A combined experimental—molecular modeling approach for ethene–propene copolymerization with C2-symmetric metallocenes

Friederichs, Nic; Wang, Bing; Budzelaar, Peter H. M.; Coussens, Betty

doi:10.1016/j.molcata.2005.06.066

Cited by 22 publications

(32 citation statements)

References 37 publications

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“…For the case of ethene polymerization, in particular, it is possible that the rate-limiting step of propagation does not correspond to the actual insertion step but rather to e.g. anion displacement [20] or chain re-orientation [21]. In that case, the agreement we find could be largely fortuitous.…”

Section: The Case Of Metallocenesmentioning

confidence: 76%

Hydrogen sensitivity – A systematic computational study of electronic effects

Budzelaar¹,

Coussens²,

Friederichs³

2007

Journal of Organometallic Chemistry

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Section: The Case Of Metallocenesmentioning

confidence: 76%

Hydrogen sensitivity – A systematic computational study of electronic effects

Budzelaar¹,

Coussens²,

Friederichs³

2007

Journal of Organometallic Chemistry

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“…The high affinity of 4-PhInd for propene has been observed experimentally. 39,40 Generally, however, the model system does not quantitatively reproduce the experimentally observed comonomer affinities. 39 This may be due to the rotation of the polymer chain requiring more energy than the ethene insertion.…”

Section: ■ Introductionmentioning

confidence: 87%

“…Insertion of propene can take place in four orientations, deciding the stereo-and regiochemistry of the produced polymer. 37 As the 4-PhInd and 4,5-BenzInd catalysts produce highly stereo-and regioregular polymer, 38,39 we focused on the primary 1,2-insertion leading to regioregular isotactic polymers. Monomer insertion is affected by the previously inserted monomer, 37 and hence the copolymerization step was studied for the second insertion step taking place after either ethene or propene insertion.…”

Section: ■ Introductionmentioning

confidence: 99%

Effect of Ligand Structure on Olefin Polymerization by a Metallocene/Borate Catalyst: A Computational Study

et al. 2015

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We have carried out a systematic computational study on olefin polymerization by metallocene/borate catalysts, using three metallocenes: Cp 2 ZrMe 2 (Cp), rac-SiMe 2 -bis(1-(2-Me-(4-PhInd))-ZrMe 2 (4-PhInd), and rac-SiMe 2 -bis(1-(2-Me-(4,5-BenzInd))ZrMe 2 (4,5-BenzInd). Detailed reaction pathways, including the structure of the catalytically active ion pair, anion displacement, chain propagation, and chain termination steps, are reported for ethene homopolymerization, alongside with investigation of ethene−propene copolymerization reactions. Initially, all catalysts form inner-sphere ion pairs ([L 2 ZrMe] + −[B(C 6 F 5 ) 4 ] − ) with a direct Zr−F interaction, which is weak enough to be displaced by the incoming monomer. In comparison to Cp, the bulky and electron-rich 4-PhInd and 4,5-BenzInd show higher barriers for anion displacement but lead to relative stabilization of the resulting π complexes. 4-PhInd enables the most feasible propene uptake, and both catalysts suppress the chain termination reactions relative to Cp. The borate counterion is shown to have a minor influence after the catalyst activation step. ■ INTRODUCTION Single-site α-olefin polymerization catalysis is an industrially important application of Group 4 organometallic complexes, 1 particularly of metallocenes. The metallocene complexes need an activator to form a catalytically active [L 2 MMe] + [A] − ion pair. 2 The catalytic properties of the resulting ion pair are highly dependent on both the ligand framework of the metallocene cation [L 2 MMe] + and the structure of the counterion [A] − . 2−4 Typical activators used in the process i n c l u d e m e t h y l a l u m i n o x a n e ( M A O ) , 5 , 6 t r i s -(pentafluorophenyl)borane (B(C 6 F 5 ) 3 ), 7 and organoborates such as [CPh 3 ] + [B(C 6 F 5 ) 4 ] − , the last giving rise to the weakly coordinating tetrakis(perfluoroaryl)borate counterion [B-(C 6 F 5 ) 4 ] − . 7,8Regarding catalyst properties, the stability of the ion pair plays a key role. 9,10 Experimental data suggest that weak coordination of the counterion is usually beneficial for catalytic activity. 11 On the other hand, the counterion needs to stay close to the metallocene cation in order to compensate for its positive charge. 12 Optimally, the counterion provides the needed stabilization for the electron-deficient metallocene cation but is easily displaced by the incoming monomer.The overall mechanisms of catalyst activation are not precisely understood. In the case of MAO, two mechanisms have been proposed: (1) abstraction of a leaving group from the precatalyst by a Lewis acidic site of MAO 2 and (2) abstraction of an AlMe 2 + end group from the MAO by the precatalyst followed by dissociation of AlMe 3 by the incoming monomer. 13,14 Recent computational studies have suggested mechanism 2 to dominate by thermodynamic considerations. 15 In any case, all computational studies dealing with the MAO activator suffer from its elusive structure, thereby requiring the use of model systems. In that respect boron activators, formin...

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“…In practice, catalyst activity is usually limited by factors other than the intrinsic propagation rate; therefore, we will focus on molecular weight here and assume that BHT is the dominant chain‐transfer mechanism . The neglect of the other chain‐transfer mechanisms outlined in the introduction is justified, as those can often be suppressed or reduced significantly, for example, through the choice of activator/scavenger system (chain transfer to aluminium) or monomer pressure (BHE, β‐methyl elimination).…”

Section: Resultsmentioning

confidence: 99%

Tuning the Relative Energies of Propagation and Chain Termination Barriers in Polyolefin Catalysis through Electronic and Steric Effects

2017

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A computational exploration of the predicted molecular weights for Ti‐ and Zr‐catalyzed olefin polymerizations shows that there are considerable opportunities for electronic tuning. Ligand variation mainly affects the propagation rate, whereas chain transfer to the monomer is hardly affected by electronic factors. The results are analyzed in terms of the effects of ligand variation on the relative energies of “connected couples” of reactant local minima and the corresponding transition states on the basis of the Hammond postulate and the Curtin–Hammett principle. For the constrained‐geometry catalysts (CGCs) and bis(amido) systems studied, better donating ligands increase the preference for a “planar” metal environment and produce higher molecular weights.

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A combined experimental—molecular modeling approach for ethene–propene copolymerization with C2-symmetric metallocenes

Cited by 22 publications

References 37 publications

Hydrogen sensitivity – A systematic computational study of electronic effects

Hydrogen sensitivity – A systematic computational study of electronic effects

Effect of Ligand Structure on Olefin Polymerization by a Metallocene/Borate Catalyst: A Computational Study

Tuning the Relative Energies of Propagation and Chain Termination Barriers in Polyolefin Catalysis through Electronic and Steric Effects

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