Fluoroalkyl Moieties Research Articles

Solubility Change Behavior of Fluoroalkyl Ether-Tagged Dendritic Hexaphenol under Extreme UV Exposure.

This study focuses on the discovery of a single-component molecular resist for extreme ultraviolet (EUV) lithography by employing the ionizing radiation-induced decomposition of carbon-fluorine chemical bonds. The target material, DHP-L6, was synthesized by bonding perfluoroalkyl ether moieties to amorphous dendritic hexaphenol (DHP) with a high glass transition temperature. Upon exposure to EUV and electron beam irradiation, DHP-L6 films exhibited a decreasing solubility in fluorous developer media, resulting in negative-tone images. The underlying chemical mechanisms were elucidated by Fourier transform-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy, and nanoindentation experiments. These analyses highlighted the possible electron-induced decomposition of C-F bonds in DHP-L6, leading to molecular network formation via recombination of the resulting C-centered radicals. Subsequent high-resolution lithographic patterning under EUV irradiation showed that DHP-L6 could create stencil patterns with a line width of 26 nm at an exposure dose of 110 mJ cm-2. These results confirm that single-component small molecular compounds with fluoroalkyl moieties can be employed as patterning materials under ionizing radiation. Nonetheless, additional research is required to reduce the relatively high exposure energy for high-resolution patterning and to enhance the line-edge roughness of the produced stencil.

Visible-light-induced photocatalytic iododi(per)fluoroalkylation of 5-amino-N-allyl-1,2,3-triazole-4-carboxamides

Readily available di(per)fluoroalkyl iodides and ethyl difluoroiodoacetate have been efficiently reacted with 5-amino-N-allyl-1,2,3-triazole-4-carboxamides in the presence of DIPEA under visible-light induction and fluorescein catalysis to produce high yields of the corresponding adducts, N-(n-propyl) carboxamides vicinally difunctionalized with the iodine atom and the di(per)fluoroalkyl or (methoxycarbonyl)difluoromethyl moiety. As shown experimentally, this regiospecific and triazole amino group tolerant reaction involves a radical process.

Base-induced azofluoroalkylation of unactivated alkenes via halogen atom transfer

A base-induced three-components coupling employing unactivated alkenes, fluoroalkyl iodides and diazonium salts under mild reaction conditions has been developed.

Modulating the ferroelectric phases in cholesteryl-based organic compounds with perfluoroalkyl tail engineering.

Here, we synthesized a series of cholesteryl-based compounds, whose phases and their transformation can be modulated by temperature and the chain length of the fluoroalkyl moieties. To our knowledge, this is the first time that the phase transition could be modulated with perfluoroalkyl tail engineering in organic single-component ferroelectric crystals.

Fluoroalkyl trimethoxysilane route to hydrophobic 2K polyurethane clearcoats and their failure mechanism

In this study, three fluoroalkyl trimethoxysilanes (FATMS) with different chain length of fluoroalkyl moiety, i.e., (3,3,3-trifluoropropyl) trimethoxysilane (C1), (1,1,2,2-tetrahydro-nonafluorohexyl) trimethoxysilane (C4), (1,1,2,2-tetrahydro-perfluorooctyl) trimethoxysilane (C6), were incorporated into component A of a two-component polyurethane (2K PU) clearcoat to assure their chemical anchoring with polymer chains, and then cured with polyisocyanate hardener. The hydrophobic durability of FATMS-modified coatings was further examined under various service conditions by water contact angle analyzer, attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and element-mapping. Hydrophobic 2K PU clearcoats could be achieved at FATMS dosage below 5.0 %, 0.5 %, and 0.5 % for C1, C4, and C6 additive, respectively. All coatings maintained their original hydrophobicity after for two years’ ambient storage, immersing in ambient water or mere UV irradiation. But if UV irradiation and/or heat (i.e., high-temperature) were imposed together with water, the coatings would quickly lose their surface hydrophobicity due to the loss of fluoroalkyl groups via hydrolysis break of Si-O-C chemical bond. The UV irradiation-induced synergistic effect on failure of surface hydrophobicity should be resulted from the increased hydrophilicity of PU matrix, which enhanced the affinity of water molecules with the coatings and hence higher hydrolysis probability of Si-O-C bond. Therefore, FATMS route is more suitable for fabrication of hydrophobic 2K PU clearcoats used indoors at room temperature.

