Triflic Research Articles

Arylative Ring Expansion of 3‐Vinylazetidin‐3‐Ols and 3‐Vinyloxetan‐3‐Ols to Dihydrofurans by Dual Palladium and Acid Catalysis

AbstractIn contrast to the well‐studied 1‐vinylcyclobutanols, the reactivity of 3‐vinylazetidin‐3‐ols 1 and 3‐vinyloxetan‐3‐ols 2 under transition metal catalysis remains largely unexplored. We report herein their unique reactivity under dual palladium and acid catalysis. In the presence of a catalytic amount of Pd(OAc)2(PPh3)2, AgTFA and triflic acid, the reaction of 1 or 2 with aryl iodides affords 2,3,4‐trisubstituted dihydrofurans, which are valuable heterocycles in organic synthesis. Mechanistic studies reveal that this arylative ring‐expansion reaction proceeds via a domino process involving Heck arylation of alkene, acid‐catalyzed transposition of allylic alcohol and ring opening of the azetidine/oxetane by an internal hydroxyl group.

Arylative Ring Expansion of 3-Vinylazetidin-3-Ols and 3-Vinyloxetan-3-Ols to Dihydrofurans by Dual Palladium and Acid Catalysis.

In contrast to the well-studied 1-vinylcyclobutanols, the reactivity of 3-vinylazetidin-3-ols 1 and 3-vinyloxetan-3-ols 2 under transition metal catalysis remains largely unexplored. We report herein their unique reactivity under dual palladium and acid catalysis. In the presence of a catalytic amount of Pd(OAc)2(PPh3)2, AgTFA and triflic acid, the reaction of 1 or 2 with aryl iodides affords 2,3,4-trisubstituted dihydrofurans, which are valuable heterocycles in organic synthesis. Mechanistic studies reveal that this arylative ring-expansion reaction proceeds via a domino process involving Heck arylation of alkene, acid-catalyzed transposition of allylic alcohol and ring opening of the azetidine/oxetane by an internal hydroxyl group.

The Divalent Lanthanoid Triflates Ln(CF3SO3)2(CH3CN) (Ln=Sm, Eu): Structure, Luminescence, and Magnetism.

The reaction of the trivalent lanthanoide triflates Ln(OTf)3 (Ln=Sm, Eu; OTf=CF3SO3 -) with the respective metals in acetonitrile leads to the Ln(II)-triflates Eu(OTf)2(CH3CN) (monoclinic, P21/n, Z=4, a=1053.54(1), b=610.28(5), c=1946.92(2) pm, β =98.611(4)) and Sm(OTf)2(CH3CN) (monoclinic, P21/n, Z=4, a=1054.41(4), b=612.16(2), c=1952.65(7) pm, β =98.524(2)). The isotypic strontium compound Sr(OTf)2(CH3CN) (monoclinic, P21/n, Z=4, a=1056.39(5), b=610.05(3), c=1950.1(1) pm, β =98.900(2)°) has been obtained from SrCO3 and triflic acid. The compounds have been investigated by X-ray diffraction, vibrational spectroscopy, luminescence spectroscopy, cyclic voltammetry, thermal analysis, and magnetic measurements.

One‐step Synthesis of Organic Terminal 2D Ti3C2T x MXene Nanosheets by Etching of Ti3AlC2 in an Organic Lewis Acid Solvent

The surface and interface chemistry are critical for controlling the properties of two‐dimensional transition metal carbides and nitrides (MXenes). Numerous efforts have been devoted to the functionalization of MXenes with small inorganic ligands; however, few etching methods have been reported on the direct bonding of organic groups to MXene surfaces. In this work, we demonstrated an efficient and rapid strategy for the direct synthesis of 2D Ti3C2Tx MXene nanosheets with organic terminal groups in an organic Lewis acid (trifluoromethanesulfonic acid) solvent, without introducing additional intercalations. The dissolution of aluminum and the subsequent in‐situ introduction of trifluoromethanesulfonic acid resulted in the extraction of Ti3C2Tx MXene (T = CF3SO3−) (denoted as CF3SO3H‐Ti3C2Tx) flakes with sizes reaching 15 µm and high productivity (over 70%) of monolayers or few layers. More importantly, the large CF3SO3H‐Ti3C2TxMXene nanosheets had high colloidal stability, making them promising as efficient electrocatalysts for the hydrogen evolution reaction.

