NMR investigations of the reactivity between zirconocenes and β-alkyl-substituted aluminoxanes

Tritto, Incoronata; Zucchi, Debora; Destro, Mara; Sacchi, Maria Carmela; Dall'Occo, Tiziano; Galimberti, Maurizio

doi:10.1016/s1381-1169(00)00237-5

Cited by 26 publications

(12 citation statements)

References 8 publications

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“…[31][32][33] In addition to the interconversion between different type III species, by exchange of terminal methyl groups against isobutyl groups, a significant reduction of their total concentrations at elevated [AliBu 3 ] add /[Zr] ratios is apparent from Figure 2. The appearance of new ligand signals (denoted as I H 2 in Figure 2) and of the signals of isobutylene at d = 1.59 and 4.73 ppm, as well as previous observations on related reaction systems, [17,34,35] suggest that the isobutylated adducts III iBuMe and III iBu 2 are partly converted to some hydride species. Results of more direct studies on these hydride species, in reaction systems containing [Me 2 SiA C H T U N G T R E N N U N G (ind) 2 ZrCl 2 ], MAO and diisobutylaluminum hydride, will be reported in a separate communication.…”

Section: à055supporting

confidence: 83%

Modification of Methylaluminoxane‐Activated ansa‐Zirconocene Catalysts with Triisobutylaluminum—Transformations of Reactive Cations Studied by NMR Spectroscopy

Babushkin¹,

Brintzinger²

2007

Chemistry A European J

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When triisobutylaluminum (AliBu(3)) is added to solutions containing methylaluminoxane (MAO) and rac-[Me(2)Si(ind)(2)ZrCl(2)] (ind: indenyl) in C(6)D(6), NMR spectra show that methyl-bridged mixed-alkylaluminum dimers Al(mu-Me)(2)Me(4-x)iBu(x) predominate. These dimers react with MAO under partial transfer of isobutyl groups and induce a conversion of the initially prevailing cationic trimethylaluminum adduct rac-[Me(2)Si(ind)(2)Zr(mu-Me)(2)AlMe(2) (+)] to rac-[Me(2)Si(ind)(2)Zr(mu-Me)(2)AlMeiBu(+)] and rac-[Me(2)Si(ind)(2)Zr(mu-Me)(2)AliBu(2) (+)]. These species are unstable and release isobutene under formation of zirconocene hydrides.

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Section: à055supporting

confidence: 83%

Modification of Methylaluminoxane‐Activated ansa‐Zirconocene Catalysts with Triisobutylaluminum—Transformations of Reactive Cations Studied by NMR Spectroscopy

Babushkin¹,

Brintzinger²

2007

Chemistry A European J

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“…Due to the high content of three coordinated Al atoms, 37 nonassociated isobutyl alumoxanes manifest a higher Lewis acidity than MAO and eliminate the Cl -anion more easily (see Scheme 1, reaction (2)). 38 It is known 29,30,38-40 that branched alumoxanes can act as efficient cocatalysts for a series of metallocene complexes, and their activity is close to or even exceeds the activity of the systems with MAO.…”

Section: Methodsmentioning

confidence: 99%

1H NMR study of the catalytic system (rac-Me2Si(2-Me,4-PhInd)2ZrCl2— polymethylalumoxane)—triisobutylaluminum

2005

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The products of the reactions of polymethylalumoxane (MAO) with triisobutylaluminum (TIBA), rac Me 2 Si(2 Me,4 PhInd) 2 ZrCl 2 (1) with MAO (1 + MAO), and (1 + MAO) + TIBA were studied by 1 H NMR at different molar ratios of the components. When the ratio Al TIBA /Al MAO is ~6, the reaction between MAO and TIBA involves the replacement of the methyl group of MAO by isobutyl groups and the formation of isobutylmethylalumoxane or mixed isobutylmethylalumoxane structures. When the TIBA content in the system increases to 30 mol.%, these structures are rearranged to form products with a low degree of association. With the equimolar ratio of the reactants, the main reaction products are tetraisobutylalumoxane and polyisobutylalumoxane. The 1 + MAO system with the molar ratio Al MAO /Zr = 50 affords a MAO bonded monomethyl monochloride derivative [L 2 ZrCl µ Me] δ+ [MAO] δ-. An in crease in this ratio to 150 produces intermediate binuclear complexes [L 2 ZrCl µ Me MeZrL 2 ] + [MAO] -and [Me 2 Al (µ Me) 2 ZrL 2 ] + [MAO] -. The addition of TIBA induces the replacement of the ZrMe groups by isobutyl groups at the first step of the interaction and formation of nonidentified reaction products at the subsequent steps.Metallocene cationic complexes of Group IVB ele ments are highly efficient catalysts for olefin homo and copolymerization. A catalyst system is formed by the reaction of a metallocene complex with an activator (cocatalyst). The concept that catalytic intermediates (precursors of the active site) are alkylmetal cationic complexes bonded to a counterion 1-4 was confirmed by numerous spectroscopic data. 5-7 Polymethylalum oxane (MAO) ( O-Al(Me) ) n (n = 4-30) contain ing a considerable amount of free or partially bound trimethylaluminum (TMA) (up to 30 mol.% with re spect to aluminum) is most frequently used as a co catalyst. 8 When activating the starting metallocene dichlo ride L 2 ZrCl 2 (L are hapto bonded cyclopentadienyl, indenyl, or fluorenyl ligands), MAO bears numerous func tions: it acts as an alkylating agent (Scheme 1, reac tion (1)), cation generating agent (reaction (2)), and, in addition, purifies the reaction medium from moisture ad mixtures. Scheme 1 L 2 ZrCl 2 + MAO L 2 ZrMeCl (1) L 2 ZrMeCl + MAO L 2 Zr + Me...ClMAO -The MAO activated catalysts are most active at low metallocene concentrations (1•10 -5 -1•10 -7 mol L -1 ) and high cocatalyst/catalyst molar ratios (1•10 3 -1•10 4 ). Disadvantages of MAO are its high cost and instability during storage. Other most popular activators are fluoaryl boranes and fluoaryl borates. 8 However, their use as acti vators is restricted, because they have no components interacting with humidity admixtures in the reaction me dium and can activate only dimethylated metallocenes. Nevertheless, there are examples for the efficient activa tion of metallocene dichlorides by a combined activator including borates and triisobutylaluminum (TIBA). 9-13 Some workers 14-16 propose an approach to metallo cene activation based on the treatment of the metallocene dichloride ...