Organoboron Reagent-Controlled Selective (Deutero)Hydrodefluorination.

(Deuterium-labeled) CF2 H- and CFH2 -moieties are of high interest in drug discovery. The high demand for the incorporation of these fluoroalkyl moieties into molecular structures has witnessed significant synthetic progress, particularly in the (deutero)hydrodefluorination of CF3 -containing compounds. However, the controllable replacement of fluorine atoms while maintaining high chemoselectivity remains challenging. Herein, we describe the development of a selective (deutero)hydrodefluorination reaction via electrolysis. The reaction exhibits a remarkable chemoselectivity control, which is enabled by the addition of different organoboron sources. The procedure is operationally simple and scalable, and provides access in one step to high-value building blocks for application in medicinal chemistry. Furthermore, density functional theory (DFT) calculations have been carried out to investigate the reaction mechanism and to rationalize the chemoselectivity observed.

Organoboron Reagent‐Controlled Selective (Deutero)Hydrodefluorination

Abstract(Deuterium‐labeled) CF2H‐ and CFH2‐moieties are of high interest in drug discovery. The high demand for the incorporation of these fluoroalkyl moieties into molecular structures has witnessed significant synthetic progress, particularly in the (deutero)hydrodefluorination of CF3‐containing compounds. However, the controllable replacement of fluorine atoms while maintaining high chemoselectivity remains challenging. Herein, we describe the development of a selective (deutero)hydrodefluorination reaction via electrolysis. The reaction exhibits a remarkable chemoselectivity control, which is enabled by the addition of different organoboron sources. The procedure is operationally simple and scalable, and provides access in one step to high‐value building blocks for application in medicinal chemistry. Furthermore, density functional theory (DFT) calculations have been carried out to investigate the reaction mechanism and to rationalize the chemoselectivity observed.

Synthesis and characterization of novel fluorinated nitriles as non-flammable and high-voltage electrolytes for lithium/lithium-ion batteries

Current carbonate or ether electrolytes for lithium-ion batteries suffer from high flammability, poor high-potential stability or complicated synthesis protocols. Herein, we design and successfully synthesize a series of novel fluorinated nitriles bridged by ether bond between the nitrile group and fluoroalkyl moiety. The relationship between the chemical structure of fluorinated nitriles (including the length of fluoroalkyl chain, partial fluorination of terminal group, and introduction of ethylene oxide units) and corresponding properties such as viscosity, dielectric constant, ionic conductivity, electrochemical stability window, flammability, solvation ability, are investigated systematically. Using the fluorinated nitriles as the main solvents, the formulated electrolytes not only exhibit non-flammable but also promise excellent stability for lithium batteries and 4.5 V high-voltage lithium-ion batteries.

Facile strategy for advanced selectivity and sensitivity of SnO2 nanowire-based gas sensor using chemical affinity and femtosecond laser irradiation

This study proposes an effective strategy to improve the selectivity and response of SnO2 nanowire (NW)-based gas sensors. Self-assembled monolayer (SAM) functionalization of SnO2 NWs enhances the gas selectivity by tuning the surface chemical states. Different chemical moieties with alkyl and fluoroalkyl of the SAM molecules are adopted for the chemical affinities toward the corresponding target gas molecules. The alkyl and fluoroalkyl moieties show excellent selectivity toward CH4 and C3F8, respectively, owing to the strong chemical affinity between the moieties and gases. Post-treatment femtosecond (FS) laser irradiation with different laser fluences is applied to the SAM-functionalized SnO2 NW-based gas sensor. The FS laser-irradiated SnO2 NWs show an enhanced sensor response with higher resistance values and shorter response and recovery times compared to those of the pristine SnO2 NWs. Transmission electron microscopy analysis reveals that the FS laser irradiation induces the formation of embossing surface on the SnO2 NW, creating additional gas adsorption sites. Moreover, twin structures develop on the SnO2 NWs with increasing laser fluences. Electron energy loss spectroscopy analysis supports that the FS laser irradiation creates non-stoichiometric SnO and SnOx phases, providing O vacancies and improved response.