One-step Synthesis of Organic Terminal 2D Ti3C2T x MXene Nanosheets by Etching of Ti3AlC2 in an Organic Lewis Acid Solvent.

The surface and interface chemistry are critical for controlling the properties of two-dimensional transition metal carbides and nitrides (MXenes). Numerous efforts have been devoted to the functionalization of MXenes with small inorganic ligands; however, few etching methods have been reported on the direct bonding of organic groups to MXene surfaces. In this work, we demonstrated an efficient and rapid strategy for the direct synthesis of 2D Ti3C2Tx MXene nanosheets with organic terminal groups in an organic Lewis acid (trifluoromethanesulfonic acid) solvent, without introducing additional intercalations. The dissolution of aluminum and the subsequent in-situ introduction of trifluoromethanesulfonic acid resulted in the extraction of Ti3C2Tx MXene (T = CF3SO3-) (denoted as CF3SO3H-Ti3C2Tx) flakes with sizes reaching 15 µm and high productivity (over 70%) of monolayers or few layers. More importantly, the large CF3SO3H-Ti3C2TxMXene nanosheets had high colloidal stability, making them promising as efficient electrocatalysts for the hydrogen evolution reaction.

Dissociative photoionization of phenyl triflate, a photoacid generator for photolithography, at 92 eV.

The dissociative photoionization of phenyl triflate (C6H5OSO2CF3), a neutral photoacid generator used in photolithography, was investigated in a gas phase experiment employing extreme ultraviolet (EUV) synchrotron radiation at 92eV and photoelectron-photoion coincidence detection. The interaction of EUV photons with the molecule leads almost exclusively to dissociation, which is dominated by a sequential fragmentation mechanism, in which SO2, CF3, CO, and C2H2 are lost. For lithographic purposes, the lack of the observation of a fragment that could serve as a precursor for the formation of triflic acid means that the effective photoacid generator concentration in a photoresist is reduced, impacting its patterning performance in EUV lithography. A better understanding of the dissociative photoionization of photoresist components and proxies thereof can provide a crucial handle that guides the design of photoresists for the upcoming technology nodes with ever decreasing feature sizes for more powerful computer chips.

Synthesis of 2-Substituted Indoles via Migration Reaction of 3-Substituted Indoles with Triflic Acid.

This study showcases the 1,2-migration reactions of alkyl and aryl groups on the indole molecule. Trifluoromethanesulfonic acid effectively facilitates the migration of the substituent from C3- to C2-position of the indole structure. The resulting C2-substituted indoles offer a valuable pathway for the synthesis of natural products and medicinal compounds.

Synthesis of 2,4-Disubstituted Oxazoles and Thiazoles via Brønsted Acid-Catalyzed Cyclization of α-diazoketones with Amides.

A novel method is described for the synthesis of 2,4-disubstituted oxazole and thiazole derivates via the coupling of α-diazoketones with (thio)amides or thioureas using trifluoromethanesulfonic acid (TfOH) as a catalyst. This protocol is characterized by mild reaction conditions, metal-free, and simplicity and also features good functional group tolerance, good to excellent yields, and a broad substrate scope with more than 40 examples. Experimental studies suggest a mechanism involving 2-oxo-2-phenylethyl trifluoromethanesulfonate as the key intermediate.

Synthesis of poly N-aryl piperidinium membrane and ionomer for anion exchange membrane fuel cell applications

Ether free backbones have recently attracted widespread attention in anion exchange membrane fuel cells (AEMFCs). Here we report the synthesis of two poly N-aryl piperidinium (PNAP) membranes from their monomers by the polycondensation method using trifluoromethanesulfonic acid as a catalyst. Density functional theory identifies the chemical reaction, and the radial distribution function represents the interactions between a water molecule and a functional group of PNAP membranes. The performance of the anion exchange membrane can be enhanced by varying the monomer ratios of PNAP. An optimized PNAP-2 membrane exhibits a hydroxide conductivity of 183 mS cm−1 at 90 °C and PNAP-2 ionomers with Pt/C catalysts display a greater half-wave potential (E1/2) of 0.81 V and a lower Tafel value of 65 mV dec−1. In fuel cell tests, a PNAP-2 ionomer alongside a 60% platinum-on-carbon (Pt/C) membrane electrode assembly achieved a peak power density of 2.07 W cm−2. The PNAP-2 remained stable for more than 230 h at a constant current density of 0.3 A cm−2. PNAP-2 also displays exceptional resistance to alkaline conditions, lasting for more than 1000 h in both 1 M and 5 M NaOH solutions at 60 °C.

