A New Class of Chiral Bridged Metallocene:  Synthesis, Structure, and Olefin (Co)polymerization Behavior of rac- and meso-1,2-CH2CH2{4-(7-Me-indenyl)}2ZrCl2

Schaverien, Colin J.; Ernst, René; Schut, and Peter; Skiff, W. M.; Resconi, Luigi; Barbassa, Elisabetta; Balboni, and Davide; Dubitsky, Y.; Orpen, A. Guy; Mercandelli, Pierluigi; Moret, and Massimo; Sironi, Angelo

doi:10.1021/ja9811290

Cited by 20 publications

(6 citation statements)

References 9 publications

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“…Bridging the two 4,4‘-positions has led to isospecific systems (Chart ): racemic C 2 -I- 37 shows a quite low activity, producing PP of moderate isotacticity ( mmmm = 63.5%, T m = 101 °C at T p = 50 °C) and viscosity average molecular weight ( M̄ v = 15 000) …”

Section: Chiral Ansa-c 2-symmetric Metallocenesmentioning

confidence: 99%

“…Bridging the two 4,4′-positions has led to isospecific systems (Chart 13): racemic C 2 -I-37 shows a quite low activity, producing PP of moderate isotacticity (mmmm ) 63.5%, T m ) 101 °C at T p ) 50 °C) and viscosity average molecular weight (M h v ) 15 000). 346 As in the classic 1,1-bridged systems, varying Cp substitution generates a notable increase in per- 347 Doubly bridged bisindenyl zirconocenes such as C 2 -I-39 315,348 have also been prepared, but polymerization results are not promising. For example, C 2 -I-40 does not seem to survive the reaction with the cocatalyst and gives very low polymer yields, presumably after degradation to a single bridged species.…”

Section: Chiral Ansa-c 2 -Symmetric Metallocenesmentioning

confidence: 99%

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Selectivity in Propene Polymerization with Metallocene Catalysts

Resconi¹,

Cavallo²,

Fait³

et al. 2000

Chem. Rev.

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Section: Chiral Ansa-c 2-symmetric Metallocenesmentioning

confidence: 99%

Section: Chiral Ansa-c 2 -Symmetric Metallocenesmentioning

confidence: 99%

Selectivity in Propene Polymerization with Metallocene Catalysts

Resconi¹,

Cavallo²,

Fait³

et al. 2000

Chem. Rev.

Self Cite

1,363

1,411

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“…Ligand modifications, with retention of a bridged bis(cyclopentadienyl)-type framework, have afforded catalysts for syndiotactic-PP, hemiisotactic-PP, and atactic-PP, whereas unbridged 2-arylindenyl zirconocenes have yielded elastomeric-PP . Increasing attention is also being paid to variations in the bridge position in the conventional bis(1-indenyl) ligand framework …”

Section: Introductionmentioning

confidence: 99%

Ethylene Bis(2-indenyl) Zirconocenes: A New Class of Diastereomeric Metallocenes for the (Co)Polymerization of α-Olefins

