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•TBAF is used for the first time to improve the performance of GPE.•The 3D crosslinked P(MMA-PEGDMA) retains high conductivity and mechanical properties.•The Li||Li cell shows an ...impressive cycle life without a short circuit.•Excellent performance of NCM811/SiC with FGPPE pouch cell is achieved.•The outstanding performance is attributed to the TBAF and 3D crosslinked GPE.
The Gel Polymer Electrolyte (GPE) is recognized as a promising alternative to conventional electrolytes, aiming to enhance the longevity and energy density of lithium-ion batteries (LIBs). However, several challenges persist, particularly concerning the conductivity and voltage window of GPE in battery systems. In this study, we introduce an in-situ 3D crosslinked GPE, using polymethyl methacrylate (PMMA) as the monomer and polyethylene glycol dimethacrylate (PEGDMA) as the crosslinking agent, to ensure structural stability and optimized ion conductivity. We also incorporate a potent nucleophilic fluorination agent, Tetrabutylammonium fluoride (TBAF), to augment the compatibility and oxidation resistance of the formulated FGPPE. The recurring (–CH2CH2O-) units of PEGDMA, coupled with in-situ lithium fluoride (LiF) and C-F groups introduced by TBAF, endow the FGPPE with a remarkable ionic conductivity of 7.8 mS cm−1 and a distinctly electrochemical stability of 4.65 V. Notably, the Li metal anode, featuring an F-rich solid-state interface (SEI), demonstrates uniform Li+ deposition, sustaining a cycling life of 1000 h and maintaining a commendable average coulomb efficiency of 98.5 % over 300 cycles. Additionally, the NCM811/SiC pouch cell integrated with FGPPE showcases superior cycling stability, retaining 99.4 % of its capacity after 600 cycles at an elevated voltage of 4.45 V. Such advancements in gel polymer electrolyte design can significantly expedite the commercial deployment of gel polymer Li-ion batteries.
•Accurate free energy profile of several mechanisms.•Cu(I)/Cu(III) mechanism explains the experiments.•Three mechanisms forming Cu(II) radical are unfavorable.
Addition of fluorine to organic ...molecules in the late stage of synthesis has been an increased interest in the past decade. Catalytic methods using fluoride salts as reagents could be especially useful, mainly with the use of organometallic catalysis with copper. Recent experimental advances have been reported for copper-mediated fluorination and the development of an efficient catalytic process needs a deep understanding of the reaction mechanism and the free energy profile. In this work, different mechanisms of copper-mediated fluorination of 2-(2-bromophenyl)pyridine using LCuF as reagent (L = N-heterocycle-carbene ligand) were investigated using very high level of theory, DLPNO-CCSD(T) method with up to quadruple-zeta basis set. The Cu(I)/Cu(III) mechanism is the predominant one, taking place via neutral (MS2) or cationic (MS2p) intermediates. Although the oxidative addition step has high barrier, the reductive elimination was found to be the rate-determining step. Three reaction pathways involving the Cu(II) radical mechanism was also investigated. The first one is the single-electron transfer mechanism and the second is the bromine atom transfer in the first step. Both pathways involve high free energy intermediates and are inviable. The third mechanism occurs via singlet-triplet spin crossover with bromine transfer from the oxidative addition intermediate MS2 to the LCuF initial reagent. However, the reductive elimination step from the MS2r doublet Cu(II) complex is much more difficult than the MS2 or MS2p singlets of Cu(III) complexes, leading to a very slow kinetics for this Cu(II) radical mechanism. The kinetics analysis of the theoretical free energy profile results in effective ΔG‡ of 30.6 kcal mol−1, in good agreement with an estimated experimental value and providing an important support for the Cu(I)/Cu(III) mechanism.