O2-promoted photocyclization of arylimines: A mild strategy of generating phenanthridines

A visible light-induced cyclization of arylimines using trifluoromethanesulfonic acid (TfOH) as the catalyst is reported. The transformation, conducted under air and mild conditions utilizes O2 as the oxidant, eliminating the need for leaving groups or excess acid. Optimization studies reveal the pivotal role of TfOH and visible light in the reaction. The methodology allows a broad substrate scope, accommodating various electron-donating and electron-withdrawing groups. The reaction conditions enable gram-scale synthesis and show inhibitory effects on cancer cell lines and low toxicity towards normal cells. Mechanistic insights indicate a visible light-induced 6π-electrocyclization. This method provides a practical and efficient approach for the synthesis of phenanthridine derivatives.

In-situ approach to porous nitrogen-doped carbon nanosheets functionalized by Brønsted acidic ionic liquids for microwave-assisted upgrading fructose to 5-hydroxymethylfurfural

In the search for robust and recoverable supported Brønsted acidic ionic liquids (BAILs) catalysts for efficient upgrading bio-sugars to value-added chemicals, an in-situ strategy of supramolecular preorganization-thermal polycondensation is designed to fabricate porous ultrathin nitrogen-doped carbon nanosheets (NCNSs), and then BAILs-functionalized NCNSs catalysts are prepared via successive quaternary ammonization by sultones and anion exchange with Brønsted acids. By adjusting the molar composition of the starting monomers, the textural properties of NCNSs supports are tuned; and by functionalization with different sultones (1,3-propanesultone and 1,4-butanesultone) and organic (trifluoromethanesulfonic acid and p-toluenesulfonic acid) or inorganic (H2SO4 and H3PO4) acids, the surface hydrophobicity and Brønsted acid strength of the catalysts are regulated. The catalysts are applied in microwave-assisted upgrading fructose to 5-hydroxymethylfurfural, and influences of Brønsted acid nature, surface hydrophobicity and textural properties on the catalytic performance are explored. For the most active [C4SO3HN][OTf]-NCNSs-MA-3 catalyst with the advantages of superstrong Brønsted acidity, higher surface hydrophobicity and perfect porous ultrathin sheet-like nanostructure, the conversion of fructose and the yield of 5-hydroxymethylfurfural of 100% and 87.7% are achieved after microwave irradiation for 15 min, outperforming Amberlyst-15 resin and HY zeolite. The catalysts also demonstrate the robust catalytic reusability, and after five consecutive catalytic runs, the obvious activity loss hardly occurs, along with little acid sites leaching.

Precision Cellulose from Living Cationic Polymerization of Glucose 1,2,4-Orthopivalates.

Cellulose serves as a sustainable biomaterial for a wide range of applications in biotechnology and materials science. While chemical and enzymatic glycan assembly methods have been developed to access modest quantities of synthetic cellulose for structure-property studies, chemical polymerization strategies for scalable and well-controlled syntheses of cellulose remain underdeveloped. Here, we report the synthesis of precision cellulose via living cationic ring-opening polymerization (CROP) of glucose 1,2,4-orthopivalates. In the presence of dibutyl phosphate as an initiator and triflic acid as a catalyst, precision cellulose with well-controlled molecular weights, defined chain-end groups, and excellent regio- and stereospecificity was readily prepared. We further demonstrated the utility of this method through the synthesis of precision native d-cellulose and rare precision l-cellulose.

Nonstoichiometric Protic Ionic Liquids: The Role of Excess Acid in Charge Transport Mechanisms.

