ansa-Metallocenes with a Ph2Si bridge: molecular structures of HfCl2[Ph2Si(η5-C13H8)(η5-C5H4)] and HfCl2[Ph2Si(C13H9)(η5-C5H4)]2†

Izmer, Vyacheslav V.; Agarkov, Anton; Nosova, V. M.; Кузьмина, Л. Г.; Howard, Judith A. K.; Beletskaya, I. P.; Voskoboynikov, Alexander Z.

doi:10.1039/b009280k

Cited by 13 publications

(16 citation statements)

References 15 publications

(19 reference statements)

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“…Following this protocol, an extended series of new constrained (aryl) 2 C-bridged proligands (2a-j) was here prepared in good yields (Scheme 3) and isolated as air-stable solids. The Ph 2 Si-bridged 2k was synthesized using a modified procedure reported for {R 2 Si(Flu)(Cp)}H 2 , where R = Me or Ph [30][31][32][33][34]. After optimization of the conditions and purification by column chromatography, proligand 2k was isolated with an acceptable yield (47%) as a crystalline solid.…”

Section: Resultsmentioning

confidence: 99%

Propylene Polymerization and Deactivation Processes with Isoselective {Cp/Flu} Zirconocene Catalysts

et al. 2021

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Industrially relevant single-site precatalysts used to produce isotactic polypropylene (iPP) include C2-symmetric {SBI} and C1-symmetric {Cp/Flu} complexes of group 4 metals. While the latter can produce iPPs with a higher degree of isotacticity, they also suffer from poor productivity compared to their {SBI} counterparts. Several causes for this trend have been suggested—2,1-Regioinsertions are frequently pointed out, as they are suspected to drive the catalyst into a dormant state. While this event does not seem to significantly impact the productivity of {SBI} systems, the influence of these regioerror is poorly documented for isoselective {Cp/Flu} precatalysts. To address this issue, new Ph2X(Cp)(Flu) (Ph2X = Ph2C, FluC, Ph2Si) proligands (2a–k) and some of the corresponding dichlorozirconocenes (3a–h,k) were synthesized. These new compounds were characterized and tested in homogeneous propylene polymerization at 60 °C and the amounts of regioerrors in the resulting polymers were examined by 13C NMR spectroscopy. A possible correlation between poor productivity and a high number of regioerrors was investigated and is discussed. Furthermore, a C-H activation process in the bulky nBu3C substituent upon activation of 4c (the dimethylated analog of 3c) by B(C6F5)3 has been evidenced by NMR; DFT calculations support this C-H activation as a deactivation mechanism.

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Section: Resultsmentioning

confidence: 99%

Propylene Polymerization and Deactivation Processes with Isoselective {Cp/Flu} Zirconocene Catalysts

et al. 2021

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“…The synthesis of Flu-SiPh 2 Cl took place by a modified literature procedure . In a 250 mL Schlenk flask, 1.83 mL (2.21 g, 8.71 mmol, 1.00 equiv) of diphenyldichlorosilane was diluted in 100 mL of dry Et 2 O.…”

Section: Methodsmentioning

confidence: 99%

“…Furthermore, the availability of stereocenters allows the synthesis of stereocontrolled polymers, whereby highly isotactic polypropylene (iPP) builds a 3/1 helix by virtue of the repulsive interaction of the methyl groups, whereas syndiotactic polypropylene (sPP) forms a trans-planar zigzag configuration in addition to a s(2/1)2 helix. , For the purpose of processing of UHMWPP in a fashion similar to that of UHMWPE, e.g., gel extrusion for fiber spinning, UHMW-sPP is considered to be far better suited than the isotactic alternative, because the zigzag configuration is similar to the microstructure of the processable UHMWPE . In general, the macromolecular characteristics of the resulting polypropylene, such as its molecular weight and melting transition, can be adjusted by a change in fundamental motifs in catalyst design: e.g., the ligand or the central group IV metal atom of ansa -metallocene dichlorides. − In the literature, for the synthesis of ultrahigh molecular weight polypropylene, hafnium is recommended instead of zirconium as the central metal atom, because the corresponding Hf homologues yielded up to a 10-fold higher molecular weight of polypropylene. , …”

