Synthesis, Structural and Chemical Characterization of Unsaturated C4- and C10-Bridged Group-4 ansa-Metallocenes Obtained Through a Ring-Closing Olefin Metathesis Reaction

Hüerländer, Doris; Kleigrewe, Nina; Kehr, Gerald; Erker, Gerhard; Fröhlich, Roland

doi:10.1002/1099-0682(200210)2002:10<2633::aid-ejic2633>3.0.co;2-4

Cited by 61 publications

(25 citation statements)

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“…However, carbon-carbon coupling reactions at the intact group 4 bent metallocene frameworks were close to nonexistent before our work (13)(14)(15). Meanwhile, a few leading examples have emerged from the literature, using, e.g., olefin-metathesis (16)(17)(18)(19) or even a variant of the Mannich reaction (20)(21)(22) for carrying out carbon-carbon coupling reactions at the reactive group 4 bent metallocene frameworks.…”

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confidence: 78%

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Paradies

Kehr

Fröhlich

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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Bis(1-methylethenyl-cyclopentadienyl)zirconium dichloride (7a) was prepared by a fulvene route. Photolysis at 0°C with Pyrexfiltered UV light resulted in a rapid and complete intramolecular [2؉2]cycloaddition reaction to yield the corresponding cyclobutylene-bridged ansa-zirconocene dichloride isomer (8a). This is one of the rare examples of an organic functional group chemistry that leads to carbon-carbon coupling at the framework of an intact sensitive group 4 bent metallocene complex. More sterically hindered open metallocenes that bear bulky isopropyl or tert-butyl substituents at their Cp rings in addition to the active 1-methylethenyl functional group undergo the photochemical ansa-metallocene ring closure reaction equally facile. The metallocene systems used and obtained in this study have served as transition metal components for the generation of active metallocene propene polymerization catalysts.photochemistry ͉ topochemical reaction M etallocene catalysis has become of great significance in olefin polymerization, especially for polyethylene, stereospecific polypropylene formation, and the production of some copolymers. The ansa-metallocenes of the group 4 metals and related systems play an essential role in this important development (1-3). Various methods have been devised and applied to construct such bent metallocene frameworks that feature a short carbon-or heteroatom-containing bridge between their substituted cyclopentadienyl, indenyl, or fluorenyl ligands. Because of the sensitive character of the organometallic group 4 metal complexes, ligand construction and variation is usually carried out at the free ligand stage before the final transmetallation step to the transition metal in the practical preparative sequences. This is a serious synthetic limitation. It would be highly desirable to have an organic functional group chemistry developed for framework variation at the actual metallocene stage. Previously, some addition reactions to metallocene frameworks had been reported, such as catalytic hydrogenation (4), hydrosilylation (5), hydroboration (6-9), or borylation (refs. 10, 11 and references therein, and 12). However, carbon-carbon coupling reactions at the intact group 4 bent metallocene frameworks were close to nonexistent before our work (13-15). Meanwhile, a few leading examples have emerged from the literature, using, e.g., olefin-metathesis (16-19) or even a variant of the Mannich reaction (20-22) for carrying out carbon-carbon coupling reactions at the reactive group 4 bent metallocene frameworks.Intramolecular photochemical [2ϩ2]cycloaddition reactions may become of a prime importance in this development. We had previously observed that bis(alkenyl-Cp)ZrCl 2 complexes such as, e.g., meso-1 underwent ansa-metallocene formation to yield meso-2 by intramolecular [2ϩ2]cycloaddition when irradiated with UV light. However, this specific reaction was not synthetically useful for a clean ansa-metallocene catalyst development because of its reversibility under the photochemical conditions t...

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confidence: 78%

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Paradies

Kehr

Fröhlich

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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“…Figure 10) were synthesized according to slightly modified literature procedures [14,15] contents. The purpose of this investigation was to compare the effect of a long bridge in combination with two differently hindering ligands with respect to the unbridged system (catalyst 1).…”

Section: Ethylene-propylene Copolymerization: Comparison Of Catalyst mentioning

confidence: 99%

Video Microscopy for the Investigation of Gas Phase Copolymerization

Fink

2005

Macro Materials & Eng

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Summary: Video microscopy as a tool for investigating olefin gas phase copolymerization is presented for the first time in this paper. The central theme of this work is the study of the comonomer effect shown by an unbridged metallocene catalyst supported on silica. By using video microscopy, it is possible to observe the increase in catalytic activity in terms of particle growth as well as monomer consumption. The observation that a more pronounced induction period in the particle growth profile is shown with increasing propylene concentration led us to investigate the copolymers obtained at different polymerization times using 13C NMR analysis and single particle energy dispersive X‐ray (EDX mapping). This allowed us to adapt the “polymer growth and particle expansion model” to the copolymerization. Besides physical causes for the comonomer effect, we wanted to determine whether the catalyst structure plays an important role in the comonomer effect. To this end we investigated two metallocenes bearing the same long bridging unit but differing in the ligand bound to the zirconium center. One metallocene bears a cyclopentadienyl ring, while the other bears an indenyl group. From a close analysis of the 13C NMR, it is clear that both catalysts insert ethylene more easily then propylene, probably due to the long bridging unit that results in a narrower aperture angle of the ligand. In addition to this, the indenyl ligand does not allow the formation of propylene blocks even at high propylene concentration.

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“…112) [351]; (2) formation of bridging zirconacene derivatives (e.g. 113) through RCM of 5-hexenylzirconacenes [352]; (3) synthesis of bridged ferrocenes; this reaction proceeds with a high degree of kinetic resolution [353]; (4) synthesis of an encased all-carbon ligand through RCM of an octatetrayne-bridged platinum complex featuring 7-octen-1-ylphosphine ligands [354]; (5) synthesis of cyclic siloxanes through RCM of vinyl siloxanes [355]; (6) synthesis of cyclic siloxanes (e.g. 114) for attenol total synthesis [356]; (7) synthesis of carbohydrate-containing cyclic siloxanes [357]; (8) preparation of cyclic phosphonate esters [358]; (9) preparation of cyclic sulfonamides (e.g.…”

Section: Ring Closing Metathesismentioning

confidence: 99%

The chemistry of the carbon–transition metal double and triple bond: annual survey covering the year 2002

Herndon

2004

Coordination Chemistry Reviews

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Synthesis, Structural and Chemical Characterization of Unsaturated C4- and C10-Bridged Group-4 ansa-Metallocenes Obtained Through a Ring-Closing Olefin Metathesis Reaction

Cited by 61 publications

References 29 publications

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Video Microscopy for the Investigation of Gas Phase Copolymerization

The chemistry of the carbon–transition metal double and triple bond: annual survey covering the year 2002

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