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  1. Article ; Online: A Hydrocarbon Soluble, Molecular and “Complete” Al-Cocatalyst for High Temperature Olefin Polymerization

    Gaia Urciuoli / Francesco Zaccaria / Cristiano Zuccaccia / Roberta Cipullo / Peter H. M. Budzelaar / Antonio Vittoria / Christian Ehm / Alceo Macchioni / Vincenzo Busico

    Polymers, Vol 15, Iss 1378, p

    2023  Volume 1378

    Abstract: The dinuclear aluminum salt {[ i Bu 2 (DMA)Al] 2 ( μ -H)} + [B(C 6 F 5 ) 4 ] − ( AlHAl ... DMA = N , N -dimethylaniline) is the prototype of a new class of molecular cocatalysts for catalytic olefin polymerization, its modular nature offering easy avenues ... ...

    Abstract The dinuclear aluminum salt {[ i Bu 2 (DMA)Al] 2 ( μ -H)} + [B(C 6 F 5 ) 4 ] − ( AlHAl

    DMA = N , N -dimethylaniline) is the prototype of a new class of molecular cocatalysts for catalytic olefin polymerization, its modular nature offering easy avenues for tailoring the activator to specific needs. We report here, as proof of concept, a first variant ( s-AlHAl ) bearing p -hexadecyl- N , N -dimethylaniline (DMA C16 ) units, which enhances solubility in aliphatic hydrocarbons. The novel s-AlHAl was used successfully as an activator/scavenger in ethylene/1-hexene copolymerization in a high-temperature solution process.
    Keywords olefin polymerization ; catalyst activation ; borate activators ; methylaluminoxane ; soluble cocatalyst ; Organic chemistry ; QD241-441
    Language English
    Publishing date 2023-03-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article ; Online: Chain Transfer to Solvent and Monomer in Early Transition Metal Catalyzed Olefin Polymerization

    Francesco Zaccaria / Peter H. M. Budzelaar / Cristiano Zuccaccia / Roberta Cipullo / Alceo Macchioni / Vincenzo Busico / Christian Ehm

    Catalysts, Vol 11, Iss 2, p

    Mechanisms and Implications for Catalysis

    2021  Volume 215

    Abstract: Even after several decades of intense research, mechanistic studies of olefin polymerization by early transition metal catalysts continue to reveal unexpected elementary reaction steps. In this mini-review, the recent discovery of two unprecedented chain ...

    Abstract Even after several decades of intense research, mechanistic studies of olefin polymerization by early transition metal catalysts continue to reveal unexpected elementary reaction steps. In this mini-review, the recent discovery of two unprecedented chain termination processes is summarized: chain transfer to solvent (CTS) and chain transfer to monomer (CTM), leading to benzyl/tolyl and allyl type chain ends, respectively. Although similar transfer reactions are well-known in radical polymerization, only very recently they have been observed also in olefin insertion polymerization catalysis. In the latter context, these processes were first identified in Ti-catalyzed propene and ethene polymerization; more recently, CTS was also reported in Sc-catalyzed styrene polymerization. In the Ti case, these processes represent a unique combination of insertion polymerization, organic radical chemistry and reactivity of a M(IV)/M(III) redox couple. In the Sc case, CTS occurs via a σ-bond metathesis reactivity, and it is associated with a significant boost of catalytic activity and/or with tuning of polystyrene molecular weight and tacticity. The mechanistic studies that led to the understanding of these chain transfer reactions are summarized, highlighting their relevance in olefin polymerization catalysis and beyond.
    Keywords olefin polymerization ; chain transfer ; solvent activation ; chain ends ; homolysis ; Ti(IV)/Ti(III) redox couple ; Chemical technology ; TP1-1185 ; Chemistry ; QD1-999
    Subject code 540
    Language English
    Publishing date 2021-02-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article ; Online: Separating Electronic from Steric Effects in Ethene/α-Olefin Copolymerization

    Francesco Zaccaria / Roberta Cipullo / Andrea Correa / Peter H. M. Budzelaar / Vincenzo Busico / Christian Ehm

    Processes, Vol 7, Iss 6, p

    A Case Study on Octahedral [ONNO] Zr-Catalysts

    2019  Volume 384

    Abstract: Four Cl/Me substituted [ONNO] Zr-catalysts have been tested in ethene/α-olefin polymerization. Replacing electron-donating methyl with isosteric but electron-withdrawing chlorine substituents results in a significant increase of comonomer incorporation. ... ...