A study of charge transport mechanisms in an electric field was conducted on nonstoichiometric protic ionic liquids (PIL) based on triethylamine (TEA), in combination with an excess of either trifluoroacetic acid (TFA) or trifluoromethanesulfonic acid (TfO). The addition of excess precursor acid adds proton-donor sites to the system to support potential structural proton transport, which could, for example, enable the use in fuel cells. Transport measurements by pulsed field gradient (PFG) NMR diffusion and, in particular, electrophoretic NMR (eNMR) are supported by NMR chemical shifts and Raman spectroscopy, where the latter techniques elucidate the local solvation structures. Migration of the acidic proton of the excess acid in the electric field occurs toward the cathode with a velocity larger than that of the anions. This intriguing feature of a rapid drift of a neutral molecule is explained by the interplay of strong correlations between anion and cation as well as between anion and acid. The neutral acid is subject to vehicular transport with the anion, while the anion is partitioning between anion-acid and anion-cation clusters, resulting in a lower average drift velocity. The negative drift direction of the neutral acid and its proton is superimposed to and thus counteracts the vehicular transport of protons with the cation. The study sheds light on the role of excess acid in PIL and reveals the versatile interactions between anion, cation, and excess acid within a PIL determining its charge transport properties.

Cooperative Covalent–Noncovalent Organocatalysis of the Knoevenagel Condensation Based on an Amine and Iodonium Salt Mixture

AbstractThe experimentally obtained kinetic data has indicated the existence of a synergetic cocatalytic effect provided by an iodonium salt in the base‐catalyzed Knoevenagel condensation. The diphenyliodonium triflate serving as the halogen bond‐donating Lewis acid provides the higher cocatalytic effect than zinc(II) triflate or triflic acid serving, respectively, as the metal cation‐based Lewis acid and Brønsted acid. Such a cocatalytic effect remains the same for a broad scope of carbonyl compounds covering aldehydes featuring electron‐withdrawing or electron‐donating substituents, as well as ketone involved in the reaction.

Synthesis and Derivatives of Beryllium Triflate.

Various pathways for the synthesis of beryllium triflate were investigated. The reaction of triflic acid or trimethylsilyl triflate with beryllium metal in liquid ammonia led to the formation of mono-, di-, and tetra-nuclear beryllium ammine complexes. Utilization of SMe2 as a solvent gave homoleptic Be(OTf)2. Various beryllium triflate complexes with N- and O-donor ligands as well as the complex anions [Be(OTf)4]2- and [Be2(OTf)6]2- were synthesized to evaluate the reactivity and solution properties of beryllium triflate. This showed that OTf- is not a weakly coordinating anion for Be2+ cations and that it exhibits good bridging properties.

Ultrastructural and glycoproteomic characterization of Prevotella intermedia: Insights into O-glycosylation and outer membrane vesicles.

Prevotella intermedia, a Gram-negative bacterium from the Bacteroidota phylum, is associated with periodontitis. Other species within this phylum are known to possess the general O-glycosylation system. The O-glycoproteome has been characterized in several species, including Tannerella forsythia, Porphyromonas gingivalis, and Flavobacterium johnsoniae. In our study, we used electron cryotomography (cryoET) and glycoproteomics to reveal the ultrastructure of P. intermedia and characterize its O-glycoproteome. Our cryoET analysis unveiled the ultrastructural details of the cell envelope and outer membrane vesicles (OMVs) of P. intermedia. We observed an electron-dense surface layer surrounding both cells and OMVs. The OMVs were often large (>200 nm) and presented two types, with lumens being either electron-dense or translucent. LC-MS/MS analyses of P. intermedia fractions led to the identification of 1655 proteins, which included 62 predicted T9SS cargo proteins. Within the glycoproteome, we identified 443 unique O-glycosylation sites within 224 glycoproteins. Interestingly, the O-glycosylation motif exhibited a broader range than reported in other species, with O-glycosylation found at D(S/T)(A/I/L/M/T/V/S/C/G/F/N/E/Q/D/P). We identified a single O-glycan with a delta mass of 1531.48 Da. Its sequence was determined by MS2 and MS3 analyses using both collision-induced dissociation and high-energy collisional dissociation fragmentation modes. After partial deglycosylation with trifluoromethanesulfonic acid, the O-glycan sequence was confirmed to be dHex-dHex-HexNAc (HPO3 -C6 H12 O5 )-dHex-Hex-HexA-Hex(dHex). Bioinformatic analyses predicted the localization of O-glycoproteins, with 73 periplasmic proteins, 53 inner membrane proteins, 52 lipoproteins, 26 outer membrane proteins, and 14 proteins secreted by the T9SS.

