Influence of the ligand structure of hafnocene polymerization catalysts: A theoretical study on chain termination reactions in ethene polymerization

Karttunen, Virve A.; Linnolahti, Mikko; Pakkanen, Tapani A.; Severn, John R.; Kokko, Esa; Maaranen, Janne; Pitkänen, Päivi; Pakkanen, Anneli

doi:10.1016/j.jorganchem.2008.09.070

Cited by 11 publications

(7 citation statements)

References 39 publications

(15 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, to the best of our knowledge, there are few systematic theoretical studies on the origin of ligand-induced catalytic performance for styrene polymerization. 22,33,34 The aim of the present contribution on styrene polymerization initiated by the five complexes 1−5 was to explore the molecular origin of their activity discrepancy. We employed the complexes 1, 2, and 3, which have the same side arm moiety, to explore the effect of electron donating of the aromatic ligands during styrene polymerization.…”

Section: ■ Introductionmentioning

confidence: 99%

“…These computations were mainly intended to investigate the intrinsic role of the chiral orientation of the growing polymeric chain on the regio- (2,1- vs 1,2-insertions) and stereo- (syndiotactic vs isotactic) selectivities. However, to the best of our knowledge, there are few systematic theoretical studies on the origin of ligand-induced catalytic performance for styrene polymerization. ,, …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

DFT Studies on Styrene Polymerization Catalyzed by Cationic Rare-Earth-Metal Complexes: Origin of Ligand-Dependent Activities

et al. 2016

View full text Add to dashboard Cite

The mechanism of styrene polymerization catalyzed by five analogous cationic rare-earth-metal complexes [(RCH2–Py)Y(CH2SiMe3)]+ (R = C5Me4 (Cp′), 1 + ; R = C9H6 (Ind), 2 + ; R = C13H8 (Flu), 3 + ), [(Flu–Py)Y(CH2SiMe3)]+ (4 + ), and [(Flu–CH2CH2–NHC)Y(CH2SiMe3)]+ (5 + ) has been studied through DFT calculations. Having achieved an agreement between theory and experiment in the activity discrepancy and selectivity, it is found that styrene polymerization kinetically prefers 2,1-insertion to 1,2-insertion. The free energy profiles for the insertion of a second monomer molecule have been computed for both migratory and stationary insertion manners, and the former resulting in a syndiotactic enchainment indicates obvious kinetic preference. The current results suggest that the coordination of styrene to the active metal center could play an important role in the observed activity difference. Interestingly, the charge on central metal of the cationic species accounts for the activities of 1 + , 2 + , and 3 + : the higher the charge on the central metal, the higher the activity. The coordination of a THF molecule to the central metal and more difficult generation of the active species could be responsible for the low activity of 4 + . For species 5 + , the resulting product of the first styrene insertion is quite stable, and the ancillary ligand and styryl group hamper the insertion of the incoming styrene molecule. This could be responsible for the absolute inertness of 5 + toward styrene polymerization. The calculated results also suggest that a longer alkyl chain of the side arm of the ancillary ligand could deter monomer coordination and thus decrease the polymerization activity.

show abstract

Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

DFT Studies on Styrene Polymerization Catalyzed by Cationic Rare-Earth-Metal Complexes: Origin of Ligand-Dependent Activities

et al. 2016

View full text Add to dashboard Cite

show abstract

“…Furthermore, the importance of a “proper” coordination sphere around the metal (namely the angle Cp centroid –M–Cp centroid in metallocenes) accounts also for the effects of the bridge in the ansa -metallocenes (e.g., −Si(CH 3 ) 2 in place of −C(CH 3 ) 2 , see systems 3 and 4 , or −Si(CH 3 ) 2 instead of −Si(Ph) 2 , see systems 6 and 7 ) Suitable modification of the metallocene skeleton, as the methyl substitution on the 2,2′ position on the indenyl or benzindenyl ligand, , can suppress the β-hydrogen transfer to the monomer increasing the average molecular mass (compare systems 4 , 8 , and 10 with 5 , 9 , and 11 , respectively). Changing the metal maintaining the same ligand scaffold allows to reach higher molecular mass (e.g., Hf complexes yield polymers with higher average molecular masses than the Zr homologues , ). Modification of ligand framework by using postmetallocene catalysts enlarges the range of olefin-based materials accessible. Typical example are the C 2 -aminophenolate octahedral complexes presenting ortho -phenolate substituents (see systems 17 - 18 of Chart ).…”

mentioning

confidence: 99%

“…Changing the metal maintaining the same ligand scaffold allows to reach higher molecular mass (e.g., Hf complexes yield polymers with higher average molecular masses than the Zr homologues , ).…”

mentioning

confidence: 99%

Buried Volume Analysis for Propene Polymerization Catalysis Promoted by Group 4 Metals: A Tool for Molecular Mass Prediction