Section: Introductionmentioning

confidence: 99%

In Situ Activation: Chances and Limitations to Form Ultrahigh Molecular Weight Syndiotactic Polypropylene with Metallocene Dichlorides

et al. 2021

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Fluorenyl cyclopentadienyl C s -symmetric ansa-metallocene (M = Zr, Hf) complexes I−IV featuring different bridging motifs (C and Si) were synthesized and subsequently examined in the syndiospecific coordinative polymerization of propylene. All complexes were activated in situ with triisobutylaluminum (TIBA) and [Ph 3 C][B(C 6 F 5 ) 4 ] (TrBCF) in order to highlight the benefits of this in situ activation, resulting in a significantly higher molecular weight and a significantly increased productivity in comparison to methylaluminoxane (MAO). The isopropylidene-bridged zirconocene Ia (ZrCl 2 [Me 2 C(η 5 -Flu)(η 5 -Cp)]) exhibited a high productivity (80000 kg PP (mol cat h) −1 ) and stereoregularity ([rrrr] up to 93%) with a moderate molecular weight of polypropylene (PP), whereas the polymerization with the corresponding hafnocene Ib (HfCl 2 [Me 2 C(η 5 -Flu)(η 5 -Cp)]) resulted in a lower productivity and stereoregularity but yielded ultrahigh molecular weight polypropylene (M w = 1100 kg mol −1 ). The backbone in II (HfCl 2 [Ph 2 C(η 5 -Flu)(η 5 -Cp)]) was associated with a higher productivity and molecular weight, while the syndiotacticity was not affected. In contrast, SC-XRD revealed a reduced dihedral angle and D value for Si-bridged hafnocenes III (HfCl 2 [Me 2 Si(η 5 -Flu)(η 5 -Cp)]) and IV (HfCl 2 [Ph 2 Si(η 5 -Flu)(η 5 -Cp)]), resulting in a more constrained geometry of the catalyst. This led to an increased molecular weight, while the productivity as well as the syndiotacticity decreased due to these structural parameters. Activation of Ib and II−IV with n-octyl-modified methylaluminoxane (MMAO) resulted in a lower molecular weight of the polymer, because the transfer of the growing polymer chain onto the Al center was enhanced. Nevertheless, the stereoregularity of MMAO-activated catalysts was slightly increased, probably due to a coordination of the ill-defined MMAO anion during the polymerization. DSC analysis exposed for syndiotactic polypropylene (sPP) produced by the highly active zirconocene Ia a defined melting transition (T m up to 145.2 °C), whereas TIBA/TrBCF-activated hafnocenes Ib and II−IV gave polymers with no observable T m value.

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“…(1) the reaction between di-lithium salts of the ligands and MCl 4 , where M = Zr, Hf [1]; (2) the reaction between metal tetrachlorides and indenyl-tin derivatives [16][17][18][19].…”

Section: Synthesis and Molecular Structures Of Ansametallocenesmentioning

confidence: 99%

Synthesis and molecular structures of zirconium and hafnium complexes bearing dimethylsilandiyl-bis-2,4,6-trimethylindenyl and dimethylsilandiyl-bis-2-methyl-4,6-diisopropylindenyl ligands

Izmer¹,

Sorokin²,

Кузьмина³

et al. 2005

Journal of Organometallic Chemistry

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ansa-Metallocenes with a Ph2Si bridge: molecular structures of HfCl2[Ph2Si(η5-C13H8)(η5-C5H4)] and HfCl2[Ph2Si(C13H9)(η5-C5H4)]2†

Cited by 13 publications

References 15 publications

Propylene Polymerization and Deactivation Processes with Isoselective {Cp/Flu} Zirconocene Catalysts

Propylene Polymerization and Deactivation Processes with Isoselective {Cp/Flu} Zirconocene Catalysts

In Situ Activation: Chances and Limitations to Form Ultrahigh Molecular Weight Syndiotactic Polypropylene with Metallocene Dichlorides

Synthesis and molecular structures of zirconium and hafnium complexes bearing dimethylsilandiyl-bis-2,4,6-trimethylindenyl and dimethylsilandiyl-bis-2-methyl-4,6-diisopropylindenyl ligands

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