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Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7885
Author(s):  
Inah Kang ◽  
Taewoong Lee ◽  
Young Rok Yoon ◽  
Jee Woo Kim ◽  
Byung-Kwon Kim ◽  
...  

We synthesized a new poly(triphenylamine), having a hyperbranched structure, and employed it in lithium-ion batteries as an organic cathode material. Two types of monomers were prepared with hydroxyl groups and nitro leaving groups, activated by a trifluoromethyl substituent, and then polymerized via the nucleophilic aromatic substitution reaction. The reactivity of the monomers differed depending on the number of hydroxyl groups and the A2B type monomer with one hydroxyl group successfully produced poly(triphenylamine). Based on thermal, optical, and electrochemical analyses, a composite poly(triphenylamine) electrode was made. The electrochemical performance investigations confirmed that the lithium-ion batteries, fabricated with the poly(triphenylamine)-based cathodes, had reasonable specific capacity values and stable cycling performance, suggesting the potential of this hyperbranched polymer in cathode materials for lithium-ion batteries.


Nature ◽  
2021 ◽  
Vol 600 (7889) ◽  
pp. 444-449
Author(s):  
Da Zhao ◽  
Roland Petzold ◽  
Jiyao Yan ◽  
Dieter Muri ◽  
Tobias Ritter

AbstractTritium labelling is a critical tool for investigating the pharmacokinetic and pharmacodynamic properties of drugs, autoradiography, receptor binding and receptor occupancy studies1. Tritium gas is the preferred source of tritium for the preparation of labelled molecules because it is available in high isotopic purity2. The introduction of tritium labels from tritium gas is commonly achieved by heterogeneous transition-metal-catalysed tritiation of aryl (pseudo)halides. However, heterogeneous catalysts such as palladium supported on carbon operate through a reaction mechanism that also results in the reduction of other functional groups that are prominently featured in pharmaceuticals3. Homogeneous palladium catalysts can react chemoselectively with aryl (pseudo)halides but have not been used for hydrogenolysis reactions because, after required oxidative addition, they cannot split dihydrogen4. Here we report a homogenous hydrogenolysis reaction with a well defined, molecular palladium catalyst. We show how the thianthrene leaving group—which can be introduced selectively into pharmaceuticals by late-stage C–H functionalization5—differs in its coordinating ability to relevant palladium(II) catalysts from conventional leaving groups to enable the previously unrealized catalysis with dihydrogen. This distinct reactivity combined with the chemoselectivity of a well defined molecular palladium catalyst enables the tritiation of small-molecule pharmaceuticals that contain functionality that may otherwise not be tolerated by heterogeneous catalysts. The tritiation reaction does not require an inert atmosphere or dry conditions and is therefore practical and robust to execute, and could have an immediate impact in the discovery and development of pharmaceuticals.


2021 ◽  
Author(s):  
Richmond Lee ◽  
Chi Bong Eric Chao ◽  
Xu Ban ◽  
Siu Min Tan ◽  
Haibo Yu ◽  
...  

Density functional theory (DFT) is used in this work to predict the mechanism for constructing congested quaternary-quaternary carbon(sp3)–carbon(sp3) bonds in a pentanidium catalyzed substitution reaction. Computational mechanistic studies were carried out to investigate the proposed SN2X manifold, which consists of two primary elementary steps: halogen atom transfer (XAT) and subsequent SN2. For the first calculated model on original experimental substrates, XAT reaction barriers were more kinetically competitive than an SN2 pathway and connects to thermodynamically stable intermediates. Extensive computational screening-modelling were then done on various substrate combinations designed to study steric influence and to understand the mechanistic rationale, and calculations reveal that sterically congested substrates prefer the SN2X manifold over SN2. Different halides as leaving groups were also screened and it was found that the reactivity increases in order of Br > Cl > F in agreement of the strength of C–X bonds. However, DFT modelling suggests that chlorides can be a viable substrate for the SN2X process which should be further explored experimentally. Finally, ONIOM calculations on the full catalyst model were carried out to rationalize the stereoselectivity which corroborates with experimental results.