2015

View full text Add to dashboard Cite

A comparison of the steric properties of homogeneous single site catalysts for propene polymerization using the percentage of buried volume (%VBur) as molecular descriptor is reported. The %VBur calculated on the neutral precursors of the active species seems to be a reliable tool to explain several experimental data related to the propene insertion and to the monomer chain transfer. Interestingly, a linear correlation between the buried volume calculated for a large set of neutral precursors and the energetic difference between propagation and termination steps calculated by density functional theory (DFT) methods is found for Group 4 metal catalysts. The "master curves" derived for Ti, Zr, and Hf confirm not only that the %VBur is an appropriate molecular descriptor for the systems considered but also that it could be used as tool for a large computational screening of new ligands

show abstract

“…QC approaches, including QM/MM techniques, were also applied to relevant research on olefin polymerization with metallocenes and properties of metallocenes themselves, including studies on monomer insertion, chain growth, chain termination, polymer rotation barriers, ligand hapticity, bridge effects, monomer oligomerization, counter‐ion effects, and copolymerization . As other examples, Green discussed the bent structure of metallocene species from a molecular orbital (MO) viewpoint .…”

Section: Introductionmentioning

confidence: 99%

Extent of structural change during the reaction and its relationship to isoselectivity in polypropylene polymerization with ansa‐zirconocene/borate catalyst: A computational study

2019

View full text Add to dashboard Cite

The mechanism of isotactic polypropylene (iPP) polymerization with an (R,R)‐ansa‐zirconocene/borate catalyst system was analyzed using quantum chemistry (QC) calculations by focusing on the extent of structural change during monomer insertion. The activation energy for migratory insertion, Ea, was compared for four possible reaction paths with regard to monomer coordination, that is, 1,2‐re, 1,2‐si, 2,1‐si, and 2,1‐re, until the seventh monomer insertion step, explicitly including a borate anion cocatalyst. This indicated that the 1,2‐re path was most favorable, except for the first step, which favored 1,2‐si. As far as the first step, the product of 1,2‐si is a conformational isomer to that of the 1,2‐re path, and the exceptional favorability of 1,2‐si does not affect the isoselectivity. These results support previous studies, except that our results address the unexplored seventh insertion step with a borate anion cocatalyst by QC calculations. The isoselectivity correlated with the extent of structural change in the whole system during the reaction. It was proved from our detail analysis that the advantage of 1,2‐re with a small Ea is attributed to its smaller structural changes due to low steric repulsion in the system compared with other paths. Conversely, larger repulsion in the systems involved in other paths results in larger structural changes to minimize the structural strain. However, the relaxation appears insufficient due to structural restriction of the enforced four‐membered ring transition state structure. A borate anion cocatalyst broke the C2 symmetry of the electronic structures of zirconocene, resulting in an odd–even Ea frequency for the monomer insertion. Molecular orbital analysis demonstrated that the d–π orbital overlaps can explain the approach direction of the olefin coordination and the bent structure of zirconocene, providing a different viewpoint from previous studies. The potential for catalyst control was discussed based on our results. © 2019 Wiley Periodicals, Inc.

show abstract

Influence of the ligand structure of hafnocene polymerization catalysts: A theoretical study on chain termination reactions in ethene polymerization

Cited by 11 publications

References 39 publications

DFT Studies on Styrene Polymerization Catalyzed by Cationic Rare-Earth-Metal Complexes: Origin of Ligand-Dependent Activities

DFT Studies on Styrene Polymerization Catalyzed by Cationic Rare-Earth-Metal Complexes: Origin of Ligand-Dependent Activities

Buried Volume Analysis for Propene Polymerization Catalysis Promoted by Group 4 Metals: A Tool for Molecular Mass Prediction

Extent of structural change during the reaction and its relationship to isoselectivity in polypropylene polymerization with ansa‐zirconocene/borate catalyst: A computational study

Contact Info

Product

Resources

About