Stereochemistry of First Monomer Insertion into a Metal−Methyl Bond:  Enantioselectivity and Diastereoselectivity in 3-Methyl-1-pentene Polymerization with Metallocene Catalysts

Barsties, Elke; Tritto, Incoronata; Locatelli, Paolo; Brintzinger, Hans‐Herbert; Stehling, Udo

doi:10.1021/ma9609801

Cited by 17 publications

(11 citation statements)

References 26 publications

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“…The evidence for isotactic polymer resulting from such polymerizations, however, is largely based on the very high polymer melting points and 13 C{ 1 H} NMR spectra . Unfortunately, these 13 C{ 1 H} NMR spectra, unlike those for polypropylenes, are not particularly diagnostic due to poor polymer solubility and broad overlapping peaks.…”

Section: Introductionsupporting

confidence: 71%

Catalyst Site Epimerization during the Kinetic Resolution of Chiral α-Olefins by Polymerization

2008

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A new enantiopure C 1-symmetric olefin polymerization precatalyst, (1,2-SiMe2)2{η5-C5H2-4-((S)-CHEtCMe3)}{η5-C5H-3,5-(CHMe2)2}ZrCl2, (S)-2, was synthesized, and its use for the kinetic resolution of 3-methyl-substituted racemic α-olefins was investigated. Upon activation with methyl aluminoxane (MAO), selectivity factors for most olefins were greater when (S)-2 was used as the catalyst as compared to its previously reported methylneopentyl analogue, (1,2-SiMe2)2{η5-C5H2-4-((S)-CHMeCCMe3)}{η5-C5H-3,5-(CHMe2)2}ZrCl2, (S)-1. Pentad analysis of polypropylene produced by the two catalysts at various propylene concentrations indicates that (S)-2 undergoes more efficient site epimerization (polymeryl chain swinging prior to subsequent monomer enchainment) at intermediate propylene concentrations compared to (S)-1. At high and low propylene concentrations, however, the two catalysts behave similarly. On the other hand, polymerization of 3,5,5-trimethyl-1-hexene at different olefin concentrations and temperatures illustrated that selectivity differences between the two catalysts are likely not a consequence of inefficient site epimerization for (S)-1.

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Section: Introductionsupporting

confidence: 71%

Catalyst Site Epimerization during the Kinetic Resolution of Chiral α-Olefins by Polymerization

2008

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“…As can be seen from Figure , the activity of MAO decreases with addition of AlMe 3 . The decrease in activity of the MAO in the presence of excess AlMe 3 is presumably due to the competition with AlMe 3 to binding Zr−R. , Tritto et al have shown the formation of [Cp 2 Zr(μ-Me) 2 AlMe 2 ] + cations, and we have shown that the reaction of Cp 2 ZrX 2 (X = Cl, Me) with Al( t Bu) 3 yields the Lewis acid−base complex Cp 2 Zr(X)(μ-X)Al( t Bu) 3 4 Polymerization activity (kg polymer per g Zr) as a function of AlMe 3 :alumoxane ratio for the [Me 2 C(Cp)(Flu)]ZrBz 2 (4.0 × 10 -7 mol) catalyzed polymerization of 1,5-hexadiene: (▪) [Al 7 (μ 3 -O) 6 ( t Bu) 6 Me 3 ]; (□) MAO.…”

Section: Resultsmentioning

confidence: 63%

Reaction of Trimethylaluminum with [(^tBu)Al(μ₃-O)]₆: Hybrid tert-Butylmethylalumoxanes as Cocatalysts for Olefin Polymerization

et al. 2001

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The reaction of trimethylaluminum with the hexameric tert-butylalumoxane, [( t Bu)Al-(µ 3 -O)] 6 , has been investigated. Reaction of [( t Bu)Al(µ 3 -O)] 6 with 1 equiv of AlMe 3 results in the formation of two isomers (A and B) of the hybrid tert-butylmethylalumoxane, [Al 7 (µ 3 -O) 6 -( t Bu) 6 Me 3 ]. The structures of compounds A and B, as determined by NMR spectroscopy and mass spectrometry, consist of [Al 6 (µ 3 -O) 6 ( t Bu) 5 Me] alumoxane cages, formed via tert-butyl/ methyl exchange, in which one of the edges of the Al 6 O 6 cage is complexed to the ( t Bu)-AlMe 2 formed during alkyl exchange. The difference between the isomers results from the geometric relationship of the cage Al-Me group and the opened edge. The activity of [Al 7 -(µ 3 -O) 6 ( t Bu) 6 Me 3 ], for the [Me 2 C(Cp)(Flu)]ZrBz 2 -catalyzed polymerization of 1,5-hexadiene, is significantly increased in comparison to [( t Bu)Al(µ 3 -O)] 6 . The effect of additional equivalents of AlMe 3 on the cocatalytic activity of [Al 7 (µ 3 -O) 6 ( t Bu) 6 Me 3 ] suggests that a maximum activity is obtained at a [( t Bu)Al(µ 3 -O)] 6 to AlMe 3 ratio of 1:6. Under conditions of equal Al:Zr ratio the [( t Bu)Al(µ 3 -O)] 6 (AlMe 3 ) 6 system has a higher activity than a representative sample of commercial methylalumoxane (MAO). 1 H NMR suggests that the reaction of [( t Bu)Al-(µ 3 -O)] 6 with 6 equiv of AlMe 3 yields ( t Bu)AlMe 2 as the only tert-butyl-containing species and a proposed AlMe 3 "free" form of MAO. Whereas the activity of [Al 7 (µ 3 -O) 6 ( t Bu) 6 Me 3 ] and MAO shows slight inhibition by the addition of Al( i Bu) 3 , the activity of the [( t Bu)Al(µ 3 -O)] 6 / (AlMe 3 ) 6 system is unaffected. The reaction of Cp 2 Zr(CD 3 ) 2 with [Al 7 (µ 3 -O) 6 ( t Bu) 6 Me 3 ] demonstrates that methyl exchange does not occur between a metallocene and the alkyls of the alumoxane cage, but does occur with the complexed ( t Bu)AlMe 2 .

