Dynamic Exchange in Intramolecular Lewis Pairs with Multiple Lewis-Acidic Functions

Körte, Leif Arne; Blomeyer, Sebastian; Peters, Jan-Hendrik; Mix, Andreas; Neumann, Beate; Stammler, Hans‐Georg; Mitzel, Norbert W.

doi:10.1021/acs.organomet.6b00935

Cited by 9 publications

(9 citation statements)

References 40 publications

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“…13 support the purity, the obtained lower value of C can be because of incomplete combustion. 37,38 However, the purity was confirmed by 1 H and 13 C spectra. Synthesis of 2-(9-Borabicyclo[3.3.1]non-9-ylmethyl)-1methyl-1H-imidazole Dimer, 2.…”

Section: ■ Experimental Sectionsupporting

confidence: 65%

“…Found: C, 70.88; H, 10.01; N, 12.93. Similar to compound 1 , the elemental analysis values of H and N support the purity, and the obtained lower value of C can be because of incomplete combustion. , In this case also, the purity was confirmed by 1 H and 13 C spectra.…”

Section: Methodsmentioning

confidence: 99%

“…1 H NMR (CDCl 3 ): δ 6.63 (br s, 1H, imidazole CH), 6.33 (br s, 1H, imidazole CH), 3.45 (s, 3H, NMe), 2.52 (d, J = 13.6, 2H, CH 2 ), 2.19 (d, J = 13.6, 2H, CH 2 ), 1.94−1.26 (m, 26H, 9-BBN), 0.87 (s, 2H, 9-BNN). 13 37,38 In this case also, the purity was confirmed by 1 H and 13 C spectra.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

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Synthesis, Reactions, and Structures of Heterocycle-Tethered Boranes and Their Precursors

Subramaniyan

Mani

2017

Organometallics

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Heterocycle-tethered organoboranes generally dimerize by using the heteroatom present in them. When this does not take place, some interesting molecules or properties are bound to be observed. This is demonstrated in this work, as well. The lithium salt of 1,2-dimethylimidazole reacts with Et2B(OMe) or 9-BBN-OMe to give the air-stable intermolecular adduct of 2-(dialkylborylmethyl)-1-methylimidazole (alkyl = Et (1) and 9-BBN (2)) after treatment with BF3·OEt2. These two dimers exist in two stereoisomers: clockwise and counterclockwise, as shown by their X-ray structures. On the contrary, in the analogous reaction between the lithium salt of 1,3,5-trimethylpyrazole and Et2B(OMe) in the presence of BF3·OEt2, an air- and moisture-sensitive adduct, 1-(diethylborylmethyl)-3,5-dimethylpyrazole·BF2(OMe) (3), was isolated as a liquid in an excellent yield, instead of its dimer. Its structure is based on 1H, 19F, 11B, and HRMS methods and supported by anion binding studies. Consequently, the reactive neat liquid 3 decomposes in air to give the bicyclo[3.3.1]nonane-like neutral bicycle 4. Notably, a CH2Cl2 solution of 3 decomposes differently to give the OH-bridged cationic analogous bicycle 5. In addition, their precursors, [2-(diethylborylmethyl)-1-methylimidazole·LiOMe(1,2-dimethylimidazole)]2 6, [(1-(diethylborylmethyl)-3,5-dimethylpyrazole·LiOMe)2THF] 7, and [(1-(diethylborylmethyl)-3,5-dimethylpyrazole·LiOMe(DMAP)2] 8, were also isolated and structurally characterized. In the crystal lattices of structures of 4, 5, and 7, both enantiomers RR and SS are present.