Brønsted Acid Catalyzed Stereospecific Dearomative Spirocyclization of Benzothiophenyl Analogues of Tertiary cis-β-Benzylstyrenes

Abstract3-Substituted benzothiophenyl analogues of tertiary cis-β-benzylstyrenes undergo triflic acid catalyzed dearomative spirocyclization at room temperature to afford compounds containing vicinal quaternary centers. Hydroarylation of the styrene is a competing process that occurs preferentially within substrates possessing electron-rich styrenyl alkenes, or an indole in place of the benzothiophene.

The O-glycan is essential for the induction of protective antibodies against lethal infection by flagella A-bearing Pseudomonas aeruginosa.

To address the problem of increased antimicrobial resistance, we developed a glycoconjugate vaccine comprised of O-polysaccharides (OPS) of the four most prevalent serotypes of Klebsiella pneumoniae (KP) linked to recombinant flagellin types A and B (rFlaA and rFlaB) of Pseudomonas aeruginosa (PA). Flagellin is the major subunit of the flagellar filament. Flagella A and B, essential virulence factors for PA, are glycosylated with different glycans. We previously reported that while both rFlaA and rFlaB were highly immunogenic, only the rFlaB antisera reduced PA motility and protected mice from lethal PA infection in a mouse model of thermal injury. Since recombinant flagellin is not glycosylated, we examined the possibility that the glycan on native FlaA (nFlaA) might be critical to functional immune responses. We compared the ability of nFlaA to that of native, deglycosylated FlaA (dnFlaA) to induce functionally active antisera. O glycan was removed from nFlaA with trifluoromethanesulfonic acid. Despite the similar high-titered anti-FlaA antibody levels elicited by nFlaA, rFlaA, and dnFlaA, only the nFlaA antisera inhibited PA motility and protected mice following lethal intraperitoneal bacterial challenge. Both the protective efficacy and carrier protein function of nFlaA were retained when conjugated to KP O1 OPS. We conclude that unlike the case with FlaB O glycan, the FlaA glycan is an important epitope for the induction of functionally active anti-FlaA antibodies.

ETFE-grafting ionomers for anion exchange membrane water electrolyzers with a current density of 11.2 A cm−2

In the quest for efficient and sustainable hydrogen production, anion exchange membrane (AEM) water electrolyzers (AEMWEs) have gained significant attention. Development of AEMs has accelerated in the past few decades while the significance of the ionomer on AEMWE performance and durability is always unrecognized. In this study, we proposed a class of electrochemically durable ionomers by introducing the piperidinium group onto the ethylene tetrafluoroethylene (ETFE) backbone using a radiation grafting technology. To avoid disruption of the conformation of the piperidinium group during the functionalization process, we grafted the piperidinium group onto the polymer backbone at the gamma position of the N-piperidinium group using trifluoromethanesulfonic acid as a catalyst. The prepared ETFE-g-poly(styryl propyl piperidinium) ionomers exhibited outstanding electrochemical properties and enhanced alkaline stability. Most notably, the corresponding AEMWEs demonstrated an impressive current density of 11.2 A cm−2 at 2.0 V under 80 °C in 1 M KOH solution. Furthermore, they were continuously operated at a current density of 0.5 A cm−2 for over 300 h with a low voltage decay rate of 0.12 mV h−1. This study offers valuable insights into the development of robust solid-state ionomers through radiation grafting, paving the way for high-performance AEMWEs.

Synthesis and Organo‐Catalyzed Ring‐Opening of a Six‐Membered Heterocycle Combining Phosphonate and Ester Functions

AbstractThe synthesis of a difunctional P‐heterocycle combining phosphonate and ester moieties in a six‐membered ring is described. Using trifluoromethane sulfonic acid HOTf as organocatalyst, ring‐opening with neopentyl alcohol readily occurs with complete selectivity for O‐acyl bond cleavage. In turn, ring‐opening polymerization proceeds in a controlled manner when an excess of P‐heterocycle is used. Copolymerization with ϵ‐caprolactone is also reported and semi‐batch conditions are shown to enable regular incorporation of the phosphonate moieties along the polymer chains.