    Abstract Four Cl/Me substituted [ONNO] Zr-catalysts have been tested in ethene/α-olefin polymerization. Replacing electron-donating methyl with isosteric but electron-withdrawing chlorine substituents results in a significant increase of comonomer incorporation. Exploration of steric and electronic properties of the ancillary ligand by DFT confirm that relative reactivity ratios are mainly determined by the electrophilicity of the metal center. Furthermore, quantitative DFT modeling of propagation barriers that determine polymerization kinetics reveals that electronic effects observed in these catalysts affect relative barriers for insertion and a capture-like transition state (TS).
    Keywords olefin copolymerization ; reactivity ratios ; electronic effects ; salan catalysts ; post-metallocene ; DFT ; insertion kinetics ; olefin capture ; Chemical technology ; TP1-1185 ; Chemistry ; QD1-999
    Language English
    Publishing date 2019-06-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article: Metal–carbon bond strengths under polymerization conditions: 2,1-insertion as a catalyst stress test

    Ehm, Christian / Peter H.M. Budzelaar / Vincenzo Busico

    Journal of catalysis. 2017 July, v. 351

    2017  

    Abstract: Quantitative agreement between experimentally determined M–C bond dissociation energies (BDE) and DFT predictions (M06-2X/TZ//TPSSTPSS/DZ) can be reached by choosing the correct anchor for experimentally derived BDE. For the example of the archetypical ... ...

    Abstract Quantitative agreement between experimentally determined M–C bond dissociation energies (BDE) and DFT predictions (M06-2X/TZ//TPSSTPSS/DZ) can be reached by choosing the correct anchor for experimentally derived BDE. For the example of the archetypical metallocene catalyst Cp2TiCl2, it is shown that titanium–carbon bonds are very weak under polymerization conditions and fluctuate; steric strain is introduced after 2,1 insertion and via olefin capture. Thus, homolysis can become competitive with chain propagation. Depending on the catalyst and temperature, 2,1 insertion can be only a temporary inconvenience (dormancy) or a definitive decay event. It is then shown for a set of nine common Ti and Zr polymerization catalysts how ligand variation affects the metal–carbon BDE. Predicted stabilities of the M(IV) oxidation state with respect to homolysis are in nice agreement with the experimentally observed temperature tolerance of the various catalysts: homolysis is easier for Ti than for Zr, and cyclopentadienyl groups in particular facilitate homolysis, especially in bis-cyclopentadienyl systems.
    Keywords catalysts ; chemical bonding ; dissociation ; dormancy ; homolytic cleavage ; ligands ; moieties ; olefin ; oxidation ; polymerization ; prediction ; temperature ; zirconium
    Language English
    Dates of publication 2017-07
    Size p. 146-152.
    Publishing place Elsevier Inc.
    Document type Article
    ZDB-ID 1468993-5
    ISSN 0021-9517
    ISSN 0021-9517
    DOI 10.1016/j.jcat.2017.04.013
    Database NAL-Catalogue (AGRICOLA)

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  5. Article: MgCl2-Supported Ziegler–Natta Catalysts: a DFT-D “Flexible-Cluster” Approach to Internal Donor Adducts

    Breuza, Emanuele / Andrea Correa / Christian Ehm / Giuseppe Antinucci / Peter H. M. Budzelaar / Vincenzo Busico

    Journal of physical chemistry. 2018 Apr. 04, v. 122, no. 16

    2018  

    Abstract: A “flexible cluster” model approach to Ziegler–Natta catalysts for the production of isotactic polypropylene, allowing the use of realistically sized MgCl2 monolayer clusters (up to 38 MgCl2 units) without any constraints, was employed to investigate the ...

    Abstract A “flexible cluster” model approach to Ziegler–Natta catalysts for the production of isotactic polypropylene, allowing the use of realistically sized MgCl2 monolayer clusters (up to 38 MgCl2 units) without any constraints, was employed to investigate the formation of adducts between the MgCl2 support and three industrially relevant internal donor classes, namely phthalates, succinates, and 1,3-dimethoxypropanes. The calculated adsorption modes and thermochemical data for adducts of single-donor molecules confirmed earlier literature trends only in part. Results for adducts with multiple donor molecules, in turn, did not confirm the indications of periodic models about steric repulsion between neighboring adsorbates hampering high degrees of surface coverage; as a matter of fact, such repulsions seem to be largely traceable to unnecessary constraints inherent in periodic calculations.
    Keywords adsorption ; catalysts ; magnesium chloride ; models ; phthalates ; polypropylenes ; succinic acid
    Language English
    Dates of publication 2018-0404
    Size p. 9046-9053.
    Publishing place American Chemical Society
    Document type Article
    ISSN 1932-7455
    DOI 10.1021/acs.jpcc.8b01500
    Database NAL-Catalogue (AGRICOLA)