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Section: ■ Experimental Sectionsupporting

confidence: 65%

Section: Methodsmentioning

confidence: 99%

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Synthesis, Reactions, and Structures of Heterocycle-Tethered Boranes and Their Precursors

Subramaniyan

Mani

2017

Organometallics

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“…In sharp contrast, a significant difference was clearly observed for the bifunctional catalyst 3b , wherein a broad resonance (fwhm = 1371 Hz) with a slight upfield chemical shift (Δδ = −0.34 ppm) was observed. This phenomenon indicates the existence of an interaction between the intramolecular quaternary ammonium salt and the boron center …”

Section: Resultsmentioning

confidence: 90%

Scalable Bifunctional Organoboron Catalysts for Copolymerization of CO₂ and Epoxides with Unprecedented Efficiency

et al. 2020

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The metallic catalyst-dominated alternating copolymerization of CO2 and epoxides has flourished for 50 years; however, the involved multistep preparation of the catalysts and the necessity to remove the colored metal residue in the final product present significant challenges in scalability. Herein, we report a series of highly active metal-free catalysts featured with an electrophilic boron center and a nucleophilic quaternary ammonium halide in one molecule for copolymerization of epoxides and CO2. The organocatalysts are easily scaled up to kilogram scale with nearly quantitative yield via two steps using commercially available stocks. The organocatalyst-mediated copolymerization of cyclohexane oxide and CO2 displays high activity (turnover frequency up to 4900 h–1) and >99% polycarbonate selectivity in a broad temperature range (25–150 °C) at mild CO2 pressure (15 bar). At a feed ratio of cyclohexane oxide/catalyst = 20 000/1, an efficiency of 5.0 kg of product/g of catalyst was achieved, which is the highest record achieved to date. The unprecedented activity toward CO2/epoxide copolymerization for our catalyst is a consequence of an intramolecular synergistic effect between the electrophilic boron center and the quaternary ammonium salt, which was experimentally ascertained by reaction kinetics studies, multiple control experiments, 11B NMR investigation, and the crystal structure of the catalyst. Density functional theory calculations further corroborated experimental conclusions and provided a deeper understanding of the catalysis process. The metal-free characteristic, scalable preparation, outstanding catalytic performances along with long-term thermostability demonstrate that the catalyst could be a promising candidate for large-scale production of CO2-based polymer.

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“…While triphenyl phosphine does not react with water under ambient conditions, we found that a bisborane-functionalized triaryl phosphine can instantaneously and quantitatively reduce water to generate dihydrogen and phosphine oxide. [46][47][48][49] This reaction features an electron relay mechanism among the borane-phosphine-borane centers, which allowed an umpolung of a proton in water to a hydride on borane driven at a phosphonium center. This then led to formation of phosphine oxide and H 2 , leaving both Lewis acidic boranes intact after the reaction.…”

Section: Introductionmentioning

confidence: 99%

Proton to hydride umpolung at a phosphonium center via electron relay: a new strategy for main-group based water reduction

et al. 2021

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Dynamic Exchange in Intramolecular Lewis Pairs with Multiple Lewis-Acidic Functions

Cited by 9 publications

References 40 publications

Synthesis, Reactions, and Structures of Heterocycle-Tethered Boranes and Their Precursors

Synthesis, Reactions, and Structures of Heterocycle-Tethered Boranes and Their Precursors

Scalable Bifunctional Organoboron Catalysts for Copolymerization of CO₂ and Epoxides with Unprecedented Efficiency

Proton to hydride umpolung at a phosphonium center via electron relay: a new strategy for main-group based water reduction

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Dynamic Exchange in Intramolecular Lewis Pairs with Multiple Lewis-Acidic Functions

Cited by 9 publications

References 40 publications

Synthesis, Reactions, and Structures of Heterocycle-Tethered Boranes and Their Precursors

Synthesis, Reactions, and Structures of Heterocycle-Tethered Boranes and Their Precursors

Scalable Bifunctional Organoboron Catalysts for Copolymerization of CO2 and Epoxides with Unprecedented Efficiency

Proton to hydride umpolung at a phosphonium center via electron relay: a new strategy for main-group based water reduction

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Product

Resources

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Scalable Bifunctional Organoboron Catalysts for Copolymerization of CO₂ and Epoxides with Unprecedented Efficiency