RZnX (R=Et, Bn, ArCH2, (CH2)3CO2Et; X=Cl, Br) leads to the formation of ZnR2 and ZnX2MAO. For EtZnCl, equilibration of ZnEt2 and ZnX2MAO is rapid at -35 degrees C; a K value of 0.19 M-1 indicates the equilibrium favours ZnEt2 (0.75-3.0 equiv MAO). Use of RZnX/MAO mixtures allows copper-catalysed 1,4-addition to 2-cyclohexenone to be achieved, but a competing cascade reaction (two subsequent Michael additions and an intramolecular aldol reaction) leads to novel tetracyclic by-products (characterised crystallographically in one case). Activation of EtZnCl is also achieved by ZnMe2 addition and the presence of intermediate EtZnMe was observed by 13C NMR spectroscopy (at equilibrium, K approximately 1). Asymmetric conjugate addition in this system can be realised (up to 92% ee for additions to 2-cyclohexenone).

Activation process of 3-alkyl-substituted ansa-bis(indenyl) zirconocenes by MAO

The ansa-indene compound {1-Me 2Si(3-C 9H 6Et) 2} ( 1) was prepared by alkylation of the unsubstituted ansa-indene. This compound was converted, by reaction with nBuLi, to the dilithium compound [Li 2{1-Me 2Si(3-C 9H 5Et) 2}] ( 2). ansa-Zirconocene [Zr{1-Me 2Si(3-η 5-C 9H 5Et) 2}Cl 2] ( 3) was prepared by the reaction of ZrCl 4 with 2 in ether/toluene at −78 °C. The molecular structure of meso- 3 was determined by single crystal X-ray diffraction studies. The ansa-zirconocene 3 exhibits a greater activity in ethylene polymerization than reference complexes such as [Zr{1-Me 2Si(η 5-C 9H 6) 2}Cl 2] and [Zr{1-C 2H 4(η 5-C 9H 5) 2}Cl 2] and, in addition, it maintained a reasonable level of activity after 12 h of contact with MAO solution. Furthermore, the different elementary steps in the activation process of ethylene polymerization for substituted complexes [Zr{1-Me 2Si(3-η 5-C 9H 5R) 2}Cl 2] (R = Et 3, Me 4, nPr 5 and nBu 6) by commercial methylaluminoxane (MAO) have been studied by UV–vis spectroscopy. Addition of MAO in large excess ([Al]/[Zr] = 2000) at −78 °C yields a previously unreported intermediate in the activation process of metallocenes; this intermediate has an absorption band centered at λ = 639 nm. We report here the influence of the type of catalyst, ring substitution, type of cocatalyst and addition of THF on the activation process of these metallocenes.

Monocyclopentadienyl Chloro Bisphenoxo Ti(η5-C5H4SiMe2Cl)(η2-MBMP)Cl Derivative: Ti−Cl, Ti−O, and Si−Cl Reactivity. Crystal Structure of Ti(η5-C5H4SiMe3)(η2-MBMP)Cl and Ti(η5-C5H4SiMe2-η1-MBMP)(CH2Ph)2

The monocyclopentadienyl η2-bisphenoxo chloro compound Ti(η5-C5H4SiMe3)(η2-MBMP)Cl (3), containing the bidentate dianionic η2-MBMP ligand coordinated to the titanium center, has been prepared in good yield by reaction of 1 equiv of Li2(MBMP) with Ti(η5-C5H4SiMe3)Cl3 in hexane, at −78 °C. The compound Ti(η5-C5H4SiMe2Cl)(η2-MBMP)Cl (1) reacts with alkylating reagents MgClR [R = Me, CH2Ph] or LiMe, in hexane or toluene, at low or room temperature, to afford the monocyclopentadienyl η2-bisphenoxo derivatives Ti(η5-C5H4SiMe2X)(η2-MBMP)R [R = Me, X = Cl (4); R = X = Me (5); R = CH2Ph, X = Cl (6); R = X = CH2Ph (7)] or the ansa-monocyclopentadienylphenoxo dibenzyl complex Ti(η5-C5H4SiMe2-η1-MBMP)(CH2Ph)2 (8), depending on the reaction conditions. ansa-Monocyclopentadienylphenoxo dialkyl complexes Ti(η5-C5H4SiMe2-η1-MBMP)R2 [R = CH2Ph (8), Me (9)] can be alternatively synthesized by treatment of Ti(η5-C5H4SiMe2-η1-MBMP)Cl2 (2) with 2 equiv of MgCl(CH2Ph) or MgClMe. Compounds 3 and 8 have been characterized by single-crystal X-ray crystallography. Upon addition of methylaluminoxane, these bisphenoxo complexes are active in the polymerization of ethylene and styrene.

