Cp-substituent additivity effects controlling the stereochemistry of the propene polymerization reaction at conformationally unrestricted (Cp-CHR1R2)2ZrCl2/methylalumoxane catalysts

Erker, Gerhard; Nolte, R.J.M.; Aul, Rainer; Wilker, Stephan; Krueger, C.; Noe, Ralf

doi:10.1021/ja00020a022

Cited by 121 publications

(68 citation statements)

References 2 publications

(4 reference statements)

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“…This increased polarity allows for selective nucleophilic attack at this double bond and not at the diene component of the fulvenes. Other examples of the nucleophilic addition of hydrides to substituted fulvenes (albeit with alkyl or unsubstituted phenyl group functionality) include the use of lithium aluminium hydride and the use of alkyllithium species as highly reactive-hydride transfer reagents [28,29].…”

Section: Synthesismentioning

confidence: 99%

Novel benzyl substituted titanocene anti-cancer drugs

Sweeney

Mendoza²,

Müller‐Bunz³

et al. 2005

Journal of Organometallic Chemistry

116

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Section: Synthesismentioning

confidence: 99%

Novel benzyl substituted titanocene anti-cancer drugs

Sweeney

Mendoza²,

Müller‐Bunz³

et al. 2005

Journal of Organometallic Chemistry

116

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“…[1] Control of the stereochemistry requires some conformational constraint because it arises mainly from steric interactions between the incoming olefin monomer and the Cp ligand; bridged cyclopentadienyl ligands (ansa-metallocenes) have often been used for this purpose. [2] However, some degree of stereocontrol is in principle possible without a rigid ligand framework if rotation of the Cp ligands is hindered, [3] for example by means of sterically demanding substituents. [4] We are currently studying the chemistry of titanium and zirconium metallocenes located at the focal point of one or two dendritic wedges.…”

Section: Introductionmentioning

confidence: 99%

Titanocene and Zirconocene Complexes containing Dendrimer-Substituted Cyclopentadienyl Ligands − Synthesis and Ethylene Polymerization

Andrés

Jesús

Mata

et al. 2002

Eur. J. Inorg. Chem.

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This paper describes the synthesis of a series of titanium and zirconium metallocenes bearing one or two first-generation silane dendritic wedges as bulky substituents at their cyclopentadienyl rings. Wedges (R 2 RЈSiCH 2 CH 2 ) 3 SiCl [R = RЈ = Et (1); R = Ph, RЈ = Me (2)] were prepared by hydrosilylation of chlorotrivinylsilane with R 2 RЈSiH. They were reacted with K(C 5 H 5 ) and, subsequently, with KH to give K[(R 2 RЈSiCH 2 CH 2 ) 3 Si(C 5 H 4 )] [R = RЈ = Et (3); R = Ph, RЈ = Me (4)]. The dendronized cyclopentadienides 3 and 4 were the starting materials for preparation of the mixed-ring titanocenes [{(R 2 RЈSiCH 2 CH 2 ) 3 SiC 5 H 4 }(C 5 RЈЈ 5 )TiCl 2 ] [R = RЈ = Et, RЈЈ = H (5), RЈЈ = Me (6); R = Ph, RЈ = Me, RЈЈ = H (7), RЈЈ =

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“…[1][2][3][4] In particular, chiral ansa-metallocene catalysts, which follow an enantiomorphic site-control mechanism, have been intensively investigated to obtain stereochemical control of propylene polymerization by varying the ligand structure. [5][6][7] Unbridgedmetallocene-based systems, on the other hand, have received little attention owing to their aspecific nature [8,9] in spite of their ability to produce iso-rich [10,11] or isotactic-atactic block polypropylene [12,13] when containing rotationally hindered ligands. As unbridged metallocenes are far easier to synthesize than ansa-metallocenes, we have been investigating isospecific, unbridged-metallocene catalytic systems that can be generated in situ during the activation step.…”

mentioning

confidence: 99%

Endowing Aspecific, Unbridged‐Metallocene Propylene‐Polymerization Catalysts with Isospecificity: The Unprecedented Role of MAO

Kim

Lee

et al. 2006

Angew Chem Int Ed

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The relationship between the nature of catalyst systems and the resulting polymer has been well established in single-site olefin-polymerization systems and now provides the opportunity to tailor the polymers properties. [1][2][3][4] In particular, chiral ansa-metallocene catalysts, which follow an enantiomorphic site-control mechanism, have been intensively investigated to obtain stereochemical control of propylene polymerization by varying the ligand structure. [5][6][7] Unbridgedmetallocene-based systems, on the other hand, have received little attention owing to their aspecific nature [8,9] in spite of their ability to produce iso-rich [10,11] or isotactic-atactic block polypropylene [12,13] when containing rotationally hindered ligands. As unbridged metallocenes are far easier to synthesize than ansa-metallocenes, we have been investigating isospecific, unbridged-metallocene catalytic systems that can be generated in situ during the activation step. To this end, we have designed "class I" unbridged metallocenes, a new class analogous to the known aspecific, unbridged metallocenes of "class II". [8,9] The Lewis basic sites E in class I complexes are found to interact with [Me-MAO] À to generate rigid, rac-like cationic active species, thereby endowing aspecific, unbridged-metallocene precatalysts with isospecificity. Herein, we report a novel example of a sterically unhindered, unbridged zirconocene system that is able to produce highly isotactic polypropylene through the unprecedented role of methyl aluminum oxane (MAO). The amine-functionalized, unbridged zirconocenes [{1-(pMe 2 NC 6 H 4 )-3,4-Me 2 C 5 H 2 } 2 ZrX 2 ] [(AP) 2 ZrX 2 ; X = Cl (2), X = Me (3)] were obtained from newly synthesized ligand 1 as outlined in Scheme 1. The molecular structure of 2 has C 2 symmetry in the solid state (Figure 1). The polymerization of propylene with 2/MAO ([Al]/[Zr] = 1000) was performed at various temperatures (T p = 0, 25, 50, and 70 8C; Table 1, entries 1-4, respectively). The 2/MAO system shows lower catalytic activity but produces higher molecular weight polypropylenes than the well-known isospecific catalyst rac-[Et(Ind) 2 ZrCl 2 ] (EBIZr)/MAO (entry 9) under identical reaction conditions. The differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) traces indicate that all the crude polypropylenes from the 2/MAO system show multiple melting transitions (T m ) and broad molecular-weight distributions (M w /M n ) of between 4.5 and 11 (Figure 2).The crude polypropylenes were fractionated by stepwise solvent extraction [14] into three portions for further analysis, 1) diethyl ether soluble, 2) diethyl ether insoluble and nheptane soluble, and 3) diethyl ether insoluble and n-heptane insoluble. The mmmm methyl pentad values in Table 2 suggest that these portions correspond to atactic-like, mod- [*] Dr.

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Cp-substituent additivity effects controlling the stereochemistry of the propene polymerization reaction at conformationally unrestricted (Cp-CHR1R2)2ZrCl2/methylalumoxane catalysts

Cited by 121 publications

References 2 publications

Novel benzyl substituted titanocene anti-cancer drugs

Novel benzyl substituted titanocene anti-cancer drugs

Titanocene and Zirconocene Complexes containing Dendrimer-Substituted Cyclopentadienyl Ligands − Synthesis and Ethylene Polymerization

Endowing Aspecific, Unbridged‐Metallocene Propylene‐Polymerization Catalysts with Isospecificity: The Unprecedented Role of MAO

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