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  6. Article: Backbone rearrangement during olefin capture as the rate limiting step in molecular olefin polymerization catalysis and its effect on comonomer affinity

    Zaccaria, Francesco / Roberta Cipullo / Peter H. M. Budzelaar / Vincenzo Busico / Christian Ehm

    Journal of polymer science. 2017 Sept. 1, v. 55, no. 17

    2017  

    Abstract: Available experimental data for several metallocenes indicate that the ethene/propene copolymerization ratio rc can be much more temperature dependent than would be expected if competing insertion transition states (TS) are rate limiting. Detailed ... ...

    Abstract Available experimental data for several metallocenes indicate that the ethene/propene copolymerization ratio rc can be much more temperature dependent than would be expected if competing insertion transition states (TS) are rate limiting. Detailed exploration of the reaction paths reveals in several cases the existence of a “capture‐like” transition state before the actual insertion, with free energies close to the insertion TS. Movement around these transition states does not just involve monomer and chain, but also clear distortion of the ligand skeleton to allow entry of the monomer. Taking these additional TSs into account leads to much improved agreement with experiment for a series of metallocenes and a constrained geometry catalyst system. Depending on catalyst and temperature, selectivity is determined by competing insertion/insertion, capture/insertion or capture/capture. It seems likely that this is a common situation especially for highly efficient catalysts, complicating (but not preventing) prediction of copolymerization performance. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2807–2814
    Keywords catalysts ; catalytic activity ; copolymerization ; ethylene ; ligands ; olefin ; polymers ; prediction ; propylene ; temperature
    Language English
    Dates of publication 2017-0901
    Size p. 2807-2814.
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ISSN 0887-624X
    DOI 10.1002/pola.28685
    Database NAL-Catalogue (AGRICOLA)

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  7. Article ; Online: Hafnium vs. Zirconium, the Perpetual Battle for Supremacy in Catalytic Olefin Polymerization

    Antonio Vittoria / Georgy P. Goryunov / Vyatcheslav V. Izmer / Dmitry S. Kononovich / Oleg V. Samsonov / Francesco Zaccaria / Gaia Urciuoli / Peter H. M. Budzelaar / Vincenzo Busico / Alexander Z. Voskoboynikov / Dmitry V. Uborsky / Christian Ehm / Roberta Cipullo

    Polymers, Vol 13, Iss 2621, p

    A Simple Matter of Electrophilicity?

    2021  Volume 2621

    Abstract: The performance of C 2 -symmetric ansa -hafnocene catalysts for isotactic polypropylene typically deteriorates at increasing temperature much faster than that of their zirconium analogues. Herein, we analyze in detail a set of five Hf/Zr metallocene ... ...

    Abstract The performance of C 2 -symmetric ansa -hafnocene catalysts for isotactic polypropylene typically deteriorates at increasing temperature much faster than that of their zirconium analogues. Herein, we analyze in detail a set of five Hf/Zr metallocene pairs—including some of the latest generation catalysts—at medium- to high-polymerization temperature. Quantitative structure–activity relationship (QSAR) models for stereoselectivity, the ratio allyl/vinyl chain ends, and 2,1/3,1 misinsertions in the polymer indicate a strong dependence of polymerization performance on electrophilicity of the catalyst, which is a function of the ligand framework and the metal center. Based on this insight, the stronger performance decline of hafnocenes is ascribed to electrophilicity-dependent stabilization effects.
    Keywords hafnocenes ; olefin polymerization ; iPP ; molecular catalysts ; QSAR ; high-temperature performance ; Organic chemistry ; QD241-441
    Language English
    Publishing date 2021-08-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  8. Article ; Online: An Integrated High Throughput Experimentation/Predictive QSAR Modeling Approach to ansa -Zirconocene Catalysts for Isotactic Polypropylene

    Christian Ehm / Antonio Vittoria / Georgy P. Goryunov / Vyatcheslav V. Izmer / Dmitry S. Kononovich / Oleg V. Samsonov / Rocco Di Girolamo / Peter H. M. Budzelaar / Alexander Z. Voskoboynikov / Vincenzo Busico / Dmitry V. Uborsky / Roberta Cipullo

    Polymers, Vol 12, Iss 1005, p

    2020  Volume 1005

    Abstract: Compared to heterogenous Ziegler–Natta systems (ZNS), ansa -metallocene catalysts for the industrial production of isotactic polypropylene feature a higher cost-to-performance balance. In particular, the C 2 -symmetric bis (indenyl) ansa -zirconocenes ... ...