Studies of the Nature of the Catalytic Species in the α‐Olefin Polymerisation Processes Generated by the Reaction of Diamido(cyclopentadienyl)titanium Complexes with Aluminium Reagents as Cocatalysts

AbstractThe reaction of the diamido(chloro)cyclopentadienyltitanium compounds TiCpRx[1,2‐C6H4(NR′)2]Cl [CpRx = η5‐C5H5, η5‐C5(CH3)5, η5‐C5H4(SiMe3); R′ = CH2tBu, Pr] with the Grignard reagent MgClR (R = Me, CH2Ph) affords the monomethyl and monobenzyl derivatives TiCpRx[1,2‐C6H4(NR′)2]R. Upon addition of methylaluminoxane (MAO), the chloro‐ and alkyltitanium complexes show low activity towards the polymerisation of ethylene and styrene. However, no methylation was observed during the treatment of trimethylaluminium with the chloro compounds TiCpRx[1,2‐C6H4(NR′)2]Cl. Instead, these reactions give the dinuclear aluminium complexes Al2[1,2‐C6H4(NR′)2]Me4 (R′ = CH2tBu, Pr) through transmetallation of the diamido ligand, suggesting a deactivation process of the catalysts in the olefin polymerisation reactions. In an additional effort to model the catalytic species, stoichiometric reactions between the methyl derivatives TiCpRx[1,2‐C6H4(NR′)2]Me and solid methylaluminoxane (MAO) were studied by NMR spectroscopy. Monitoring of these reactions revealed the formation of zwitterionic species depending on the nature of the solvent. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2005)

An Unprecedented Dimerization of 1,2,3-Butatriene Catalyzed by Palladium Complexes

Abstract Dehydrogenative dimerization of (Z)-1,4-bis(trimethylsilyl)-1,2,3-butatriene was catalyzed by Pd complexes in the presence of allyl halides to give predominantly an acyclic conjugated enyne, while addition of methylaluminoxane (MAO) instead of allyl halides produced an unprecedented dimer that has an alkynyl-substituted cyclopentadienyl structure.

Monocyclopentadienyl and ansa-Monocyclopentadienylalkoxo Complexes of Titanium Containing the 2,2‘-Methylenebis(6-tert-butyl-4-methylphenoxo) Ligand. Synthesis, Characterization, and Polymerization Catalyst Behavior. Molecular Structure of Ti(η5-C5H5)(η2-MBMP)Cl, Ti(η5-C5Me5)(η2-MBMP)Cl, and Ti(η5-C5H4SiMe2-η1-MBMP)Cl2

The dialkoxo titanium complexes TiCp‘(η2-MBMP)Cl [Cp‘ = η5-C5H5 (1); η5-C5Me5 (2)] have been prepared in good yields by reaction of Li2(MBMP) with the corresponding monocyclopentadienyltrichloro titanium derivative. In a similar reaction the addition of 1 equiv of Li2(MBMP) to Ti(η5-C5H4SiMe2Cl)Cl3 generates the analogous titanium compound Ti(η5-C5H4SiMe2Cl)(η2-MBMP)Cl (3), while the ansa-cyclopentadienylalkoxo complex Ti(η5-C5H4SiMe2-η1-MBMP)Cl2 (4) is formed when MBMPH2 is treated with Ti(η5-C5H4SiMe2Cl)Cl3 in the presence of NEt3 in 1:1:2 molar ratio. Compounds 1, 2 and 4 have been characterized by single-crystal X-ray crystallography. DFT calculations were performed in order to elucidate the energies and geometries for these compounds. Upon addition of methylaluminoxane (MAO), the bisphenoxo complexes are active in the polymerization of α-olefins.

Elementary mechanisms of metallocene activation by methylaluminoxane cocatalysts for olefin polymerization

