Preparation of doubly-silylene-bridged zirconocene alkyl complexes, Me2Si)2{η5-C5H2-4-CHMe2}{η5-C5H-3,5-(CHMe2)2}ZrR2 (RCH3, CH2Ph) and investigations of their activity in 1-pentene polymerization. Molecular structure of (Me2Si)2{η5-C5H2-4-CHMe2}{η5-C5H-3,5- (CHMe2)2}Zr(CH2Ph)2

Veghini, Dario; Day, Michael; Bercaw, John E.

doi:10.1016/s0020-1693(98)00061-9

Cited by 19 publications

(15 citation statements)

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“…The [MAO]/[Zr] ratio significantly influences the catalyst activity, but the polymer tacticity is unaffected, at least over the range examined . No regioerrors (“2,1” or “3,1” errors) with any of the catalysts under any conditions investigated were detected by 13 C NMR spectroscopy, as was reported earlier for catalyst 2a . 3a, …”

Section: Resultssupporting

confidence: 79%

“…C s -Symmetric precatalysts such as 1a − c and 2a enchain α-olefins with regularly alternating enantiofaces and consequently produce syndiotactic polymer. , Methyl-substituted 2b generates polypropylene, whose microstructure closely approximates hemiisotactic, one in which every other propylene has been enchained with the same enantioface and the intervening one stereorandomly. Syndiospecificity is believed to arise from three key features: (1) the C s -symmetric ansa -metallocene structure has one cyclopentadienyl possessing bulky substituents flanking the center of the metallocene wedge to direct the polymer chain segment (up) toward the less substituted cyclopentadienyl, whether it resides on the left or right side in the transition structure for propagation (Scheme ); (2) an open region between the bulky substituents on the lower cyclopentadienyl to accommodate the α-olefin alkyl (methyl for propylene), which is directed by the polymer segment trans (down), the dominant steric interaction in the transition structure; , and (3) migratory insertions that result in regular alternation of the monomer approach from the left and right side of the metallocene wedge.…”

Section: Introductionmentioning

confidence: 99%

“…Our laboratory recently reported the preparation of C s - and C 1 -symmetric catalysts 1a − d along with some preliminary data on their polymerization behavior 3a. The C s -symmetric precatalysts 1a − c , when activated with methylaluminoxane, display high activity and syndioselectivity and produce high-molecular-weight polymers.…”

Section: Introductionmentioning

confidence: 99%

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Mechanisms of Stereocontrol for Doubly Silylene-BridgedC_s- andC₁-Symmetric Zirconocene Catalysts for Propylene Polymerization. Synthesis and Molecular Structure of Li₂[(1,2-Me₂Si)₂{C₅H₂-4-(1R,2S,5R-menthyl)}{C₅H-3,5-(CHMe₂)₂)}]·3THF and [(1,2-Me₂Si)₂{η⁵-C₅H₂-4-(1R,2S,5R-menthyl)}{η<

et al. 1998

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Doubly [SiMe 2 ]-bridged metallocenes (1,2-SiMe 2 ) 2 {η 5 -C 5 H 2 -4-R}{η 5 -C 5 H-3,5-(CHMe 2 ) 2 }ZrCl 2 (R ) H (1a), CHMe 2 (1b), SiMe 3 (1c), CHMe(CMe 3 ) (1d), (+)-menthyl (1e)), when activated by methylaluminoxane (MAO), catalyze propylene polymerization with high activities. The preparations and X-ray structures of the dilithio salt of an enantiopure, doubly silylene-bridged bis(cyclopentadienyl 1e), are reported. The C ssymmetric systems 1a-c are highly regiospecific and syndiospecific (>99.5%) in neat propylene. At lower propylene concentrations, polymers with lower molecular weights and tacticity (mostly m-type stereoerrors) are obtained. The microstructures of polymers produced under differing reaction conditions are consistent with stereocontrol dominated by a site epimerization process, an inversion of configuration at zirconium resulting from the polymer chain swinging from one side of the metallocene wedge to the other without monomer insertion. The relative importance of chain epimerization (at the β carbon) has been established by parallel polymerization of 2-d 1 -propylene and d 0 -propylene with 1b/MAO at low propylene concentrations. The C 1symmetric systems 1d,e/MAO display an unusual dependence of stereospecificity on propylene concentration, switching from isospecific to syndiospecific with increasing propylene pressure, consistent with a competitive unimolecular site epimerization process and a bimolecular chain propagation. The microstructures of the polypropylenes produced by 1d/MAO and 1e/MAO with [r] ≈ 50% resemble the hemiisotactic microstructure produced by Me 2 C(η 5 -C 5 H 3 -3-Me)(η 5 -C 13 H 8 )ZrCl 2 (2b)/MAO. Contrastingly, the hemiisotactic polypropylene microstructure obtained with 2b/MAO is found to be maintained at all propylene concentrations examined.