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“…A soluble enantiopure single site catalyst, ( S )-ethylene-bis(4,5,6,7-tetrahydro-1-η 5 -indenyl)Zr(O-acetyl-( R )-mandelate) 2 /MAO (MAO = methylaluminoxane), has been used to effect a low efficiency resolution of 4-substituted chiral olefins such as 4-methyl-1-hexene ( s = k faster / k slower = 1.4). , Unfortunately, poor catalyst activity prohibited the polymerization of chiral α-olefins with substituents in the 3-position. Although 3-methyl-1-pentene can be successfully polymerized with related metallocene catalysts, prior to the present work, only C s - and racemic C 2 -symmetric catalysts have been used, precluding any possible kinetic resolution …”

Section: Introductionmentioning

confidence: 99%

Kinetic Resolution of Chiral α-Olefins Using Optically Active ansa-Zirconocene Polymerization Catalysts

et al. 2004

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A series of enantiopure C1-symmetric metallocenes, [(SiMe2)2[eta5-C5H(CHMe2)2][eta5-C5H2((S)-CHMeCMe3)]]ZrCl2, (S)-2, [(SiMe2)2[eta5-C5H(CHEt2)2][eta5-C5H2((S)-CHMeCMe3)]]ZrCl2, (S)-6, and [(SiMe2)2[eta5-C5HCy2][eta5-C5H2((S)-CHMeCMe3)]]ZrCl2, (S)-7 (Cy = cyclohexyl), zirconocene dichlorides that have an enantiopure methylneopentyl substituent on the "upper" cyclopentadienyl ligand, and diastereomerically pure precatalysts, [(SiMe2)2[eta5-C5H((S)-CHMeCy)(CHMe2)][eta5-C5H3]]ZrCl2, (S)-8a and (S)-8b, which have an enantiopure, 1-cyclohexylethyl substituent on the "lower" cyclopentadienyl ligand, has been synthesized for use in the polymerization of chiral alpha-olefins. When activated with methylaluminoxane, these metallocenes show unprecedented activity for the polymerization of bulky racemic monomers bearing substitution at the 3- and/or 4-positions. Due to the optically pure nature of these single site catalysts, they effect kinetic resolution of racemic monomers: the polymeric product is enriched with the faster reacting enantiomer, while recovered monomer is enriched with the slower reacting enantiomer. The two components are easily separated. For most olefins surveyed, a partial kinetic resolution was achieved (s = k(faster)/k(slower) approximately 2), but, in one case, the polymerization of 3,4-dimethyl-1-pentene, high levels of separation were obtained (s > 15). (13)C NMR spectroscopy of poly(3-methyl-1-pentene) produced with (S)-2 indicates that the polymers are highly isotactic materials. X-ray crystal structure determinations for (S)-2, [(SiMe2)2[eta5-C5H(CHMe2)2][eta5-C5H2((S)-CHMeCMe3)]]Zr(SC6H5)2, (S)-6, and (S)-7 have been used in combination with molecular mechanics calculations to examine the prevailing steric interactions expected in the diastereomeric transition states for propagation during polymerization. Precatalysts (S)-8a and (S)-8b are less selective polymerization catalysts for the kinetic resolution of 3-methyl-1-pentene than are (S)-2, (S)-6, and (S)-7.

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Stereochemistry of First Monomer Insertion into a Metal−Methyl Bond: Enantioselectivity and Diastereoselectivity in 3-Methyl-1-pentene Polymerization with Metallocene Catalysts

Cited by 17 publications

References 26 publications

Catalyst Site Epimerization during the Kinetic Resolution of Chiral α-Olefins by Polymerization

Catalyst Site Epimerization during the Kinetic Resolution of Chiral α-Olefins by Polymerization

Reaction of Trimethylaluminum with [(^tBu)Al(μ₃-O)]₆: Hybrid tert-Butylmethylalumoxanes as Cocatalysts for Olefin Polymerization

Kinetic Resolution of Chiral α-Olefins Using Optically Active ansa-Zirconocene Polymerization Catalysts

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Stereochemistry of First Monomer Insertion into a Metal−Methyl Bond: Enantioselectivity and Diastereoselectivity in 3-Methyl-1-pentene Polymerization with Metallocene Catalysts

Cited by 17 publications

References 26 publications

Catalyst Site Epimerization during the Kinetic Resolution of Chiral α-Olefins by Polymerization

Catalyst Site Epimerization during the Kinetic Resolution of Chiral α-Olefins by Polymerization

Reaction of Trimethylaluminum with [(tBu)Al(μ3-O)]6: Hybrid tert-Butylmethylalumoxanes as Cocatalysts for Olefin Polymerization

Kinetic Resolution of Chiral α-Olefins Using Optically Active ansa-Zirconocene Polymerization Catalysts

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Reaction of Trimethylaluminum with [(^tBu)Al(μ₃-O)]₆: Hybrid tert-Butylmethylalumoxanes as Cocatalysts for Olefin Polymerization