A simplified approach for the metal-free polymerization of propylene oxide

Vogler, Charlotte; Naumann, Stefan

doi:10.1039/d0ra08970b

Cited by 17 publications

(22 citation statements)

References 32 publications

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“…In some cases, triethylborane was added as a cocatalyst, which accelerates monomer consumption and facilitates the preparation of very long PPO blocks (Scheme ). − For synthetic details, please refer to the Experimental Section and the SI.…”

Section: Resultsmentioning

confidence: 99%

“…This approach is based on the tailored synthesis of so-called “Reverse Pluronics” with high molar masses, preparation of which is enabled by recent advances in polymerization catalysis. Notably, the synthesis of these polyether SDAs can be conducted with fully commercially available and cheap catalyst setups . Combined with the facile carbon material synthesis, which is based on literature precedent and in every aspect a standard procedure, it is hoped to herewith deliver a user-friendly tool for rapid OMC screening.…”

Section: Discussionmentioning

confidence: 99%

“…Notably, the synthesis of these polyether SDAs can be conducted with fully commercially available and cheap catalyst setups. 38 Combined with the facile carbon material synthesis, which is based on literature precedent and in every aspect a standard procedure, it is hoped to herewith deliver a user-friendly tool for rapid OMC screening.…”

Section: ■ Conclusionmentioning

confidence: 99%

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Ordered Mesoporous Carbons via Self-Assembly of Tailored Block Copolyethers for Pore Size-Dependent Applications

Markus

Vogler

Bruckner

et al. 2021

ACS Appl. Nano Mater.

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Using an organocatalytic polymerization method for the preparation of well-defined, amphiphilic block copolyethers of the type PPO n/2 -PEO m -PPO n/2 ("Reverse Pluronics", M n up to 50 000 g/mol, Đ M = 1.01−1.08, >100 examples), it is demonstrated that the application of these polymers as structure-directing agents (SDAs) in a standard softtemplating process delivers ordered mesoporous carbons (OMCs), whereby the resulting pore diameters are monomodal and narrowly distributed. Moreover, by the judicious choice of the SDA properties (total molar mass, ratio of n and m, and PPO block length), pore diameters in the range of 6−18 nm can be selectively addressed, notably within the same arrangement pattern (2D hexagonal, p6mm). This provides a rational, operationally simple method to tailor pore properties of otherwise uniform carbons, also significantly reducing the effort necessary to obtain systematically altered materials. Ready access to such quick screenings is assumed to be immensely useful for pore size-dependent applications from numerous disciplines such as sensing, catalysis, or energy storage and conversion. Surprisingly, it is not only found that a minimum of M n = 13 000 g/mol is required to deliver ordered (nondistorted) materials under these conditions but also that very high-molar-mass SDAs are best suited to achieve optimum results, potentially providing an explanation for why "Reverse Pluronics" are frequently, and wrongly, thought to be per se unsuitable for the preparation of well-ordered mesoporous carbons.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Ordered Mesoporous Carbons via Self-Assembly of Tailored Block Copolyethers for Pore Size-Dependent Applications

Markus

Vogler

Bruckner

et al. 2021

ACS Appl. Nano Mater.

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“…Although the organocatalyzed ROP of epoxides has advanced significantly in recent years, these organocatalysts cannot overcome the dominance of the metal-based catalysts in terms of cost and catalytic performance . However, a fully commercially available catalyst setup of organoboron and organobases has displayed strong competitiveness with metallic catalysts in producing polyethers …”

Section: Dinuclear Organoboron Catalysts For Rop Of Epoxidesmentioning

confidence: 99%

Modular Organoboron Catalysts Enable Transformations with Unprecedented Reactivity

2021

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Metrics & MoreArticle Recommendations CONSPECTUS: Electron-deficient boron-based catalysts with metalfree but metallomimetic characteristics provide a versatile platform for chemical transformations. However, their catalytic performance is usually lower than that of the corresponding metal-based catalysts. Furthermore, many elaborate organoboron compounds are produced via time-consuming multistep syntheses with low yields, presenting a formidable challenge for large-scale applications of these catalysts. Given this context, the development of organoboron catalysts with the combined advantages of high efficiency and easy preparation is of critical importance. Therefore, we envisioned that the construction of a dynamic Lewis multicore system (DLMCS) by integrating the Lewis acidic boron center(s) and a Lewis basic ammonium salt in one molecule would be particularly efficient for on-demand applications because of the intramolecular synergistic effect. This Account summarizes our recent efforts in developing modular organoboron catalysts with unprecedented activities for several chemical transformations. A series of mono-, di-, tri-, and tetranuclear organoboron catalysts was readily designed and prepared in nearly quantitative yields over two steps using commercially available feedstocks. Notably, these catalysts can be modularly tailored by fine control over the electrophilic property of the Lewis acidic boron center(s), electronic and steric effects of the electropositive ammonium cation, linker length between the boron center and the ammonium cation, the number of boron centers, and the nucleophilic anion. This modular design allows systematic manipulation of the reactivity and efficacy of the catalysts, thus optimizing suitable catalysts for versatile chemical transformations. These include the coupling of CO 2 and epoxides, copolymerization of CO 2 and epoxides, ring-opening polymerization (ROP) of epoxides, and ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides. The utilization of mononuclear organoboron catalysts provided a turnover frequency of 11050 h −1 for the CO 2 /propylene oxide coupling reaction, an unprecedented efficiency of 5.0 kg of polymer/g of catalyst for the copolymerization of CO 2 and cyclohexene oxide, and a record-breaking catalytic efficiency of 7.4 kg of polymer/g of catalyst for the ROCOP of epoxides with cyclic anhydrides. A turnover number of 56500 was observed at a catalyst loading of 10 ppm for the ROP of epoxides using the dinuclear catalysts. The tetranuclear organoboron catalysts realized the previously intractable task of the copolymerization of CO 2 and epichlorohydrin, producing poly(chloropropylene carbonate) with the highest molecular weight of 36.5 kg/mol reported to date. Furthermore, the study revealed that the interaction between the dynamic Lewis multicore, that is, the intramolecular synergistic effect between the boron center(s) and the quaternary ammonium salt, plays a key role in mediating the catalytic activity and selectivity. This was based o...

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“…[21][22] This borane can be employed together with a range of organobases, including very simple nitrogen bases. 23 Intriguingly, elegant work by Zhao and Ling has demonstrated that with such a setup even poly(ester-ether) multiblock motifs can be constructed -excessive transesterification is avoided during growth of the polyether blocks. 24 What deserves particular attention is the proposed mechanism, which necessitates two equivalents of Et3B per organobase, a stoichiometry inherently linked to the simultaneous monomer activation and chain-end deactivation/coordination, which is also well-known from Lewis-pair polymerization (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

Chiral diboranes as catalysts for the stereoselective organopolymerization of epoxides

Sirin-Sariaslan

Naumann

2022

Chem. Sci.

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A simplified approach for the metal-free polymerization of propylene oxide

Abstract: Mild organobases and Et3B constitute an operationally simple, user-friendly catalyst setup for polymerizing propylene oxide.

Cited by 17 publications

References 32 publications

Ordered Mesoporous Carbons via Self-Assembly of Tailored Block Copolyethers for Pore Size-Dependent Applications

Ordered Mesoporous Carbons via Self-Assembly of Tailored Block Copolyethers for Pore Size-Dependent Applications

Modular Organoboron Catalysts Enable Transformations with Unprecedented Reactivity

Chiral diboranes as catalysts for the stereoselective organopolymerization of epoxides

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