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Section: Resultssupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

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Mechanisms of Stereocontrol for Doubly Silylene-BridgedC_s- andC₁-Symmetric Zirconocene Catalysts for Propylene Polymerization. Synthesis and Molecular Structure of Li₂[(1,2-Me₂Si)₂{C₅H₂-4-(1R,2S,5R-menthyl)}{C₅H-3,5-(CHMe₂)₂)}]·3THF and [(1,2-Me₂Si)₂{η⁵-C₅H₂-4-(1R,2S,5R-menthyl)}{η<

et al. 1998

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“…The complexes with bulky substituents on the fluorenyl group such as 9 and 10 afford highly syndiotactic polypropylene with rrrr > 0.9 (43,47). C s -symmetric zirconocenes with doubly-silylene bridges (11,12) are also effective for syndiospecific polymerization of propylene (48)(49)(50)(51).…”

Section: Stereoregular Polymersmentioning

confidence: 99%

Stereoregular Polymers

Takeuchi

2013

Encyclopedia of Polymer Science and Technology

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Control of structure of polymers is an important issue in polymer synthesis because it affects properties such as solubility, crystallinity, and thermal properties. The polymers having stereogenic centers on a main chain can be synthesized by vinyl polymerization of olefinic monomers or ring-opening polymerization of cyclic monomers. Control of trans-cis selectivity is also important for the polymers containing C C double bonds in the main chain. The progress of homogeneous metal complex catalysts for coordination and ring-opening polymerization enables tailor-made control of the stereoregularity of the polymers. In this article, general aspects of stereoregular polymers, especially the polymer of monosubstituted vinyl monomers, are described. Recent progress in stereospecific polymerization of propylene, α-olefins, and styrenes is also summarized. Propylene Polymerization.Isospecific Polymerization of Propylene by Ziegler-Natta Catalysts. In 1954, Natta found that TiCl 3 /Et 2 AlCl catalyst is effective for the synthesis of isotactic polypropylene (4,5). Ti(III) is the active species of the polymerization, whereas other Ti species are also included in the catalyst. Moreover, the stereospecific Ti(III) site as well as nonstereospecific Ti(III) site exists in the catalyst.

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“…16 Bercaw and coworkers developed a series of C s -symmetric zirconocenes with two silylated bridges ( Figure 1.5) that, when activated with MAO, produce polypropylene that ranges from moderately to highly syndiotactic. [27][28][29][30] Me His group also developed a series of bridged and unbridged neutral scandocene alkyl complexes (Cp 2 ScR) that are isoelectronic to the cationic group IV metallocenes (Cp 2 MR + ). They then replaced the two cyclopentadienyl groups with the dianionic bifunctional chelating ligand [(C 5 Me 4 )SiMe 2 (N-t-Bu)] 2-.…”

Section: Phwdo Fhqwhu Wr Wkh Lqfrplqj Rohilq 7kh Vkruwhu Eulgjh Dovr mentioning

confidence: 99%

Synthesis and characterization of group IV metal complexes featuring tridentate diamidoamine ligands

