Tailored Strength Neighboring Group Interactions Switch Polymerization to Dimerization Catalysis

Schiebel, Eva; Santacroce, Stefano; Falivene, Laura; Göttker‐Schnetmann, Inigo; Caporaso, Lucia; Mecking, Stefan

doi:10.1021/acscatal.9b00129

Cited by 28 publications

(15 citation statements)

References 26 publications

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“…The steric effect has been documented to play a vital role in ethylene dimerization catalyzed by Ni-based homogeneous catalysts. Hence, we evaluated this effect and found that the Ni center in Ni-ZIF-8 had a 51.7% buried volume within a 5 Å radius spherical space (Figure S19), which is similar to the values of the four-coordinated molecular Ni catalyst , and smaller than those of metal complexes with higher coordination numbers . Moreover, the two free ligands are loosely bonded to the Ni center and tend to leave during the reaction, providing sufficient space and vacant sites to facilitate ethylene adsorption and insertion.…”

Section: Results and Discussionmentioning

confidence: 99%

Highly Active Heterogeneous Catalyst for Ethylene Dimerization Prepared by Selectively Doping Ni on the Surface of a Zeolitic Imidazolate Framework

et al. 2021

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The production of 1-butene by ethylene dimerization is an important chemical industrial process currently implemented using homogeneous catalysts. Here, we describe a highly active heterogeneous catalyst (Ni-ZIF-8) for ethylene dimerization, which consists of isolating Ni-active sites selectively located on the crystal surface of a zeolitic imidazolate framework. Ni-ZIF-8 can be easily prepared by a simple one-pot synthesis method in which site-specific anchoring of Ni is achieved spontaneously because of the incompatibility between the d 8 electronic configuration of Ni 2+ and the three-dimensional framework of ZIF-8. The full exposure and square-planar coordination of the Ni sites accounts for the high catalytic activity of Ni-ZIF-8. It exhibits an average ethylene turnover frequency greater than 1 000 000 h −1 (1-butene selectivity >85%) at 35 °C and 50 bar, far exceeding the activities of previously reported heterogeneous catalysts and many homogeneous catalysts under similar conditions. Moreover, compared to molecular Ni complexes used as homogeneous catalysts for ethylene dimerization, Ni-ZIF-8 has significantly higher stability and shows constant activity during 4 h of continuous reaction. Isotopic labeling experiments indicate that ethylene dimerization over Ni-ZIF-8 follows the Cossee-Arlman mechanism, and detailed characterizations combined with density functional theory calculations rationalize this observed high activity.

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Section: Results and Discussionmentioning

confidence: 99%

Highly Active Heterogeneous Catalyst for Ethylene Dimerization Prepared by Selectively Doping Ni on the Surface of a Zeolitic Imidazolate Framework

et al. 2021

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“…In this case, the Ni•••O intermediate appears to be rather stable and similar in energy to key species of catalysis (β-agostic and alkyl olefin complexes) but barely not yet an energetic sink that would impede catalysis. 47 In search for other suitable electron-withdrawing groups, we also explored pentafluorosulfanyl substituents. The SF 5 group (σ m = 0.61) has been well established in stoichiometric applications but curiously not in catalysis.…”

Section: Catalyst Development and Polymer Microstructurementioning

confidence: 99%

Neutral Nickel(II) Catalysts: From Hyperbranched Oligomers to Nanocrystal-Based Materials

Mecking

Schnitte

2020

Acc. Chem. Res.