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“…Calculated quantities of L 2 ZrCl 2 solution (in toluene for 13 C and in toluene-d 8 for 1 H measurements) and MAO or AlMe 3 /CPh 3 ' B(C 6 F 5 ) 4 ( were combined under vacuum in NMR tubes (5 and 10 mm) and the tubes were sealed off from the vacuum line. The data on Al and Zr concentrations and Al/Zr ratios of the samples prepared are given.…”

Section: Preparation Of L 2 Zrcl 2 /Mao and L 2 Zrcl 2 /Alme 3 / Cphmentioning

confidence: 99%

“…In this work, we have undertaken a 1 H-and 13 C-NMR spectroscopic study of the cationic intermediates formed upon activation of L 2 ZrCl 2 with MAO at various Al/Zr ratios. The following catalysts were studied: (Cp-R) 2 (R 0/Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , n -Bu, t -Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems.…”

Section: Introductionmentioning

confidence: 99%

1H-, 13C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics

Bryliakov

Semikolenova

Yudaev

et al. 2003

Journal of Organometallic Chemistry

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Using 1 Hand 13 C-NMR spectroscopies, cationic intermediates formed by activation of L 2 ZrCl 2 with methylaluminoxane (MAO) in toluene were monitored at Al/Zr ratios from 50 to 1000 (L 2 are various cyclopentadienyl (Cp), indenyl (Ind) and fluorenyl (Flu) ligands). The following catalysts were studied: (Cp-R) 2 ZrCl 2 (R0/Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , Me 5 , n-Bu, t-Bu), racethanediyl(Ind) 2 ZrCl 2 , rac-Me 2 Si(Ind) 2 ZrCl 2 , rac-Me 2 Si(1-Ind-2-Me) 2 ZrCl 2 , rac-ethanediyl(1-Ind-4,5,6,7-H 4) 2 ZrCl 2 , (Ind-2-Me) 2 ZrCl 2 , Me 2 C(Cp)(Flu)ZrCl 2 , Me 2 C(Cp-3-Me)(Flu)ZrCl 2 and Me 2 Si(Flu) 2 ZrCl 2. Correlations between spectroscopic and ethene polymerization data for catalysts (Cp-R) 2 ZrCl 2 /MAO (R 0/H, Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , Me 5 , n-Bu, t-Bu) and rac-Me 2 Si(Ind) 2 ZrCl 2 were established. The catalysts (Cp-R) 2 ZrCl 2 /AlMe 3 /CPh 3 ' B(C 6 F 5) 4 ((R0/Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , n-Bu, t-Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems. Complexes of type (Cp-R) 2 ZrMe ' 1/Me (-Al /MAO (IV) with different [Me-MAO] (counteranions have been identified in the (Cp-R) 2 ZrCl 2 /MAO (R 0/n-Bu, t-Bu) systems at low Al/Zr ratios (50 Á/200). At Al/Zr ratios of 500 Á/1000, the complex [L 2 Zr(m-Me) 2 AlMe 2 ] ' [Me-MAO] ((III) dominates in all MAO-based reaction systems studied. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr 0/200 Á/1000) for the systems (Cp-R) 2 ZrCl 2 /MAO (R 0/H, Me, n-Bu, t-Bu), while it is virtually constant in the same range of Al/Zr ratios for the catalytic systems (Cp-R) 2 ZrCl 2 /MAO (R0/1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4) and rac-Me 2 Si(Ind) 2 ZrCl 2 /MAO. The data obtained are interpreted on assumption that complex III is the main precursor of the active centers of polymerization in MAO-based systems.

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NMR investigations of the reactivity between zirconocenes and β-alkyl-substituted aluminoxanes

Cited by 26 publications

References 8 publications

Modification of Methylaluminoxane‐Activated ansa‐Zirconocene Catalysts with Triisobutylaluminum—Transformations of Reactive Cations Studied by NMR Spectroscopy

Modification of Methylaluminoxane‐Activated ansa‐Zirconocene Catalysts with Triisobutylaluminum—Transformations of Reactive Cations Studied by NMR Spectroscopy

1H NMR study of the catalytic system (rac-Me2Si(2-Me,4-PhInd)2ZrCl2— polymethylalumoxane)—triisobutylaluminum

1H-, 13C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics

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