Mechanism for the stereospecific polymerization of olefins by Ziegler–Natta catalysts

Ivin, K. J.; Rooney, John J.; Stewart, Cecil D.; Green, Malcolm L. H.; Mahtab, Rahina

doi:10.1039/c39780000604

Cited by 210 publications

(87 citation statements)

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“…1,1727 It is well known that in situ an activated catalyst must be formed from a parent catalyst using a cocatalyst to initiate the propagation steps, and as shown in Scheme 1 this activated cationic complex catalyzes polymerization. The most widely accepted CosseeArlman mechanism 28,29 has been used in discussion of reaction steps, while a modified GreenRooney mechanism 30 also has come into play when αCH agostic interaction with metal occurs prior to insertion. In our earlier studies with ab initio MO method on ethylene insertion with [H 2 Si(C 5 H 4 ) 2 …”

Section: Introductionmentioning

confidence: 99%

Revisiting the Stereochemistry of Propylene Isotactic Polymerization Reaction Mechanism on C2 Symmetric [SiH2(Ind)2ZrCH3]+ and [SiH2(Ind)2ZrCH3]+[CH3B(C6F5)3]−

Sandhya¹,

Koga²,

Nagaoka³

2016

Bulletin of the Chemical Society of Japan

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The [SiH 2 (Ind) 2 ZrCH 3 ] + (Ind = indenyl) catalyzed stereoregularity of propylene polymerization mechanism has been investigated at M06 level of theory. Four different approaches of propylene to the reactive catalyst lead to four isomeric products due to the C 2 symmetry of bridged Ind ligand of the catalyst. Consequently, various possibilities of propylene attack as well as orientation of polymer chain yield numerous stereoisomers. The calculations of the first and second insertions with various conformers clarified the most favorable reaction pathway and showed that isotactic propagation is more favorable (3.5 kcal mol ¹1 ) than syndiotactic propagation. The structures of resting state catalysts displayed various agostic interactions of the CH bond with the Zr center which stabilize the catalytic systems and play important roles in determining the favorable reaction pathway. The influence of counter anion¹ on the reactivity of the catalyst was also studied. The results also confirm that the trans orientation of the counter anion with respect to propylene is more favorable than its cis orientation and clarify the most favorable reaction pathway in the first and second insertion. Because agostic interactions are involved in various aspects, AIM analysis has been used to find the bonding nature of agostic interactions as well as ion-pair bonds. The overall results suggest that rigidity of ansa-zirconocene, unique structure of C 2 symmetric ansa ligand, influence of [CH 3 B(C 6 F 5 ) 3 ]¹ and β agostic interaction may restrict the attack of propylene only to isotactic polymerization and not to syndiotactic polymerization.

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Section: Introductionmentioning

confidence: 99%

Revisiting the Stereochemistry of Propylene Isotactic Polymerization Reaction Mechanism on C2 Symmetric [SiH2(Ind)2ZrCH3]+ and [SiH2(Ind)2ZrCH3]+[CH3B(C6F5)3]−

Sandhya¹,

Koga²,

Nagaoka³

2016

Bulletin of the Chemical Society of Japan

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“…For the -complex formation step, one side of cocatalysis works actively to weak the Ti᎐CH bond. For the olefin insertion 3 step, the cocatalysis works to break the old Ti᎐CH 3 bond, and the other side of cocatalysis works to form a new Ti᎐C bond. As the results, the cocatalysis play a role in facilitating the pull᎐push mechanism through the Al᎐Cl bonds alternation.…”

Section: Discussionmentioning

confidence: 99%

Ab initio studies on the Ziegler-Natta polymerization mechanisms of ethylene and propylene. Role of cocatalysis and stereoregulation

Sakai

1997

Int. J. Quant. Chem.

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As a model of olefin polymerization for a heterogeneous Ziegler᎐Natta catalyst, the mechanisms of the insertion of ethylene and propylene into R-Ti-Ž . q Ž . Ž . Cl AlH R s CH , C H are studied by ab initio self-consistent field SCF methods 2 2 2 3 3 7and many-body perturbation theory. The structures of the reactant, the intermediate, the transition state, and the product are optimized by the Hartree᎐Fock molecular orbital calculation level. The reactions are classified into two steps: the first forms of olefin᎐Ti complex, and the second step is the carbon᎐carbon bond formation through the pull᎐push mechanisms. The cocatalysis play a role in facilitating the pull᎐push mechanism with the Al᎐Cl bonds alternation. For the insertion reaction of propylene, the four-type Ž conformations for attacking of propylene two primary forms: methyl-substituted carbon attacks to the carbon side of Ti᎐C bond; two secondary forms: methyl-substituted carbon . attack to Ti atom are studied. For the complex formation, the secondary forms are more stable in energy than the primary forms. For the transition state, the primary forms are more stable in energy than the secondary forms.

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“…These authors conclude that lower steric repulsions appear to be implied for a coordination of the polymeric chain on the more hindered octahedral position at a titanium atom (at the (110) surfaces, or at edges, steps and reliefs on (111) surfaces of all the layered modifications of TiCI 3 ) and this, in turn, causes a chiral orientation of the first carbon-carbon bond of the chain: such orientation may be the main factor in determining the isospecificity. A monoatomic model for the catalytic centre has also been proposed by Ivin et al [402] who suggest the growing polymeric chain to be bound to the transition metal through a double bond (carbene complex) and the insertion reaction to occur through the formation of a metalcyc10butane intermediate (cf scheme i, Figure 24). This mechanism has however been objected to by Zambelli et al [367] on the basis of 13C-NMR analysis ofisotactic polypropylenes obtained in the presence of catalytic systems prepared starting from 13C enriched organometallic compounds.…”

Section: Models Of Catalytic Centresmentioning

confidence: 92%

Catalytic Olefin Polymerization

Pasquon

Giannini²

1984

Advances in Comparative and Environmental Physiology

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Mechanism for the stereospecific polymerization of olefins by Ziegler–Natta catalysts

Cited by 210 publications

References 0 publications

Revisiting the Stereochemistry of Propylene Isotactic Polymerization Reaction Mechanism on C2 Symmetric [SiH2(Ind)2ZrCH3]+ and [SiH2(Ind)2ZrCH3]+[CH3B(C6F5)3]−

Revisiting the Stereochemistry of Propylene Isotactic Polymerization Reaction Mechanism on C2 Symmetric [SiH2(Ind)2ZrCH3]+ and [SiH2(Ind)2ZrCH3]+[CH3B(C6F5)3]−

Ab initio studies on the Ziegler-Natta polymerization mechanisms of ethylene and propylene. Role of cocatalysis and stereoregulation

Catalytic Olefin Polymerization

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