et al. 2001

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Sequential additions of NaOEt and benzyl chloride (BzCl) to diethyl adipate in THF afforded EtOOCCH(Bz)CH 2 CH 2 CH(Bz)COOEt (3) in high yield via successive Dieckmann condensations. This was converted to CH 2 CH 2 (2-indene) 2 (2) using standard synthetic methodology, from which 436 g of CH 2 CH 2 (2-indenyl) 2 ZrCl 2 (1) was prepared. Incorporation of a 1-alkyl substituent gave rac and meso isomers CH 2 CH 2 (1-R-2-indenyl) 2 ZrCl 2 (R ) Me, 12r, 12m; R ) Et, 14r, 14m). Methylation gave rac-and meso-CH 2 CH 2 (1-Me-2-indenyl) 2 -ZrMe 2 (15r, 15m) and CH 2 CH 2 (2-indenyl) 2 ZrMe 2 (16). CH 2 CH 2 (4-Ph-2-indene) 2 (20) was prepared similarly to 2 using 2-phenyl benzylbromide and diethyladipate/NaOEt, from which rac-and meso-CH 2 CH 2 (4-Ph-2-indenyl) 2 ZrCl 2 (19r and 19m) were prepared. Alkylation of 19m gave meso-CH 2 CH 2 (4-Ph-2-indenyl) 2 ZrMe 2 (23m). The 4-phenyl metallocenes rac-and meso-CH 2 CH 2 (1-Me-4-Ph-2-indenyl) 2 ZrCl 2 (25r and 25m) were prepared via 20. C 2 -symmetric CH 2 CH 2 (1,3-Me 2 -2-indenyl) 2 ZrCl 2 (29) was prepared to compare its polymerization behavior with 1. These zirconocenes displayed activities of up to 4320 kg PE/(g Zr‚h) for the polymerization of ethylene (9.6 bar, 80 °C, hexane) to linear PE. The activity was much lower (2-20 kg/(g Zr‚h); liquid propylene, 50 °C) for the polymerization of propylene to low molecular weight atactic polypropylene. Alkyl groups in the 1-and/or 3-positions led to a significant reduction of 2,1-insertions from 9.4% in the polymer from 1/MAO, and 9.9% from 19/MAO, to 0.1-0.4%. Attempts to prepare an isospecific catalyst were unsuccessful; substituent variation i.e., 4-phenyl in 19, did not provide effective enantiomorphic site control. Addition of H 2 has a dramatic activation effect (>100-fold) in propylene polymerization and afforded saturated propylene oligomers with activities up to 6240 kg/(g Zr‚h). The low polymer molecular weights allowed detailed NMR analysis of the end groups, which enabled the chain transfer and metallocene activation mechanisms to be identified. Copolymerization of ethylene and propylene (in liquid propylene at 50 °C with 6 mol % ethylene) afforded copolymers with activities of 1300-12500 kg/(g Zr‚h). Reactivity ratios (r E ) 41-98, r P ) 0.0025-0.0084, r E r P ) 0.1-0.7) indicate a very high preference for sequential ethylene insertions. Copolymerization of ethylene and 1-hexene (4.4 bar ethylene, heptane, 70 °C) gave copolymers with activities of up to 1100 kg/(g Zr‚h) using 12r/MAO. The copolymer microstructure showed highly preferential sequential ethylene incorporation: r E ) ca. 200, r H ) 0.004.

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“…As observed under homogeneous conditions, supp- meso -2 proved a much more productive polymerization catalyst than supp- rac -2 , regardless of the amount of comonomer introduced. This is remarkable since, to date, only a limited number of meso -metallocenes have displayed higher catalytic activity than their corresponding rac -isomers [ 24 , 25 ]. It is tentatively proposed that such difference could arise either from a faster deactivation of the rac complex, possibly due to the formation of dormant heterobimetallic Al/Zr species [ 26 , 27 , 28 ], or to the occurrence, for the meso isomer, of a “stationary chain” polymerization mechanism, in which the monomer coordinates the active center always from the same (more accessible) side [ 24 , 29 ].…”

Section: Resultsmentioning

confidence: 99%

Meso- and Rac-[bis(3-phenyl-6-tert-butylinden-1-yl)dimethylsilyl]zirconium Dichloride: Precatalysts for the Production of Differentiated Polyethylene Products with Enhanced Properties

et al. 2022

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Ansa-zirconocene complexes are widely employed as precatalysts for olefin polymerization. Their synthesis generally leads to mixtures of their rac and meso isomers, whose separation is often problematic. In this contribution, we report on the synthesis of a novel silyl-bridged bis(indenyl)-based metallocene, and on the separation of its rac and meso isomers by simple recrystallization from toluene. The two complexes, activated by methylaluminoxane (MAO), have been used as precatalysts in ethylene/1-hexene copolymerization. Regardless of the reaction conditions, the meso complex outperformed its rac congener. A similar trend was observed by performing the process in the presence of the silica-supported versions of the complexes. This is remarkable, since meso metallocenes generally display lower activities than their rac analogues. Furthermore, the meso isomer generates polymer products that are more in line with the targets for the preparation of a bimodal PE grade made of a lower-MW high-density (HDPE) fraction and a higher-MW linear low-density (LLDPE) fraction.

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A New Class of Chiral Bridged Metallocene: Synthesis, Structure, and Olefin (Co)polymerization Behavior of rac- and meso-1,2-CH₂CH₂{4-(7-Me-indenyl)}₂ZrCl₂

Cited by 20 publications

References 9 publications

Selectivity in Propene Polymerization with Metallocene Catalysts

Selectivity in Propene Polymerization with Metallocene Catalysts

Ethylene Bis(2-indenyl) Zirconocenes: A New Class of Diastereomeric Metallocenes for the (Co)Polymerization of α-Olefins

Meso- and Rac-[bis(3-phenyl-6-tert-butylinden-1-yl)dimethylsilyl]zirconium Dichloride: Precatalysts for the Production of Differentiated Polyethylene Products with Enhanced Properties

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