The role of free ions in reactions of olefins with soluble complex catalysts

D'yachkovskii, F.S.; Shilova, A. K.; Шилов, А. Е.

doi:10.1002/polc.5070160445

Cited by 82 publications

(10 citation statements)

References 5 publications

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“…Before the discovery of the metallocene-based syndiospecific catalyst system there existed, thanks to intensive investigations by several research groups worldwide, sufficient evidence to assume that the active species involved in metallocene-based olefin polymerization catalysis are cationic in nature [77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96]. It is now widely accepted that the active site species are cationic metallocenium-monoalkyl complexes.…”

Section: Crystal Structure Of the Metallocenium-monoalkyl Cation And mentioning

confidence: 99%

Syndiotactic Polypropylene: Discovery, Development, and Industrialization via Bridged Metallocene Catalysts

Razavi¹

2013

Advances in Polymer Science

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This chapter covers the discovery that enabled, for the first time, the manufacturing of high molecular weight, highly stereoregular syndiotactic polypropylene polymers with narrow molecular weight distribution via the new class of metallocene molecules with bridged cyclopentadienyl-fluorenyl ligands. First, the salient crystal structural features of the neutral metallocene molecules and the crystal structure of the corresponding mono-alkyl-zirconocenium cation is introduced. Then, by employing the structural and geometrical data, a realistic working model for the active site precursor is developed and presented. The stereochemistry of the catalytic propylene poly-insertion reaction and the formation of syndiotactic polypropylene according to the enantiomorphic site control mechanism at the enantiotopic cationic active sites, formed after the activation of the prochiral metallocene dichloride with methylaluminoxane, MAO, is reviewed and further delineated. In the following sections, the impact of the introduction of substituents with proper size and composition at some selected positions of the ligand is discussed and the methods for increasing the molecular weight and stereoregularity of syndiotactic polypropylene polymers are elaborated. With the aid of computational calculations on real and hypothetical catalyst systems with substitutionally altered ligand structures, it is shown that the degree of enantioselectivity of syndiospecific catalyst systems can be determined and/or predicted for these systems quantitatively and with high precision. The calculations confirm that the introduction of substituent(s) reinforcing the preferential conformational orientation of the polymer chain enhances the overall enantioselectivity of the active site, and to certain extends stereoselectivity in general, by affecting the site epimerization processes. The computational calculations reveal that to account correctly for the frequency of the site epimerization-dependent m-type stereo-errors it is essential to include the counter-ion, as an integrated part of the A. Razavi (*) 35 Domaine de la Brisee, 7034 Obourg, Belgium e-mail: abbasrazavi@skynet.be catalyst system, into the calculations. The relevance of the symmetry and stereorigidity of the metallocene structure for the syndiospecificity of the final catalyst is debated by presenting a few "non-conforming" catalyst examples.Finally, the challenges involved in the manufacture of syndiotactic polypropylene in commercial scale continuous production processes are highlighted as well as the polymer's unique structural, physical, mechanical and rheological properties.

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Section: Crystal Structure Of the Metallocenium-monoalkyl Cation And mentioning

confidence: 99%

Syndiotactic Polypropylene: Discovery, Development, and Industrialization via Bridged Metallocene Catalysts

Razavi¹

2013

Advances in Polymer Science

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“…The other is the formation of an ion-pair. Shilov and Dyachkovskii (38), Eisch (39), and Bochmann (40) showed that the activity of metallocene catalysts depends on the formation of cationic species. The bulky MAO cluster takes a chlorine atom or a methyl group from the metallocene together with an electron forming a cationic metallocene and an anionic MAO complex (eq.…”

Section: Cocatalystmentioning

confidence: 99%

Metallocene Catalysts

Kaminsky

2015

Kirk-Othmer Encyclopedia of Chemical Technology

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Metallocene catalysts are useful for the polymerization of olefins and copolymerization of ethene or propene with cyclic olefins, styrene, and polar vinyl monomers. These catalysts contain two components such as a metallocene or half‐sandwich complex of transition metals and an organoaluminum compound, methylaluminoxane (MAO), or a perfluorinated boron aromatic compound. Most polymerization active metallocenes contain zirconium or titanium as transition metal but also hafnium, chromium, scandium, or others. The use of metallocene catalysts and their modifications has widely increased the synthetic and technical possibilities in more precisely controlling the polymer composition, polymer structure, tacticity, and other special properties. They allow the synthesis of polyolefins with short‐ or long‐chain branches, different tacticities and stereoregularities, copolymers with high‐compositional uniformity, new norbornene or styrene copolymers, and polyolefin composite materials in a purity that cannot be obtained by Ziegler–Natta catalysts. Today, industries mainly produce metallocene‐based linear low‐density polyethylene (LLDPE) and ethene/propene (EPM and EPDM) copolymers. These polyolefins show a higher growing rate than similar polymers obtained by conventional catalysts. The single‐site character of metallocene/MAO or other metallocene/borate catalysts has led to a better understanding of the mechanism of olefin polymerization.

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“…Conductivity and electrodialysis studies by Shilov et al [101,102] suggested that the catalytically active species in polymerisations is actually cationic. Direct evidence for the involvement of a cationic active species was provided by electrochemical synthesis of [Cp 2 TiMe] ?…”

Section: Historical Backgroundmentioning

confidence: 99%

Group 4 metal complexes for homogeneous olefin polymerisation: a short tutorial review

2015

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The discovery of transition metal-catalysed polymerisation of olefins in the 1950s by Ziegler and Natta was of huge importance. Over the last 30 years, the interest in homogenous polymerisation has not only grown but has changed focus from primarily studying the metallocene complexes of Group 4 to widespread exploration of postmetallocene systems. This is a consequence of extensive patenting of the metallocene catalyst systems, as well as for general interest in the improvement of polyolefin catalysis. The plastics industry produces more than 10 7 tonnes of polyethylene, polypropylene and polystyrene each year worldwide, and the study of well-defined homogenous catalysts is invaluable in uncovering the mechanism of polymerisation and the fundamental properties of the active species. This short Tutorial Review gives an overview of homogenous transition metal Ziegler-Natta catalysis in general as well as an overview of a selection of Group 4 post-metallocene catalysts. An overview of the synthesis and reactions of alkyl cations relevant to olefin polymerisation is also given. Finally, this review summarises recent advances in bimetallic catalysts for olefin polymerisation.

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The role of free ions in reactions of olefins with soluble complex catalysts

Cited by 82 publications

References 5 publications

Syndiotactic Polypropylene: Discovery, Development, and Industrialization via Bridged Metallocene Catalysts

Syndiotactic Polypropylene: Discovery, Development, and Industrialization via Bridged Metallocene Catalysts

Metallocene Catalysts

Group 4 metal complexes for homogeneous olefin polymerisation: a short tutorial review

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