Ziegler-Natta catalysis. A theoretical study of the isotactic polymerization of propylene

Castonguay, Laurie A.; Rappé, Anthony K.

doi:10.1021/ja00040a053

Cited by 251 publications

(153 citation statements)

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“…Numerous theoretical studies have been carried out to explore the insertion stage for alkene polymerization. [68][69][70][71] Most concur with the experimental results described above, that an a-agostic bond stabilizes the transition state for CÀC bond formation. These studies have revealed also that b-and, to a lesser extent, g-agostic interactions stabilize the growing alkyl chain in the resting state between periods of chain growth.…”

Section: The Agostic Bond As a Labile Ligand Interactionsupporting

confidence: 82%

Agostic Interactions in d⁰Metal Alkyl Complexes

2004

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The phenomenon of agostic interactions is reviewed and the nature of the interaction is revisited. A historical perspective is followed by an overview of experimental techniques used to diagnose agostic behavior, and previous interpretations of agostic bonding are presented. A series of simple metal alkyl complexes is considered and a new model for the phenomenon in d(0) systems is developed which sets them apart from agostic late-transition-metal complexes. Factors such as the valence electron count and coordination number of the metal center are revealed to be unimportant in facilitating the interaction in most d(0) systems. The charge density distribution in several transition-metal alkyl complexes is explored by experimental and theoretical techniques, including the powerful "Atoms in Molecules" approach. Local charge concentrations are shown to play an important role in the agostic interaction. Finally, we demonstrate for the first time a way to manipulate and control the magnitude and disposition of such local charge concentrations, and hence the strength of agostic interactions in d(0) metal alkyl complexes.

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Section: The Agostic Bond As a Labile Ligand Interactionsupporting

confidence: 82%

Agostic Interactions in d⁰Metal Alkyl Complexes

2004

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“…It might seem that our notion about a preference for backside insertion leads to predictions, eq. [7], in contradiction with experimental observation. However, it is also possible that the orientation of the methyl group on the incoming propylene is dictated by the chain rather than the L2M+ fragment.…”

Section: Discussioncontrasting

confidence: 61%

“…In the corresponding back-side attack of eq. [7], the chain remains on one side and propylene is always approaching with the methyl group in the same position if its position is dictated by the steric requirement of the L,M+ fragment. Thus, the backside attack would seemingly not produce the observed syndiotactic chain but instead result in a isotactic polymer.…”

Section: Discussionmentioning

confidence: 99%

“…If the former is correct, back-side attack in eq. [7] would lead to syndiotactic polymers. We intend to explore this possibility by a combined DFT and molecular mechanics study in which the steric bulk of the ancillary ligands on the metal as well as the growing chain are taken into account., We intend further to explore the front-side insertion, step A of Scheme 1, in more detail, although it seems that a possible transition state should be of high energy.…”

Section: Discussionmentioning

confidence: 99%

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A density functional study on olefin insertion and hydrogen transfer in the reaction between Cl2Ti⁺–ethyl and ethylene. Possible implications for the stereochemistry and chain termination in olefin polymerization

Fan¹,

Harrison²,

Deng³

et al. 1995

Can. J. Chem.