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Conspectus Plastics materials are a vital component of modern technologies. They are applied, e.g., in construction, transportation, communication, water supply, or health care. Consequently, polyolefins–the most important plastics by scale–are produced in vast amounts by catalytic polymerization. Effective and selective as the catalysts used may be, their high sensitivity toward any polar compounds limits these methods to hydrocarbon reaction media and monomers like ethylene and propylene, respectively. This can be overcome by less oxophilic late transition metal catalysts, and here particularly neutral nickel(II) catalysts have seen major advances in the past few years. They stand out due to being capable of aqueous catalytic polymerizations. Aqueous polymerizations are benign processes that advantageously yield polymers in the form of particles. Moreover, these catalysts can incorporate polar monomers like acrylates, a realm previously restricted to noble metal catalysts. The introduction of polar moieties can induce properties like compatibility with metals or fibers in high performance composite materials or a desirable degradability. This Account provides a personal account of developments in the past decade. Prior findings are outlined briefly as a background. Aqueous polymerizations afford unique polyethylene morphologies as a result of the unusual underlying particle growth mechanism. Polymer single crystals are formed, which can be composed of a single ultrahigh molecular weight chain. This represents a completely disentangled state of such extremely long polymer chains, which has been long sought-after in order to overcome the difficult processing of high performance ultrahigh molecular weight materials. A key prerequisite for this approach and utilization of these catalysts, in general, is control of polymer branching and molecular weight. This is achieved via remote substituents on the Ni(II)-chelating ligand. Despite their distal position to the active site, weak secondary interactions control whether branching and chain transfer pathways compete very effectively with chain growth or are suppressed entirely. This provides access to hyperbranched oligomers, on the one hand, and enables living polymerizations to strictly linear high molecular weight polymer, on the other hand. Other advanced catalysts provide linear copolymers with in-chain polar monomer repeat units for the first time with non-noble metal active sites. Mechanistic studies further revealed that for copolymerizations with polar vinyl monomers the decisive limiting factor is irreversible termination reactions with neutral Ni(II) catalysts, rather than the well-recognized reversible blocking of coordination sites by the polar functional groups found for other types of catalysts. The mechanistic picture also implies the possibility of free-radical pathways, and their role in the formation of desirable polymer end groups and polymer blends is now being recognized. The area of neutral Ni(II) catalysts has progressed significantly in the...

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“…Cyclic voltammetry (CV) was employed as a further probe for the electron density of the metal site in the Ni–Me catalyst precursors. The obtained forward peak potentials of the Ni(II)/Ni(III) oxidation are indeed in the typical range for electron-rich , as well as electron-poor Ni(II)/Ni(III) pairs, whereas the corresponding salicylaldimines would show significantly higher oxidation potentials (Table ). For the nonprotonated complexes, half wave potentials of E = 27 mV ( 2 Me ) and E = 283 mV ( 2 CF3 ), respectively, were measured.…”

Section: Resultsmentioning

confidence: 69%

The Impact of Charge in a Ni(II) Polymerization Catalyst

et al. 2021

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A direct comparison between neutral active sites and their corresponding cationic analogues is enabled by protonation of neutral bis(imino)phenoxy complexes, active for ethylene polymerization. The additional imine motif compared to parent salicylaldiminato catalysts does not influence the microstructure of the products in ethylene polymerization, but allows for the incorporation of a proton right next to the active center in an N•••H + •••O bridge yielding cationic complexes. These show an increased Ni−O bond length and a drastically reduced electron density on the Ni atom. In pressure reactor experiments, two different catalysts that produce linear HDPE or undergo extensive chain walking, respectively, in their neutral version, both produce short chain oligomers when the catalyst is charged cationically. A mechanistic analysis by DFT methods reveals an increased propensity for β-hydride elimination compared to ethylene insertion chain growth for the cationic complexes. This results from a higher relative stability of β-agostic species vs olefin-coordinated species.

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Tailored Strength Neighboring Group Interactions Switch Polymerization to Dimerization Catalysis

Abstract: L, et al. (2019) Tailored strength neighboring group interactions switch polymerization to dimerization catalysis. ACS Catalysis.

Cited by 28 publications

References 26 publications

Highly Active Heterogeneous Catalyst for Ethylene Dimerization Prepared by Selectively Doping Ni on the Surface of a Zeolitic Imidazolate Framework

Highly Active Heterogeneous Catalyst for Ethylene Dimerization Prepared by Selectively Doping Ni on the Surface of a Zeolitic Imidazolate Framework

Neutral Nickel(II) Catalysts: From Hyperbranched Oligomers to Nanocrystal-Based Materials

The Impact of Charge in a Ni(II) Polymerization Catalyst

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