Morgan¹

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New synthetic routes for the preparation of five-coordinate zirconium and titanium complexes featuring tridentate diamidoamine ligands were developed. Zirconium dichloride complexes, [(Mes)N(CH 2) 2 NR(CH 2) 2 N(Mes)]ZrCl 2 (R = H, SiMe 3), were synthesized via a onestep toluene elimination reaction. Analogous titanium dichloride complexes, [(Mes)N(CH 2) 2 NR(CH 2) 2 N(Mes)]TiCl 2 (R = H, SiMe 3), were prepared using a one-step amine elimination reaction. Table of Contents iv List of Tables vi List of Figures vii Chapter 1. Introduction 1 Chapter 2. Results and Discussion 2.1. Preparation and Characterization of Triamines (Mes)NH(CH 2) 2 NR(CH 2) 2 NH(Mes), R = H, SiMe 3 2.2. Preparation and Characterization of Five-Coordinate Zirconium Complexes 2.3. Preparation and Characterization of Five-Coordinate Titanium Complexes 2.4. Description of the Crystal Structures of 10, 11, and 13 Chapter 3. Concluding Remarks Chapter 4. Experimental Section 4.1. Reagents 4.2. General Considerations 4.3. Preparation of Starting Materials 4.3.1. Preparation of Zr(NMe 2) 4 , 1 4.3.2. Preparation of Ti(NMe 2) 4 , 2 4.3.3. Preparation of Ti(NMe 2) 2 Cl 2 , 3 4.3.4. Preparation of LiNEt 2 , 4 4.3.5. Preparation of Ti(NEt 2) 4 , 5 4.3.6. Preparation of Ti(NEt 2) 2 Cl 2 , 6 4.4. Preparation of Triamines (Mes)NH(CH 2) 2 NR(CH 2) 2 NH(Mes), R = H, SiMe 3 4.4.1. Preparation of (Mes)NH(CH 2) 2 NH(CH 2) 2 NH(Mes), Mes = Mesityl, 7 4.4.2. Preparation of (Mes)NH(CH 2) 2 N(SiMe 3)(CH 2) 2 NH(Mes), Mes = Mesityl, 8 4.5. Preparation of Five-Coordinate Zirconium Bis(dimethylamido) Complexes v 4.5.1. Preparation of [(Mes)N(CH 2) 2 NH(CH 2) 2 N(Mes)]Zr(NMe 2) 2 , Mes = Mesityl, 9 4.6. Preparation of Five-Coordinate Zirconium Dichloride Complexes 4.6.1. Preparation of [(Mes)N(CH 2) 2 NH(CH 2) 2 N(Mes)]ZrCl 2 , Mes = Mesityl, 10 4.6.1.1. Reaction of 9 with SiMe 3 Cl 4.6.1.2. Toluene Elimination Reaction 4.6.2. Preparation of [(Mes)N(CH 2) 2 N(SiMe 3)(CH 2) 2 N(Mes)]ZrCl 2 , Mes = Mesityl, 11 4.7. Preparation of Five-Coordinate Titanium Dichloride Complexes 4.7.1. Preparation of [(Mes)N(CH 2) 2 NH(CH 2) 2 N(Mes)]TiCl 2 , Mes = Mesityl, 12 4.7.1.1. Amine Elimination Reaction with 3 4.7.1.2. Amine Elimination Reaction with 6 4.7.2. Preparation of [(Mes)N(CH 2) 2 N(SiMe 3)(CH 2) 2 N(Mes)]TiCl 2 , Mes = Mesityl, 13 4.8. Description of the X-ray Structural Analyses Chapter 5. References Vita

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Preparation of doubly-silylene-bridged zirconocene alkyl complexes, Me2Si)2{η5-C5H2-4-CHMe2}{η5-C5H-3,5-(CHMe2)2}ZrR2 (RCH3, CH2Ph) and investigations of their activity in 1-pentene polymerization. Molecular structure of (Me2Si)2{η5-C5H2-4-CHMe2}{η5-C5H-3,5- (CHMe2)2}Zr(CH2Ph)2

Cited by 19 publications

References 37 publications

Stereoregular Polymers

Synthesis and characterization of group IV metal complexes featuring tridentate diamidoamine ligands

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Preparation of doubly-silylene-bridged zirconocene alkyl complexes, Me2Si)2{η5-C5H2-4-CHMe2}{η5-C5H-3,5-(CHMe2)2}ZrR2 (RCH3, CH2Ph) and investigations of their activity in 1-pentene polymerization. Molecular structure of (Me2Si)2{η5-C5H2-4-CHMe2}{η5-C5H-3,5- (CHMe2)2}Zr(CH2Ph)2

Cited by 19 publications

References 37 publications

Mechanisms of Stereocontrol for Doubly Silylene-BridgedCs- andC1-Symmetric Zirconocene Catalysts for Propylene Polymerization. Synthesis and Molecular Structure of Li2[(1,2-Me2Si)2{C5H2-4-(1R,2S,5R-menthyl)}{C5H-3,5-(CHMe2)2)}]·3THF and [(1,2-Me2Si)2{η5-C5H2-4-(1R,2S,5R-menthyl)}{η<

Mechanisms of Stereocontrol for Doubly Silylene-BridgedCs- andC1-Symmetric Zirconocene Catalysts for Propylene Polymerization. Synthesis and Molecular Structure of Li2[(1,2-Me2Si)2{C5H2-4-(1R,2S,5R-menthyl)}{C5H-3,5-(CHMe2)2)}]·3THF and [(1,2-Me2Si)2{η5-C5H2-4-(1R,2S,5R-menthyl)}{η<

Stereoregular Polymers

Synthesis and characterization of group IV metal complexes featuring tridentate diamidoamine ligands

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