Crystal structures and stereospecific propylene polymerizations with chiral hafnium metallocene catalysts

Ewen, John A.; Haspeslagh, Luc; Atwood, Jerry L.; Zhang, Hongming

doi:10.1021/ja00255a068

Cited by 213 publications

(69 citation statements)

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“…In a similar fashion, the methyl signal at δ ϭ 0.34 ppm and the methine signals at δ ϭ 6.84 and 5.83 ppm show considerable broadening at 218Ϫ188 K, and split into two resonances below 178 K. Finally, at 173 K a 6.3 Hz 3 J coupling was observed for the methine protons of the six-membered ring. Similar splitting was observed for most of the 13 C NMR signals of 51 recorded at 173 K. Analogous to the amino-substituted zirconocenes 12 and 13 described by Erker and co-workers, and discussed earlier in this microreview (vide supra), [44] the signal splitting indicates a single C 2 -symmetric bent-metallocene conformation that is detected when the equilibration of 51 with its nonsuperimposable mirror image becomes frozen on the NMR time scale (Scheme 17). [111] The calculated activation barrier for 51,…”

Section: Siloxy-substituted Group 4 Bis(indenyl)metallocenessupporting

confidence: 80%

“…[66,67] Likewise, analogous to the 2-amino-substituted complexes rac-and meso-9, the β-protons in the five-membered rings of all ethylene-bridged rac-and meso-2-siloxy-substituted bis(indenyl) complexes 42, 43, 47 and 49 are shielded and the signals shifted by 0.6Ϫ0.7 ppm to a higher field relative to the corresponding resonances of the 2-alkyl or unsubstituted analogues. Similar effects are observed in the 13 C NMR spectra for the chemical shifts of the β-carbon atoms of the five-membered rings. The only exception in this series is the benzo-fused complex rac-54, for which a 1 H NMR β-H resonance of δ ϭ 6.51 ppm, similar to that observed for the unsubstituted parent complex rac-ethylenebis(indenyl)zirconium dichloride rac-2 (δ ϭ 6.58 ppm), [66][118] was detected.…”

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confidence: 76%

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Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

2004

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The synthesis, characterization and applications of heteroatom‐substituted group 4 bis(indenyl)metallocene complexes is reviewed. In recent years, an increasing number of group 4 metallocenes with electronically modified cyclopentadienyl ligands have been reported with, in some cases, considerably altered catalytic properties. This microreview focuses on bis(indenyl) complexes of titanium, zirconium and hafnium that contain nitrogen, oxygen and sulfur atoms directly bonded to the five‐ or six‐membered rings of the indenyl ligand framework. The catalytic performance is briefly reviewed, with emphasis on catalytic olefin polymerization. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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Section: Siloxy-substituted Group 4 Bis(indenyl)metallocenessupporting

confidence: 80%

supporting

confidence: 76%

Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

2004

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“…Polymerization with one metallocene catalyst has the highest catalytic activity which may be due to differences in electron density and steric hindrance of the metal centers 12,13) . As shown in Tab.…”

Section: Resultsmentioning

confidence: 99%

Variation of molecular weight distribution (MWD) and short chain branching distribution (SCBD) of ethylene/1-hexene copolymers produced with different in-situ supported metallocene catalysts

Chu

Soares²,

Penlidis

2000

Macromol. Chem. Phys.

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Copolymerization of ethylene and 1‐hexene was carried out with different catalysts: homogeneous Et[Ind]2ZrCl2, Cp2HfCl2 and [(C5Me4)SiMe2N(tert‐Bu)]TiCl2, the corresponding in‐situ supported metallocenes, and combined in‐situ supported metallocene catalysts (mixtures of Et[Ind]2ZrCl2 and Cp2HfCl2, and Et[Ind]2ZrCl2 and [(C5Me4)SiMe2N(tert‐Bu)]TiCl2). Carbon‐13 nuclear magnetic resonance spectroscopy (13C NMR), gel permeation chromatography (GPC) and crystallization analysis fractionation (CRYSTAF) studies showed that, compared to the corresponding homogeneous metallocenes, in‐situ supported metallocenes produced polymers having different 1‐hexene fractions, molecular weight distributions (MWD) and short chain branching distributions (SCBD). It was also demonstrated that polymers with broader MWD and SCBD can be produced by combining two different in‐situ supported metallocenes.

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“…Zirconocenes obviously showed higher catalytic activity than hafnocenes (1 > 2, 3 > 4, 5 > 6), in agreement with other reports. 7,27,28 The catalytic activities of complexes 1-9 increased with polymerization temperature rising from 60 to 80…”

Section: Synthesis Of Complexesmentioning

confidence: 99%

Ethylene and propylene polymerization by the new substituted bridged (cyclopentadienyl)(fluorenyl) zirconocenes

Yang

Zhang

Huang

2005

Applied Organom Chemis

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Eight Cs-symmetric complexes, R 1 R 2 C(Cp)(Flu)MCl 2 [R 1 = R 2 = CH 3 CH 2 CH 2 , M = Zr (1), Hf (2); R 1 = R 2 = p-CH 3 OC 6 H 4 , M = Zr (3), Hf (4); R 1 = p-t BuC 6 H 4 , R 2 = Ph, M = Zr (5), Hf (6); R 1 = R 2 = p-t BuC 6 H 4 , M = Zr (7); R 1 = R 2 = PhCH 2 , M = Zr (8)] have been synthesized and characterized. Zirconocenes all showed the same high catalytic activities in ethylene polymerization as complex Ph 2 C(Cp)(Flu)ZrCl 2 (9). However, in the propylene polymerization, the catalytic activities decreased in the order 5 ≈ 9 > 7 > 8. Introduction of t Bu decreased the activities, probably due to the bulk steric hindrance. The polypropylene produced by 5 and 7 with t Bu substituent showed a higher molecular weight (Mη) than that produced by 9. The 13 C NMR spectrum revealed the polymers from 7 and 8 to have shorter average syndiotactic block length than polymer produced by 9. It was noted that [mm] stereodefect of polypropylene by 8 could not be observed from 13 C NMR, which showed that the benzyl on bridge carbon 8 prevented chain epimerization and enatiofacial misinsertion in polymerization.

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Crystal structures and stereospecific propylene polymerizations with chiral hafnium metallocene catalysts

Cited by 213 publications

References 1 publication

Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

Variation of molecular weight distribution (MWD) and short chain branching distribution (SCBD) of ethylene/1-hexene copolymers produced with different in-situ supported metallocene catalysts

Ethylene and propylene polymerization by the new substituted bridged (cyclopentadienyl)(fluorenyl) zirconocenes

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