Vacuum Interfacial Structure and X-ray Reflectivity of Imidazolium-Based Ionic Liquids with Perfluorinated Anions from a Theory and Simulations Perspective.

We report studies of the vacuum interfacial structure of a series of 1-methyl-3-alkylimidazolium bis(perfluoroalkanesulfonyl)imide ionic liquids (ILs) and predict and explain their Fresnel-normalized X-ray reflectivity. To better interpret the results, we use a theory we recently developed dubbed “the peaks and antipeaks analysis of reflectivity” which splits the overall signal into that of different pair subcomponents. Whereas the overall reflectivity signal is not very informative, the peak and trough intensities for the pair subcomponents provide rich information for analysis. When species containing cationic alkyl or anionic fluoroalkyl tails are present at the interface, a tail layer is found next to a vacuum, and this tail layer can be composed of both alkyl and fluoroalkyl moieties. To maintain the positive–negative alternation of charged groups, alkyl and fluoroalkyl tails must necessarily be nearby and cannot segregate. Charged groups are found in the subsequent layer just below the interface and arranged to achieve lateral charge neutrality. In general, fluctuations at and away from the interface are based on polarity (i.e., heads and tails) and not on charge; when there are no significant alkyl or fluoroalkyl moieties in the IL, atomic density fluctuations away from the interface are small and appear to exist for the purpose of achieving lateral charge balance. For all the systems reported here, the persistence length of density fluctuations does not go beyond ∼7 nm.

Rose Bengal-photocatalyzed perfluorohexylation reactions of organic substrates in water. Applications to late-stage syntheses.

The Rose Bengal-photocatalyzed perfluorohexylation of olefins, alkynes, and electron-rich aromatic compounds in water was achieved employing perfluorohexyl iodide as fluoroalkyl source and TMEDA as sacrificial donor under green LED irradiation. Alkenes and alkynes rendered products derived from the atom transfer radical addition (ATRA) pathway, and in the case of alkynes, exclusively as E-stereoisomers. These are the first examples of photocatalyzed ATRA reactions carried out excursively in water alone. The reactions of aromatic compounds under the current protocol in water present the advantage of employing a perfluoroalkyl iodide (C6F13-I) as source of perfluorohexyl radicals. Examples of photocatalytic late-stage incorporations of fluoroalkyl moieties into two commercial drugs of widespread use are reported.

Cover Feature: Electrochemical Installation of CFH2−, CF2H−, CF3−, and Perfluoroalkyl Groups into Small Organic Molecules (Chem. Rec. 9/2021)

The cover picture displays fluoroalkyl radicals as reactive intermediates in the electrochemical (per)fluoroalkylation and representative examples of electrochemically fluoroalkylated small molecules. The installation of fluoroalkyl moieties into drug candidates significantly promotes their potency. Electrosynthesis is a sustainable and powerful technology to tackle this challenging synthetic task. Consequently, electrochemical fluoroalkylation of small organic molecules has become a vivid area of research, which is surveyed by S. R. Waldvogel and co-workers in their Record Review (DOI: 10.1002/tcr.202100065).

Catalytic Fluoroalkylation Reactions of Alkoxy‐substituted (Hetero)Arenes

AbstractElectron‐rich alkoxy‐substituted (hetero)arenes and electrophilic fluoroalkyl moieties represent advantageous partners for substitution reactions due to their electronic match. Fluoroalkylation strategies of alkoxy‐substituted (hetero)arenes are herein presented which depict photocatalytic and thermal methods. Photocatalytic methods rely on the use of diverse photocatalysts such as Ru(bpy)3Cl2, tetrabutylammonium decatungstate TBADT, N‐doped carbon nanodots NCNDs, and vitamin derivatives which can partner with the Langlois reagent NaSO2CF3, CF3CO2H, and perfluoroalkyl iodides RF‐I as fluoroalkylating reagents. Also, electrocatalytic methods that make use of the cathodic reduction of CF3SO2Cl to generate CF3 radicals can achieve trifluoromethylation reactions of alkoxy‐substituted (hetero)arenes. On the other hand, thermal methodologies comprising Pd(OAc)2 catalysis and using CF3Br as trifluoromethylating source have been implemented.