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Since the incorporation of fluorine into biologically active compounds often enhances the properties of the parent compounds, there is a considerable demand for efficient enantioselective ...fluorination reactions. Over the past decade, a range of metal‐catalyzed and organocatalyzed fluorination reactions has been developed. Nowadays, fluorine can be catalytically introduced into many compounds in good yield and with high enantioselectivity, and the scope of these reactions is broad. Herein, we review recent progress in the field of catalytic enantioselective fluorination reactions, including their scope and mechanism.
We prepared four structurally modified bis‐tert‐alcohol functionalized crown ether‐strapped calix4arene promoters, that is, bis‐tert‐alcohol functionalized crown‐5‐calix4arene (BA5C), ...bis‐tert‐alcohol functionalized crown‐7‐calix4arene (BA7C), bis‐1,1‐dimethylbutanol functionalized crown 6‐calix4arene (B3A6C), and bis‐1,1‐dimethylhexanol functionalized crown 6‐calix4arene (B5AC6C). Nucleophilic fluorinations were conducted using alkali metal fluorides to investigate phase‐transfer catalytic activities with respect to the sizes of crown ether‐strapped calix4arene (CEC) subunits and lengths of alkyl chain spacers between tert‐alcohol and CEC subunits. The reactivity of potassium fluoride was significantly enhanced by BA5C promoter because its crown‐5‐calix4arene subunit had cavity size appropriate for K+ capture. In contrast, BA7C did not efficiently enhance cesium fluoride SN2 fluorination because its crown‐7‐calix4arene cavity was too large to capture Cs+. The alkyl spacer of bis‐tert‐alcohol functionalized CEC provided sufficient distance between F– and Cs+. In particular, the three‐component alkyl carbon chain of B3A6C was optimal in terms of increasing CsF reactivity. Systematic quantum chemical analysis predicted that fluorination reactions facilitated by bis‐tert‐alcohol‐substituted crown‐6‐calix4arene (BACCA) and B3A6C might proceed via separated ion‐pair type pre‐reaction complexes, which suggested that these two promotors act as Lewis bases that essentially separate CsF ion‐pairs. The lower (by 0.4 kcal/mol) Gibbs free energy of activation for the reaction promoted by B3A6C than that facilitated by BACCA concurred with the experimentally observed slightly greater efficiency of B3A6C than BACCA.
Structurally modified bis‐tert‐alcohol functionalized crown ether‐strapped calix4arenes (CECs) were studied and their catalytic activities in alkali‐metal fluoride‐based SN2 fluorinations were examined. Systematic quantum chemical calculations were also performed to identify the drivers of the fluorination reaction rates achieved using bis‐tert‐alcohol functionalized CEC derivatives.
The selective C−H functionalization of aliphatic molecules remains a challenge in organic synthesis. While radical chain halogenation reactions provide efficient access to many halogenated molecules, ...the use of typical protocols for the selective halogenation of electron‐deficient and strained aliphatic molecules is rare. Herein, we report selective C−H chlorination and fluorination reactions promoted by an electron‐deficient manganese pentafluorophenyl porphyrin catalyst, Mn(TPFPP)Cl. This catalyst displays superior properties for the aliphatic halogenation of recalcitrant, electron‐deficient, and strained substrates with unique regio‐ and stereoselectivity. UV/Vis analysis during the course of the reaction indicated that an oxo‐MnV species is responsible for hydrogen‐atom ion. The observed stereoselectivity results from steric interactions between the bulky porphyrin ligand and the intermediate substrate radical in the halogen rebound step.
A deficiency that's a bonus: A highly electron‐deficient manganese porphyrin was found to effectively catalyze the radical halogenation of strained, electron‐deficient aliphatic substrates under mild conditions (see scheme). The bulkiness of the catalyst resulted in unique stereo‐ and regioselectivity.
•Nucleophilic fluorination of alkyl bromides with trace of elimination product.•Enhanced reaction rate using fluorinated bulky alcohol and crown ether.•Modulation of hydrogen bonding interaction is ...key for rate acceleration.
