Borane catalysis for epoxide (co)polymerization

Naumann, Stefan

doi:10.1039/d3py00018d

“…The rule for bifunctional catalyst design is also suitable for the metal‐free catalyst system [12a–m] . For example, we have reported the construction of organoboron catalysts featuring intramolecular electrophilic boron center(s) and a nucleophilic quaternary ammonium salt, which have shown higher catalytic performance and selectivity than their binary analogues (Figure 1a, 1b).…”

Section: Introductionmentioning

confidence: 99%

A Binary Silicon‐Centered Organoboron Catalyst with Superior Performance to That of Its Bifunctional Analogue

Xu,

Yang,

Lu

et al. 2023

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This work reported a silicon‐centered alkyl borane /ammonium salt binary (two‐component) catalyst exhibits much higher activity than its bifunctional analogue (one‐component) for ring‐opening polymerization of propylene oxide, showing 7.3 times the activity of its bifunctional analogue at a low catalyst loading of 0.01 mol%, and even 15.3 times at an extremely low loading of 0.002 mol%. Via 19F NMR, control experiments, and theoretical calculation, we discovered that the central silicon atom displays appropriate electron density and a larger intramolecular cavity, which is useful to co‐activate the monomer and to deliver propagating chains, thus leading to a better intramolecular synergic effect than its bifunctional analogue. A unique two‐pathway initiation mode was proposed to explain the unusual high activity for the binary catalytic system. This study breaks the traditional impression of the binary Lewis acid/nucleophilic catalyst with poor activity due to the increase in entropy.

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“…[ 1 ] This limitation has inspired the development of advanced (organo)catalysts. [ 21–27 ] For example, Taton et al. introduced the application of N ‐heterocyclic carbenes (NHCs) as organocatalysts for the metal free polyether synthesis.…”

Section: Introductionmentioning

confidence: 99%

“…[1] This limitation has inspired the development of advanced (organo)catalysts. [21][22][23][24][25][26][27] For example, Taton et al introduced the application of N-heterocyclic carbenes (NHCs) as organocatalysts for the metal free polyether synthesis. The polymerization of PO was realized, however, the absence of allyl species was only ensured for molecular weights below 4 500 g mol −1 .…”

Section: Introductionmentioning

confidence: 99%

Revealing the Monomer Gradient of Polyether Copolymers Prepared Using N‐Heterocyclic Olefins: Metal‐Free Anionic versus Zwitterionic Lewis Pair Polymerization

Kersten

¹

,

Linker

²

,

Blankenburg

³

et al. 2023

Macro Chemistry & Physics

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2

0

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N‐Heterocyclic olefin (NHO)‐based polymerization pathways for the copolymerization of ethylene oxide (EO) and propylene oxide (PO) are investigated in detail. Employing in situ 1H NMR spectroscopy, both an organocatalytic, anionic polymerization setup (system A) and a zwitterionic, Lewis pair‐type approach (system B) are studied comparatively. The obtained kinetics data are fitted to the non‐terminal model (Jaacks and Ideal Integrated) and terminal Mayo–Lewis model (Meyer Lowry) to determine the reactivity ratios, revealing striking differences in copolyether microstructure and achievable molar masses. While for the metal‐free catalysis (system A) reactivity ratios of rEO = 3.4 and rPO = 0.30 are found, indicating a soft gradient structure, the presence of Mg(HMDS)2 (system B) entails exclusively zwitterionic propagation. This results in enhanced selectivity, displaying corresponding parameters of rEO = 7.9 and rPO = 0.13, in line with the proposed monomer‐activated mechanism. The block‐like, strongly tapered copolyether microstructure is also reflected in the thermal properties, showing a melting point for the latter sample and much higher molar masses (Mn >50 000 g mol−1). Notably, this study not only identifies capable polymerization systems for EO/PO, but also underlines that via in situ 1H NMR kinetics key questions regarding the polymerization mechanism can be illuminated quickly and reliably, simplifying access to essential structure‐property relations.

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“…The rule for bifunctional catalyst design is also suitable for the metal‐free catalyst system [12a–m] . For example, we have reported the construction of organoboron catalysts featuring intramolecular electrophilic boron center(s) and a nucleophilic quaternary ammonium salt, which have shown higher catalytic performance and selectivity than their binary analogues (Figure 1a, 1b).…”

Section: Introductionmentioning

confidence: 99%

A Binary Silicon‐Centered Organoboron Catalyst with Superior Performance to That of Its Bifunctional Analogue

Xu,

Yang,

Lu

et al. 2023

Angewandte Chemie

0

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This work reported a silicon‐centered alkyl borane /ammonium salt binary (two‐component) catalyst exhibits much higher activity than its bifunctional analogue (one‐component) for ring‐opening polymerization of propylene oxide, showing 7.3 times the activity of its bifunctional analogue at a low catalyst loading of 0.01 mol%, and even 15.3 times at an extremely low loading of 0.002 mol%. Via 19F NMR, control experiments, and theoretical calculation, we discovered that the central silicon atom displays appropriate electron density and a larger intramolecular cavity, which is useful to co‐activate the monomer and to deliver propagating chains, thus leading to a better intramolecular synergic effect than its bifunctional analogue. A unique two‐pathway initiation mode was proposed to explain the unusual high activity for the binary catalytic system. This study breaks the traditional impression of the binary Lewis acid/nucleophilic catalyst with poor activity due to the increase in entropy.

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Borane catalysis for epoxide (co)polymerization

Abstract: Since 2016, when simple triethylborane (Et3B) was revealed as a very capable catalyst for the copolymerization of epoxides and carbon dioxide, research effort regarding this type of organic Lewis acid...

Cited by 27 publications

References 164 publications

A Binary Silicon‐Centered Organoboron Catalyst with Superior Performance to That of Its Bifunctional Analogue

A Binary Silicon‐Centered Organoboron Catalyst with Superior Performance to That of Its Bifunctional Analogue

Revealing the Monomer Gradient of Polyether Copolymers Prepared Using N‐Heterocyclic Olefins: Metal‐Free Anionic versus Zwitterionic Lewis Pair Polymerization

A Binary Silicon‐Centered Organoboron Catalyst with Superior Performance to That of Its Bifunctional Analogue

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