Author(s):  
Ibon Alkorta ◽  
José Elguero

AbstractThis communication gives an overview of the relationships between four reactions that although related were not always perceived as such: SN2, Walden, Finkelstein, and Menshutkin. Binary interactions (SN2 & Walden, SN2 & Menshutkin, SN2 & Finkelstein, Walden & Menshutkin, Walden & Finkelstein, Menshutkin & Finkelstein) were reported. Carbon, silicon, nitrogen, and phosphorus as central atoms and fluorides, chlorides, bromides, and iodides as lateral atoms were considered. Theoretical calculations provide Gibbs free energies that were analyzed with linear models to obtain the halide contributions. The M06-2x DFT computational method and the 6-311++G(d,p) basis set have been used for all atoms except for iodine where the effective core potential def2-TZVP basis set was used. Concerning the central atom pairs, carbon/silicon vs. nitrogen/phosphorus, we reported here for the first time that the effect of valence expansion was known for Si but not for P. Concerning the lateral halogen atoms, some empirical models including the interaction between F and I as entering and leaving groups explain the Gibbs free energies.


Molecules ◽  
2021 ◽  
Vol 26 (15) ◽  
pp. 4618
Author(s):  
Alvaro Leonel Robles Grana ◽  
Hortensia Maldonado-Textle ◽  
José Román Torres-Lubián ◽  
Claude St Thomas ◽  
Ramón Díaz de León ◽  
...  

Herein, we report a novel type of symmetrical trithiocarbonate chain transfer agent (CTA) based diphenylmethyl as R groups. The utilization of this CTA in the Reversible Addition-Fragmentation chain Transfer (RAFT) process reveals an efficient control in the polymerization of methacrylic monomers and the preparation of block copolymers. The latter are obtained by the (co)polymerization of styrene or butyl acrylate using a functionalized macro-CTA polymethyl methacrylate (PMMA) previously synthesized. Data show low molecular weight dispersity values (Đ < 1.5) particularly in the polymerization of methacrylic monomers. Considering a typical RAFT mechanism, the leaving groups (R) from the fragmentation of CTA should be able to re-initiate the polymerization (formation of growth chains) allowing an efficient control of the process. Nevertheless, in the case of the polymerization of MMA in the presence of this symmetrical CTA, the polymerization process displays an atypical behavior that requires high [initiator]/[CTA] molar ratios for accessing predictable molecular weights without affecting the Đ. Some evidence suggests that this does not completely behave as a common RAFT agent as it is not completely consumed during the polymerization reaction, and it needs atypical high molar ratios [initiator]/[CTA] to be closer to the predicted molecular weight without affecting the Đ. This work demonstrates that MMA and other methacrylic monomers can be polymerized in a controlled way, and with “living” characteristics, using certain symmetrical trithiocarbonates.


Synthesis ◽  
2021 ◽  
Author(s):  
Fei Wang ◽  
Junyi Yi ◽  
Yoshihiro Nishimoto ◽  
Makoto Yasuda

We have accomplished homologation of alkyl acetates, alkyl ethers, acetals, and ketals via formal insertion of diazo esters into carbon-carbon σ-bonds. The combined Lewis acid of InI3 with Me3SiBr catalyzed the homologation of alkyl acetates and alkyl ethers. That of acetals and ketals was catalyzed solely by the use of InBr3. The key point of the homologation mechanism is that the indium-based Lewis acids have the appropriate amount of Lewis acidity to achieve both the abstraction and release of leaving groups. The abstraction of a leaving group by an indium-based Lewis acid, the electrophilic addition of carbocation or oxonium intermediates to diazo esters followed by the rearrangement of carbon substituents provides the corresponding cation intermediates. Finally, the leaving group that is captured by the Lewis acid bonds with cation intermediates to furnish the homologated products.


Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3394
Author(s):  
Surya B. Adhikari ◽  
Anji Chen ◽  
Guijun Wang

Glycomacrolactones exhibit many interesting biological properties, and they are also important in molecular recognitions and for supramolecular chemistry. Therefore, it is important to be able to access glycomacrocycles with different sizes and functionality. A new series of carbohydrate-based macrocycles containing triazole and lactone moieties have been designed and synthesized. The synthesis features an intramolecular nucleophilic substitution reaction for the macrocyclization step. In this article, the effect of some common sulfonate leaving groups is evaluated for macrolactonization. Using tosylate gave good selectivity for monolactonization products with good yields. Fourteen different macrocycles have been synthesized and characterized, of which eleven macrocycles are from cyclization of the C1 to C6 positions of N-acetyl D-glucosamine derivatives and three others from C2 to C6 cyclization of functionalized D-glucosamine derivatives. These novel macrolactones have unique structures and demonstrate interesting anion binding properties, especially for chloride. The macrocycles containing two triazoles form complexes with copper sulfate, and they are effective ligands for copper sulfate mediated azide-alkyne cycloaddition reactions (CuAAC). In addition, several macrocycles show some selectivity for different alkynes.


2021 ◽  
Vol 10 (2) ◽  
pp. 107-115
Author(s):  
Andrea Morone ◽  
Simone Nuzzo ◽  
Tiziana Temerario

Recent literature on individual vs. group decision-making, in risky contexts, has brought about divergent results, mainly depending on the institutional rules through which groups take decisions. Some studies where group decisions relied on majority rule showed no appreciable difference between individuals and groups’ preferences, others where unanimity among group members was required found collective decisions to be less risk-averse than individual ones. We elicited groups’ preferences over risk using what we defined “endogenous-decision-rule”, i.e. leaving groups free to endogenously solve the potential disagreement among their members. Our results unambiguously show that individuals are more risk seeker than groups when facing gambles with positive expected payoff difference and more risk-averse in the opposite case.


2021 ◽  
Vol 9 ◽  
Author(s):  
Tyler J. Jaynes ◽  
Mona Sharafi ◽  
Joseph P. Campbell ◽  
Jessica Bocanegra ◽  
Kyle T. McKay ◽  
...  

This work presents the first transition metal-free synthesis of oxygen-linked aromatic polymers by integrating iterative exponential polymer growth (IEG) with nucleophilic aromatic substitution (SNAr) reactions. Our approach applies methyl sulfones as the leaving groups, which eliminate the need for a transition metal catalyst, while also providing flexibility in functionality and configuration of the building blocks used. As indicated by 1) 1H-1H NOESY NMR spectroscopy, 2) single-crystal X-ray crystallography, and 3) density functional theory (DFT) calculations, the unimolecular polymers obtained are folded by nonclassical hydrogen bonds formed between the oxygens of the electron-rich aromatic rings and the positively polarized C–H bonds of the electron-poor pyrimidine functions. Our results not only introduce a transition metal-free synthetic methodology to access precision polymers but also demonstrate how interactions between relatively small, neutral aromatic units in the polymers can be utilized as new supramolecular interaction pairs to control the folding of precision macromolecules.


2021 ◽  
Author(s):  
Matthias Tanriver ◽  
Yi-Chung Dzeng ◽  
Erwin Lam ◽  
Jeffrey Bode

<div><div><div><p>Potassium acyltrifluoroborates (KATs) undergo chemoselective amide-forming ligations with hydroxylamines. Under aqueous, acidic conditions these ligations can proceed rapidly, with rate constants of ~20 M-1 s-1. The requirement for lower pH to obtain the fastest rates, however, limits their use with certain biomolecules and precludes in vivo applications. By mechanistic investigations into the KAT ligation, including kinetic studies, X-ray crystallography, and DFT calculations, we have identified a key role for a proton in accelerating the ligation. We applied this knowledge to the design and synthesis of 8-quinolyl acyltrifluoroborates, a new class of KATs that ligates with hydroxylamines at pH 7.4 with rate constants >4 M-1 s-1. We trace the enhanced rate at physiological pH to unexpectedly high basicity of the 8-quinoline-KATs, which leads to their protonation even under neutral conditions. This proton assists the formation of the key tetrahedral intermediate and activates the leaving groups on the hydroxylamine towards a concerted 1,2-BF3shift that leads to the amide product. We demonstrate that the fast ligations at pH 7.4 can be carried out with a protein substrate at micromolar concentrations.</p></div></div></div>


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