AbstractThe different elementary steps in the activation process of racEt(Ind)2ZrCl2 by commercial methylaluminoxane (MAO) have been studied by UV/visible spectroscopy and correlated with hexene polymerization kinetics. After monomethylation of the zirconocene dichloride (λ = 396 nm), abstraction of Cl ligand by MAO at low Al/Zr ratios (Al/Zr = 150) yields tight ion pairs, with an absorption band centred at λ = 440 nm, which are inactive towards hexene polymerization. Addition of MAO in large excess (Al/Zr = 2000) is required to form the active species. The latter, characterized by an absorption at λ = 470 nm, were identified as trimethylaluminium (TMA) separated ion pairs. The activation by commercial MAO of racEt(Ind)2ZrX2, with X being methyl, benzyl or dimethylamino as extractable group, instead of chloride, reveals much easier and complete activation at low Al/Zr ratios (Al:Zr = 50–150). For these systems, formation of active ion pairs of different catalytic activities and absorbing in the range λ = 430–440 nm is observed. The use of TMA‐depleted MAO instead of commercial MAO, as cocacalyst for racEt(Ind)2ZrCl2 actvation also allows the formation of active tight ion pairs absorbing at λ = 440 nm at low Al/Zr ratio. These results underline the negative role of chloride ligands when associated with TMA (contained in MAO) in the activation process of zirconocene for olefin polymerization, and also suggest interesting alternatives to reduce the amount of MAO necessary for metallocene activation.© 2002 Society of Chemical Industry

The negative role of chloride counter-anion in the activation process of zirconocene dichloride by methylaluminoxane

The different elementary steps in the racEt(Ind) 2ZrCl 2 activation process by commercial methylaluminoxane (MAO) are studied by UV–VIS spectroscopy technique and correlated with hexene polymerization kinetics. After monomethylation of the zirconocene dichloride ( λ=396 nm), abstraction of Cl ligand by MAO at low Al:Zr ratios (Al:Zr=150) yields tight ion pairs, [racEt(Ind) 2ZrMe] +, [MAOCl] − with an absorption band centered at λ=440 nm, inactive towards hexene polymerization. Addition of MAO in large excess (Al:Zr=2000) is therefore required to form active species identified as TMA separated ion pairs, [racEt(Ind) 2Zr +(μ-Me) 2AlMe 2], [MAO-Cl] − ( λ=470 nm). The activation of racEt(Ind) 2ZrMe 2 by MAO reveals much easier and is complete at low Al:Zr ratios (Al:Zr=150), yielding directly active ion pairs [racEt(Ind) 2ZrMe] +, [MAOMe] −, absorbing at λ=439 nm. These data underline the negative role of [MAOCl] − as a counter-anion in the activation process of zirconocene dichloride precursor for olefin polymerization. In the same conditions, the use of TMA-depleted MAO allows the direct formation, at low Al:Zr ratio, of active tight ion pairs ( λ=440 nm).

Covalent titanium aryldioxy one-, two-, and three-dimensional networks and their examination as Ziegler-Natta catalysts.

Treatment of ((i)PrO)4Ti with 2,7-dihydroxynaphthalene at 100 degrees C afforded the one-dimensional ladder [cis-Ti(mu(2,7)-OC10H6O)2py2]n (1: C30H22N2O4Ti, orthorhombic, P2(1)2(1)2(1), a = 9.866(2) A, b = 15.962(3) A, c = 16.223(3) A, Z = 4), in pyridine, and the stacked ladder, two-dimensional [Ti(mu(2,7)-OC10H6O)2(4-picoline)2.(4-picoline)(0.5)]n (2: C70H59N5O8Ti2, triclinic, P1, a = 10.814(2) A, b = 16.785(3) A, c = 18.020(4) A, alpha = 93.88(3) degrees, beta = 107.31(3) degrees, gamma = 108.77(3) degrees, Z = 2), in 4-picoline. A disruption of intramolecular edge-to-face and intermolecular face-to-face pi-stacking interactions in 1 by the Me group of the 4-picoline causes the structural change to 2. These derivatives and related two- and three-dimensional covalent metal organic networks (CMON) were assayed for ethylene and propylene polymerization activity via the addition of methylaluminoxane. CMON are mediocre Ziegler-Natta catalysts that generate polydisperse, linear polyethylene and atactic polypropylene. The data are best accommodated by viewing the degradation of CMON into numerous active sites of differing activity.

Titanium Complexes Having Chelating Diaryloxo Ligands Bridged by Tellurium and Their Catalytic Behavior in the Polymerization of Ethylene

A series of titanium complexes having tellurium-bridged chelating bis(aryloxo) ligands, [TiX2{2,2‘-Te(4-R-6-R‘-C6H2O)2}]2 (5b, X = Cl, R = Me, R‘ = tBu; 6a, X = OiPr, R = R‘ = H; 6b, X = OiPr, R = Me, R‘ = tBu), were prepared. 5b and 6b were determined by X-ray crystallography to have chloro- and isopropoxo-bridged dimeric structures. The structural data for these complexes indicated that the Ti−Te coordination bonds were stronger than the similar Ti−S coordination bonds in the corresponding sulfur-bridged complexes. The reaction of (C5R5)TiCl3 (R = H, Me) with 2,2‘-Te(4-R-6-R‘-C6H2OLi)2 gave monocyclopentadienyl derivatives, (C5R5)TiCl{2,2‘-Te(4-Me-6-tBu-C6H2O)2} (7, R = H; 8, R = Me). The monomeric four-legged piano-stool geometry of 8 was revealed by X-ray analysis. Upon addition of methylaluminoxane (MAO), these complexes catalyzed the polymerization of ethylene. The activities of the tellurium-bridged complexes were found to be significantly higher than those of the corresponding methylene-bridged complex.