    Abstract Compared to heterogenous Ziegler–Natta systems (ZNS), ansa -metallocene catalysts for the industrial production of isotactic polypropylene feature a higher cost-to-performance balance. In particular, the C 2 -symmetric bis (indenyl) ansa -zirconocenes disclosed in the 1990s are complex to prepare, less stereo- and/or regioselective than ZNS, and lose performance at practical application temperatures. The golden era of these complexes, though, was before High Throughput Experimentation (HTE) could contribute significantly to their evolution. Herein, we illustrate a Quantitative Structure – Activity Relationship (QSAR) model trained on a robust and highly accurate HTE database. The clear-box QSAR model utilizes, in particular, a limited number of chemically intuitive 3D geometric descriptors that screen various regions of space in and around the catalytic pocket in a modular way thus enabling to quantify individual substituent contributions. The main focus of the paper is on the methodology, which should be of rather broad applicability in molecular organometallic catalysis. Then again, it is worth emphasizing that the specific application reported here led us to identify in a comparatively short time novel zirconocene catalysts rivaling or even outperforming all previous homologues which strongly indicates that the metallocene story is not over yet.
    Keywords olefin polymerization ; stereoselectivity ; regioselectivity ; molecular weight capability ; molecular catalysts ; QSAR ; Organic chemistry ; QD241-441
    Subject code 540
    Language English
    Publishing date 2020-04-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  9. Article: Connection of Stereoselectivity, Regioselectivity, and Molecular Weight Capability in rac-R′₂Si(2-Me-4-R-indenyl)₂ZrCl₂ Type Catalysts

    Ehm, Christian / Antonio Vittoria / Georgy P. Goryunov / Pavel S. Kulyabin / Peter H. M. Budzelaar / Alexander Z. Voskoboynikov / Vincenzo Busico / Dmitry V. Uborsky / Roberta Cipullo

    Macromolecules. 2018 Oct. 03, v. 51, no. 20

    2018  

    Abstract: A set of 19 silicon-bridged C₂-symmetric zirconocenes rac-R′₂Si(2-Me-4-R-indenyl)₂ZrCl₂ of varying steric demand in position 4 were synthesized and screened in propene homopolymerization in a high-throughput experimental setup. The size and accuracy of ... ...

    Abstract A set of 19 silicon-bridged C₂-symmetric zirconocenes rac-R′₂Si(2-Me-4-R-indenyl)₂ZrCl₂ of varying steric demand in position 4 were synthesized and screened in propene homopolymerization in a high-throughput experimental setup. The size and accuracy of the experimental data set allow to identify surprisingly good correlations among stereoselectivity, regioselectivity, and molecular weight capability (R² ≈ 0.8–0.9) over a broad range. We rationalize this trend by assuming that steric tuning in the 4-position affects both preferred insertion and stereoerror formation similarly but leaves other barriers largely unaffected. A quantitative structure–activity relationship based on one single computational descriptor, Δ%VBᵤᵣ—using the difference in the percent of buried volume between the “blocked” and “open” quadrants of the catalyst precursor—is established. Provided that a large sphere of 5.0 Å is used, stereoselectivity can be predicted with unprecedented accuracy, i.e., a mean average deviation (MAD) of 0.18 kcal/mol (ΔΔG‡ₑₙₐₙₜᵢₒ), 0.0007 (σ, probability that the preferred propene enantioface is selected at an active site of given chirality), or 0.3% (mmmm pentads). On the basis of this empirical model, we predicted that the catalyst with R = o-tolyl is an ideal candidate for high stereoselectivity/high MW capability. Ad hoc synthesis and testing of the precursor confirmed the expectations: the catalyst shows the highest stereoselectivity reported so far (σ = 0.9999) for metallocenes at 60 °C, while maintaining a high MW capability (Mw > 1 MDa) and relatively high regioselectivity.
    Keywords active sites ; catalysts ; empirical models ; molecular weight ; optical isomerism ; probability ; propylene ; quantitative structure-activity relationships ; regioselectivity ; stereoselectivity
    Language English
    Dates of publication 2018-1003
    Size p. 8073-8083.
    Publishing place American Chemical Society
    Document type Article
    ZDB-ID 1491942-4
    ISSN 1520-5835 ; 0024-9297
    ISSN (online) 1520-5835
    ISSN 0024-9297
    DOI 10.1021/acs.macromol.8b01546
    Database NAL-Catalogue (AGRICOLA)

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