Fluxional bis(phenoxy-imine) Zr and Ti catalysts for polymerization

Escayola, Sílvia; Brotons-Rufes, Artur; Bahri‐Laleh, Naeimeh; Ragone, Francesco; Cavallo, Luigi; Solà, Miquel; Poater, Albert

doi:10.1007/s00214-021-02747-8

Cited by 4 publications

(2 citation statements)

References 99 publications

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“…Before moving to the ASM−NEDA analysis of the stereoselectivity promoted by systems 1 – 6 we inspected the steric maps obtained from “buried volume” evaluations. Buried volume (abbreviated to % V Bur ) is a descriptor for the visualization of ligand steric hindrance in coordination complexes [49,50] . The corresponding steric maps are shown in Figure 5, and details are provided in the SI.…”

Section: Resultsmentioning

confidence: 99%

Revisiting Stereoselective Propene Polymerization Mechanisms: Insights through the Activation Strain Model

Romano,

Barone,

Budzelaar

et al. 2024

Chemistry An Asian Journal

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The stereoelectronic factors responsible for stereoselectivity in propene polymerization with several metallocene and post‐metallocene transition metal catalysts have been revisited using a combined approach of DFT calculations, the Activation Strain Model, Natural Energy Decomposition Analysis and a molecular descriptor (%VBur). There are in most cases two different paths leading to the formation of stereoerrors (SE), and the classical model does not suffice to fully understand stereoregulation. Improving stereoselectivity requires raising the energies of both SE insertion transition states. Our analyses show that the degrees of deformation of the active site (catalyst+chain) and the prochiral monomer differ for these two paths, and between different catalyst classes. Based on such analyses we discuss: a) the subtle differences in SE formation between stereoselective catalysts with different ligand frameworks; b) the reason for exceptional stereoselectivity reported for a special ansa‐metallocene catalyst; c) the (double) stereocontrol origin for isoselective catalysts; d) the electronic contribution for isoselective catalysts generating SE by a modification of the ligand wrapping mode during the polymerization. Although this study will not immediately suggest new catalyst structures, we believe that understanding stereoregulation in great detail will increase our chances of success.

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Section: Resultsmentioning

confidence: 99%

Revisiting Stereoselective Propene Polymerization Mechanisms: Insights through the Activation Strain Model

Romano,

Barone,

Budzelaar

et al. 2024

Chemistry An Asian Journal

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“…Several quantum calculations were performed to study the ethylene polymerization reaction [25,49]. Hence, to validate the accuracy of our model, the octahedral dichloride complex of Ti-FI was optimized using the Gaussian 09 software [50], and the optimized structure was compared with the X-ray structure [18].…”

Section: Dft Calculationsmentioning

confidence: 99%

Theoretical study of ethylene polymerization by phenoxy-imine catalyst

Apilardmongkol

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Reaction mechanisms of ethylene polymerization catalyzed by the phenoxy-imine (FI) and the�nickel phenoxyphosphine polyethylene glycol (Ni-PEG) with alkali metals were explored using DFT calculations. For FI catalysts, the effect of group IVB transition metals substitutions was investigated. The trend of calculated activation energies (Ea) at the rate-determining step is Zr < Hf < Ti and is in good agreement with experiments. The effect of ligands of the Ti-FI-based catalysts when changing the parent nitrogen (O, N) to oxygen (O, O), phosphorus (O, P), and sulfur (O, S) ligands on activity was also monitored. The results indicated that the sulfur (O, S) ligand gives the lowest activation energy. Additionally, the reactivity of Ni-phenoxy-imine (Ni-FI)-based catalysts for polyethylene polymerization was studied. Our calculations suggested that the square planar complex of Ni-FI is more reactive than its C2 symmetric octahedral complex. For Ni-PEG(M) catalysts, the trend for activation energies of four Ni-PEG(M) systems is Li < Na < K < Cs, which corresponds to experimentally observed activities. Moreover, the roles of secondary metals in Ni-PEG catalysts in terms of steric, electronic, and electrostatic effects were elucidated. The DFT results suggested that the active catalyst should have strong cooperative metal-metal/metal-ligand interactions and less positive charge on the secondary metal. Finally, to gain insight into the design of the novel Ni-PEG catalysts with alkali-earth metals, the effect of catalyst structure on experimental activity was investigated. This work provides fundamental understandings of the reaction mechanisms for the FI and Ni-PEG(M) catalysts, which could be used for the design and development of catalysts for ethylene polymerization.

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