Effect of Fluoroalkyl-Substituent in Bistolane-Based Photoluminescent Liquid Crystals on Their Physical Behavior

Photoluminescent liquid crystals (PLLCs) have attracted significant attention owing to their broad applicability in thermosensing and PL switching. Extensive efforts have been made to develop bistolane-based PLLCs containing flexible units at both molecular terminals, and it has been revealed that their PL behavior can switch with the phase transition between the crystalline and LC phases. Although slight modulation of the flexible unit structure dramatically alters the LC and PL behaviors, few studies into the modification of the flexible units have been conducted. With the aim of achieving dynamic changes in their physical behaviors, we developed a family of bistolane derivatives containing a simple alkyl or a fluoroalkyl flexible chain and carried out a detailed systematic evaluation of their physical behaviors. Bistolanes containing a simple alkyl chain showed a nematic LC phase, whereas switching the flexible chain in the bistolane to a fluoroalkyl moiety significantly altered the LC phase to generate a smectic phase. The fluoroalkyl-containing bistolanes displayed a stronger deep blue PL than their corresponding non-fluorinated counterparts, even in the crystalline phase, which was attributed to the construction of rigid molecular aggregates through intermolecular F···H and F···F interactions to suppress non-radiative deactivation.

Synthetic Approaches to Fluoroalkyltelluryl‐Substituted Compounds

Fluorinated substituents confer specific properties to molecules. In the last years, the merging of chalcogenes with trifluoromethyl or fluoroalkyl moieties has known a growing interest. However, the last non‐radioactive family member, namely tellurium, did not receive much attention. This review will present and discuss the state of the art chemistry of RFTe, to describe the available methods and highlight the future developments to consider.

Ethylene oxide–based polymer electrolytes with fluoroalkyl moieties for stable lithium metal batteries

In this study, we have developed a new ethylene oxide (EO)-based polymer electrolyte (PE) that contains fluoroalkyl moieties. The developed PE possesses high oxidative decomposition potential as well as adequate ionic conductivity (σ) and favorable mechanical properties for application to Li metal batteries. In particular, we designed a partially fluorinated copolymer, which is improved in conventional polyethylene oxide systems and could be used both as stable electrolyte matrix and electrode binder for high-voltage applications. The results indicated that the stabilization of the EO-based PE during the high-voltage operation of Li metal batteries was significantly improved by the introduction of a fluoroalkyl moiety via simple radical copolymerization. The synthesized copolymer exhibited satisfactory physical stability and unprecedented high oxidation decomposition voltage threshold, which exceeded 4.5 V. Moreover, the copolymer-based PEs presented moderate σ values (> 0.3 mS cm−1 at 60 °C) and retained the intrinsic properties of the EO-based PE.

A Dynamic Interface Based on Segregation of an Amphiphilic Hyperbranched Polymer Containing Fluoroalkyl and Oligo(ethylene oxide) Moieties

An amphiphilic hyperbranched polymer (HBP) containing both fluoroalkyl (Rf: −C6F13) pendants and oligo(ethylene oxide) (nEO) parts was synthesized as a novel type of interfacial modifier to confer ...

Degradation of Perfluoroalkyl Ether Carboxylic Acids with Hydrated Electrons: Structure-Reactivity Relationships and Environmental Implications.

This study explores structure-reactivity relationships for the degradation of emerging perfluoroalkyl ether carboxylic acid (PFECA) pollutants with ultraviolet-generated hydrated electrons (eaq-). The rate and extent of PFECA degradation depend on both the branching extent and the chain length of oxygen-segregated fluoroalkyl moieties. Kinetic measurements, theoretical calculations, and transformation product analyses provide a comprehensive understanding of the PFECA degradation mechanisms and pathways. In comparison to traditional full-carbon-chain perfluorocarboxylic acids, the distinct degradation behavior of PFECAs is attributed to their ether structures. The ether oxygen atoms increase the bond dissociation energy of the C-F bonds on the adjacent -CF2- moieties. This impact reduces the formation of H/F-exchanged polyfluorinated products that are recalcitrant to reductive defluorination. Instead, the cleavage of ether C-O bonds generates unstable perfluoroalcohols and thus promotes deep defluorination of short fluoroalkyl moieties. In comparison to linear PFECAs, branched PFECAs have a higher tendency of H/F exchange on the tertiary carbon and thus lower percentages of defluorination. These findings provide mechanistic insights for an improved design and efficient degradation of fluorochemicals.