A new phase transfer system for nucleophilic fluorination of alkyl halides with potassium fluoride, based on the combination of 18-crown-6 and the bulky fluorinated alcohol 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, was found to be very effective. A primary alkyl bromide was fluorinated in 24 h of reaction time with a mild temperature of 82 °C using acetonitrile solvent, obtaining 80% yield and only a trace of elimination product. The rational choice of this alcohol was based on a free energy profile of a reaction model including the solubilization of the KF salt and on the theoretical calculations of the stability of the KF(18-crown-6)(alcohol) complexes. The fluorinated bulky alcohol leads to a substantial increase in the concentration of KF complexed with 18-crown-6, which compensates for the decreased reactivity of the solubilized complex. The present study shows the importance of the modulation of the hydrogen bonding strength to obtain the rate acceleration effect.
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We report the practical synthesis of a key fragment of islatravir (MK-8591), a novel nucleoside reverse transcriptase translocation inhibitor (NRTTI) currently under investigation for treatment and ...pre-exposure prophylaxis (PrEP) against HIV infection. The fragment, the unnatural nucleobase 2-fluoroadenine, is incorporated into MK-8591 via a biocatalytic aldol-glycosylation cascade, which imposes stringent requirements for its synthesis and isolation. Presented herein is the development work leading to a practical, scalable route from guanine, featuring a dual fluorination approach to a novel 9-THP-2,6-difluoropurine intermediate that enables a mild, highly selective, direct amination. This one-pot fluorination/amination sequence utilizes a direct isolation to deliver high purity 9-THP-2-fluoroadenine, which features ideal properties with respect to reactivity, solubility, and crystallinity. An acid-catalyzed liberation of 2-fluoroadenine in aqueous buffer delivers the appropriate purity profile to facilitate the enzymatic cascade to access MK-8591.
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•Cu(I) and Ag(I) are tetracoordinated by acetonitrile molecules in solution.•Cu(I) in the CuF is coordinated by two acetonitrile molecules.•Ag(I) in the AgF can coordinate to one or ...two acetonitrile molecules.•ΔGsolv calculated for Cu+ and Ag+ in close agreement with experimental data.•CuF could be an active species in the copper catalyzed fluorination.
The CuF species in acetonitrile solution is a potential intermediate in copper catalyzed fluorination. In the process, different species such as Cu+, Ag+, CuF and AgF could be involved. The objective of this work is to provide relevant data on the structure of these species in solution phase, as well as the corresponding solvation thermodynamics to better understand the equilibrium for formation of CuF. To attain this goal, ab initio Car-Parrinello molecular dynamics method and cluster-continuum quasichemical approach were used. It was found that Cu+ and Ag+ ions are tetracoordinated by acetonitrile molecules, being possible to observe the release of one coordinated acetonitrile to the solution to form a tricoordinate structure, suggesting a dissociative mechanism for ligand exchange. The CuF species was found to form a predominant tricoordinate complex, with copper coordinated to two acetonitrile molecules. The AgF species have presented more labile ligand feature, with silver ion interconverting between bi- and tricoordinate structure, involving coordination to one and two acetonitrile molecules, respectively. The solvation free energy calculated for Cu+ and Ag+ are in good agreement with available experimental data. The present results indicate that CuF can be easily formed from dissolved AgF and Cu+ species in acetonitrile solution. Consequently, CuF could play an important role in copper catalyzed fluorination.
Hydrogen bonding phase-transfer catalysis offers a convenient solution to activate safe and economical metal alkali fluorides for enantioselective nucleophilic fluorination. Herein, we demonstrate ...the scalability of this protocol with the fluorination of 200 g of racemic trans-N,N-dibenzyl-2-bromocyclohexan-1-amine in a mechanically stirred 1 L glass reactor using 0.5 mol % of a bis-urea organocatalyst. In these experiments, full conversions were obtained for high mixing intensities (impeller average shear rate >10 000 s–1; maximum energy dissipation per unit of mass >300 W/kg). The thermal safety of the reaction was assessed by differential scanning calorimetry and reaction calorimetry, assigning the reaction to Stoessel’s critical class 3.
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