Ion pairing in transition metal catalyzed olefin polymerization

Zaccaria, Francesco; Sian, Leonardo; Zuccaccia, Cristiano; Macchioni, Alceo

doi:10.1016/bs.adomc.2019.08.001

Cited by 41 publications

(72 citation statements)

References 452 publications

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“…It is generally accepted that the MAO activation of group 4 metallocenes proceeds through alkylation steps, which occurs via halide/alkyl exchange equilibria possibly up to complete substitution. 34 In this work no evidence of Cl ions coordination to titanium is obtained pointing to methyl or alkyl bridges, even though oxygen coordination cannot be denitely excluded. 14,18 Recent experimental and theoretical studies 17,60,61 on the activation of transition metal catalysts with MAO proved that the strong Lewis acid [AlMe 2 ] + cation, resulting from the heterolytic dissociation of AlMe 3 coordinated to the surface of the MAO cage, is responsible for the in situ generation of the alkylmetallocenium cation from the neutral dialkylmetallocene.…”

Section: Electronic and Geometrical Structure Of Ti-hmentioning

confidence: 63%

“…These values are in agreement with previous studies on related systems. [32][33][34] When the sample is le to evolve at room temperature, the intensity of the doublet spectrum smoothly decreases over time as a second species gradually appears, while the total paramagnetic fraction stays constant. Besides the already discussed doublet, the 95 minute spectrum ( Fig.…”

Section: Solution X-band Cw Eprmentioning

confidence: 99%

“…NMR spectroscopy has been instrumental in elucidating the activation and the structure of Ti(IV) cationic complexes and their stabilization through formation of ion pairs formed upon MAO/MMAO activators. [34][35][36][37] Similar detailed spectroscopic studies of the corresponding Ti(III) open-shell complexes are completely lacking. EPR is especially suited for this task as the magnetic hyperne couplings between the electron spin and the surrounding magnetically active nuclei encode geometrical information such as the distance between the magnetic nuclei and the electron spin-carrying centre and their relative orientation.…”

Section: Introductionmentioning

confidence: 99%

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Structure and dynamics of catalytically competent but labile paramagnetic metal-hydrides: the Ti(iii)-H in homogeneous olefin polymerization

et al. 2020

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Section: Electronic and Geometrical Structure Of Ti-hmentioning

confidence: 63%

Section: Solution X-band Cw Eprmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structure and dynamics of catalytically competent but labile paramagnetic metal-hydrides: the Ti(iii)-H in homogeneous olefin polymerization

et al. 2020

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“…64 Furthermore, reactions are modeled assuming naked ions in a solvent continuum, rather than the ion pairs typically formed in the low polarity solvents used (see below for further discussion on this point). 7 , 65 , 66 …”

Section: Resultsmentioning

confidence: 99%

“… 6 , 7 The ability of MAO to generate large anions with a delocalized negative charge has been proposed as one of the origins of the excellent cocatalytic properties of this aluminoxane. 6 , 7 , 70 , 71 In the presence of a neutral monodentate donor like py , all reactions are predicted to be significantly easier ( Table 2 , entries 4–6). The dissociation of AlMe 3 becomes exergonic for B (−8 kcal/mol) and particularly for C (−34 kcal/mol), and nearly energetically neutral for A .…”

Section: Resultsmentioning

confidence: 99%

Reactivity Trends of Lewis Acidic Sites in Methylaluminoxane and Some of Its Modifications

et al. 2020

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The established model cluster (AlOMe) 16 (AlMe 3 ) 6 for methylaluminoxane (MAO) cocatalyst has been studied by density functional theory, aiming to rationalize the different behaviors of unmodified MAO and TMA-depleted MAO/BHT (TMA = trimethylaluminum; BHT = 2,6-di- tert -butyl-4-methylphenol), highlighted in previous experimental studies. The tendency of the three model Lewis acidic sites A – C to release neutral Al fragments (i.e., AlMe 2 R; R = Me or bht) or transient aluminum cations (i.e., [AlMeR] + ) has been investigated both in the absence and in the presence of neutral N-donors. Sites C are most likely responsible for the activation capabilities of TMA-rich MAO, but TMA depletion destabilizes them, possibly inducing structural rearrangements. The remaining sites A and B , albeit of lower Lewis acidity, should be still able to release cationic Al fragments when TMA-depleted modified MAOs are treated with N-donors (e.g. [AlMe(bht)] + from MAO/BHT). These findings provide tentative interpretations for earlier observations of donor-dependent ionization tendencies of MAO and MAO/BHT and how TMA depleted MAOs can still be potent activators.

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Improvement of catalytic activity for α‐diimine nickel complex with active sites stabilized by bulky boron counterions at elevated temperature

Wang

Feng

Guo

et al. 2022

Applied Organom Chemis

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Three α‐diimine Ni (II) catalysts (Cat.1, Cat.2 and Cat.3) were synthesized and investigated for ethylene polymerization using alkyl aluminum and organoboron compounds as binary cocatalyst. The effects of different alkyl aluminum and boron complexes on ethylene polymerization catalyzed by Cat.1, Cat.2, and Cat.3 were studied. The sodium tetrakis[3,5‐bis (trifluoromethyl)phenyl]borate (NaBArF) was found to have best promotion for the catalytic activity of Cat.1, compared to negative effect of dimethylanilinium tetrakis (pentafluorophenyl)borate (TTB) and trityl tetrakis (pentafluorophenyl)borate (AB). All the three catalysts showed higher catalytic activity when NaBArF was introduced into the catalytic system, especially for Cat.3 (increased by 41.3% at 70°C). There was still minor increase of the catalytic activity for Cat.2 which have much better thermostability than Cat.3. The charging sequence of NaBArF and the [B]/[Ni] ratio have significant effects on the catalytic activity. The better catalytic performance of Cat.1/AlEt2Cl/NaBArF could be explained by its ability to raise the number of active centers. Namely, the molar percentage of active centers of Cat.1/AlEt2Cl/NaBArF was still above 30%, which was 1.7 times that of Cat.1/AlEt2Cl even if polymerization ran up to 30 min based on 2‐thiophenecarbonyl chloride (TPCC) quench‐labeling method. Lower [Al]/[Ni] ratio but more active centers and longer active centers lifetime of this binary cocatalyst is promising for improving the activity of ethylene polymerization industrially at elevated temperature.

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Ion pairing in transition metal catalyzed olefin polymerization

Cited by 41 publications

References 452 publications

Structure and dynamics of catalytically competent but labile paramagnetic metal-hydrides: the Ti(iii)-H in homogeneous olefin polymerization

Structure and dynamics of catalytically competent but labile paramagnetic metal-hydrides: the Ti(iii)-H in homogeneous olefin polymerization

Reactivity Trends of Lewis Acidic Sites in Methylaluminoxane and Some of Its Modifications

Improvement of catalytic activity for α‐diimine nickel complex with active sites stabilized by bulky boron counterions at elevated temperature

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