Mechanism and Origin of Enantioselectivity in Nickel-Catalyzed Alkyl-Alkyl Suzuki Coupling Reaction.

Enantioselective Suzuki coupling reactions are a widely used method in asymmetric synthesis of chiral compounds. In an important extension of this protocol, 1-bromo-1-fluoroalkanes were coupled with alkyl-9-BBN using chiral NiCl2L* as the catalyst (where L* = bis(pyrrolidine) ligand) under Suzuki conditions to obtain a product with a stereogenic center bearing a fluorine. In view of the current interest in chiral fluorine-containing compounds as well as lack of clarity on the mechanism of Ni-catalyzed asymmetric Suzuki coupling reactions, we decided to examine various mechanistic pathways of the title reaction. The (U)M06 density functional theory computations have been employed to identify the energetically preferred pathway first and then to probe the origin of high enantioselectivity. In particular, we have compared the likely involvement of different redox couples such as Ni(0)/Ni(II) and Ni(I)/Ni(III) in the catalytic cycle. For the Ni(0)/Ni(II) pathway, both singlet and triplet spin states have been considered whereas a doublet spin multiplicity has been examined in the case of the Ni(I)/Ni(III) system. The most preferred catalytic pathway is found to proceed through a Ni(I)/Ni(III) redox cycle with key mechanistic steps such as (a) a transmetalation involving the transfer of the alkyl group of 9-BBN to the Ni-catalyst, (b) an oxidative addition of bromo(fluoro) alkane to give a penta-coordinate Ni(III) intermediate, and (c) an enantio-controlling reductive elimination (RE) that facilitates the C-C bond formation between the Ni-bound fluoroalkyl and alkyl moieties to yield the final product. The transmetalation is found to be the turnover determining transition state (TS) according to the activation span model. The RE is found to be the enantio-controlling step, wherein the TS for the addition of the si prochiral face of the Ni-bound fluoro alkyl moiety to the alkyl group is 4.3 kcal/mol lower than the corresponding re face addition. Distortion-Interaction analysis suggested that the extent of distortion in the catalyst Ni(Br)L* fragment in the si face reductive elimination TS is much lower than in the re face addition, thus making a vital contribution to the energy difference between diastereomeric TS.

Electrochemistry Study of Permselectivity and Interfacial Electron Transfers of a Branch-Tailed Fluorosurfactant Self-Assembled Monolayer on Gold.

We investigated the permselectivity and interfacial electron transfers of an amphiphilic branch-tailed fluorosurfactant self-assembled monolayer (FS-SAM) on a gold electrode by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The FS-SAM was prepared by a self-assembly technique and a “click” reaction. The barrier property and interfacial electron transfers of the FS-SAM were also evaluated using various probes with different features. The FS-SAM allowed a higher degree of permeation by small hydrophilic (Cl− and F−) electrolyte ions than large hydrophobic (ClO4− and PF6−) ones. Meanwhile, the redox reaction of the Fe(CN)63− couple was nearly completely blocked by the FS-SAM, whereas the electron transfer of Ru(NH3)63+ was easier than that of Fe(CN)63−, which may be due to the underlying tunneling mechanism. For hydrophobic dopamine, the hydrophobic bonding between the FS-SAM exterior fluoroalkyl moieties and the hydrophobic probes, as well as the hydration resistance from the interior hydration shell around the oligo (ethylene glycol) moieties, hindered the transport of hydrophobic probes into the FS-SAM. These results may have profound implications for understanding the permselectivity and electron transfers of amphiphilic surfaces consisting of molecules containing aromatic groups and branch-tailed fluorosurfactants in their structures.