Comparison of activities of homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) for synthesis of syndiotactic polystyrene by UV/visible spectroscopic study

The catalytic activities in syndiospecific polymerization of styrene in hydrocarbon using homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) were investigated through UV/visible spectroscopic analysis. A strong UV absorption band of CpTiCl3, itself, incipiently appeared at λmax = 400 nm in toluene, followed by a bathochromic shift with its remarkable decrease by the addition of MAO. The absorption band intensity at λmax = 400 nm arising from delocalization of π-electrons on the cyclopentadienyl ring decreased by methylation in the presence of MAO with regard to the mechanism for production of an active center (“cation-like”), for example, the change of the ionic nature. The intensity decrease at λmax = 400 nm was suppressed over 2000 of the [Al]/[Ti] ratio. In the case of Ti(OC4H9)4 having a σ-ligand, new and broad UV absorption bands were developed at λmax = 340 nm and 410 nm in the presence of MAO in contrast with the CpTiCl3/MAO system. Comparison between the relative absorption intensities at λmax = 340 nm and 410 nm led to the determination of a maximum catalytic activity of Ti(OC4H9)4 in the presence of MAO related to the polymerization yield. The maximum polymerization yield was observed with regard to the relative maximum value of the absorption intensity at λmax = 410 nm with the [Al]/[Ti] ratio (500). From observation for polymorphism of the final products via differential scanning calorimetric analysis (DSC), the thermally unstable β-form seemed to be produced by the CpTiCl3/MAO system independent of the MAO concentration, the Ti(OC4H9)4/MAO system produced a thermally stable α-form in the low MAO concentration (up to 100 of the [Al]/[Ti] ratio), and a mixture of α- and/or β-forms over 200 of the [Al]/[Ti] ratio under our experimental conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1733–1741, 1998

Komplexkatalyse LI. Komplexe des Tris(allyl)lanthans mit verschiedenen Donorliganden La( η3-C 3H 5) 3 · L (L:DME, TMED, 2HMPT) und ihre katalytischen Eigenschaften in der stereospezifischen Butadienpolymerisation

The dimeric tris(allyl)lanthanum dioxane complex [La( η 3-C 3H 5) 3 · (C 4H 8O 2) 1.5] 2 1 can be transformed by reaction with other donor ligands in monomeric complexes of the type [La( η 3-C 3H 5) 3 · L] (L:DME = dimethylethyleneglycolether ( 2), TMED = tetramethylethylenediamine ( 3) and 2HMPT = hexamethylphosphorictriamide ( 4)). The complexes were characterized by elemental analysis, 1H, 13C and 139La NMR spectroscopy. Single crystal X-ray structure analysis of 3 gave the formula [La( η 3-C 3H 5) 3 ( η 2-Me 2NC 2H 4NMe 2)] in the monoclinic space group P2 1/ n with cell parameters a = 8.124(4) Å, b = 14.458(6) Å c = 15.233(7) Å and β = 94.14(2)°. The complexes catalyze polymerization of butadiene in toluene at 50°C with high 1,4- trans selectivity. The catalytic activity decreases accordingly to 1 ≈ 2 > 3 ≫ 4 depending on the bond strength of the ligands. With addition of methylaluminoxane (MAO) the catalytic activity increases correspondingly and a 1,4- cis selectivity of 40–60% is obtained.

A method for the prediction of metallocene‐type catalyst activity in olefin (co)polymerisation reactions

AbstractThe use of ultraviolet/visible spectroscopy (UV‐Vis) for the prediction of metallocene catalyst potential for the polymerisation of olefins is described. Upon addition of methylaluminoxane (MAO) to rac‐[C2H4(1‐indenyl)2ZrCl2] ([Al]/[Zr] = 200) the ligand‐to‐metal charge transfer band shows a hypsochromic shift while a bathochromic shift is observed when more MAO is added ([Al]/[Zr] = 2000). These shifts can be explained by assuming that methylation of the zirconocene by MAO occurs in the case of [Al]/[Zr] = 200 while a cationic complex, the active catalytic system, is formed upon addition of more MAO, e.g., [Al]/[Zr] = 2000.