ansa-Metallocene derivatives

Gutmann, S.; Burger, Peter; Hund, Hans-Ulrich; Hofmann, Josef; Brintzinger, Hans‐Herbert

doi:10.1016/0022-328x(89)85185-x

Cited by 65 publications

(49 citation statements)

References 23 publications

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“…6,6-Diethylfulvene was prepared from cyclopentadiene and 3-pentanone analogously to the procedure described for 6,6-pentamethylenefulvene, 37 and 3-tert-butyl-6,6-dimethylfulvene was prepared from tert-butylcyclopentadiene and acetone analogously to 3-(R,R-dimethylbenzyl)-6,6-dimethylfulvene. 35 The titanium complexes (η 5 -C5H4CMe2Ph)TiCl3 (1), 9a (η 5 -C5H4-CMe2-3,5-Me2C6H3)TiCl3 (3), 10 (η 5 -C5H4CMe3)TiCl3 (4), 38 (η 5 -C5H4CMe2Ph)TiMe3 (5), 9a (η 5 -C5H4CH2Ph)TiCl3 (6), 9c (η 5 -C5H4-SiMe2Ph)TiCl3 (7), 9a and (η 5 -C5H4CMe2CH2Ph)TiCl3 (8) NMR spectra were recorded on Varian Gemini 200/300 spectrometers in NMR tubes equipped with a Teflon (Young) valve. The 1 H NMR spectra were referenced to resonances of residual protons in the deuterated solvents (δ 7.15 ppm for C6D6, δ 7.24 ppm for CDCl3).…”

Section: Methodsmentioning

confidence: 99%

Catalytic Trimerization of Ethene with Highly Active Cyclopentadienyl−Arene Titanium Catalysts

2002

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Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The mono(cyclopentadienyl-arene)titanium complexes [η 5 -C 5 H 3 R-(bridge)-Ar]TiCl 3 , activated by methylalumoxane (MAO) cocatalyst, form a family of highly active catalysts for the trimerization of ethene, giving 1-hexene as the main product. Concomitant cotrimerization of ethene and 1-hexene, to give mainly 5-methylnon-1-ene, is also observed. The selectivity for trimerization depends on the presence of a pendant arene group on the cyclopentadienyl ligand and the nature of the bridge between these two ligand moieties. In the absence of a pendant arene, polyethene is the main product. The highest activity and selectivity for trimerization was observed for catalysts with a disubstituted C 1 bridge between the cyclopentadienyl and arene ligand moieties. A SiMe 3 substituent on the cyclopentadienyl ligand improves catalyst activity and selectivity, whereas methyl substitution of the arene decreases activity. Nevertheless, combining cyclopentadienyl SiMe 3 substitution with arene Me substitution gives rise to a catalyst with the highest activity and selectivity, evidence of the strongly nonlinear additivity of ligand substituent effects in this system. The cyclopentadienyl-arene ligand is likely to exhibit hemilabile behavior during catalysis, stabilizing intermediates by η 6 coordination and dissociating or slipping to make room for the incoming substrate. The presence of two pendant arene groups on the cyclopentadienyl ligand diminishes the activity of the catalyst but greatly enhances its stability.

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Section: Methodsmentioning

confidence: 99%

Catalytic Trimerization of Ethene with Highly Active Cyclopentadienyl−Arene Titanium Catalysts

2002

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“…3) The synthesis of the bridge and the metallocene complex in a single step. This approach is usually realized in form of reductive dimerizations of fulvenes and related precursors that are treated with sodium, magnesium, calcium (giving a calcocene), or other strong reducing agents, followed by a transmetalation with TiCl 3 ⋅AlCl 3 or TiCl 4 , for example . Alternatively, the reductive dimerization was directly carried out with in situ formed TiCl 2 , ZrCl 2 , or HfCl 2 …”

