Ethylene polymerization catalyzed by metallocene/methylaluminoxane systems: quantum-mechanical study on the role of olefin separated ion pairs (OSIP) in the polymerization mechanism

Fusco, Roberto; Longo, Luca; Proto, Antonio; Masi, Francesco; Garbassi, F.

doi:10.1002/(sici)1521-3927(19980501)19:5<257::aid-marc257>3.3.co;2-3

Cited by 35 publications

(79 citation statements)

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“…Fusco et al [7,8] have analyzed the ion-pair formation in the system Cp 2 ZrMe 2 /MAO using density functional theory (DFT) quantum-chemical simulations. They presented MAO as the cyclic structure of composition [Al 3 (Me) 3 O 2 (H) 2 ] N 2Al(Me) 3 .…”

Section: Introductioncontrasting

confidence: 55%

“…This value is the same as for AlMe 3 ( Table 2). As a result the calculated data confirm the weak acid-base interaction between Cp 2 ZrMe 2 and Al 4 O 2 Me 8 (Table 2, Figure 3): (i) the calculated equilibrium distance r(Al-lMe) = 2.54 , (ii) the energy of formation DH = -8.1 kcal N mol -1 , (iii) Dq from zirconocene to aluminoxane is 0.16 e. Notice that experimental data [9] show that no noticeable reaction proceeded at the interaction of Cp 2 ZrMe 2 with aluminoxane Al 4 O 2 (t-Bu) 8 which contains tri-coordinated aluminum centers with the composition OAl(t-Bu) 2 .…”

Section: Methods and Details Of Calculationsmentioning

confidence: 99%

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A DFT Quantum-Chemical Study of Ion-Pair Formation for the Catalyst Cp2ZrMe2 /MAO

Захаров

Захаров²

2002

Macromol. Theory Simul.

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A process of ion‐pair formation in the system Cp2ZrMe2/methylaluminoxane (MAO) has been studied by means of density functional theory quantum‐chemical calculations for MAOs with different structures and reactive sites. An interaction of Cp2ZrMe2 with a MAO of the composition (AlMeO)6 results in the formation of a stable molecular complex of the type Al5Me6O5Al(Me)O–Zr(Me)Cp2 with an equilibrium distance r(Zr–O) of 2.15 Å. The interaction of Cp2ZrMe2 with “true” MAO of the composition (Al8Me12O6) proceeds with a tri‐coordinated aluminum atom in the active site (OAlMe2) and yields the strongly polarized molecular complex or the μ‐Me‐bridged contact ion pair (d) [Cp2(Me)Zr(μMe)Al≡MAO] with the distances r(Zr–μMe) = 2.38 Å and r(Al–μMe) = 2.28 Å. The following interaction of the μ‐Me contact ion pair (d) with AlMe3 results in a formation of the trimethylaluminum (TMA)‐separated ion pair (e) [Cp2Zr(μMe)2AlMe2]+–[MeMAO]– with r[Zr–(MeMAO)] equal to 4.58 Å. The calculated composition and structure of ion pairs (d) and (e) are consistent with the 13C NMR data for the species detected in the Cp2ZrMe2/MAO system. An interaction of the TMA‐separated ion pair (e) with ethylene results in the substitution of AlMe3 by C2H4 in a cationic part of the ion pair (e), and the following ethylene insertion into the Zr–Me bond. This reaction leads to formation of ion pair (f) of the composition [Cp2ZrCH2CH2CH3]+–[Me‐MAO]– named as the propyl‐separated ion pair. Ion pair (f) exhibits distance r[Zr–(MeMAO)] = 3.88 Å and strong Cγ‐agostic interaction of the propyl group with the Zr atom. We suppose this propyl‐separated ion pair (f) to be an active center for olefin polymerization.

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Section: Introductioncontrasting

confidence: 55%

Section: Methods and Details Of Calculationsmentioning

confidence: 99%

A DFT Quantum-Chemical Study of Ion-Pair Formation for the Catalyst Cp2ZrMe2 /MAO

Захаров

Захаров²

2002

Macromol. Theory Simul.

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“…The resulting heterodinuclear complexes are not necessarily inactive, as is supported by calculations of reaction pathways via an "olefin-separated ion pair" (OSIP). [27,28] The results presented in this study are not in contradiction to the findings that have been explained in terms of different pathways of termination, e.g. via chain transfer to the cocatalyst.…”

Section: Discussionmentioning

confidence: 99%

Deviation from Single-Site Behavior in Zirconocene/MAO Catalyst Systems, 1. Influence of Monomer, Catalyst, and Cocatalyst Concentration

Frauenrath¹,

Keul²,

Höcker³

2001

Macromol. Chem. Phys.

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The polymerization of 1‐hexene with the catalyst systems Cp2ZrCl2/MAO and Me2SiInd2ZrCl2/MAO is investigated in order to elucidate the nature of the active species in zirconocene/MAO catalyzed polymerizations. Varying monomer concentration and monomer conversion does not result in any unexpected behavior. However, changing catalyst and cocatalyst concentration leads to broadened, or even bimodal, molecular weight distributions under certain reaction conditions. These results may be interpreted in terms of a coexistence of two active species with different rates of propagation and of termination.

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“…(7)). [22,26] (9) Increasing the MAO concentration, increase the ionic pair concentration i. e. by dissociation of binuclear cations (Eq. (8) to the left).…”

Section: Discussionmentioning

confidence: 99%

Addition of Lewis bases and acids. Effect on α-olefins polymerization with soluble metallocenes, 2 Propylene

Belelli

Ferreira

Damiani³

2000

Macromol. Chem. Phys.

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Ethylene polymerization catalyzed by metallocene/methylaluminoxane systems: quantum-mechanical study on the role of olefin separated ion pairs (OSIP) in the polymerization mechanism

Cited by 35 publications

References 0 publications

A DFT Quantum-Chemical Study of Ion-Pair Formation for the Catalyst Cp2ZrMe2 /MAO

A DFT Quantum-Chemical Study of Ion-Pair Formation for the Catalyst Cp2ZrMe2 /MAO

Deviation from Single-Site Behavior in Zirconocene/MAO Catalyst Systems, 1. Influence of Monomer, Catalyst, and Cocatalyst Concentration

Addition of Lewis bases and acids. Effect on α-olefins polymerization with soluble metallocenes, 2 Propylene

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