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Abstract:Calculations based on density functional theory have been canied out on the reaction between Cl,Ti+-ethyl(l) and ethylene. In this study 1 was taken as a model for the cationic metallocenes of group-4 elements, which have been developed by Kaminsky and Brintzinger as efficient catalysts for the polymerization of olefins. The ground state structure of 1 has a P-agostic conformation in which a single CB-H bond is directed towards the metal center. It was assumed that this conformation also serves as a model for the resting state of the growing chain attached to the cationic group-4 metallocenes between insertions. Two paths were considered for the reaction between 1 and ethylene. The first (2) has ethylene approaching the agostic Cp-H bond, whereas ethylene in the second approach (3) attacks the Ti-C, link from the side opposite to the Cp-H bond. The front-side attack (2) results in a transfer of hydrogen from the P-carbon of ethyl to ethylene and represents a chain-terminating step with an activation energy of 5.3 kcallmol. It was not possible to locate a path leading to olefin insertion from the front-side attack (2). The back-side attack (3) resulted readily in insertion with an activation energy of 3.9 kcallmol. The study made use of full transition state optimization as well as a tracing of the reaction paths by the intrinsic reaction coordinate (IRC) method of Fukui. Previous investigations have all assumed that olefin insertion takes place via a front-side approach (2) based on the known stereochemistry of a-olefin polymerization. The present study suggests that insertion takes place by a back-side approach (3), and this suggestion is discussed in connection with the known stereochemistry of olefin polymerization.Key words: Ziegler-Natta, olefin polymerization, density functional. Resum6: On a effectuC des calculs basks sur la thCorie de la densit6 fonctionnelle sur la reaction du C1,Ti' -Cthyl (1) et I'Cthylkne. Dans cette Ctude, on a utilisC le composC 1 comme modtle pour les mCtallocknes cationiques des ClCments du groupe 4 qui ont Ct C dCveloppCes par Kaminsky et Brintzinger comme des catalyseurs efficaces pour la polymCrisation des olefines. La strucutre de 1'Ctat fondamental du composC 1 posskde une conformation agostique-0 dans laquelle la liaison simple Cp-H est dirigCe vers le centre mCtallique. On a fait l'hypothkse que cette conformation sert aussi de modkle pour 1'Ctat au repos de la chaine qui croit attachCe au niveau des mCtallocknes cationiques du groupe 4 entre les insertions. On a considCrC deux voies rCactionnelles pour la reaction du compost 1 et I'Cthylkne. Dans la premikre (2), 1'Cthyltne approche de la liaison Cp-H alors que dans la deuxikme approche (3), 1'Cthylkne attaque la liaison Ti-C, a partir de la face opposCe i la liaison Cp-H. L'attaque frontale (2) provoque un transfert d'hydrogkne du carbone P du groupe Cthyle de I'tthylkne et elle correspond 2 une Ctape de terminaison de chaine avec une Cnergie d'activation de 5,3 kcallmol. I1 n'a pas Ct C possible de localiser un...

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“…2 Single-point calculations at polymer chain has also been reported by means higher electronic correlation level have also been of molecular mechanics calculations. 8 reported. Density Functional Theory (DFT) modThe different advantages and disadvantages of els including both local and nonlocal corrections each computational method are well known.…”

Section: Introductionmentioning

confidence: 99%

A theoretical study of the comonomer effect in the ethylene polymerization with zirconocene catalytic systems

Cruz

Muoz-Escalona²,

Martínez‐Salazar

1998

J. Polym. Sci. A Polym. Chem.

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Ziegler-Natta catalysis. A theoretical study of the isotactic polymerization of propylene

Cited by 251 publications

References 0 publications

Agostic Interactions in d⁰Metal Alkyl Complexes

Agostic Interactions in d⁰Metal Alkyl Complexes

A density functional study on olefin insertion and hydrogen transfer in the reaction between Cl2Ti⁺–ethyl and ethylene. Possible implications for the stereochemistry and chain termination in olefin polymerization

A theoretical study of the comonomer effect in the ethylene polymerization with zirconocene catalytic systems

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Ziegler-Natta catalysis. A theoretical study of the isotactic polymerization of propylene

Cited by 251 publications

References 0 publications

Agostic Interactions in d0Metal Alkyl Complexes

Agostic Interactions in d0Metal Alkyl Complexes

A density functional study on olefin insertion and hydrogen transfer in the reaction between Cl2Ti+–ethyl and ethylene. Possible implications for the stereochemistry and chain termination in olefin polymerization

A theoretical study of the comonomer effect in the ethylene polymerization with zirconocene catalytic systems

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Product

Resources

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Agostic Interactions in d⁰Metal Alkyl Complexes

Agostic Interactions in d⁰Metal Alkyl Complexes

A density functional study on olefin insertion and hydrogen transfer in the reaction between Cl2Ti⁺–ethyl and ethylene. Possible implications for the stereochemistry and chain termination in olefin polymerization