Section: General Synthetic Remarksmentioning

confidence: 99%

Strategies for the Synthesis of Chiral Carbon‐Bridged Group IV ansa‐Metallocenes

Bau

Wiesler

Younas

et al. 2019

Chemistry A European J

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This minireview provides a survey of the various synthetic approaches to chiral ansa‐metallocenes of Ti, Zr, and Hf containing a carbon‐based bridge. The individual strategies to install substitution patterns at either the cyclopentadienyl framework or the bridging unit are highlighted with focus on the progress made towards a direct preparation of single complex stereoisomers. The review further includes the discussion of potential problems such as the formation of undesired diastereomers, the threat of racemization of enantiopure material, and synthetic challenges originating from the synthesis, purification, and isolation of the target complexes. The review has been written with the goal in mind to facilitate the design and synthesis of new chiral ansa‐metallocene derivatives for emerging research areas in asymmetric catalysis and organometallic chemistry.

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“…132 Synthesis of the racemic and meso diastereomers of disubstituted tetramethylethanediyl-bridged titanocene derivatives Me 4 C 2 (1-C 5 H 3 -3-R) 2 TiCl 2 (R = t-Bu, SiMe 3 , i-Pr, α, α-dimethylbenzyl, or 1-phenylcyclohexyl) is accomplished by reductive coupling of the appropriately substituted 6,6-dimethylfulvenes with Mg/CCl 4 and reaction of the resulting di-Grignard reagents with TiCl 3 ·3THF, followed by oxidative work-up. 133 Several titanium ansa-metallocenes have been prepared which incorporate chiral centers in the backbone as a way of influencing the stereoselectivity of ansametallocene formation. Chiral backbones that have been TITANIUM: ORGANOMETALLIC CHEMISTRY 13 prepared and used in this fashion include (1R, 2R)-trans-1,2-bis(1-indenylmethyl)cyclopentane, 134 (S, S)-2,3-butylene-1,1 -bis(indenyl), 135 and 2,3-bis[3-(1,1-dimethylethyl)-1,3-cyclopentadien-5-yl]-2,3-dimethylbutane.…”

Section: Ansa-metallocenesmentioning

confidence: 99%

Titanium: Organometallic Chemistry

Mintz

2005

Encyclopedia of Inorganic and Bioinorganic Chemistry

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The majority of titanium organometallic chemistry involves complexes in which the titanium is in its highest oxidation state (+4) with cyclopentadienyl derivatives as ancillary ligands. However, considerable chemistry has also been developed for complexes with titanium in the +3 and +2 oxidation state, with lesser amounts of chemistry developed for titanium in lower oxidation states (+1, 0). Since the early 1980s, chemists have placed considerable emphasis on the fine‐tuning of the structure and reactivity of titanium organometallic complexes. Particular emphasis has been devoted to tailoring the structure and reactivity of bis(cyclopentadienyl)titanium derivatives by incorporating electron‐donating, electron‐withdrawing, sterically demanding, or chiral substituents on the cyclopentadienyl ring. Considerable effort has gone into preparing ansa‐metallocenes with a wide variety of bridging groups and substituents to fine‐tune the reactivity catalysts prepared from them. In a similar manner, considerable effort has gone into the development of constrained geometry complexes. Several types of chiral substituted cyclopentadienyl, annulated cyclopentadienyl, ansa ‐metallocenes, and constrained geometry complexes have been prepared and applied to olefin polymerization and organic synthesis. Additional efforts at modifying the structure and reactivity by focusing on varying the oxidation state or coordination geometry at the titanium center have expanded over the past decade.

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ansa-Metallocene derivatives

Cited by 65 publications

References 23 publications

Catalytic Trimerization of Ethene with Highly Active Cyclopentadienyl−Arene Titanium Catalysts

Catalytic Trimerization of Ethene with Highly Active Cyclopentadienyl−Arene Titanium Catalysts

Strategies for the Synthesis of Chiral Carbon‐Bridged Group IV ansa‐Metallocenes

Titanium: Organometallic Chemistry

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